U.S. patent number 3,711,812 [Application Number 05/202,754] was granted by the patent office on 1973-01-16 for drive and control system for diagnostic and therapeutic exercise treadmill.
This patent grant is currently assigned to Del Mar Engineering Laboratories. Invention is credited to Raymond I. Cherry.
United States Patent |
3,711,812 |
Cherry |
January 16, 1973 |
DRIVE AND CONTROL SYSTEM FOR DIAGNOSTIC AND THERAPEUTIC EXERCISE
TREADMILL
Abstract
An improved drive and control system for an exercise treadmill
is provided which incorporates safety features for the prevention
of a start-up at high belt speed after the treadmill has been
turned off, or upon the resumption of power after a power failure,
and to prevent rapid acceleration of the belt to a high speed
condition in the case of certain control circuit failures.
Circuitry, or other means, has been included in the drive system as
an interlock whereby the manual on-off switch which activates the
drive motor will not be effective until the motor speed control has
been reset to the zero speed position. In addition, circuitry is
included to provide for shutting down the drive motor in the event
of a failure or malfunction in its control circuitry which could
cause an unscheduled rapid increase in the treadmill belt speed to
a high speed condition.
Inventors: |
Cherry; Raymond I. (Torrance,
CA) |
Assignee: |
Del Mar Engineering
Laboratories (Los Angeles, CA)
|
Family
ID: |
22751122 |
Appl.
No.: |
05/202,754 |
Filed: |
November 29, 1971 |
Current U.S.
Class: |
338/200; 482/4;
200/50.32; 482/54 |
Current CPC
Class: |
A63B
22/02 (20130101); A63B 22/025 (20151001); A63B
2071/0072 (20130101) |
Current International
Class: |
A63B
22/00 (20060101); A63B 22/02 (20060101); A63b
023/06 () |
Field of
Search: |
;338/200,201,198,172,173
;272/69 ;200/42R,172R,172A,5C ;318/430 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Gilheany; Bernard A.
Assistant Examiner: Tone; D. A.
Claims
What is claimed is:
1. In an exercise treadmill having an endless belt and an electric
drive motor for the belt, a drive and control system for said motor
including: an input circuit adapted to be connected to a source of
electrical energy; a control circuit connected to said input
circuit and responsive to electrical energy from said source for
introducing control energy to said drive motor; a manually
adjustable speed control for controlling the speed of said motor;
an electric switch for controlling the activation of said motor;
and interlocking means intercoupling said speed control and said
electric switch to prevent said motor from being activated until
said speed control is adjusted to a particular position.
2. The combination defined in claim 1, in which said speed control
comprises potentiometer means included in said control circuit, and
said electric switch is interconnected between said input circuit
and said control circuit, said interlocking means preventing said
control circuit from being energized until said potentiometer means
is adjusted to a particular position corresponding to zero speed of
the motor.
3. The combination defined in claim 2, in which said electric
switch includes a manually movable button member having a slot
therein, and which includes a slide member mechanically coupled to
said potentiometer means and movable into said slot to prevent
actuation of said switch when said potentiometer means is turned
away from a position corresponding to zero speed of said motor.
4. The combination defined in claim 3, and which includes a
spring-loaded latch mounted on said button member to cause said
button member to latch with said slide member when said switch is
actuated to its "off" position during a time when said
potentiometer means is turned away from its aforesaid zero speed
position.
5. The combination defined in claim 2, and which includes a relay
switch in circuit with said input circuit to disconnect said input
circuit from said source of electrical energy; and a second switch
in circuit with said relay switch and mechanically coupled to said
potentiometer means to cause said relay switch to disconnect said
input circuit from said source of electrical energy whenever said
potentiometer means is moved from a position representing zero
speed of said motor.
6. The combination defined in claim 1, and which includes circuitry
connected to said control circuit for disconnecting said input
circuit from said source of electrical energy whenever the
electrical control energy introduced to said drive motor by said
control circuit exceeds a particular reference level.
7. The combination defined in claim 6, in which said circuitry
includes variable potentiometer means included in said speed
control, a source of reference potential connected to said variable
potentiometer means to establish different reference potential
levels for different settings of said potentiometer means, a
differential relay circuit connected to said source of reference
potential, and a second circuit for introducing a second potential
to said differential relay representing the potential introduced to
said motor for any particular setting of said potentiometer means,
said relay responding to a predetermined differential between said
reference potential and said second potential to disconnect said
input circuit from said source of electrical energy.
