U.S. patent number 3,913,153 [Application Number 05/496,211] was granted by the patent office on 1975-10-21 for electronic controls for a hospital bed.
This patent grant is currently assigned to Hill-Rom Company, Inc.. Invention is credited to James S. Adams, William M. Stevens.
United States Patent |
3,913,153 |
Adams , et al. |
October 21, 1975 |
Electronic controls for a hospital bed
Abstract
Improved electronic controls for an adjustable hospital bed
incorporating various logic devices. These devices result in the
concurrent operation of several motors in response to the
activation of a single switch to produce a desired bed
configuration. The motors may operate simultaneously or
sequentially depending upon the particular selection and the
involved circuit logic. Moreover, the logic allows the position of
one adjustable bed portion to prevent the functioning of the motor
for another bed portion. The circuit logic may also preclude the
operation of a motor absent the secure engagement of mechanical
parts. Further, the logic circuitry permits switches on the
selection panel to control one adjustable bed portion, but over
different ranges. This becomes particularly advantageous where one
switch also operates a different bed portion.
Inventors: |
Adams; James S. (Batesville,
IN), Stevens; William M. (Loveland, OH) |
Assignee: |
Hill-Rom Company, Inc.
(Batesville, IN)
|
Family
ID: |
23971694 |
Appl.
No.: |
05/496,211 |
Filed: |
August 9, 1974 |
Current U.S.
Class: |
5/616;
318/65 |
Current CPC
Class: |
A61G
7/018 (20130101) |
Current International
Class: |
A61G
7/002 (20060101); A61G 7/018 (20060101); B60R
021/10 (); H02P 007/74 (); A61G 007/10 () |
Field of
Search: |
;340/52E,278
;318/65,103,290,300 ;74/365 ;5/63,66,68 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Nunberg; Casmir A.
Attorney, Agent or Firm: Haight, Hofeldt, Davis &
Jambor
Claims
Accordingly, what is claimed is:
1. In an adjustable bed of the type having:
a. a bed portion movable to a plurality of at least three
positions, and
b. an electric motor for moving said bed portion from one of said
positions to another,
the improvement which comprises:
A. first selection means for selecting between at least two of said
positions of said bed portion;
B. second selection means for selecting between at least two of
said positions of said bed portion, at least one of said positions
selectable by said first selection means not being selectable by
said second selection means; and
C. logic means coupled between said electric motor and said first
and second selection means for actuating said motor in response to
said first or said second selection means to move said bed portion
to a selected position.
2. The improvement of claim 1 wherein said bed portion has a
continuous range of positions with all of the positions within said
range being selectable by said first selection means and a portion
of said range of positions being selectable by said second
selection means.
3. The improvement of claim 2 wherein, said bed portion being a
first bed portion and said electric motor being a first electric
motor,
a. said bed includes a second bed portion movable over a continuous
range of positions and a second electric motor for moving said
second bed portion from one of said positions of said second bed
portion to another; and
b. said logic means in response to said second selection means
actuates said second motor to move said second bed portion.
4. The improvement of claim 3 wherein said logic means is
electronic logic means.
5. The improvement of claim 3 wherein said first bed portion is a
knee portion, said second bed portion is a head portion and said
second selection means actuates said first electric motor to raise
said knee portion to no higher than about 15.degree. and actuates
said first motor to lower said knee portion when said head portion
is at or below about 30.degree..
6. The improvement of claim 5 wherein said first and said second
selection means each includes at least one manually activated
on-off switch and a bed portion position-indicating switch.
7. The improvement of claim 3 wherein said electronic logic means
includes switching means for controlling the flow of electricity
through said electric motors, and wherein both said selection means
and said logic means, with the exception of said switching means,
only include components operating at voltages below about 25
volts.
8. The improvement of claim 7 wherein said switching means includes
triacs coupled to said electric motors and reed relays coupled to
said triacs.
9. The improvement of claim 7 including ground test means.
10. The improvement of claim 7 wherein said electronic logic means,
with the exception of said switching means, includes components
selected from the group consisting of inverters, and AND, NAND, OR,
and NOR gates.
11. The improvement of claim 7 in a bed which includes a bed
elevation portion, an elevation motor for moving said elevation
portion, and an elevation selection means coupled to said logic
means, said logic means, in response to said elevation selection
means, actuating said elevation motor to move said elevation bed
portion.
12. The improvement of claim 11 further including a bed-flat
selection means coupled to said logic means, said logic means in
response to said bed-flat selection means actuating said head motor
to lower said head portion, said knee motor to lower said knee
portion, and said elevation motor to raise said elevation
portion.
13. The improvement of claim 3 wherein said first and second motors
being reversible, said logic means includes ambiguity control means
for precluding the actuation of said first or said second motor
when said logic means in response to selections on said selection
means would actuate said first or said second motor respectively to
operate simultaneously in both its forward and reverse
directions.
14. The improvement of claim 3 wherein said first and second motors
being reversible, said selection means includes indicating means
for developing an indication of when said first or second bed
portions has reached the end of its range of positions and said
logic means includes avoidance means for precluding the actuation
of said first or second motors, respectively, except in a direction
to move said first or second bed portions respectively, away from
the end of its range of positions.
15. The improvement of claim 2 including lockout means for
precluding actuation of said motor in response to the selection on
either of said selection means.
16. In an adjustable bed of the type having:
a. first and second bed portions, each of said bed portions being
movable to a plurality of positions; and
b. an electric motor for moving said first bed portion from one
position to another;
the improvement comprising:
A. selection means for selecting between said positions of said
first bed portion;
B. indicating means for developing an indication of whether the
position of said second bed portion is in a first or in a second
set of positions, said first and second sets of positions (a) being
mutually exclusive, (b) including all the positions of said second
bed portion, and (c) each containing at least one position; and
C. logic means coupled between said electric motor and said
selection means and said indicating means for actuating said motor
in response to said selection means to move said first bed portion
to a selected position only when the position of said second bed
portion is in said first set of positions.
17. The improvement of claim 16 wherein said first bed portion has
a continuous range of positions.
18. The improvement of claim 17 wherein said second bed portion has
a continuous range of positions.
19. The improvement of claim 18 wherein said second bed portion is
the head portion of the bed and said first set of positions
includes those with elevation of 30.degree. or less and said second
set of positions includes all those with elevation above
30.degree..
20. The improvement of claim 19 wherein said selection means
includes on-off switches and bed portion position-indicating
switches and said indicating means includes position-indicating
switches.
21. The improvement of claim 19 which includes lockout means for
precluding actuation of said motor in response to the selection of
a position on said selection means.
22. The improvement of claim 19 wherein said logic means includes
switching means for controlling the flow of electricity through
said electric motor and wherein said selection means and said logic
means, with the exception of said switching means, includes only
components operating at voltages below about 25 volts.
23. The improvement of claim 22 wherein said switching means
includes triacs coupled to said motors and read realys coupled to
said triacs.
24. The improvement of claim 23 wherein said logic means includes
components selected from the group consisting of inverters, and
AND, OR, NAND, and NOR gates.
25. The improvement of claim 19 wherein, said motor being a
reversible motor, said logic means includes ambiguity control means
for precluding the actuation of said motor when said logic means in
response to selections on said selection means would actuate said
motor to operate in both its forward and reverse directions.
26. The improvement of claim 19 including ground test means.
27. The improvement of claim 19 which, said selection means being a
first selection means, includes a second selection means coupled to
said logic means, said logic means actuating said motor in response
to said second selection means independently of the position of
said second bed portion.
28. The improvement of claim 19 in a bed which, said motor being a
first motor, includes a second reversible electric motor coupled to
said logic means wherein said second motor operates to move said
second bed portion between its positions and wherein said logic
means, in response to a selection on said first selection means,
actuates said second motor to move said second bed portion.
29. The improvement of claim 28 wherein said first bed portion is
the knee portion of said bed, said second bed portion is the head
portion of said bed, and said bed includes an elevation portion, a
reversible elevation motor coupled to said logic means, and
elevation selection means coupled to said logic means, said logic
means, in response to a selection on said elevation selection
means, actuating said elevation motor to move said elevation bed
portion over a continuous range of positions.
30. The improvement of claim 29 including a bed-flat selection
means coupled to said logic means, said logic means, in response to
a selection on said bed-flat selection means, actuating said head
motor to lower said head portion, said knee motor to lower said
knee portion, and said elevation motor to raise said elevation
portion.
31. The improvement of claim 29 including
a. indicating selection means for developing an indication of when
said head portion reaches an end of its range of positions, when
said knee portion reaches an end of its range of positions and when
said elevation portion reaches an end of its range of positions,
and
b. logic avoidance means for, when said head portion is at an end
ot its range of positions, precluding actuation of said head motor
except in the direction to move said head portion away from said
end of its range of positions; when said knee portion is at an end
of its range of positions, precluding actuation of said knee motor
except in the direction to move said knee portion away from said
end of its range of positions; and, when said elevation portion is
at an end of its range of positions, precluding actuation of said
elevation motor except in the direction to move said elevation
portion away from said end of its range of positions.
32. In an adjustable bed of the type having:
a. a first and a second bed portion, said first and second bed
portions being movable to a plurality of positions; and
b. a first and a second electric motor for moving said first and
second bed portions respectively from one position to another,
the improvement which comprises:
A. selection means for selecting between the position of said first
bed portion; and
B. logic means coupled between said selection means and said first
and second motors for actuating, in response to said selection
means, said first and second motors to move said first and second
bed portions, respectively.
33. The improvement of claim 32 wherein said logic means actuates
said first and second motors sequentially.
34. The improvement of claim 32 wherein both said first and said
second bed portions have a continuous range of positions; said
selection means selects a direction of movement of said first bed
portion; said first and second motors are reversible; and said
logic means, in response to said selection means, actuates said
first motor to move said first bed portion in the selected
direction
35. The improvement of claim 34 which, said selection means being a
first selection means, includes a second selection means coupled to
said logic means, said logic means, in response to a selection on
said second selection means, actuating said first but not said
second electric motor.
36. The improvement of claim 35 wherein:
a. said first bed portion is the head portion of said bed and said
first motor is a head motor;
b. said second bed portion is the knee portion of said bed and said
second motor is a knee motor; and
c. said logic means in response to a selection on said first
selection means to lower said head portion, actuates said knee
motor to lower said knee portion when said head portion is elevated
30.degree. or less, and said logic means in response to a selection
on said first selection means to raise said head portion actuates
said knee motor to raise said knee portion to no higher than
15.degree. elevation.
