U.S. patent number RE34,934 [Application Number 08/132,715] was granted by the patent office on 1995-05-09 for coin sorter with counter and brake mechanism.
Invention is credited to Richard A. Mazur, Richard D. Primdahl, Donald E. Raterman.
United States Patent |
RE34,934 |
Raterman , et al. |
May 9, 1995 |
Coin sorter with counter and brake mechanism
Abstract
A coin sorter having a rotatable disc includes a brake mechanism
for stopping rotation of the disc in response to a predetermined
number of counted coins. The disc is driven through a gear train by
an electric motor. The brake mechanism includes a first brake
mechanism coupled to the motor for stopping rotation thereof, a
second brake mechanism coupled to the coin disc for stopping
rotation thereof, and a control mechanism for operating the brake
mechanisms in a synchronous manner so as to avoid any shock loads
upon the gear train due to existence of torque differentials on
either ends thereof. The brake mechanisms are adapted to have
substantially identical stopping times and are operated in such a
manner as to be energized in a substantially instantaneous manner
when the braking sequence is initiated.
Inventors: |
Raterman; Donald E. (Deerfield,
IL), Mazur; Richard A. (Naperville, IL), Primdahl;
Richard D. (Hoffman Estates, IL) |
Family
ID: |
46248155 |
Appl.
No.: |
08/132,715 |
Filed: |
October 6, 1993 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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113869 |
Oct 27, 1987 |
4921463 |
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Reissue of: |
475127 |
Feb 5, 1990 |
05055086 |
Oct 8, 1991 |
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Current U.S.
Class: |
453/10; 453/32;
453/57 |
Current CPC
Class: |
G07D
3/128 (20130101); G07D 3/16 (20130101) |
Current International
Class: |
G07D
3/00 (20060101); G07D 3/12 (20060101); G07D
3/16 (20060101); G07D 003/16 () |
Field of
Search: |
;453/6,10,32,57
;188/72.1,161 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Other References
Inertia Dynamics Product Catalog, "Electric Clutches and Brakes",
Catalog CB485, pp. 1-20 Apr. 1986..
|
Primary Examiner: Bartuska; F. J.
Attorney, Agent or Firm: Arnold, White & Durkee
Parent Case Text
This is a continuation-in-part of application, Ser. No. 07/113,869,
filed on Oct. 27, 1987, now U.S. Pat. No. 4,921,463.
Claims
We claim:
1. In a coin sorter having a rotatable disc with a resilient
surface and a stationary guide plate positioned adjacent said
resilient surface for guiding coins on said resilient surface as
said disc is rotated,
counting means for counting coins of at least one denomination as
the coins are processed by said sorter,
an electric motor having an output shaft for driving said rotatable
disc,
a speed-reducing gear train connected between the output shaft of
said electric motor and said rotatable disc,
first brake means coupled to the output shaft of said motor and
adapted to stop rotation thereof,
second brake means coupled to said coin disc and adapted to stop
rotation thereof, and
means responsive to said counting means for controlling the
operation of said first and second brake means in such a manner as
to stop said rotatable disc when a preselected number of coins have
been counted.
2. The coin sorter of claim 1 wherein each of said brake means
comprises an electrically powered brake, and the coin sorter
includes means for de-energizing said motor and energizing said
braking means in response to the counting of said preselected
number of coins.
3. The coin sorter of claim 2 wherein said first and second brake
means are adapted to be energized in a substantially simultaneous
manner in response to a signal from said counting means indicating
that said preselected number of coins have been counted.
4. The coin sorter of claim 3 wherein said brake control means is
adapted to energize said first and second brake means in response
to said count indicating signal in such a way that the time
required for said first brake means to stop the rotation of said
motor output shaft is substantially equal to the time required for
said second brake means to stop the rotation of said coin disc.
5. The coin sorter of claim 3 wherein each of said brake means
includes an armature coil adapted to receive an energizing voltage
for energizing and operating said brake means, and wherein said
brake control means is adapted to maintain said energizing voltages
for said brake means at a first high level for a first
predetermined period of time so as to energize both of said brake
means at substantially the same times, and for maintaining said
energizing voltages at a second level substantially lower than said
first level for a second predetermined time which exceeds said
stopping times of both of said brake means.
6. The coin sorter of claim 5 wherein said control means includes
means for insuring that said brake means are activated only when
said electric motor is deactivated and vice versa.
7. The improved coin sorting and counting apparatus as set forth in
claim 6 wherein said brake control means includes means for
energizing said first and second brake means in a substantially
simultaneous manner whereby said first and second brake means
respectively begin stopping said motor and said coin disc at the
same time.
8. Improved apparatus for sorting and counting coins at a high
speed and level of accuracy, comprising:
a coin disc rotatably mounted within a housing;
a motor mounted in said housing, said motor including an output
shaft rotated by said motor,
means for mechanically coupling said coin disc to said output shaft
of said motor;
first brake means coupled to said motor and operable to stop the
rotation of said output shaft of said motor when said brake means
is energized;
second brake means coupled to said coin disc and operable to stop
the rotation of said coin disc when said brake means is energized;
and
means for controlling the energization of said first brake means
and said second brake means to stop the rotation of said motor and
said coin disc at substantially the same time.
9. The apparatus for sorting an counting coins as set forth in
claim 8 wherein said first and second brake means are electrically
activatable friction brakes.
10. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said second brake means is a disc brake including a
brake disc secured to said coin disc, an electrical coil secured to
said housing adjacent to said brake disc, and friction means
engageable by said brake disc upon energization of said second
brake means.
11. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said second brake includes an electrical coil
secured to said housing, a brake disc adjacent to and engageable
with said coil, and a diaphragm spring flexibly connecting said
brake disc to said coin disc.
12. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said coin disc includes a thin plate with a rim, a
hub and an upper planar surface and a lower planar surface, said
lower planar surface of said coin disc extending from said rim to
said hub having fins formed thereupon, said fins being thicker at
said hub than at said rim.
13. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said coin disc includes a thin plate, a central hub
secured to said plate, and a hollow come extending below said plate
and secured to said plate and said hub.
14. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said coin disc includes a metal plate brazed to a
honeycomb disc.
15. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said coin disc includes a planar member of
composite material.
16. The apparatus for sorting and counting coins as set forth in
claim 8 wherein said first brake and said second brake, in
combination, stop the rotation of said coin disc in about ten
milliseconds.
17. An improved braking method for quickly and accurately halting
the rotation of a coin disc in a coin sorting and counting system
wherein an electrical motor is rotatably coupled to the coin disc
through speed reducer means, said method comprising the steps
of:
(i) providing a first brake means disposed on one side of said
speed reducer means and operable to halt the rotation of said
motor;
(ii) providing a second brake means disposed on the other side of
said speed reducer means and operable to halt the rotation of said
coin disc; and
(iii) operating said first and second brake means so that the time
taken by said first braking means to halt the rotation of said
motor is substantially equal to the time taken by said second brake
means to halt the rotation of said coin disc.
18. The improved braking method as set forth in claim 17 wherein
said first and second brake means are energized in a substantially
simultaneous manner when the halting of said coin disc is
initiated.
19. The improved braking method as set forth in claim 18 wherein
said brake means are both responsive to an energizing voltage
applied thereto and wherein the method includes the steps of
applying a first high energizing voltage to both of said brake
means for a first predetermined time period so as to energize said
brake means at substantially the same time, and
applying a second low energizing voltage to both of said brake
means for a second predetermined time period which is equal to or
larger than the stopping times of each of said brake means.
20. A braking system for quickly and accurately stopping the
rotation of a coin disc in a coin sorting and counting system
comprising an electric motor rotatably driving a coin disc through
a mechanical coupling means, said system comprising:
first brake means coupled to said motor for stopping the rotation
thereof;
second brake means coupled to said coin disc for stopping the
rotation thereof; and
control means for operating said first and second brake means in
synchronism so as to stop the rotation of said coin disc without
exerting shock loads on said mechanical coupling means.
21. The braking system according to claim 20 wherein said first and
second brake means are electrically activatable brakes adapted to
respectively stop the rotation of said motor and said coin disc
within substantially identical time periods.
22. The braking system as set forth in claim 21 wherein both of
said brake means are activated by application of an energizing
voltage thereto, and said control means includes means for applying
a first, relatively high energizing voltage to said brakes for a
first predetermined time period so as to energize both of said
brake means at substantially the same time, and means for applying
a second, relatively low energizing voltage to said brakes for a
second predetermined time period which is substantially longer than
said first time period. .Iadd.
23. In a coin sorter having a rotatable disc with a resilient
surface and a stationary guide plate positioned adjacent said
resilient surface for guiding coins on said resilient surface as
said disc is rotated,
counting means for counting coins of at least one denomination as
the coins are processed by said sorter,
an electric motor having an output shaft for driving said rotatable
disc,
a speed-reducer connected between the output shaft of said electric
motor and said rotatable disc,
a first rotation arrestor coupled to the output shaft of said motor
and adapted to stop said rotatable disc from being rotated by said
motor,
a second rotation arrestor coupled to said coin disc and adapted to
stop rotation thereof, and
means responsive to said counting means for controlling the
operation of said first rotation arrestor and said second rotation
arrestor in such a manner as to stop said rotatable disc when a
preselected number of coins have been counted. .Iaddend. .Iadd.24.
The coin sorter of claim 23 wherein each of said first rotation
arrestor and said second rotation arrestor comprises an
electrically powered brake, and the coin sorter includes means for
de-energizing said motor and energizing said first rotation
arrestor and said second rotation arrestor in response to the
counting of
said preselected number of coins. .Iaddend. .Iadd.25. The coin
sorter of claim 24 wherein said first rotation arrestor and said
second rotation arrestor are adapted to be energized in a
substantially simultaneous manner in response to a signal from said
counting means indicating that said preselected number of coins
have been counted. .Iaddend. .Iadd.26. A braking system for quickly
and accurately stopping the rotation of a coin disc in a coin
sorting and counting system comprising an electric motor rotatably
driving a coin disc through a mechanical coupling means, said
system comprising:
a first rotation arrestor coupled to said motor for stopping said
coin disc from being rotated by said motor;
a second rotation arrestor coupled to said coin disc for stopping
the rotation thereof; and
control means for operating said first rotation arrestor and said
second rotation arrestor in synchronism so as to stop the rotation
of said coin disc without exerting shock loads on said mechanical
coupling means. .Iaddend. .Iadd.27. The braking system according to
claim 26 wherein said first rotation arrestor and said second
rotation arrestor are electrically activatable brakes adapted to
respectively stop the rotation of said motor and said coin disc
within substantially identical time periods. .Iaddend.