Description
BACKGROUND OF THE INVENTION
The drive and control system of the present invention may be used,
for example, in conjunction with the diagnostic and therapeutic
exercise treadmill described and claimed in copending application,
Ser. No. 103,155, which was filed Dec. 31, 1970, in the name of
Joseph A. Hesen, and which is assigned to the present assignee.
However, it will become evident as the present description
proceeds, that the drive and control system of the invention has
general utility in conjunction with a wide variety of exercise
treadmills, and the like.
As described in the aforesaid copending application, it is the
usual prior art practice for electrocardiograms to be taken of
patients in a resting position on a table or bed. However, it has
been found that a resting patient may often produce a normal
electrocardiogram, even though there is clinical or other evidence
of abnormalities. It has been found, for example, that more
conclusive electrocardiograms may be obtained if the patient is
subjected to a continuous exercise representing a constant work
load which may be graded at various time intervals. The treadmill
has proven to be a suitable instrument for that, and other
purposes, and clinical treadmill stress testing has become
widespread as a basis for the study and diagnosis of the physical
condition of patients.
An important objective of the present invention is to provide an
appropriate drive and control system which renders the electric
motor power driven treadmill absolutely safe, and easy to operate.
For example, it is known to the art to provide a manual speed
control in conjunction with the power driven treadmill, whereby the
attending physician, or the patient himself, may control the
treadmill belt speed from a low to a relatively high value.
It is usual in the prior art power driven treadmills to drive the
treadmill belt with an alternating current electric motor, and to
vary the speed of the motor over a limited range by varying the
applied voltage. Some treadmills have been provided in the art with
mechanical variable speed control mechanisms, and some with
hydraulic drives. However, with such equipment, it is difficult to
obtain a smooth control to zero speed while operating under load.
An improved drive for the treadmill belt which permits a smooth
speed control to zero speed is obtained by using a
high-permeability permanent magnet direct-current motor, and by
varying the direct-current voltage applied to the motor by an
appropriate speed controller. Such a motor provides the necessary
high torque at low speeds, and is capable of providing, for
example, smoothly variable belt speeds in a range from 0-10 miles
an hour.
A suitable speed controller for use in conjunction with such a
direct-current motor incorporates, for example, a bridge rectifier
including silicon controlled rectifiers, or the like, which are
controlled so that a varying amplitude direct-current voltage may
be applied to the direct-current motor for speed control. However,
there is a possibility for the silicon controlled rectifiers, or
other elements in such a controller to burn out or malfunction, and
this can result in the controller introducing maximum
direct-current voltage to the motor which, in turn, results in an
unanticipated abrupt rise in the motor speed from the controlled
level to a maximum level.
Such an unscheduled increase in the motor speed can be hazardous,
and gives rise to the possibility of injury to the patient using
the treadmill. The control system to be described incorporates
appropriate circuitry which responds to an unanticipated rise in
the direct-current voltage applied to the motor which could result,
for example, from the aforesaid malfunction in the control circuit,
and which serves to de-energize the motor and shut down the system
in the presence of such a condition.
The control system to be described also includes interlocking means
which may be of a mechanical or electrical nature, and which
prevents the drive motor from being activated until the speed
control has been set to a zero or reset position. Such an
interlocking means prevents the activation of the drive motor by
the main switch when the speed control is in any position other
than zero. Without this feature, it would be possible for a patient
to be standing on the belt, with the speed control setting at some
value other than zero, and with the resulting unanticipated and
rapid acceleration of the belt up to the set speed, with possible
injury to the patient, when the switch is turned on.
A further feature of the electrical interlocking circuit to be
described is that in the event of a power failure, or should the
power cable for the treadmill be unplugged from the power main
receptacle, while the treadmill is operating; the drive motor will
not be energized when power is restored, unless the speed control
is first reset to zero. This latter control prevents possible
injury to a patient who is standing on the belt when power is
restored, since it prevents the belt from rapidly accelerating to
the preset speed, and requires a resetting of the system before it
again becomes operational.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective representation of treadmill apparatus which
may be constructed to incorporate the improved drive and control
system of the invention;
FIG. 2 is a front view of a control unit for the treadmill of FIG.