37. The improvement of claim 35 wherein said logic means is
electronic logic means.
38. The improvement of claim 37 wherein said first and second
selection means includes on-off switches and bed portion
position-indicating switches.
39. The improvement of claim 35 including first lockout means for
precluding actuation of said first motor in response to said first
selection means and second lockout means for precluding actuation
of said second motor in response to said second selection
means.
40. The improvement of claim 35 in which said logic means includes
switching means for controlling the flow of electricity through
said first and second electric motors and wherein said first and
second selection means and said logic means, with the exception of
said switching means, includes only components operating at
voltages below about 25 volts.
41. The improvement of claim 40 wherein said switching means
includes triacs coupled to said motors and reed relays coupled to
said triacs.
42. The improvement of claim 41 wherein said electronic logic
means, with the exception of said switching means, includes
components selected from the group consisting of inverters and
NAND, AND, NOR and OR gates.
43. The improvement of claim 35 wherein said logic means includes
ambiguity control means for precluding the actuation of any
particular motor when selections on said selection means would
result in the actuation of said particular motor in both its
forward and reverse directions.
44. The improvement of claim 35 including ground test means.
45. The improvement of claim 35 wherein said bed includes an
elevation portion with a continuous range of positions, a
reversible elevation motor coupled to said logic means to raise and
lower said elevation portion; and elevation selection means for
choosing a direction of motion of said elevation portion, said
logic means in response to a selection on said elevation selection
means actuating said elevation motor to move said elevation portion
in the direction chosen.
46. The improvement of claim 45 including bed-flat selection means,
said logic means in response to said bed-flat selection means
actuating said head motor to lower said head portion said knee
motor to lower said knee portion and said elevation motor to raise
said elevation portion.
47. The improvement of claim 45 including
a. indicating selection means for developing an indication of when
said head portion reaches an end of its range of positions, when
said knee portion reaches an end of its range of positions and when
said elevation portion reaches an end of its range of positions,
and
b. logic avoidance means for, when said head portion is at an end
of its range of positions, precluding actuation of said head motor
except in the direction to move said head portion away from said
end of its range of positions; when said knee portion is at an end
of its range of positions, precluding actuation of said knee motor
except in the direction to move said knee portion away from said
end of its range of positions; and, when said elevation portion is
at an end of its range of positions, precluding actuation of said
elevation motor except in the direction to move said elevation
portion away from said end of its range of positions.
48. In an adjustable bed of the type having:
a. a bed portion movable to a plurality of positions; and
b. a reversible electric motor for moving said bed portion from one
of said positions to another,
this improvement comprising:
A. selection means for selecting between said position of said bed
portion;
B. indicating means for developing an indication of when said bed
portion is at a predesignated position; and
C. logic means coupled between said motor and said selection means
and indicating means for, when said bed portion is not in said
predetermined position and in response to said selection means:
1. actuating said motor to operate in a first direction to move
said bed portion to said predetermined position, and
2. when said bed portion reaches said predetermined position,
reversing said motor to operate in a second direction.
49. The improvement of claim 48 wherein, when said bed portion is
in said predetermined position prior to a selection on selection
means, said logic means, in response to said selection means,
actuates said motor to operate in said second direction.
50. The improvement of claim 49 wherein said bed portion has a
continuous range of positions, said predetermined position is at
one end of said range of positions, and said indicating means is a
limit switch actuated when said bed portion is in said
predetermined position.
51. The improvement of claim 50 wherein the operation of said motor
in said second direction in response to said selection means places
the top of said bed at a non-zero angle with respect to the surface
on which it sets.
52. The improvement of claim 51 wherein said motor operating in
said first direction raises said bed; said improvement further
includes alternate selection means coupled to said logic means; and
said logic means, in response to said alternate selection means,
actuates said motor to lower said bed.
53. The improvement of claim 52 in a bed which further includes a
movable head portion with a continuous range of positions; a
movable knee portion with a continuous range of positions; a
reversible head motor coupled to said logic means and connected to
said head portion for moving said head portion over its range of
positions; a reversible knee motor coupled to said logic means and
connected to said knee portion for moving said knee portion over
its range of positions; knee selection means coupled to said logic
means; and head selection means coupled to said logic means, said
logic means, in response to said knee selection means actuating
said knee motor to move said knee portion and in response to said
head selection means, actuating said head motor to move said head
portion.
54. In an adjustable bed of the type having:
a. a head portion, a knee portion, and an elevation portion, each
of said portions being movable over a continuous range of
positions;
b. a reversible head motor for moving said head portion, a
reversible knee motor for moving said knee portion, and a
reversible elevation motor for moving said elevation portion;
and
c. head selection means for choosing the direction of movement of
said head portion, knee selection means for choosing the direction
of movement of said knee portion, and elevation selection means for
choosing the direction of movement of said elevation portion,
the improvement which comprises electronic logic means coupled
between said head, knee, and elevation motors and said head, knee
and elevation selection means for:
A. actuating said elevation motor when a direction of movement of
said elevation portion is chosen on said elevation selection means
to move said elevation portion in the chosen direction;
B. actuating said knee motor when a direction of movement of said
knee portion is chosen on said knee selection means to move said
knee portion in the chosen direction; and
C.
1. when the raising of said head portion is chosen on said head
selection means, actuating said head motor to raise said portion
and, when said knee portion is in a predesignated portion of its
range of movement, actuating said knee motor to raise said knee
portion; and
2. when the lowering of said head portion is chosen on said head
selection means, actuating said head motor to lower said head
portion and, when said head portion is in a predetermined portion
of its range of movement, actuating said knee motor to lower said
knee portion.
55. The improvement of claim 54 which includes a bed-flat selection
means wherein said logic means upon the activation of said bed-flat
selection means actuates said head and knee motors to move said
head and knee portions to their lowest positions and said elevation
motor to move said elevation portion to its highest position.
56. The improvement of claim 55 which further includes
Trendelenberg selection means wherein said logic means in response
to the activation of said Trendelenberg selection means actuates
said elevation motor to place the top of said bed at a non-zero
angle with respect to the surface on which said bed sets.
57. The improvement of claim 56 wherein said logic means:
a. when the raising of said head portion is chosen on said head
selection means,
1. actuates said knee motor to raise said knee portion when said
knee portion is below 15.degree. and
2. ceases to actuate said knee motor at least when said knee
portion raises to 15.degree.; and
b. when the lowering of said head portion is chosen on said head
selection means, actuates said knee motor to lower said knee
portion when said head portion is 30.degree. or lower.
58. The improvement of claim 57 which includes head lockout means
for precluding actuation of said head motor in response to the
selection of a direction on said head selection means, elevation
lock-out means for precluding actuating of said elevation motor in
response to a direction selected on said elevation selection means,
and knee lock-out means for precluding actuation of said knee motor
in response to the selection of a direction on said knee selection
means.
59. The improvement of claim 58 wherein said logic means includes
switching means for controlling the flow of electricity through
said electric motors and wherein said selection means and said
logic means, with the exception of said switching means, only
includes components operating at voltages below about 25 volts.
60. The improvement of claim 59 wherein said logic means includes
ambiguity control means for precluding the actuation of any
particular motor if said logic means in response to a first
selection made on said selection means would actuate said
particular motor in a first direction and in response a second
selection made on said selection means would actuate said
particular motor in the reverse of said first direction.
61. The improvement of claim 60 wherein each of said selection
means includes at least one manual on-off switch and one bed
portion position-indicating switch.
62. The improvement of claim 61 wherein said elevation selection
means includes
a. a first manual on-off switch and said logic means actuates said
elevation motor to raise said elevation bed portion only during the
time of a selection being made on said first switch, and
b. a second manual on-off switch and said logic means actuates said
elevation motor to lower said elevation portion from the time of a
selection being made on said second switch until said elevation
portion reaches the lower limit of its range of positions or until
the making of a selection on any manual switch in response to which
said logic means would actuate said elevation motor to raise said
elevation bed portion.
63. The improvement of claim 62 including:
a. indicating selection means for developing an indication of when
said head portion reaches an end of its range of positions, when
said knee portion reaches an end of its range of positions and when
said elevation portion reaches an end of its range of positions:
and
b. logic avoidance means for when said head portion is at an end of
its range of positions, precluding actuation of said head motor
except in the direction to move said head portion away from said
end of its range of positions; when said knee portion is at an end
of its range of positions, precluding actuation of said knee motor
except in the direction to move said knee portion away from said
end of its range of positions; and, when said elevation portion is
at an end of its range of positions, precluding actuation of said
elevation motor except in the direction to move said elevation
portion away from said end of its range of positions.
64. The improvement of claim 63 wherein said logic means with the
exception of said switching means includes components selected from
the group consisting of inverters and AND, OR, NAND and NOR
gates.
65. The improvement of claim 64 wherein said switching means
includes reed relays coupled to said gates and triacs coupled
between said reed relays and said motors.
66. The improvement of claim 65 including ground test means
Description
BACKGROUND
Hospital beds fill a variety of functions because of the infirmed
nature of many of their occupants. Furthermore, the hospital
setting results in the patient spending most of his time in the
actual occupancy of the bed. Consequently, these beds generally
include some mechanism for altering and adjusting their
configuration.
One of the bed's functions obviously includes providing a place for
the patient to sleep. However, the bed must also provide a place
for the patient to lounge and engage in customary daily activities,
such as reading, watching television, eating, as well as some
personal hygiene. Further, when the physician makes his rounds in
the hospital, the hospital bed frequently provides for the
examination and treatment of the patient. Recently, medical science
has discovered that placing the patient at a slight angle with
respect to the horizontal - the Trendelenburg or reverse
Trendelenburg positions - provides some benefit for various types
of infirmities. Accordingly, some beds possess the ability to place
the patient in such a position.
Beds other than those used strictly in hospitals must also display
similar advantages as those described above. Nursing homes, which
perform many similar functions to hospitals, display a need for
such flexible beds. On occasion, an infirmed person at home may
also need this type of bed.
Various types of adjustable beds have attempted to accommodate
these needs. Two of these in particular have found acceptance in
the hospital and nursing home industries.