.Iadd.28. The braking system as set forth in claim 27 wherein said
first rotation arrestor and said second rotation arrestor are both
activated by application of an energizing voltage thereto, and said
control means includes means for applying a first, relatively high
energizing voltage to said brakes for a first predetermined time
period so as to energize said first and second rotation arrestors
at substantially the same time, and means for applying a second,
relatively low energizing voltage to said brakes for a second
predetermined time period which is substantially longer than said
first time period. .Iaddend.
Description
BACKGROUND OF THE INVENTION
1. Field Of The Invention
The present invention relates generally to coin sorters of the type
which use a rotatable disc having a resilient surface operating
with an adjacent stationary guide plate and, more particularly, to
such sorters which have a counter for counting the number of coins
sorted and a brake for stopping the disc when the counter indicates
that a preselected number of coins have been sorted.
2. Summary of the Invention
It is a primary object of the present invention to provide a coin
sorter of the type described above which has an improved drive and
brake system for stopping the rotatable disc quickly and reliably
over a large number of operating cycles.
It is another important object of this invention to provide such a
coin sorter having a drive and brake system which is relatively
inexpensive to install and maintain.
A further object of the invention is to provide such a coin sorter
having a drive and brake system which permits the use of a
relatively small brake mechanism.
Other objects and advantages of the invention will become apparent
from the following detailed description and the accompanying
drawings.
In accordance with the present invention, the foregoing objectives
are realized by providing a coin sorter having a rotatable disc
with a resilient surface and a stationary guide plate positioned
adjacent to the resilient surface for guiding coins on the
resilient surface as the disc is rotated; counting means for
counting coins of at least one denomination as the coins are
processed by the sorter; an electric motor having an output shaft
for driving the rotatable disc; a speed-reducing gear train
connected between the output shaft of the electric motor and the
rotatable disc; and first braking means responsive to the counting
means for stopping the rotatable disc when a preselected number of
coins have been counted, the braking means being connected to the
output shaft of the motor, and, in an alternative embodiment, a
second braking means is coupled to the rotatable disc.
The first braking means preferably comprises an armature fixed to
the output shaft cf said motor and including a disc forming a flat
surface to which braking pressure can be applied, and an
electromagnetic actuator for applying braking pressure to the flat
surface of said disc when said actuator is supplied with electrical
power. The second braking means is preferably a tension brake
including an electromagnetic coil secured to the coin sorter and a
brake disc secured to the rotatable disc. According to a preferred
embodiment, the first and second feature of braking means are
operated in synchronism during the braking sequence in such a
manner that (i) both the braking means are activated simultaneously
with a minimal activation delay and, (ii) the stopping times
corresponding to both the braking means are substantially
identical. The effect of the synchronized braking action is to
minimize damaging torque being applied to the speed-reducing gear
train and to reduce the possibility of gear train wind-up and the
associated errors in coin counting.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a vertical section of a coin sorter embodying the present
invention;
FIG. 2 is a perspective view, on a reduced scale, of the coin
sorter shown in FIG. 1;
FIG. 3 is a vertical section of the brake mechanism included in the
coin sorter of FIGS. 1 and 2;
FIG. 4 is a vertical cross sectional view of a second embodiment of
a coin sorter including first and second brakes;
FIG. 5 is an enlarged, bottom plan view of a finned coin disc for
use with the coin sorter illustrated in FIG. 4;
FIG. 6 is a view taken along line 6--6 in FIG. 5;
FIG. 7 is a vertical cross sectional view of a coin disc including
three sheets of material secured together for use with the coin
sorter of FIG. 4;
FIG. 8 is a vertical cross sectional view of a hollow coin disc for
use with the coin sorter of FIG. 4; FIG. 9 is a diagram
illustrating a dual-brake synchronous braking system according to
the principles of this invention;
FIG. 10 is a schematic diagram of an illustrative arrangement for
controlling the motor and disc brakes shown in the system of FIG.
9; and
.[.FIG. 11 is.]. .Iadd.FIGS. 11A-G are .Iaddend.a graphical
representation of various control and status signals associated
with the control system of FIG. 10.
While the invention is susceptible to various modifications and
alternative forms, specific embodiments thereof have been shown by
way of example in the drawings and will be described herein in
detail. It should be understood, however, that it is not intended
to limit the invention to the particular forms disclosed, but, on
the contrary, the intention is to cover all modifications,
equivalents and alternatives falling within the spirit and scope of
the invention as defined by the appended claims.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Turning now to the drawings, there is shown a coin sorter which
includes a hopper 10 for receiving coins of mixed denominations and
feeding them through central openings in a housing 11 and an
annular sorting head or guide plate 12 inside the housing. The
coins are deposited on the top surface of a disc 13 mounted for
rotation on a splined stub shaft 14 which fits into a hub 15
affixed to the bottom of the disc. The hub 15 in turn is mounted
within ball bearings 16 in the base of the housing 11.
The disc 13 comprises a resilient pad 17 bonded to the top surface
of a solid metal disc 18. The top surface of the resilient pad 17
is typically covered with a durable fabric bonded to the pad
itself, which is typically made of a resilient rubber material As
the disc 13 is rotated, the coins deposited on the top surface
thereof tend to move outwardly over the surface of the pad due to
centrifugal force. The coins which are lying flat on the pad travel
outwardly beneath the guide plate 12 because the underside of this
plate is spaced above the pad 17 by a distance which is slightly
greater than the thickness of the thickest coin.