1, illustrating certain indicators and controls for the
treadmill;
FIG. 3 is an enlarged fragmentary perspective view of a mechanical
interlock between a power switch and speed control which are
included in the unit of FIG. 2;
FIG. 4 is a sectional view of a latch component of the interlock of
FIG. 3, taken essentially along the line 4--4 of FIG. 3;
FIG. 5 is a circuit diagram of an equivalent electrical interlock
between the power switch and speed control of the unit of FIG. 2;
and
FIG. 6 is a circuit diagram of an overspeed protection circuit for
the drive motor of the treadmill of FIG. 1.
DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS
The treadmill shown in FIG. 1 includes an endless belt 10 riding on
rollers 11 and 13 which, in turn, are mounted on appropriate
bearings attached to a frame 15. The belt 10 is driven, for
example, by means of a motor 12 through an appropriate drive such
as a toothed belt 14. Power in the form of 110-volt AC current from
the usual mains is supplied through a connector 16 to an electric
control module 18 which, in turn, is controlled by a speed control
rheostat 22 in a control unit 20, to control the speed of the motor
12. The control unit 20, as described in the aforesaid copending
application, may be mounted on a handle section 21 of the
treadmill, for appropriate control by the patient himself, or it
may be removed for remote control by the attending physician, or
other attendant. When activated, the motor 12 drives the belt 10 in
the direction of the arrow, and at a speed set by the setting of
the speed control 22.
As shown in FIG. 2, the speed control rheostat 22 in the control
unit 20 includes a knob which is turned, for example, in a
clockwise direction to increase the motor speed, and which is
turned in a counterclockwise direction to reduce motor speed. The
speed control 22 may be turned in the counterclockwise direction to
a zero "reset" position, at which the motor speed is zero. A
snap-acting toggle-type manual on-off master power switch 24 is
positioned on the control unit 20 adjacent to the speed control 22,
as shown in FIG. 2. A speed control indicator 25 is also mounted on
the control unit, and it may be directly calibrated in miles per
hour (mph).
As stated above, an important objective of the present invention is
to prevent any activation of the drive motor 12 when the on-off
switch 24 is turned on, unless the speed control 22 has been turned
back to its zero "reset" position, at which the speed of the belt
10 is reduced to zero. As will be described, this objective may be
achieved in accordance with the invention, either mechanically, as
shown in FIGS. 3 and 4, or electrically as shown in FIG. 5.
The mechanical assembly of FIG. 3 comprises a pinion 26 which
engages a rack 30 on a slide 32, the slide being held in position
by bearing surfaces in bulkheads 34 and 36, such that its left-hand
end will enter the area 42 in the switch button 40 of the power
switch 24 when the slide is moved to the left in FIG. 3. The pinion
is attached to the shaft 28 of the speed control 22, so that
rotation of the speed control 22 results in corresponding rotation
of the pinion. In order to cause the left-hand end of the slide 32
to be removed completely from the area 42 of the switch button 40,
so as to permit full freedom in the movement of the master switch
24 from one position to the other, the speed control 22 must be
turned in the counterclockwise direction to its zero or "reset"
position, at which position the shaft 28 turns the pinion 26 to an
angular position so as to displace the slide 32 to the right in
FIG. 3, thereby removing the left-hand end of the slide from the
aforesaid area 42.
With the master switch 24 in the "off" position, illustrated in
FIG. 3, rotation of the speed control 22 and pinion 26 in the
clockwise direction from the "reset" position to increase the speed
of the belt 10, drives the left-hand end of the slide into the area
42 and over a spring-loaded latching cam 44. The latching cam 44 is
a part of the latch assembly shown in FIG. 4. As illustrated in
FIG. 4, the latching cam 44 is contained in the body of the switch
button 40, and in its normal position is caused to protrude by the
force of a spring 48. The master switch is now prevented from being
switched to its "on" position by the presence of the latch cam 44,
so long as the left-hand end of the slide 32 is in the area 42.
However, when the speed control is returned to the zero "reset"
position, the left-hand end of the slide 32 is removed from the
area 42, and the switch 24 may then be turned on by depressing the
switch button 40 so as to pivot the button in a counterclockwise
direction about the axis A in FIG. 3.