The first type incorporates a single electric motor which effects a
single adjustment to allow the patient to sit up. It does so first
by elevating the head portion of the bed which thus assumes an
elevational angle with respect to the horizontal. In this position,
however, gravitation causes the patient to slide towards the foot
of the bed and assume an uncomfortable and perhaps unhealthy
position. To preclude this gravitation, the same motor
simultaneously elevates the knee portion of the bed. The raised
knee portion, in effect, provides a stop mechanism to abate the
sliding. Some beds of this type incorporate a separate
hand-actuated mechanism for raising the overall level of the
bed.
U.S. Pat. No. 3,821,821 to F. J. Burst et al. provides a drastic
improvement in this general type of bed. It includes a clutching
mechanism which utilizes the motor's power to raise and lower the
bed, as well as to configure it. Furthermore, it permits the
disengagement of the knee mechanism from the head portion and,
additionally, includes a separate hand crank to independently
adjust the knee. This bed also provides a hooking mechanism which,
upon the elevating of the bed to its highest position, can retain
either end while the other lowers to achieve one of the
Trendelenburg positions.
The other type of bed permits three separate adjustments
accomplished through either one or three electric motors. This bed
includes a first adjustment to elevate the head, a second and
independent adjustment to elevate the knee, and a third mechanism
to raise the level of the bed.
The bed with a single motor also possesses complicated mechanisms
through which the motor adjusts the different bed portions. U.S.
Pat. Nos. 3,290,956 to W. R. Black et al., 3,602,784 to G. M.
Eluer, 3,710,404 to W. J. Peterson, and 3,716,876 to A. P. Petzon
et al. show a single motor and various types of electrical and
mechanical devices to separately adjust the head, knee and
elevation portions of the bed.
Where the bed incorporates three motors, the activation of a
particular motor adjusts a single bed section. The expenditure of
appreciable effort with sufficient readjustments of the various
parts allows the placing of the bed in a satisfactory position for
the particular activity undertaken by the patient. Goodman et al.'s
U.S. Pat. No. 3,743,905 shows separate switches controlling the
three motors for the movable bed portions.
Both types of beds, nonetheless, suffer unavoidable drawbacks in
their general utilization by patients who must occupy them for
various purposes. The first type of bed, with the coordinated head
and knee motion, simply lacks versatility in the different types of
positions achievable for a patient. Less knee elevation for a
particular head elevation, for example, generally falls beyond the
capacities of the bed. Obviously, such sophistications as the
Trendelenburg or reverse Trendelenburg position present no
possibility for most of these beds.
The beds having separate controls for the head, knee, and elevation
portions do possess the desired versatility. They, however, do not
allow for the coordinated movement of different bed portions. Each
portion undergoes movement only upon the activation of the
particular switch designated for that portion. Consequently,
achieving the exact desired bed configuration presents a
significant and deleterious burden. Moreover, to achieve certain
frequently used positions, such as the Trendelenburg position or
the simple, straight, flat position for sleeping often requires the
manipulation of a multitude of the switches. This bed lacks the
desired simplicity and ease of operation.
SUMMARY
Incorporating logic devices within the control circuitry of a
hospital bed combines versatility of bed adjustments with
simplicity of operation. Moreover, the logic devices allow types of
control over the bed's operation not previously attempted.
Typically, a hospital bed includes at least one bed portion which
moves to a number of positions and an electric motor for moving
that bed portion from one position to another. Through the use of
logic means, two different selection means can control the motor
with the second of these two not achieving all of the positions
available with the first. Consequently, the logic, in response to
the first selection means, will actuate the motor to move the bed
portion to positions to which the bed portions will not move in
response to the second selection means.
The bed's knee mechamism reveals a number of advantages resulting
from this type of dual control. The knee switch, of course,
represents the first selection means and moves the knee portion
through its full range of positions for whatever reason desired,
such as an examination of the patient. The switch to raise the head
portion should also elevate the knee portion but only enough to
prevent gravitation of the patient and desirably no further. The
logic in conjunction with the selection means determines the
particular ranges of knee movement for the head and knee
buttons.
The logic means also has utility where the bed includes two bed
portions, each movable to a number of positions, and an electric
motor for moving the first bed portion between its positions. Here,
the logic will permit the operation of the electric motor, and thus
the movement of the first bed portion, to depend upon the position
occupied by the second bed portion. Consequently, when the second
bed portion occupies one of a first set of positions, activation of
the selection means produces the usual motion of the first portion.
When the second bed portion occupies a position in the second set
of positions, no such motion results, notwithstanding a selection
made on the selection means.
The lowering of the head and knee portions represents an example of
this latter situation. When the head portion lowers to the
horizontal, the knee portion should similarly flatten. However, the
head portion may, of course, begin its descent from an almost
vertical position. To prevent patient gravitation, the knee portion
should not lower until the head portion has gone below a
predetermined level, typically 30.degree.. Depressing the switch to
lower the head portion accordingly will lower the knee portion only
when the head portion occupies a position below the desired level.
With the head portion above that level, the knee portion will not
lower in response to the lowering of the head.
The head and knee also exemplify the third type of benefits
accruing from the incorporation of logic means in the bed. In this
instance, the bed again includes two movable portions and an
electric motor for each. However, the logic actuates both motors in
response to a selection made on a single selection means. This, of
course, refers to the raising or lowering of both the head and knee
portions merely upon selection on the head selection switch.
Furthermore, the logic means allows for the reversing, in a single
operation, of a motor when a bed portion reaches a particular
point. In addition to the movable bed portion, the reversible
electric motor, and the selection means, this improvement requires
some means for indicating tha the bed portion had reached the
position where the motor reverses.
This ability to reverse a motor's direction finds particular
advantage in the Trendelenburg operation. In this operation, the
elevation motor often first raises the bed to its highest position
and then reverses. Acting with some means to retain one end of the
bed in its raised position, the reversal lowers the other end and
produces the desired inclination. The indicating means shows that
the bed has reached its highest position and that the motor can
reverse its direction.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 diagrams the electrical components of an adjustable
three-motor bed.
FIG. 2 shows the power supply components providing the various
potentials of the bed's circuit.
FIG. 3 gives a detailed circuit diagram of the electrical
components in the bed except the motors and the power supply.
FIG. 4 provides an alternate ground test device for the one shown
in FIG. 3 .
DETAILED DESCRIPTION
Adjustable beds possess at least one portion that moves between a
number of positions. Frequently, in fact, the bed has three movable
portions. These generally include the head portion, the knee
portion and the elevation portion, as discussed in U.S. application
Ser. No. 496,212 of James S. Adams, William H. Peck and Daniel R.
Tekulve entitled ELEVATING AND TRENDELENBURG MECHANISM FOR AN
ADJUSTABLE BED.
The elevation portion represents the mechanism of the bed which
allows the general level of the mattress to rise or lower with
regards to the floor or any surface upon which the bed sits. In a
three-motor bed, a separate elevation motor moves this mechanism to
achieve the desired mattress height.
The head portion of the bed includes the mechanism which raises and
lowers the head of the spring and mattress. Actually, the mechanism
causes the head portion of the mattress to rotate about an axis
which lies transverse to the longitudinal axis of the bed and
parallel to the ground. This transverse axis falls at an
intermediary point between the head and the foot of the bed. It
comes sufficiently close to the head to also allow for a knee
portion. Since the elevation of the head portion proceeds as a
rotation about an axis, the angle of this rotation represents the
actual amount of elevation.
A recent and remarkable development in hospital beds concerns the
overall motion of the bed upon the elevation of the head. As shown
in U.S. Pat. No. 3,237,212 to Hillenbrand et al., a general
movement of the overall bed structure toward the head may accompany
the elevation of the head. This allows the patient's head to remain
close to the wall and accessory equipment for greater comfort,
convenience, and safety, as well as greater maneuvering area in the
hospital room. This development, of course, represents an extremely
desirable facet associated with the rising of the bed's head
portion.
The knee section accomplishes its elevation by rotating bed
sections about two transverse axes. The first axes occurs just
below the head portion of the bed. Rotation of the bed portion
below this axis results in the elevation of the lower portion of
the patient's body. The second axis of rotation, of course, occurs
in the region of the patient's knee and permits the usual flexing
of the knee. The amount of rotation about the second axes at the
knee may suffice for the foot of the bed to remain at the same
height it occupied prior to the elevation of the knee. Recent
practice, however, prefers to elevate somewhat the foot of the bed
and the feet of the patient from the position they occupied before
the knee bending. Producing less rotation about the knee, of
course, results in the desired elevation of the feet.
FIG. 1 diagrammatically shows the three bed motors, with the
elevation motor at 11, the knee motor at 12 and the head motor at
13. The various selection means, labeled as INPUTS, ultimately
control the operation of these motors. These include first of all
the patient controls 14 and 15 on either side of the bed. One of
the patient controls would suffice, of course, but having two
provides greater convenience for the patient.
The bed position indicators at 16 provide another type of input
into the control circuitry. As one of their several functions, they
indicate when a bed portion has reached its limit of operation in
order to turn off its motor. Further, they indicate the relative
positions of various bed portions to provide coordinated operation
of their motors and motions.
Lastly, most electrical adjustable beds include some sort of master
control 17. The master control, when desired by the hospital or
medical staff, precludes operation of any or all of the various
movable portions of the bed. It may also have the switches for
esoteric configurations, such as the Trendelenburg positions.
The inputs feed into the control logic 18 along the connections 19,
20, 21 and 22. The control logic 18 in turn controls the elevation
motor 11, the knee motor 12, and the head motor 13 through the
double connections 23, 24 and 25, respectively. The doubled
representations of the connections 23, 24 and 25 result from the
fact that each motor may operate in a forward and in a reverse
direction; one of the connections stands for the forward direction
and the other for the reverse direction. The reversibility of the
motors allows for both the raising and lowering of the pertinent
bed portion.
The power supply system of FIG. 2 represents one of many that can
provide the various a.c. and d.c. potentials required for the
operation of the bed's circuitry shown in FIG. 3. The power for the
circuit appears on the leads 31 and 32 with the fuse 33 interposed
for safety. The potential then appears across the primary winding
34 of transformer 35 which also connects to ground 36 for safety.
Typically, the voltage supplied along the leads 31 and 32 lies
within the range of 115 to 120 volts a.c. The design of the
circuit, however, allows it to operate properly with the
alternating current in the range of 90 to 130 volts.