The bottom surface of the guide plate 12 is configured to sort the
coins by denomination as the coins are rotated beneath the plate 12
by the disc 13. All illustrated in FIG. 2, different denominations
of coins are eventually ejected at different circumferential
locations around the periphery of the guide plate 12. The
particular configuration of the guide plate surface which affects
the sorting may be any of a variety of different designs, one
example of which is described in the assignee's co-pending U.S.
Pat. application Ser. No. 034,271 filed Apr. 1, 1987, the
disclosure of which is incorporated herein by reference.
It is important that the disc 13 remain flat, without any flexing,
twisting or other physical distortion, in order to prevent any
missorting of the coins. To provide such stability, the metal disc
18 must be made rigid and massive enough to withstand the pressure
exerted thereon by the rotating coins as they are pressed down into
the pad 17 by the fixed guide plate 12.
In order to drive the disc 13 at a controlled angular velocity, an
electric motor 20 is connected to the disc through a speed-reducing
gear train. Thus, the motor 20 has an output shaft 21 which carries
a helical pinion gear 22. The pinion 22 meshes with a gear wheel 23
carrying a pinion 24 which, in turn, meshes with a gear wheel 25 on
the lower end of the stub shaft 14. With this speed-reducing gear
train, the disc 13 is typically driven at 200 rpm by a motor
turning at 1750 rpm.
Because of the torque-multiplying effect of the gear train, the
output torque of the motor 20 can be much less than the torque
required to drive the disc 13. For example, with the type of gear
train illustrated, an electric motor producing a starting torque of
84 inch-pounds and a running torque of 60 inch-pounds can bring a
3-pound, 11-inch diameter disc 13 up to speed within about 0.3
second, even when the sorter is loaded with coins.
For the purpose of counting the number of coins of each
denomination discharged from the sorter, an electronic counter 30
receives signals from multiple photosensors S1-S5 located adjacent
the respective coin discharge paths. These photosensors S1-S5
normally receive light from corresponding light sources L1-L5, but
the light beam is interrupted each time a coin passes between one
of the sources L1-L5 and the corresponding one of the sensors
S1-S5. Whenever one of the light beams is interrupted, the
interruption produces a positive transition in the electrical
output of the corresponding photosensor S1-S5, and this transition
is detected by the counter 30. Each positive transition is treated
as a separate count, and the number of counts from each sensor is
accumulated until it reaches a preselected level. Typically, the
preselected level represents the number of coins desired in a
particular type of receptacle such as a coin bag attached to the
sorter. As an alternative, the sensing arrangement may use magnetic
sensors, with coin correcting being based on the change in
electromagnetic field generated each time a coin passes across the
sensors
In accordance with one important aspect of the present invention, a
brake mechanism responsive to the counter 30 is connected to the
motor output shaft 21 for stopping the rotating disc 13 when a
preselected number of coins has been counted. When the disc 13 is
rotating, it has a moment of inertia which is a function of the
mass, size and shape of the disc. The torque applied to the drive
train by the rotating disc is a function of both the moment of
inertia and the angular acceleration of the disc. In order to bring
the rotating disc to a stop, this load torque produced by the disc
must be overcome by the braking torque and the frictional
resistance applied to the disc by any coins thereon and the
pressure of the stationary guide plate 12 on those coins. By
applying the braking force to the output shaft of the drive motor,
a relatively small torque is sufficient to brake the rotating disc
because the braking torque applied to the motor shaft is multiplied
by the speed-reducing gear train. Thus, the disc can be quickly and
reliably stopped with a relatively inexpensive brake mechanism
which has a long operating life, e.g., in excess of a million
operating cycles.
The preferred brake mechanism for use in this invention is an
electrically powered disc brake. Thus, in the illustrative
embodiment shown in FIG. 3, an armature 40 mounted on the lower end
of the motor shaft 21 forms a disc with a flat surface 40a to which
braking pressure may be applied to stop the drive train. The
armature 40 is mounted for limited axial movement relative to the
shaft 21 by means of a plurality of spring elements 41. To apply
braking pressure to the disc 40, a stationary electromagnetic
actuator 42 is mounted directly beneath the disc 40. The actuator
42 includes a friction ring 43 for gripping the disc surface 40a
with a minimum of slippage. The actuator also includes a coil 44
which, when energized from an electrical power source, magnetizes a
stator 45 to draw the disc 40 into tight engagement with the
friction ring 43. The braking torque thus applied to shaft 21 is
multiplied by the speed-reducing gear train and applied to the disc
13 via the stub shaft 14.
One example of a commercially available brake mechanism of the type
described above is the Type FB17 Power-On Disc Brake made by
Inertia Dynamics, Inc. of Collinsville, Conn.
To control the energization of the electromagnetic brake, the
output signal from the counter 30 is supplied to a driver circuit
31 which controls the electrical current fed to the coil 44. This
same driver circuit 31 also controls the electrical power supplied
to the electric drive motor 20. When the counter output indicates
that the desired number of coins have been discharged from one of
the sorter exit slots, the driver circuit 31 de-energizes the motor
20 and energizes the coil 44 so that the motor 20 is no longer
driving its output shaft when the brake is applied.