Should the speed control be turned while the switch 24 is in its
"on" position, the end of the slide 32 enters the area 38 under the
latching cam 44. Now, when the switch button 40 is pivoted in a
clockwise direction about the axis A to its "off" position, the end
of the slide 32 moves up the inclined surface 46 of the latching
cam 44, and forces the cam into the cavity in the switch button 40
against the force of the spring 48. The left-hand end of the slide
32 then moves into the area 42, and the latching cam 44 snaps out
to its outer position, thereby trapping the slide 32, and
preventing the switch 24 to be returned to its "on" state, until
the speed control 22 has been returned to zero, thereby removing
the left-hand end of the slide 32 from the area 42.
The interlock between the power switch 24 and the speed control 22
can be achieved electrically, as shown by the circuit of FIG. 5.
The circuit of FIG. 5 includes a normally open solenoid-operated
relay switch 50 which includes a relay coil 54 connected in series
with the incoming alternating-current power line. The relay switch
50 is connected, for example, to the control module 18 which
supplies the direct-current power to the motor 12. In its normal
state, the relay switch 50 prevents the flow of alternating current
to the control module 18, so that the drive motor 12 which, in
turn, drives the treadmill belt 10, is deenergized. The coil 54 of
the relay switch 50, which when energized closes the relay switch,
is included in the circuit in series with a switch 56. The switch
56 is an integral part of the speed control 22, and is closed only
when the speed control is returned to its "reset" position.
As shown in FIG. 5, the master switch 24 is a two-pole switch. One
of the poles of the switch 24 completes the circuit to the relay
coil 54, only when the switch 56 is closed, so that the relay 54
can be energized only when the speed control 22 is in its "reset"
position. The other pole of the switch 24 serves as a holding
circuit to maintain the relay coil 54 energized after the speed
control is subsequently turned from its "reset" position and the
switch 56 is open. However, when the power switch 24 is actuated to
its "off" position, the circuit cannot be energized until the speed
control 22 has again been turned to the "reset" position to close
the switch 56. Also, if power is lost for any reason, such as a
power failure, or the power cable becoming unplugged, the speed
control 22 must be turned back to "reset" before the motor 12 can
again be activated.
It is clear, therefore, that the speed control 22 must be returned
to its "reset" position before any belt speed can be resumed. In
this way, the belt 10 of the treadmill can be started only after
the speed control 22 has been turned back to the zero speed
condition of the belt.
As mentioned above, the circuit of FIG. 6 shows the drive system
for the motor 12, and it includes a safety circuit for preventing
overspeed of the belt 10 of the treadmill due to a failure in the
control circuit of the motor 12.
In the circuit of FIG. 6, the control module 18 includes a
rectifier power supply 19 which is energized from the
alternating-current power source when the relay switch 50 is
closed. The rectifier 19 develops the direct-current voltage for
the motor 12, and the amplitude of this voltage is controlled so as
to control the speed of the motor. For example, the rectifier power
supply 19 may include a usual bridge rectifier which incorporates
silicon controlled rectifiers in two of its arms. The
direct-current voltage supplied to the motor 12 from the rectifier
power supply 19 may be in the form of unfiltered, partial
half-waves which, in turn, are controlled by the setting of the
speed control 22 which, in turn, controls the silicon controlled
rectifiers in the bridge network. Such variable controlled
rectifier power supplies are known. However, should a silicon
controlled rectifier, or other element in the power supply
malfunction, an unscheduled and abrupt rise to maximum
direct-current output could result, and this could result in an
unexpected rapid acceleration of the motor 12 from its set speed to
a maximum speed, with possible injury to the person using the
treadmill. For that reason, a safety circuit designated 62 is
incorporated into the control module, which will now be
described.
The direct-current output from the rectifier 19 is connected to a
potentiometer R4A which is included in the speed control 22, and
which has a movable element connected to the base of a PNP
transistor Q1. The collector of the transistor Q1 is connected to
the negative output terminal of the power supply 19, and the
emitter is connected to the cathode of a diode CR1. The anode of
the diode CR1 is connected through the coil of a relay K1, through
a further diode CR2, and through a resistor R3 to one terminal of
the motor 12. The positive terminal of the power supply 19 is
directly connected to the other terminal of the motor 12. The speed
control 22 includes a further potentiometer R4B which moves in
unison with the potentiometer R4A, and which is connected by way of
terminals P1, P2 and P3 to the rectifier power supply 19. The
potentiometer R4A serves to control the timing of the firing of the
aforesaid silicon controlled rectifiers, and thereby controls the
effective amplitude of the direct-current voltage applied to the
motor 12, in a manner known to the art.