Two secondary windings 40 and 50 obtain power from the transformer
35. Current from the secondary winding 40 passes to the rectifier
41. After filtering by the capacitor 42, the voltage appears as -6
volts d.c. on the connection 43 labeled V.sub.D. The connections,
as shown, add -.notident.V. d.c. onto the high voltage side 32 of
the basic a.c. current supply. Thus, with respect to ground, the
voltage appearing at V.sub.D will have the usual 120 V. a.c.
configuration superimposed on a -6V d.c. background.
The other secondary winding 50 supplies its current to the
rectifier 51 followed by filtering through the capacitor 52, which
supplies a d.c. potential of 12V., labeled V.sub.E, with respect to
ground, along the connection 53. The 12 V. also passses through the
resistor 54 and regulator 55 which, with the assistance of resistor
56, provides a regulated 5 V., V.sub.C, along the connection 56.
The power supply shown in FIG. 2 suffices to provide the potentials
required to operate the control circuits shown in FIG. 3.
While other designs would suffice, the unit in FIG. 2 has the
advantage of isolating the V.sub.D supply of -6V. appearing on
connection 43 from both the ground connection 35 and the two a.c.
connections 31 and 32. This insulates the sensitive reed relay
switches of FIG. 3 from the very high potential tests required by
the Underwriters Laboratories. In that test, the two a.c. wires
providing the operating voltage supply connect to each other and to
one side of a 1,240 V. potential. The other side of the high
potential connects to the ground of the system. The test, of
course, requires the absence of any breakdown current leakage
between the high potential connections. However, this high
potential could, in fact, injure the reed relays. The separate
winding 40 precludes that injury.
A particular circuit diagram incorporating logic devices and
including all of the electrical components for an adjustable bed
with the exclusion of the power supply and the motors appears in
FIG. 3. The circuit, as shown, incorporates electronic logic
components. Other classes of logic devices, including mechanical
and hydraulic types, have found service in other settings.
Conceivably, with the appropriate supporting structures, they too
could suffice for an adjustable bed.
The diagram of FIG. 3 shows the inputs from the various types of
selection means or switches at the left. To the far right lie the
leads to the electric motors which, when directed by the rest of
the circuit, will carry the current to operate the appropriate
motors in their proper directions. In the middle appear the
electronic logic components which translate the signals from the
various switches and selection devices into the appropriate motor
operations.
The selection means includes the various switches indicated
generally at 70. These fall into the two categories of manually
actuated switches and position-indicating switches.
When activated, the manual switches provide electrical signals
which initiate changes in the bed configuration. Where an
adjustable bed portion merely has a limited and discrete number of
positions, a manual switch may have a separate setting for each of
the positions the bed portion may move to. A rotary switch having
the same number of positions as bed positions would suffice in this
instance. Moving the switch to the appropriate setting would induce
the bed portion to move to the corresponding position.
Generally, however, the adjustable bed portion possesses a
continuous range of positions. A manual switching device for this
situation could involve a selector moving over a circular or linear
dial having a range of positions corresponding to those of the bed
portion. The switch itself may involve a potentiometric device and
connect to a servo system which moves the bed portion to a selected
position.
More typically and preferably, the bed includes an on-off, or
single-pole, single-throw switch, to induce movement of the bed
portion in one direction and a second switch to produce motion in
the other direction. This represents the situation for the manual
switches shown at 70.
These switches include an elevation-up switch, labeled EU at 71.
Depression of the EU switch 71 will generally induce the elevation
motor of the bed to raise the elevation bed portion. The
elevation-down ED switch 72 performs a similar function to lower
the elevation portion of the bed. For the head portion, the head-up
HU switch 73 and the head-down HD switch at 74 perform similar
functions as do the knee-up KU switch at 75 and the knee-down KD
switch at 76 for the knee portion.
The bed includes five further manual switches. The bed-flat BF
switch at 77 has a three-fold function which can proceed
simultaneously. First, it lowers the knee portion; second, it
lowers the head portion; and third, it raises the elevation portion
so that the bed assumes a high and flat configuration. The bed-flat
BF switch 77 has two important purposes. The first occurs to
provide a particularly desirable configuration when the physician
or a nurse desires to examine the patient. Second, this switch also
induces the motion to retrieve the bed from a Trendelenburg or
reverse Trendelenburg position.
The Trendelenburg switch 78, of course, places the bed into the
Trendelenburg or reverse Trendelenburg position. For the schematic
shown in FIG. 3, the distinction between the Trendelenburg or
reverse Trendelenburg positions does not derive from the
electronics, but rather from mechanical couplings to the
Trendelenburg switch, as shown in F. J. Burst et al.'s U.S. Pat.
No. 3,821821 or J. S. Adams et al.'s U.S. application Ser. No.
996,212.
The switches discussed above normally take the form of
spring-loaded on-off switches loaded in the off position. In this
circuit which operates at low voltages, membrane switches present
the ideal performance characteristics.
The remaining three manual switches do not possess spring-loading.
These include the lock-out-elevation LOE switch at 79, the
lock-out-head LOH switch at 80 and the lock-out-knee LOK switch at
81. These normally appear, together with the bed-flat BF switch 71
and the Trendelenburg T switch 78, on a separate master-control
panel 17, in FIG. 1. Located away from the patient's normal reach,
and frequently at the foot of the bed, the switches control bed
motions which the hospital staff should undertake and not the
patient.
The lock-out switches preclude operation of the indicated motors,
notwithstanding the activation of other switches which otherwise
would result in the movement of the bed portion. In particular, the
LOE switch 79 immobilizes the elevation motor, the LOH switch 80
the head motor, and the LOK switch 81 the knee motor.
The position-indicating and dependent switches do not provide for
manual activation. Rather, they indicate to the logic circuitry the
positions occupied by various parts of the bed. More accurately,
they indicate which of a variety of possible situations the bed
occupies. For example, the limit-head-up LHU switch at 90 indicates
that the head portion of the bed has reached its highest limit. The
limit-head-down LHD switch at 91 similarly indicates that the head
portion occupies its lowest limit. Thus, either end of the
continuous range of positions produces a special indication. When
the head portion assumes a position intermediate these extreme
limits, no special indication results from these switches.
Intermediate the uppermost and the lowermost positions of the head
portion, the limit-head-contour LHC switch 92 comes into play. The
LHC switch 92 divides the range of head positions into two sets.
The first set includes all positions at and above a certain point,
generally 30.degree. of elevation, while the second set includes
those positions below that point. As discussed below, the LHC
switch 92 operates upon the depression of the head-down HD switch
74 to lower the knee portion of the bed but only when the head
portion occupies its lower range, or second set, of positions
mentioned above.
Similarly, the limit-knee-contour LKC switch 93 functions in the
simultaneous raising of the knee portion upon the depression of the
head-up HU switch 73. The LKC switch 93 stops the elevation of the
knee portion by the head-up HU switch 73 when the knee portion
reaches a certain height, generally 15.degree. of elevation.
As with the head portion, the knee portion also has a limit-knee-up
LKU switch 94 and a limit-knee-down LKD switch 95. The bed also
includes a limit-elevation-up LEU switch 96 and a
limit-elevation-down LED switch 97, as well as the
limit-Trendelenburg LT switch 98 for when the bed has reached its
greatest angle of inclination in either the Trendelenburg or
reverse Trendelenburg positions.
The hook H switch 99 represents the last position-indicating switch
in the drawing. It provides an extra measure of safety in operating
the Trendelenburg mechanism. The type of bed shown in U.S. Pat. No.
3,821,821 to Burst et al. or in Adams et al's application Ser. No.
496,212 rises to its highest point before inclining into the
Trendelenburg position. While in its highest position, one of two
hooks, depending upon which end of the bed declines, engages a
catch in order to retain the other end in an elevated position. If
not securely engaged, that end of the bed could possibly slip and
fall when the first end lowers. Accordingly, the hook H switch 99
indicates the secure hook engagement before either end of the bed
may decline.
A position-indicating switch need only translate the relative
mechanical motion of the two bed parts into electrical signals.
Accordingly, it may attach to one of the parts and abut against the
other when the latter has reached a preselected point of travel.
Alternately, it may follow a cam attached to the second part. Other
common arrangements would also clearly suffice.
Most of the components for the circuit in FIG. 3 may attach to a
printed circuit board with their interconnections printed upon the
board itself. The switches, however, because of their locations at
various points on the bed do not constitute part of the board.
Accordingly, they attach to the board through the series of bus
bars indicated generally at 20. The figure shows a generally
convenient arrangement of the bars.
For the safety of the bed's occupant, the switches, as well as most
of the circuit components, operate at voltages below about 25 V.
and generally in the range of 5 to 12 V. These low voltages do not
allow the current in the switches to arc over the small gap that
exists immediately prior to their closing and after their opening
as with higher voltages. This sparking across the gap has the
desirable effect of burning off corrosion and other residues on the
metallic contacts. Without such sparking, the corrosion will
remain. Consequently, the low voltage switches indicated at 70 will
give somewhat improved performance over an extended period of time
if their contacts include a noncorrosive metal. The noble metal
gold, of course, represents an ideal choice. Silver cadmium oxide
represents another possibility.
However, the circuitry incorporates a further safety feature in the
event that a switch does malfunction and remain open. This
malfunction will result in the inoperation of a motor rather than
vice versa. Thus, the inability of a switch to close properly will
not cause undesired and perhaps dangerous motion of the bed.
The resistors, indicated generally at 130, translate the openings
and closings of the switches 70 into electrical impulses suitable
for further processing by the circuit logic components. Generally,
for the logic components to operate, the signals must vary between
two voltage levels, for example, between 0 V. and 5 V. Handbooks
published by component producers list the voltages required for
their products.
The EU switch 71, the particular resistor 131, and the connection
to the voltage source V.sub.C exemplify the voltages resulting from
a switch's opening and closing. While the EU switch 71 remains
open, the juncture 132 connects electrically only to the resistor
131 and thence to the source of voltage V.sub.C. Inasmuch as little
or no current flows through the resistor 131 in the event of the
open switch 71, no voltage drop occurs across the resistor 131.
Accordingly, the juncture 132 and the lead attached to it, labeled
EU, remain substantially at the voltage level of V.sub.C, 5 V. in
this instance. On the other hand, closing the switch 71 results in
the juncture 132 connecting directly through the switch 71 to
ground at 133 which, of course, lies at 0 V. Thus, closing and
opening the switch results in the juncture 132 and the lead EU
going between 5 V. and 0 V., respectively.