The actuator coil 44 is preferably energized initially at a
relatively high power level to quickly initiate the braking action,
and then at a lower power level to bring the disc 13 and its drive
train to a complete stop. For example, with the particular brake
mechanism identified above, the driver circuit 31 preferably
applies 36 volts across the coil for about 5 milliseconds, and then
12 volts for a further 25 milliseconds. With these voltage levels,
the disc 13 can be brought to a complete stop in about 20
milliseconds. This braking time corresponds to an angular movement
of the disc of only about 15 degrees, which is small enough to
prevent the discharge of additional unwanted coins in most
situations.
In accordance with a further aspect of the invention, the helical
pinion gear on the output shaft of the motor 20 has teeth pitched
in a direction to urge the shaft axially away from the
electromagnetic actuator of the brake mechanism in response to a
driving torque from the motor, so that application of a braking
torque to the shaft urges the shaft axially toward to
electromagnetic actuator. Thus, in the particular embodiment
illustrated in FIG. 2, the pitch of the teeth on the pinion gear 22
produces a force vector in the direction of the axis of the motor
shaft 21 which biases the shaft downwardly so that the armature 40
is urged away from the stationary actuator 42 when the motor is
driving the disc 13 during a sorting operation. When the motor is
de-energized and the brake energized to stop the disc 13, the
direction of the axial force vector is reversed so that the motor
shaft 21 is biased upwardly to draw the armature 40 toward the
electromagnetic actuator 42. This provides a brake boost which
supplements the braking force applied by the energization of the
electromagnetic actuator.
Referring to FIG. 4, there is illustrated an alternative coin
sorter generally designated by the reference number 100. The coin
sorter 100 is similar to the coin sorter illustrated in FIGS. 1-3
in that it includes a hopper 102 mounted on a chassis 103 of the
coin sorter 100. The hopper 102 receives coins of mixed
denominations and directs the coins onto an upper surface of a coin
pad 104. The coin pad 104 corresponds to the resilient pad 17
included with the coin sorter illustrated in FIGS. 1-3.
The coin pad 104 is secured to a finned coin disc 106 that is made
of a light-weight material of high structural strength such as cast
aluminum. The disc 106 is connected to a splined stub shaft 108 by
elongated fasteners such as bolts 110 that extend through apertures
112 in the finned disk 106 and are anchored in a bushing 114. The
bushing 114 is securely affixed to the splined stub shaft 108 and
is rotatably mounted within the chassis 103 by bearings 116.
To rotate the coin disc, the splined stub shaft 108 is connected to
a gear motor 118 through a speed reducing gear train 120. The gear
motor 118 is substantially the same as the electric motor 20 in the
coin sorter illustrated in FIGS. 1-3. The gear train 120 is
substantially the same as the speed reducing gear train including
gear wheel 23, pinion 24 and gear wheel 25 illustrated in FIG. 2.
The gear motor 118 functions to rotate the disc 106, and a disc
brake 122 stops in rotation. The disc brake 122 corresponds to the
brake mechanism in the coin sorter illustrated in FIGS. 1-3.
It has been determined that the rotation of the finned disk 106 can
be stopped in approximately 20 milliseconds using the disc brake
122. Although this period of time is considered very good, it is
desirable to attain faster stopping of the finned coin disc 106 to
minimize overcounting of coins. Overcounting of coins occurs when
rotation of the coin disc is not stopped upon counting the
programmed number of coins. This occurs when, as the last coin of
the programmed number of coins is counted, one or more additional
coins are passed through the counter before rotation of the coin
disc can be completely stopped. This overcounting is problematic
since the operator is required to remove the extra coins from the
coin bag before the bag is sealed. It is a goal of the coin sorting
industry to eliminate or minimize overcount by stopping the coin
disc instantly after the programmed number of coins has been
counted.
An additional problem with prior art coin sorters is angular
deflection of the shaft of the gear motor, of the gears in the
speed reducing gear train, and of the splined stub shaft of the
gear motor. This angular deflection occurs upon abrupt stopping of
the gear motor and the coin disc. In prior art coin sorters this
angular deflection is due to the resilience of the motor shaft of
the gear motor, the gears of the speed reducing gear train, and the
splinted stub shaft and results in a whipping or oscillating motion
of the coin disc. If a coin is partially in a coin chute and
partially on the coin disc, this oscillation causes the coin to
move into and out of the counter resulting in the same coin being
counted several times.
A further problem experienced by prior-art coin sorters occurs as a
braking action is applied to the gear motor. This causes abrupt
stopping and the torque displacement generated by the high inertia
of the coin disc applies a potentially destructive torque on the
gears in the speed reduction gear train. Repeated application of
this torque eventually results in a break down of the gear
train.
To overcome these problems in the prior art, the coin sorter 100 is
provided with a tension or friction brake assembly generally
designated by the reference numeral 124. The tension or fiction
brake assembly 124 is mounted adjacent to the finned coin disc 106
and is energized at substantially the same time as the disc brake
122 in accordance with a synchronized braking arrangement, as will
be described in detail below. The combined effect of the disc brake
122 and the tension or friction brake assembly 124 brings the
finned coin disc 106 to a complete stop within a substantially
small time period of about 10 milliseconds or less. This period of
time substantially reduces the likelihood of overcount. The
synchronized braking arrangement also assures that the gear motor
118 is stopped by the disc brake 122 at substantially the same
instant that the finned coin disc 106 is stopped by the tension or
friction brake assembly 12, as will also be described in detail
below. Accordingly, the torque applied to the speed reducing gear
train 120 is substantially reduced. As a result, virtually no load
is applied on the speed reducing gear train 120, significantly
extending the life expectancy of the gear train 120. Furthermore,
the quick, complete stopping of the coin disc 106 eliminates or
reduces the overcount due to a coin oscillating into and out of the
counter due to torsional elasticity of the coin disc 106, speed
reducing gear train 120 and the gear motor 118.