A resistor R1 and capacitor C1 are connected from the junction of
the diode CR1 and relay coil K1 to the positive terminal of the
power supply 19, and a resistor R2 and capacitor C2 are connected
from the junction of the diode CR2 and resistor R3 to the aforesaid
positive terminal. The relay K1 has a normally closed contact in
circuit with the energizing coil 54 of the power switch 50.
The setting of the potentiometer R4A provides a reference voltage
at the base of a PNP transistor Q1. The transistor Q1 is connected
as an emitter follower, the emitter of which being connected
through a diode CR1 to a resistor R1. The collector of the
transistor Q1 is connected to the negative terminal of the power
supply 64, whereas the resistor R1 is connected to the positive
terminal. The resistor R1 is shunted by a capacitor C1. The diode
CR1, resistor R1 and capacitor C1 are all connected to the other
side of the energizing coil of the relay K1.
The setting of the potentiometer R4A provides a reference voltage
at the base of the emitter follower transistor Q1, and this results
in a negative reference voltage across the resistor R1 in the
emitter circuit of the transistor. This voltage is stored in the
capacitor C1 for a period of time sufficient to permit the voltage
lag of the motor 12 to equalize any change in the field current,
when the potentiometer R4B section of the speed control is changed
rapidly for a reduced belt speed. This storage across the capacitor
C1 is necessary to prevent operation of the relay K1, with a
resulting full shutdown of the system, when the speed control 22 is
rapidly turned in the reduce speed direction. The voltage stored by
the capacitor C1 provides a reference voltage for the relay K1.
The relay K1 is a conventional 12-volt relay, for example, which
typically operates when 6 volts is placed across the coil or across
its energizing coil, or when the current in its energizing coil in
either direction exceeds a minimum value. The relay K1, therefore,
acts as a differential switch, and opens the circuit of the
energizing coil 54 of the relay switch 50 to shut down the system
whenever the voltage differential across the capacitor C1 and
resistor R2 exceeds a predetermined level. When the relay coil 54
is energized, the motor 12 cannot again be energized until the
speed control 22 is returned to the "reset" position to close the
switch 56.
Therefore, if, for any reason, the voltage introduced to the motor
12 by the control module 18, and which appears across the terminals
B1 and B2, exceeds by a predetermined amount the reference voltage
established by the setting of the speed control 22, the relay K1 is
activated to shut down the system, thereby preventing an unexpected
acceleration of the motor 12. Since the shut down operation is
desired only where the motor voltage materially exceeds the
reference voltage, the diode CR2 is included in the circuit to
prohibit any excitation of the relay K1 except when the motor
voltage exceeds the reference voltage, and not vice versa. In this
way, inadvertent shut down of the system is obviated, for any
condition except when the motor voltage 12 rises above the
reference voltage so as to indicate the existence of a runaway
condition.
The drive circuit of FIG. 6 causes the treadmill to continue to
operate satisfactorily so long as the motor and reference voltages
are in balance. However, the safety circuit 62 in the drive circuit
constantly compares the reference voltage and the motor voltage, so
that any failure, for example, in the control module 18, whereby
the direct current output voltage to the motor 12 increases beyond
a predetermined amount, causes a flow of current in the
differential relay K1. This, in turn, causes the relay K1 to be
activated to open the circuit of the energizing coil 54 of the
relay switch 50. As mentioned above, with the coil 54 deenergized,
the relay switch 50 reverts to its normally open position thereby
interrupting the flow of alternating current to the control unit
18, and effectively arresting the motion of the treadmill belt 10.
The response to such an unbalance beyond a predetermined amount
between the reference voltage and the motor voltage is almost
instantaneous and the shut down of the treadmill is accomplished
without the patient sensing any particular increase in belt
speed.
The invention provides, therefore, an improved drive and control
system for an exercise treadmill, and one which incorporates safety
features, so that the use of the treadmill, and especially for
therapeutic purposes, is safe and foolproof.
While particular embodiments of the invention have been shown and
described, modifications may be made. It is intended in the
following claims to cover all modifications which fall within the
spirit and scope of the invention.
* * * * *