The symbolism of EU for the switch 71, and EU for the lead after
the resistor 131 results from the standards adopted for a logic
circuit. Generally, the voltages used in a logic circuit can exist
at either one of two levels; in this case, for example, 0 V. and 5
V. represent those levels. Usually, the higher voltage level
represents the positive state with the lower voltage called
negative. The output of the logic components, of course, depends
upon the positive or negative values of the inputs to that
component.
Frequently, a component with a single input will produce the
negative of that input as its output. In this case, a symbol
standing by itself represents the input variable and the same
symbol with a bar over its top represents the negative of the
input. Alternately, the symbol with a bar may stand for the input,
and the symbol itself used for the output.
In this case, for example, EU stands for the functioning of the
switch 71. In particular EU is defined as positive upon an actual
depression and closing of the switch 71. As discussed above, when
the EU switch 71 closes and thus achieves its positive state, the
juncture 132 and, thus, the lead labeled EU assumes the negative
state of 0 V. Thus, the lead EU always has the negative value of
the EU switch 71. Accordingly, for convenience, the lead itself has
the label EU which represents its value. Similarly, other leads in
the diagram will bear labels actually representing their voltage
states.
Similar to the EU switch 71, most of the manually actuated switches
assume their positive state when closed and their negative state
when open, In addition to the EU switch 71, these include the ED
switch 72, HU 73, HU 74, KU 75, KD 76, BF 77, and T 78. The
lock-out switches LOE 79, LOH 80, and LOK 81 perform in the reverse
fashion. To lock out a motor, the switch opens and assumes its
positive state.
With the exception of the Trendelenburg hook H switch 99 and
excluding the limit-head-contour LHC switch 92 and the
limit-knee-contour LKC switch 93, all of the bed-position
indicating switches have a positive value when open and a negative
value when closed. All of the above states accord with the notion
that because of corrosion possibly preventing a switch's closure,
an open switch results in the inactivation of its respective motor.
Thus, for example, the limit-head-up LHU switch 90, opens when the
head portion reaches its upper limit. This causes inactivation of
the head motor. Yet, the head portion at its upper limit represents
the positive state of the corresponding switch. With the LHU switch
90 open, however, the juncture 134 reaches the higher level of 5 V.
and, accordingly, assumes the positive state as does the lead LHU
connecting to it.
Conversely, when the head portion does not occupy its highest
position, the LHU switch 90 remains closed. This represents the
negative state of the switch 90, as well as the LHU lead to the
right of juncture 134.
The Trendelenburg hook H switch 99 has the opposite function of the
other bed-position switches. When the hook actually engages, the
switch closes to allow actuation of the motor to achieve the proper
Trendelenburg tilt. This represents its positive state but H then
descends to its negative state and, thus, has a converse behavior
of the switch 99.
The lock-out-elevation LOE switch 79, the lock-out-head LOH switch
80, the limit-head-contour LHC switch 92, and the
limit-knee-contour LKC switch 93, do not provide information to the
more usual circuit logic components in the drawing. The first two
disconnect the elevation and head switches from ground to
inactivate them. The latter two interconnect the
head-and-knee-motor leads to coordinate the movements of the head
and knee sections.
As discussed above, the elevation-up EU switch 71 operates by
connecting the junction 132 to ground potential. Thus, to raise the
bed, the junction 132 must go from 5 V. to ground.
However, the connection between ground at 133 and the EU switch 71
first passes through the lock-out-elevation LOE switch 79.
Depressing and thus opening the LOE switch 79 disconnects the EU
switch 71 and the juncture 132 from their ground. Unable to
connect, upon the activation of the LOE switch 79, to ground, the
EU switch 71 thus becomes inoperative. For the same reason, the
elevation-down ED switch 72 cannot operate upon the opening of the
LOE switch 79. Accordingly, the LOE switch 79 renders both the ED
switch 71 and the EU switch 72 nonfunctional and the bed will not
rise or lower in response to them.
Similarly, both the head-up HU switch 73 and the head-down HD
switch 74 connect to ground through the lock-out-head LOH switch
80. Activating and thus opening the LOH switch 80 prevents the
raising or lowering of the head portion through the HU or HD
switches 73 or 74.
The notations of EU, ED, HU and HD in FIG. 3 signifies the actual
functioning of the appropriate switches. The inactivation of these
switches by the LOE switch 79 or the LOH switch 80 precludes them
from supplying the electrical information characteristics of the
EU, ED, HU, or HD functions. Thus, this notation on the leads in
FIG. 3 and in the following discussion implies that the EU switch
71, the ED switch 72, the HU switch 73, and the HD switch 74 have
not undergone inactivation by the LOE switch 79 or LOH switch 80,
respectively.
The LHC and LKC switches 92 and 93 also work through other
switches. In particular, upon the simultaneous closing of the LKC
switch 93 and the head-up HU switch 73, the ground potential of 0
V. passes through the HU switch 73 to the juncture 135, through the
diode 136, and the LKC switch 93, back up to the junction 137 on
the lead to the knee-up KU switch 75. Supplying approximately 0 V.
to this lead, as seen from above, produces the same effect as
closing the knee-up KU switch 75 to raise the knee portion of the
bed. Thus, upon actuating the head-up switch 73, the knee portion
of the bed also receives a signal to raise, provided the
limit-knee-contour LKC switch 93 remains closed. And, the
position-indicating LKC switch 93 opens only when the knee portion
of the bed rises above a preselected level, conveniently 15.degree.
of knee elevation.
When the knee portion elevates beyond 15.degree., the LKC switch 93
opens and precludes the transmission of the signal from the switch
73 to the knee-up KU lead at 137. This terminates the raising of
the knee portion in response to the depression of the head-up HU
switch 73. Nonetheless, the knee-up switch 75, of course, will
permit further elevation of the knee portion if desired.
Conversely, with the head-up HU switch 73 open, the juncture 135
stays at the postive potential of 5 V. Upon closing the KU switch
75, however, the juncture 137 goes to 0 v. and remains unaffected
by the 5 V. at the point 135, due to the blocking action of the
diode 136.
Similarly, the head-down HD switch 74 connects to the juncture 138,
the diode 139, the limit-head-contour LKC switch 92 and back up to
the juncture 140 on the knee-down KD lead. As with the
limit-knee-contour LKC switch 93, this connection causes the knee
portion to descend upon the simultaneous closing of the head-down
HD switch 74 and the limit-head-contour LHC switch 92. The LHC
switch 92, however, only closes when the head portion descends
below a predetermined position, typically 30.degree. of head
elevation. Lowering the head portion from a position above
30.degree. will not cause the knee portion to descend until the
head portion goes below 30.degree.. Again, in going in the reverse
direction, the diode 139 prevents the actuation of the knee-down KD
switch 76 from affecting the operation of the head portion of the
bed.
The notation employed in FIG. 3 and the discussion below does not
indicate the operation of the knee portion upon the depressing of
the head-up or head-down switches. Accordingly, whenever the symbol
HU occurs, it also connotes the operation of the knee-up motor
provided the knee portion of the bed remains below 15.degree..
Similarly, the symbol HD also includes the operation of the
knee-down motor provided the head of the bed has no more than
30.degree. of elevation.
The above discussion shows that proper interaction of the knee and
head portions of the bed procedes through the diodes 136 and 139.
Consequently, in this circuit, they function as very simple logic
devices.
The circuit in FIG. 3 receives its power supply and also connects
to the motors at the bus bars at the right of the drawing,
indicated generally at 150. The connections at 151 and 152 in
particular provide the basic source of a.c. power.
The bus bars at 50 also include two connections between the circuit
and each of the three motors in the bed. One of these two
connections supplies current to the winding of the motor which
results in the elevation of the relevant bed portion. The other
connection provides current along an alternate winding on the motor
and causes the motor to operate in the reverse direction and lower
the bed portion. As an example, the connection 153 provides current
to the winding of the elevation motor which raises the bed. Current
provided along connection 154 goes to the winding of the elevation
motor that lowers the bed.
According to the typical convention, the output from connection 153
to the elevation-motor-up EMU winding is defined as positive when
current actually flows through that connection to the winding.
Otherwise, it remains in its negative state. This also holds true
for the other connections including the elevation-motor-down EMD
connection 154, and those for the head-motor-up HMU,
head-motor-down HMD, knee-motor-up KMU, and knee-motor down
KMD.
The current to the elevation-motor-up EMU connection 153, flows
from the 120 V. a.c. connection 151, to the juncture 155, and
through the electronically controlled triac switch 156. Thus, the
triac 156 controls the current supply through the EMU connection
153 and consequently to the winding of the elevation motor which
raises the bed.
The triac switch 156 in turn receives its control voltages from the
resistor 157 and then from the reed relay device 158. The closing
of the reed switch 159 within the reed relay 158 allows the
potential V.sub.D to pass from the junction 160 and through the
switch 159 and the resistor 157.
As discussed above, V.sub.D comes from a separate winding 40 on the
transformer 35 in FIG. 2 and provides a d.c. potential of -6 V. on
top of usual a.c. voltage of approximately 120 V. The V.sub.D
voltage when applied to the triac 156 closes it and allows the
current of 120 V. from the connection 151 to pass to the
elevation-motor-up EMU connection 153. With the reed 159 open, the
switch 156 also opens and no current passes to the EMU connection
153.
The reed 159, in turn, closes only when current flows in the coil
portion 161 of the reed relay 158 establishing the appropriate
magnetic fields. However, to have current in the coil 161, the
potential EMU at the junction 162 must be in its negative state of
0 V. With EMD at the lower potential of 0 V., current from the
higher potential source V.sub.C at 5 V. passes through the coil 161
and to the juncture 162, allowing the reed 159 to close. When EMU
becomes positive it closely approximates the potential V.sub.C and
no current flows. The diode 164 allows energy in the coil 161 to
dissipate.
Thus, a negative value for EMU results in the EMU connection 153
going positive and in the operation of the elevation motor to raise
the bed. Conversely, when EMU becomes positive, no current flows
through the coil 161; the reed 159 opens; the EMU connection 153
becomes negative; and the elevation motor will not raise the bed.
Thus EMU display opposite behavior; when one becomes negative, the
other goes positive, and vice versa.
The triac 156, the resistor 157, and the reed relay 158 have
greater significance than merely taking the negative of EMU to
provide EMU. These components separate the high a.c. 120 V. needed
to operate the elevation motor from the lower voltages generally
under 25 volts which appear on the circuit logic components and,
more particularly, the selection means 70 and thus near the
patient.