The tension or friction brake assembly 124 may be a Warren 825
tension brake that includes an electromagnetic coil 126 rigidly
mounted to the chassis 103. The coil 126 includes an upper surface
128 that is covered with a friction material. The tension or
friction brake assembly 124 also includes a brake disc 130 mounted
by a diaphragm spring 132 to position the brake disc 130 in slight
contact with the upper surface 128 of the coil 126. The diaphragm
spring 132 is fixed at a first edge to the brake disc 130 by a
fastener 134, and is secured at a second edge by fasteners 136 to a
hub 138. The hub 138 is rigidly fixed to the finned disc 106 by the
fasteners 110. This mechanical connection allows the brake disc 130
to rotate with the finned disc 106 while the brake disc 130 lightly
engages the upper surface 128 of the coil 126.
When the coil 126 is energized, such as when a preselected number
of coins have been sorted and counted, the magnetic field created
by the coil 126 draws the brake disc 130 and the diaphragm spring
132 is flexed thereby allowing the brake disc 130 to move into
tight engagement with the upper surface 128 of the coil 126. This
engagement stops the rotation of the finned coin disc 106. Once the
coin disc 106 is stopped, the brake coil 126 can be de-energized.
The diaphragm spring 132 will then return to its normal position
lifting the brake disc 130 slightly off the upper surface 128 of
the coil 126. Since only a minimum amount of movement of the brake
disc 130 and the diaphragm spring 132 is required in order to
engage the tension or friction brake assembly 124, the tension or
friction brake assembly 124 has a faster braking action. Thus, the
only limitation to how fast the tension or friction brake assembly
124 can be actuated to brake the rotation of the finned coin disk
106 is how fast the coil 126 can be saturated with current.
The coil 126 is relatively large and requires considerable current
in order to generate the desired magnetic field. Since the coil 126
is larger than the coil in the brake 122, if the tension or
friction brake assembly 124 receives the same current at the same
time as the coil in the brake 122, the tension or friction brake
assembly 124 will be actuated slower than the brake 122. A delay
between the actuation of the brake 122 and the tension or friction
brake assembly 124 can result in the application of damaging torque
to the gears in the gear box section 120. Therefore, there is a
need to control the amount of current directed to the coil 126 and
to the coil in the brake 122 so that the brake 122 and the tension
or friction brake assembly 124 are both activated at the same
time.
In coin sorters it is desireable that the coin disc be rigid to
minimize deflection at the rim and to increase sorting accuracy.
Rigidity should not be provided, however, by structure that adds
weight since the coin disc should be light weight to minimize the
load on the gear box and to allow quick stopping. Typically, only a
very slight deflection at the rim of a coin disc can be tolerated
in order to maintain the desired accuracy in sorting and counting.
The deflection that can be tolerated is generally about 0.005
inches.
Rigidity and light weight are best attained by maintaining strength
at the rim of the coin disc while moving most of the mass of the
coin disc to the center of the disc. The finned coin disc 106 has
this combination of rigidity and weight. As shown in FIG. 5, the
finned disc 106 is defined by a thin, aluminum upper plate 140 that
is integral with a central hub 142. A plurality of thin ribs or
fins 144 are integrally formed on the underside of the thin
circular plate 140 (FIGS. 5 and 6). As measured from the edge or
rim of the plate 140 toward the hub 142, the fins 144 are narrow in
width and of increasing height, with the greatest height of the
ribs 144 being adjacent the hub 142. The fins 144 allow the coin
disc 106 to be of low mass and relatively thin at the rim to reduce
spinning inertia and yet be thick adjacent the hub to provide high
deflection strength.
The light weight and strong coin disc 106 works with the tension or
friction brake assembly 124 and the brake 122 to reduce the overall
braking time of the coin disc 106. In addition, the weight of the
coin disc 106 reduces the load imposed on the speed reducing gear
box 120 during start-up and braking, thus minimizing any
destructive torque applied to the gears disposed in the speed
reducing gear box 120.
Alternative coin discs can also be used with the coin sorter 100.
One alternative disc is the coin disc 206 illustrated in FIG. 7.
The coin disc 206 includes a central hub 208 with a top sheet of
metal 210 and a bottom sheet of metal 212. A honeycomb metal sheet
214 is positioned between the top sheet 210 and the bottom sheet
212. In one preferred embodiment, the top sheet 210 and the bottom
sheet 212 are solid aluminum sheets and the central honeycomb sheet
214 is also made of aluminum. The top sheet 210 is bonded to the
honeycombed sheet 214 by an adhesive. A similar adhesive bonds the
bottom sheet 212 to the honeycomb sheet 214, and the disc 206 so
formed is secured to the hub 208. The hub 208 includes a central
aperture or bore 216 into which the splined stub shaft 108 is
positioned to connect the disc 206 to the gear motor 118.
An alternative to using adhesive to join the top sheet 210 and the
bottom sheet 212 to the aluminum honeycomb sheet 214 is to use a
brazing process. Another alternative of the disc 206 is to use a
top metal sheet 210 fabricated of aluminum that is brazed to a
steel honeycomb sheet 214; a bottom aluminum sheet 212 is then
brazed to the honeycomb sheet 214.