Specifically, the reed relays physically separate the two voltages.
The coil 161 operates at the lower d.c. voltage; the reed 159
operates at the high a.c. voltage; and a section of glass with
other material separates and insulates the two from each other. The
high voltage appearing at the other motor connections have the
separation from the low voltages of the diode, reed relay, resistor
and triac indicated generally at 170.
Furthermore, on the actual circuit board a printed ground line
separates the high from the low voltage connections and prevents
the passage of undesired current from the former to the latter. The
low voltage connections of the reed relays appear on one side of
the ground line with the high voltage connections on the other.
An explanation of the operation of the circuit in FIG. 3 requires a
statement of the motor operation EMU, EMD, and so forth or,
equivalently, of their negatives EMU, in terms of the inputs from
the selection means at 70. In other words, the actual operation of
the elevation, head, and knee motors depend upon the state of the
various switches at 70 as indicated by their alphabetic symbols;
accordingly, an analysis of the circuit relates the operation of
the various motors to these inputs.
An analysis of the circuit in FIG. 3 utilizes standard symbolic
logic with its techniques and notations. Since the various
components shown in the logic portion of the circuit operate upon
their inputs, they analogize directly to logic operator
symbols.
The figure includes three basic types of components, the inverter,
the NAND gate, and the NOR gate. Each of these operates only on
inputs which generally assume only one of two values such as that
provided by the inputs 70 in FIG. 3. Furthermore, the output of
each component assumes only one of two values; the higher voltage
value corresponds to the positive state, and the lower value of 0
V. to the negative state.
In this type of system where each connection assumes one of two
values, the operation of each component finds expression in terms
of a "truth table." This table merely relates the state of the
output of a component to the state or states of the inputs.
The inverter represents one of the simpler logic devices. It merely
converts a positive input into a negative output and vice versa. IN
terms of the voltages used in FIG. 3, where a 5 V. potential enters
the inverter, a 0 V. potential exits.
According to the operation described above, the inverter has the
following truth table:
Table 1 ______________________________________ Truth Table for an
Inverter Input Output ______________________________________ POS.
NEG. NEG. POS. ______________________________________
The entries to the left of the vertical double line include all of
the possible inputs to the inverter with the entries on the right
side representing the outputs.
An example of the inverter appears at 181 in FIG. 3. It converts
the value of the input, shown as HD to its negative which could
carry the notation of HD. However, the negative of a negative
becomes the positive and, accordingly, the output of the inverter
181 appears as HD.
The little circle attached to the right point of the triangle of
the inverter symbol 181 signifies the negative functioning of the
component. The same notation also appears on other items.
The NOR gate represents a further type of logic device used in FIG.
3. An example of a NOR gate appears schematically at 182. However,
the NOR gate combines two other components -- an OR gate followed
by an inverter; the little circle on the right of the NOR gate 182
represents the inverting function as with the inverter.
Consequently, considering each step sequentially simplifies the
explanation of the NOR gate.
The OR gate provides a positive output when it has at least one
input in the positive state. Only when all of its inputs are
negative does the output of the OR gate become negative.
Accordingly, it has the following truth table:
Table 2 ______________________________________ Truth Table for an
OR gate Inputs Output ______________________________________ POS.
POS. POS. POS. NEG. POS. NEG. POS. POS. NEG. NEG. NEG.
______________________________________
The NOR gate has almost the same effect except that it then inverts
the output of its OR-gate portion. Accordingly, the NOR gate has
the following truth table which also includes the OR function.
Table 3 ______________________________________ Truth Table for a
NOR gate OR gate NOR gate Inputs Output Output
______________________________________ POS. POS. POS. NEG. POS.
NEG. POS. NEG. NEG. POS. POS. NEG. NEG. NEG. NEG. POS.
______________________________________
Thus, the NOR gate's output becomes positive only when both inputs
occupy the negative state; with either input positive, it has a
negative output.
Where an OR gate has inputs of A and B, the output has the notation
A + B, because of similarities to the ordinary arithmatic function
of addition. The NOR gate simply negatives the output of the OR
gate and, accordingly, for the same inputs of A and B, A +to B
symbolizes its output.
The NOR gate 182 exemplifies the device's functioning in the
circuit. It has the value HD as one input. As seen from the figure,
the other input has the value T.sub.1 + BF. From above, this
results from a prior OR gate with T.sub.1 and BF as its inputs. The
component T.sub.1 represents the first stage of the Trendelenburg
operation in which the head and knee descend and the bed rises, as
discussed below. Were gate 182 merely an OR gate, it would have the
output of HD + T.sub.1 + BF; as a NOR gate, however, it has the
output of HD + T.sub.1 + BF. Consequently, if HD, T.sub.1, or BF or
any combination of them is positive, then the NOR gate 182 has a
negative output. Where HD, T.sub.1, and BF all remain negative,
then the NOR gate 182 has a positive output.
The NAND gate represents a further type of device used in FIG. 3
and appears schematically at 183. Again, the NAND gate combines the
sequential application of two separate devices, the AND and the
inverter. The AND gate, which appears the same as the NAND gate 183
without the little circle adjacent to its right, produces a
negative output unless both of its inputs occupy the positive
state. Accordingly, the AND gate has the following truth table:
Table 4 ______________________________________ Truth Table for an
AND gate Inputs Output ______________________________________ POS.
POS. POS. POS. NEG. NEG. NEG. POS. NEG. NEG. NEG. NEG.
______________________________________
To achieve the results of a NAND gate requires the inversion of the
output of an AND gate. Accordingly, Table 5 prevents the results
for a NAND gate and also includes an AND gate having the same
inputs.
Table 5 ______________________________________ Truth Table for a
NAND gate AND gate NAND gate Inputs Output Output
______________________________________ POS. POS. POS. NEG. POS.
NEG. NEG. POS. NEG. POS. NEG. POS. NEG. NEG. NEG. POS.
______________________________________
Where the AND gate has the two inputs A and B, its output has the
notation of A. B. The NAND gate inverts the AND gate output and,
accordingly, has the notation A. B. This notation indicates an
underlying similarity to the usual mathematical function of
multiplication.
Despite their apparent dissimilarities, the NOR and NAND functions
bear a relationship to each other, which receives expression in
DeMorgan's Theorems. These state the following:
A + B = A . B (1)
A . B = A + B. (2)
These theorems submit to immediate proof using the usual truth
tables.
DeMorgan's Theorems allow an understanding of the NAND gate 183 and
the NOR gate 184 which provides one of its inputs. The NOR gate 184
receives one input from the NOR gate 182 which, from above, has the
output HD + T.sub.1 + BF. LHD represents the other input to NOR
gate 184. Accordingly, the NOR gate 184 has, as its output, (HD +
T.sub.1 + BF) + LHD. However, applying DeMorgan's Theorems to the
plus sign between the parenthesis and LHD gives (HD + T.sub.1 +
BF). LHD. Lastly, since the negative of a negative becomes
positive, the input of the NOR gate 184 has the following
expression (HD + T.sub.1 + BF) . LHD.
The output of the NOR gate 184 has a simple interpretation
according to this expression. Recalling that the dot symbolizes the
AND function, the expression assumes a positive value when the
terms on either side of the plus sign are also positive. The
expression within the parenthesis is positive when HD, T.sub.1, or
BF or any combination of them becomes positive. This occurs when
depressing the HD switch 74 or the BF switch 77 or the bed
undergoes the first phase of the Trendelenburg operation. For the
other term, a positive LHD requires a negative LHD. Thus, the NOR
gate 184 becomes positive only when the head portion has not
reached the limit-head-down and the head-down, the bed-flat, or the
first phase of the Trendelenburg operation is selected.
The output of the NOR gate becomes one of the inputs to the NAND
gate 183. The NAND gate 183, in turn, prevents ambiguous signals to
the HMD line which goes to the head-motor-down winding. By the
above rules and with HU as the other input to the NAND gate 183,
its output becomes
(HD + T.sub.1 + BF) .sup.. LHD .sup.. HU = HMD. (3)
Taking the negative of both sides, the expression for when the
head-motor-down operates becomes
HMD = (HD + T.sub.1 + BF) .sup.. LHD .sup.. HU. (4)
Accordingly, the head motor operates to lower the head when:
1. the head-up HU switch 73 is not depressed;
2. the head portion has not reached its limit of downward motion;
and
3. the head-down operation, the bed-flat operation, or phase one of
the Trendelenburg operation, all of which have the effect of
lowering the head portion, is selected. Thus, the logic has
precluded ambiguous commands to the head motor by preventing any
current to the head-motor-down winding upon the depressing of the
head-up HU switch 73. Moreover, it causes the head-motor-down to
cease operation upon the activation of the limit-head-down LHD
switch 91. Lastly, and when the above two conditions have become
satisifed, it allows the actual operation of the head-motor-down
upon the activation of any of the three switches which lower the
head; these include the head-down switch 74, the bed-flat switch
77, or the Trendelenburg T switch 78 while the bed remains in the
first phase of the Trendelenburg operation.
By a similar process of reasoning, and from the NOR gate 185 and
the NAND gate 186, the functioning of the head-motor-up HMU follows
the expressions:
HMU = HU . LHU . (HD + T.sub.1 + BF). (5)
Equation (5) also has a simple interpretation in terms of the
inputs to the logic circuitry. First, the operation of the
head-motor-up requires, of course, the activation of the head-up HU
switch 73. Further, according to the second term, the head portion
must not have reached its upper limit; otherwise, the circuitry
will turn off the head-motor-up.
The parenthesized expression represents selections on the inputs 70
which would normally cause the head motor to lower the head. To
preclude ambiguous commands to the head motor, if any of these
become activated, the head-motor-up will not operate.
Expressions (4) and (5) do not completely determine the functioning
of the head motor. As discussed above, the lock-out-head LOH switch
80, when open, will prevent the operation of the head motor by
either the head-up HU switch 73 or the head-down switch 74. This,
of course, allows the hospital staff to preclude the operation of
the head motor when required for a particular patient.
The same reasoning process, applied to the inverter 191, the NOR
gates 192 through 196, and the NAND gates 197 and 198, leads to the
following expressions for the operation of the knee-motor-down KMD
and the knee-motor up KMU:
KMD = [(KD .sup.. LOK) + T.sub.1 + BF]. LKD .sup.. (KU .sup.. LOK)
(6)
KMU = (KU .sup.. LOK) .sup.. LKU .sup.. [(KD .sup.. LOK + T.sub.1 +
BF]. (7)
These equations resemble each other, and basically have the same
effect. They state that the knee motor will operate in either the
up or down direction provided first, that the lock-out-knee LOK
switch 81 has opened; second, that the limit of motion in the
desired direction has not been reached; third, that a switch
selecting the direction of the knee motor opposite from that
desired has not been depressed; and fourth, that a manual switch
that would cause the knee motor to operate in the desired direction
has, in fact, closed. With regards to these conditions, only the
knee-up KU switch 75 causes the knee motor to raise the knee while
either the knee-down KD switch 76, the bed-flat BF switch 77 or
T.sub.1 of the Trendelenburg operation, actuated by the T switch
78, would cause the knee portion to go down. Accordingly, the
latter three must not close while the knee-up KU switch 75 attempts
to raise the knee. Analogous remarks also apply for the
knee-motor-down KMD. Thus, the logic components prevent current
flowing ambiguously through both windings of the knee motor.
Moreover, the logic also incorporated the lock-out function as well
as turning off the motor when the knee portion has reached its
limit of motion in the desired direction.
Lastly, with regards to the knee motors, the head-up HU switch 73
and the head-down HD switch 74 activate the knee-up and the
knee-down directions provided that the knee portion remains below
15.degree. and the head portion falls below 30.degree.,
respectively. As discussed above, depressing the head-up HU switch
73, for example, with the knee portion below 15.degree. will
activate the knee-up KU leads exactly as though the knee-up KU
switch 75 had closed. This satisfies the KU condition of equations
(6) and (7) as fully as the actual closing of the KU switch 75.
NAND and NOR gates may further combine into various groupings with
different behavior characteristics. The two NOR gates 201 and 202
represent one such grouping, called a NOR-gate flip-flop. In the
NOR-gate flip-flop, the output of each NOR gate constitutes one of
the inputs to the other NOR gate. The interconnections between the
NOR gates 201 and 202 satisfy this criterion.
With one input thus already occupied, each NOR gate has one
remaining available input. The relationships between the outputs of
the NOR gates forming the flip-flop to these available inputs also
finds expression in a truth table, such as the following:
Table 6 ______________________________________ Truth Table for a
NOR gate flip-flop Input to Input to Output from Output from NOR
gate1 NOR gate 2 NOR gate 1 NOR gate 2
______________________________________ NEG. POS. POS. NEG. POS.
NEG. NEG. POS. POS. POS. NEG. NEG.(6) NEG. NEG. (last POS. NEG.
POS.) NEG. (last NEG NEG. POS. POS.)
______________________________________
Leading to the flip-flop of NOR gates 201 and 202, the inverter 203
changes ED to ED and supplies it as the input to the NOR gate 201.
The input to the NOR gate 202, which comes from the NOR gate 204
and the NAND gate 205, has the value of EU + H + T.sub.1 + BF.
However, the circuit only utilizes the output from the NOR gate
202, which bears the notation of MED for
"maintained-elevation-down." According to Table 6 above, the output
MED has the value given by the following table:
Table 7 ______________________________________ Truth Table for the
value of MED Input to NOR Input to NOR MED gate 201 gate 202 ED EU
+ H + T.sub.1 + BF ______________________________________ NEG. POS.
NEG. POS. NEG. POS. POS. POS. NEG. NEG. NEG. (last POS.) NEG. NEG.
(last POS.) NEG. POS. ______________________________________
The last two lines of Table 7 merit particular attention. On both
of those lines, both inputs have a negative value. Yet, the outputs
on the two lines very from each other and depend not only upon the
present values of the inputs, but upon their prior history.
Specificallly, the value of the output in the instance where both
inputs remain negative depends upon which of the two inputs last
had a positive value. Thus, the flip-flop operates as a memory
device, remembering which of the two inputs last had a positive
value.
Lines 2 and 5 of Table 7 show that the maintained-elevation-down
MED value becomes positive under two circumstances. Both of these
require a negative input of EU + H + T.sub.1 + BF to the NOR gate
202. That implies that not one of these is positive. EU, T.sub.1,
and BF represent functions which would raise the bed and, thus, go
contrary to the elevation-down ED function. The hook H becomes
positive during a Trendelenburg operation. Any of these four will
disenable the maintained-elevation-down MED function.
As for the ED input to the NOR gate 201, MED becomes positive when
the elevation-down Ed output of the NOR gate 202 first gores
positive; the latter occurs upon the depressing of the ED switch
72. However, after the releasing of the ED switch 72, ED becomes
negative but will have been the last positive. This fact allows the
MED value to remain positive even though the elevation-down ED
switch 72 has returned to its negative value.
Thus the flip-flop of the NOR gates 201 and 202 allow the bed to
start down upon the depressing of the ED switch 72 and to continue
descending even after the release of the ED switch. Pressing the
elevation-up EU switch 71, the Trendelenburg T switch 78 or the
bed-flat BF switch 77 will stop the downward movement of the
bed.
The above description of MED then allows the expression of the
elevation-motor-up EMU and the elevation-motor-down EMD in terms of
the inputs 70, MED, and T.sub.3, where T.sub.3 represents the third
and inclining phase of the Trendelenburg operation. Following the
various inputs through the inverter 206, the NOR gates 207 through
213, and the NAND gates 214 and 215, EMU and EMD become:
EMD = [MED + (T.sub.3 .sup.. LT)].sup.. LED .sup.. [(EU .sup.. H) +
T.sub.1 + BF] (8)
EMU = [(EU .sup.. + T.sub.1 + BF].sup.. LEU .sup.. ED .sup.. [MED +
(T.sub.3 .sup.. LT)].sup.. LED. (9)
The capacitor 220 connects between the potential source V.sub.C and
the NOR gate 201, while the resistor 221 couples between V.sub.C
and the output of the NOR gate 201. Upon the application of power
to the circuit, the capacitor 220 retards the rise of power to the
NOR gate 201 and the resistor 221 forces its output to the positive
state. The resistor 222 connects to ground from the output of the
NOR gate 202, forcing it to the negative state. As a result, the
NOR gate 202 initially controls the flip-flop which cannot assume a
positive maintained-elevation-down MED state. Consequently, the bed
will not start down on its own.
The resistor-capacitor combinations of 223-224 and 225-226,
respectively, retard the intial supply of power to the separate
windings of the elevation motor. This delay allows the motor tot
stop momentarily before rversing its direction. Depressing a swtich
which would induce the motor to raise the bed also retracts the
motor from its maintained-elevation-down MED condition. The slight
delay thus introduced dissipates what cold otherwise amount to
signficant torque forces on the motor.
To remove the flip-flop action of the NOR gates 201 and 202, the
figure also shows, in phatom, a connection from the input of the
NOR gate 201 to ground at 227, instead of to the output of the NOR
gate 202. Making this change on the circuit board converts the NOR
gate 201 into an inverter and produces for output of the NOR gate
202 the value of ED .sup.. (EU + H + T.sub.1 + BF). As a result,
the elevation-motor-down EMD operates only during the time of the
actual depression of the elevation-down ED switch 72.
As alluded to above, the Trendelenburg operation has three phases,
symbolized by T.sub.1, T.sub.2 and T.sub.3. The relationship
between the phases derives from another type of flip-flop, composed
of the two NAND gates 241 and 242 near the bottom of FIG. 3. As
with the NOR-gate flip-flop, the output of the first NAND gate 241,
labeled Q, constitutes one input to the second NAND gate 242.
Similarly, the output of the second NAND gate 242; labeled Q*,
provides an input to the first NAND gate 241. The typical NAND-gate
flip-flop has the following truth table:
Table 8 ______________________________________ Truth Table for a
NAND-gate flip-flop Input to Input to Output from Output from NAND
gate NAND gate NAND gate NAND gate 1 2 1 2
______________________________________ POS. NEG. NEG. POS. NEG.
POS. POS. NEG. NEG. NEG. POS. POS. POS. POS. (last NEG. POS. NEG.)
POS. (last POS. POS. NEG. NEG.)
______________________________________
This table compares closely to the NOR-gate flip-flop's table,
Table 6. Nonetheless, unlike the NOR-gate flip-flop, with inputs to
the flip-flop positive the outputs depend upon which inputs had
last been negative.
The input to the NAND gate 241 derives from the usual reasoning
applied to the inverters 243 and 244, the NOR gate 245, and the
NAND gates 246 and 247. Accordingly, this input has the value of
LHD + LKD + LEU + H. The value of the input to the NAND gate 242
has the value of BF + LEU as derived from the inverter 250 and the
NAND gate 251.
The output from the flip-flop of NAND gates 241 and 242 appears in
the following table which also has the negatives of the Q and Q*
values.
Table 9
__________________________________________________________________________
Truth Table for the value of Q, Q, Q*, and Q* Input to Input to
NAND gate 241 NAND gate 242 Q Q Q* Q* LHD + LKD + LEU + H BF + LEU
__________________________________________________________________________
POS. NEG. NEG. POS. POS. NEG. NEG. POS. POS. NEG. NEG. POS. NEG.
NEG. POS. NEG. POS. NEG. POS. POS (last NEG.) NEG. POS. POS. NEG.
POS. (last 0) POS. POS. NEG. NEG. POS.
__________________________________________________________________________
The NOR gate 260 has the output of T .sup.. Q. This defines T.sub.1
as the occurrence of the closing of the Trendelenburg T switch 78
simultaneously with the flip-flop providing a positive value for Q.
The first and fourth lines of Table 9 show that Q has a positive
value only upon the nonsatisfaction of one of the conditions of
limit-head-down LHD, limit-knee-down LKD, limit-elevation-up LEU,
or the engagement of the hook H. In fact, T.sub.1 has the purpose
of allowing the head and knee portions to reach their lower limits,
the bed to reach its highest level, and the engagement of the
hook.
After the flip-flop, the NOR gate 261 combines T.sub.1 with
bed-flat BF. The inverter 262 provides the output seen above in the
diagram of T.sub.1 + BF. That, of course, has a positive value
during either the first phase of the Trendelenburg operation or the
bed-flat operation.