It is known that the forces imposed upon a coin disc include a
tension load on the upper surface of the coin disc and a
compression load on the underside. It has been determined that
material in the center of the underside of a coin disc is not under
load and can be eliminated without lessening the structural
strength of the coin disc. In accordance with this determination,
the hollow coin disc 306 illustrated in FIG. 8 may be used with the
coin sorter 100.
The hollow coin disc 306 includes a top aluminum plate 310
including an aluminum facing 308 bonded to the plate 310. The
aluminum plate 310 is welded to a machined steel hub 312. The steel
hub 312 may be secured to the splined stub shaft 108. A hollow
conical steel housing 314 is seam-welded to the aluminum plate 310
and the machined steel hub 312. During rotation of the hollow coin
disc 306, tension forces are experienced on the plate 310 and a
compressive load is applied to the hollow steel housing 314. The
hollow coin disc 306 minimizes the amount of material needed while
maintaining the desired rigidity. As a result, the hollow coin disc
306 is light weight. Since the weight of the hollow coin disc 306
is minimized, the destructive torque applied on the speed reducing
gear box 120 is also reduced.
Although each of the coin discs 106, 206 and 306 has been described
as being fabricated of metal such as aluminum, other materials can
be used. For example, commercially available injection-molded
composite plastic material available can be used instead of metal.
Composite materials have the advantage of being very light weight
yet strong and resistant to deflection.
As can be seen from the foregoing detailed description, this
invention provides a coin sorter with an improved drive and brake
system which stops the rotatable disc of the sorting mechanism
quickly and reliably over a large number of operating cycles.
Equally important is the fact that the drive and brake system is
relatively inexpensive to install and maintain.
Referring now to FIG. 9, there is shown a preferred arrangement for
implementing a synchronous braking system in accordance with the
principles of the present invention. The arrangement is
particularly suited for achieving the synchronous operation of the
dual-brake braking system described above. As shown in FIG. 9
therein, the drive motor 402 for the coin sorter means is connected
through a speed reducer 404 to the coin disc 406 used for the
sorting operation. The motor 402 operates at a nominal speed V1
with an effective moment of inertia J1 to generate a torque T1 at
its output. The speed reducer 404 is in the form of a conventional
gear train adapted to down-convert the motor speed to the speed V2
at which the coin disc is to be rotated. On the basis of its mass,
the coin disc 406 operates under a moment of inertia J2 and
generates an output torque designated as T2.
The motor 402 is provided with a brake B1 (designated as 408) which
is normally inactive during the operation of the motor 402 and is
adapted to bring the rotation of the motor 402 to a halt upon being
activated. The arrangement described so far is conventional and
generally includes some means for controlling the operation of the
motor 402 through a motor control signal C-M and for controlling
the brake 408 through a brake control signal C-B1. The control
means required with such a conventional arrangement is relatively
simple since the control aspect is restricted to insuring that the
motor 402 and the brake 408 associated therewith are operated in a
mutually exclusive manner. More specifically, it only needs to be
insured that the motor control signal C-M is deactivated anytime
the brake control signal C-B1 is activated in order to operate the
brake 408 when it is desired that the motor 402 be braked to a
halt.
As discussed above, a conventional single-brake arrangement of the
above type has a variety of inherent practical problems, the most
significant of which is the fact that the braking torque generated
by the brake 408 is necessarily transmitted through the speed
reducer 404 to the load connected thereto, i.e., to the coin disc
404. While the torque multiplication resulting from the action of
the speed reducer 404 allows a small amount of braking torque at
the motor end to be amplified sufficiently enough to bring about
braking of the coin disc, the high torque level at the speed
reducer, in combination with the inertia generated at the coin disc
end, can have a potentially destructive effect on the gears used in
the speed reducer gear train.
More specifically, when the brake 408 is activated, the spinning
mass corresponding to the motor end of the speed reducer 404
rapidly decelerates. At the same time, the spinning mass
corresponding to the coin disc end of the speed reducer 404
continues spinning virtually at full speed under its own inertia.
The braking action, thus, produces a substantial torque
displacement on either side of the speed reducer, thereby
subjecting the speed reducer to high shock loads, each time the
brake is activated. Accordingly, repeated application of the
braking torque using a conventional single-brake arrangement
results in early breakdown of the gear train and substantially
reduces the life of the operating system.
Conventional single-brake systems also suffer from counting errors
resulting from wind-up or oscillations of the speed reducer when
braking occurs. The torque differential existing on the two ends of
the speed reducer when the braking action is applied produces a
relative angular deflection of the shafts connected to the speed
reducer which, in turn, produces a whipping or oscillating motion
of the coin disc. Such oscillations can, in turn, cause a single
coin to oscillate across the coin sensor arrangement, thereby
leading to multiple counting of the same coin.
These and other problems associated with conventional brake braking
systems are obviated in accordance with the system of this
invention, by the provision of a second brake B2 (designated as
410) operating in association with the coin disc 406. The brake 410
is similar to the motor brake 408 and is controlled by a brake
control signal C-B2 which, when activated, energizes the brake 410
in such a way as to supplement the action of the first brake 408
and bring the rotating coin disc 406 to a halt.