The NOR gate 263 whose output by definition provides T.sub.3, shows
that the third phase occurs when Q* has a negative value and
simultaneously the Trendelenburg T switch 78 remains closed. Thus,
as shown in the second line of Table 9, Q* reaches a positive value
to begin T.sub.3 only after the first phase accomplishes the four
objectives of LHD, LKD, LEU and H. The short period of time between
T.sub.1 accomplishing its objectives and Q* becoming negative
constitutes T.sub.2.
The last line of Table 9 indicates that after meeting the four
conditions of T.sub.1, the bed remains in T.sub.3 even though one
or more no longer remain satisfied. This occurs for two reasons.
First, in T.sub.3, the bed lowers and tilts precluding it from
staying at its limit-elevation-up LEU position. Second, in either
Trendelenburg positions, the head or knee portions may raise upon
the selection of the appropriate switch.
While the hook H remains engaged, the elevation-up EU switch 71 and
elevation-down ED switch 72 becomes inoperative. This readily
appears from the H term in Equation (9) for EMU and in the truth
table, Table 7, for MED. Thus, to raise the bed out of a
Trendelenburg position requires the activation of the bed-flat BF
switch 77. When the bed reaches the limit-elevation-up LEU by
depressing the bed-flat switch, it no longer remains in
T.sub.3.
Providing an idication of a proper connection with ground becomes
especially important in the case of equipment occupied by patients.
For this bed, the bulb 270 in FIG. 3 lights when the bed and its
circuitry have lost contact with ground. It also shines when the
common connection and the 120 V. potential have crossed in their
wiring. Lastly, it indicates when the potential of the common
connection, which should stay near ground, has risen unacceptably
above that value.
The resistors 271 through 274 on the one hand and 275 on the other
provide a potential divider to control the normal input voltage of
the gate of the field-effect transistor 276. The output of that
transistor, in turn, controls the state of conductivity of the more
usual p-n-p transistor 277. In the absence of the proper connection
to ground or the proper wiring, the voltage on the gate of the FET
276 lowers, allowing it to conduct. This lowers the potential on
its drain, and thus on the base of the transistor 277 which also
becomes conducting allowing the lighting of the bulb 270. The
diodes 278 and 279, as well as the resistors 280 and 281, assist in
the control of the transistor 277. The switch 282 tests various
components of the testing circuit. By raising the grid of the
field-effect transistor 276 to a value of V.sub.E = 12 V., closing
the switch 282 turns on the bulb 270 provided the transistor 276
and 277 as well as the bulb 270 have not become inoperative.
An alternate ground test device appears in FIG. 4. This unit could
connect to the circuit of FIG. 3 by interposing the diode 300
between potential supply V.sub.D and the juncture 160 leading to
the switch portion 159 of the reed relay 158.
As discussed above, each time a motor operates, current must flow
from V.sub.D through the juncture 160 and across one of the
switches. As a result, in FIG. 4, any selection which operates a
motor will produce current flowing across the diode 300.
The resistance of the diode 300 produces a potential drop across
itself and also between the emitter and the base of the transistor
301, turning it on. At the instant the transistor 301 turns on, as
well as before, the capacitor 302 bears no charge having previously
discharged through the resistor 303.
Carrying no charge, the capacitor 302 remains in the negative state
which, after passing through the resistor 304, provides the input
to the NOR gate 305. Having both of its inputs tied together, as
seen in Table 3 for the NOR gate, the NOR gate 305 acts as an
inverter and provides a positive output to the NOR gate 306.
Thus, with either of its inputs positive, the NOR gate 306 provides
a negative output to the NOR gate 307, which forms part of the
flip-flop composed of itself and the NOR gate 308. Table 6 for the
NOR-gate flip-flop shows that this negative input to the NOR gate
307 cannot affect the state of the flip-flop as initially set by
the resistors 309 and 310 and the capacitors 311 and 312 to provide
a negative input to the base of the transistor 313. This negative
input to the transistor 313 does not allow current to pass through
it or the incandescent bulb 314 which, accordingly, remains
off.
When the transistor 301 turns on, the capacitor 302 begins to
charge, drawing current through the coil 305 of a reed relay. The
current passes through the coil 305 closing the switch portion 306
of the reed relay.
When the switch 306 closes and with a proper ground connection, a
potential drop of 120 V. a. c. exists across the resistors 320
through 323. The portion of this potential appearing across the
resistor 320 passes through the diode 324 to charge capacitor 325.
This charging of the capacitor 325 raises the lower input to the
NOR gate 306 from the negative to the positive state and,
accordingly, the output of the NOR gate 306 stays in the negative
state.
As the capacitor 302 charges, so do the capacitors 326 and 327. A
proper choice of these capacitors, as well as the resistor 304,
will cause the capacitors to charge more slowly than the capacitor
325. Upon charging, they raise the input to the NOR gate 305 from
the negative to the positive causing the NOR gate 305 to provide a
negative input to the NOR gate 306. However, the negative input to
NOR gate 306 from the NOR gate 305 does not induce a positive
output from the former; the capacitor 325 previously charged
sufficiently to provide the NOR gate 306 with at least one positive
input. The output of the NOR gate 307 remains positive and the
transistor 313 and the bulb 314 remain off.
As the capacitor 302 reaches its limit of charge, the current
diminishes in the coil 305, opening switch 306. However, the
capacitor 325 stands almost isolated in the circuit at this point
because of the diode 324. Accordingly, it retains its charge while
the capacitors 325 and 326 discharge through the resistor 304 after
the transistor 301 turns off. Accordingly, the input to the NOR
gate 305 goes negative and its output becomes positive causing the
output of the NOR gate 306 to remain in the negative state and bulb
314 not to light.
If the circuit has no connection to ground, then closing the switch
306, of course, does not allow the establishment of a potential
drop across resistor 320. Similarly, should the wiring in the 120
V. supply line become reversed, then the upper connection 330 of
the resistor 320 will no longer connect to the 120 V. line. Rather
it will connect to the common line of the power supply and have a
voltage near the ground. Thus, without a ground, or with reversed
polarity in the a.c. supply, no potential develops across the
resistor 320 and the capacitor 325 cannot charge. Consequently, the
lower input to the NOR gate 306 remains negative.
Nonetheless, the capacitor 302 still charges when the transistor
301 conducts. This allows the capacitors 326 and 327 to charge and
provide a positive input to the NOR gate 305 which consequently
provides a negative input to the NOR gate 306. At this point, with
either missing ground or reversed polarity, the NOR gate 306 has
two negative inputs and provides a positive output to the flip-flop
consisting of the NOR gates 307 and 308. As shown in Table 6, this
resets that flip-flop so that the NOR gate 307 which previously had
a positive output now provides a negative output to the base of the
transistor 313. This turns on the transistor 313 and allows current
to flow through it and through the bulb 314, lighting it. This lit
bulb indicates that some problem exists in the wiring.
Moreover, the bulb 314 remains lit after the circuit has concluded
the test. Providing a positive input to the transistor 313
represents the only way to turn off the bulb 314. This requires the
flip-flop to produce a positive output from the NOR gate 307. Only
a positive input to the NOR gate 308 will properly reset the
flip-flop as required. However, this input remains permanently
connected to the negative common line and, accordingly, cannot
reset the flip-flop to turn off the bulb 314.
Thus, upon the amelioration of whatever difficulty caused the bulb
to light, it can turn off only by unplugging and reconnecting the
entire circuit with the power supply. When connected to the power,
the resistor 309 and capacitor 311 draw the output of the NOR gate
307 to the positive state provided by the potential V.sub.D.
Simultaneously, the resistor 310 and the capacitor 312 pull the
output of the NOR gate 308 to the negative state. In view of the
interconnections between the two NOR gates, these states properly
set the flip-flop to keep the transistor 313 turned off.
After the transistor 301 becomes nonconducting, the coil 305
retains an appreciable amount of stored energy. The diode 330
dissipates this energy by allowing current to flow in the reverse
direction than it has during the charging of the capacitor 302.
The Underwriters Laboratories high-potential test, discussed above,
imposes 1,240 V. a.c. between ground and the 120 V. line. In FIG.
4, this places 1,240 V. across the resistor 320 and charges the
capacitor 325 to levels that could damage many of the circuit
components. The Zener diode 331 limits the potential across the
resistor 320 to its breakdown voltage, frequently on the order 14
V.
The switch 306 remains closed only while appreciable current flows
through the coil 305. Further, the capacitor 302 charges once for
each operation of a bed motor and only for a small fraction of a
second. Accordingly, only small intermittent pulses of electricity
enter the ground system. This compares favorably with most
ground-testing devices which frequently place a constant milliamp
of current into the ground system. In a hospital having several
hundred beds, this represents a potentially dangerous amount of
electricity on a supposedly safe line.
Because of the flexibility and versatility of logic electronic
components, other circuits could effectively accomplish the same or
similar results as those in FIGS. 2, 3 and 4. However, the circuits
in those figures have, in fact, performed the desired tests. The
components used in them appear in the following Table 10.
Table 10 ______________________________________ Components Used in
the Figures Component Number Identification
______________________________________ 33 1/16 A., 250 V. 34
290-12021 41, 51 FWB, 1 A., 50 V. 42, 52 330.mu.F., 25 V. 54
3.OMEGA., 1.5 W. 55 5 V., 1/2 A., TO-220 56 100.OMEGA., 1 W. 130,
131, 281 4.7 K.OMEGA. 136, 139, 164, 278, 1N4148 279, 324, 330 156
10 A., 400 V., SC146D-5. 157 82.OMEGA. 158 R 4534-1 181, 191, 203,
206, 7404 P.C. 243, 244, 250, 262 182, 184, 185, 192- 7402 P.C.
196, 201, 202, 204, 207-213, 245, 260, 261, 263 183, 186, 197, 198
7400 P. C. 208, 214, 2115, 241, 242, 246, 247, 251 220 0.1 .mu. F.,
25 V. 221 1 K.OMEGA. 222 3.3 K.OMEGA. 223, 225 330.OMEGA. 224, 226,
302 100.mu.F. 271-274 2.7 M.OMEGA. 275 10 M.OMEGA. 276 2N5484 277
2N5142 280 470.OMEGA. 300 1N4001 301 2N3906 303, 309, 310 10
K.OMEGA. 304 2.2 K.OMEGA. 305-308 4001 311, 312, 325-327 .01.mu.F.
313 2N3906 314 14 V. 320 240 K.OMEGA. 321-323 1 M.OMEGA. 331 14 V.
d.c., 5%, 1 W. ______________________________________
* * * * *