In accordance with a significant aspect of this invention, the two
brakes 408 and 410 are operated in synchronism so that both brakes
are energized simultaneously when it is desired that the motor 402
be brought to a halt from its rotating action. According to a
preferred embodiment, a microprocessor-based motor/brake controller
412 is provided for selectively controlling the motor control
signal C-M, the brake control signal C-B1 and the brake control
signal C-B2 so as to achieve synchronized braking action of the
motor brake B1 and the disc brake B2. The controller 412 receives
the various power signals necessary for controlling the motor 402
and the brakes B1 and B2 from a power supply unit 414. In addition,
the controller 412 receives a motor status signal SM and a brake
status signal SB which respectively correspond to the operational
status of the motor 402 and the coin disc 406, as required by the
overall coin sorter system.
According to the principles of this invention, the synchronized
operation of the two brakes is achieved with respect to two
separate aspects of the braking operation. According to the first
aspect, an arrangement is provided for improving the activation
times of the brakes to such an extent that both the brakes respond
almost instantaneously when control signals associated therewith
are activated; the arrangement ensures synchronism in the
activation of the two brakes. The motor/brake controller 412
essentially functions to utilize the motor and brake status signals
SM, SB to respectively generate the brake control signals C-B1 and
C-B2 in such a way that the time required for initiating the
braking action of the brake B1 corresponds substantially to the
time required for initiating the braking action of the brake B2, as
will be discussed in detail below.
According to the second aspect, the brakes are individually
designed and operated in such a way that the time taken by the
motor brake to halt motor rotation corresponds substantially to the
time taken by the coin disc brake to halt rotation of the coin
disc. Thus, synchronism of the stopping times of the two brakes is
ensured. The synchronism of the stopping times of the motor and
disc brakes is important in view of the differing values of inertia
and braking torque on the two ends of the speed reducer 404. By
realizing substantial equality between the braking times of the
motor 402 and the coin disc 406, the application of any damaging
torque to the gear train in the speed reducer 404 as a result of
the independent braking actions of the two brakes is avoided.
More specifically, the speed reducer 404 in the arrangement of FIG.
7 is adapted to bring about a speed reduction corresponding to a
selected ratio N:1, where N is typically about 7-10. Thus, when
only the motor-end brake B1 is used and energized, the motor speed
and the rotational speed at the output of the speed reducer 404 is
gradually reduced to zero so that the coin disc is brought to a
halt. However, because of the higher speed at the motor end, the
braking torque associated therewith is substantially lower than the
braking torque at the coin disc end where the operational speed is
substantially lowered by the action of the speed reducer 404. When
braking occurs, the torque generated as a result of the rotation of
the coin disc 406 acts upon the speed reducer gear train even as
the rotational action of the motor 402 is brought to a halt,
thereby raising the possibility of severe damage to the speed
reducer gear train due to the substantial torque displacement on
its ends. It should be noted that a similar effect would occur even
if the disc brake B2 were used in combination with the motor brake
B1, if the braking time of the motor 402 is not matched with the
braking time of the coin disc 406.
This important synchronizing function is achieved by controlling
the amount of energizing current that is used to activate the two
brakes B1 and B2 so as to bring about identical stopping times.
Preferably, the coin disc brake B2 is first selected or designed in
terms of the braking torque T2 required for counteracting the coin
disc-end inertia J2 so as to halt the rotation of the disc within a
selected stopping time S2. Subsequently, the motor brake B1 is
selected or designed in terms of the braking torque T1 required for
counteracting the motor-end inertia J1 so as to halt the rotation
of the motor within a selected stopping time ST-1. Preferably, the
stopping time ST-1 is selected to be substantially shorter than the
stopping time ST-2. When the system is subsequently operated with
brakes designed on the above basis, the lower torque requirements
at the motor-end necessitate an extension of the stopping time ST-1
of the motor brake B1 in order to equalize that time within the
stopping time ST-2 of the coin disc brake B2.
This equalizing of the two stopping times ST-1 and ST-2 is
conveniently realized by the use of a load resistance in series
with the brake coil of the motor brake B1. Preferably, the
resistance is of the variable resistance type so that its value can
be varied easily to correspondingly vary the stopping time ST-1 of
the motor brake B1 until the time ST-1 corresponds substantially to
the stopping time ST-2 of the disc brake B2. Such an arrangement
essentially decreases the energizing current for brake B1 to such
an extent that the braking torques on both the motor and the disc
ends are substantially identical, thereby bringing about
correspondingly identical braking times. Under the conditions,
synchronism of the stopping times of the motor and disc brakes is
achieved.
Referring now to FIG. 10, there is shown a schematic diagram of an
illustrative arrangement for controlling the motor and disc brakes
used with the synchronous braking system of FIG. 9 in such a way as
to achieve simultaneous activation of the brakes. The control
arrangement 450 receives a plurality of power signals U1 and U3
from the power supply unit 414 (see FIG. 9). The power signal U1 is
a standard 120 volt a.c. signal and is connected through a switch
S1 to the motor 302. The action of the switch S1, i.e., its open or
closed status, is controlled by a signal from a switch driver SD-1
which, in turn, is activated by the motor status signal SM supplied
as one of the inputs to the motor/brake controller 412. The
motor/brake controller 412 activates the driver SD-1 when it is
desired that the motor be activated for performing the coin sorting
operation. As a result, the switch S1 is also activated, i.e.,
closed, so that the voltage signal U1 is applied to the motor 302,
thereby activating it.
Preferably, the switch S1 is a solid-state switch having an
insignificant off delay or activation time. With conventional a.c.
or triac-based switches, a significant delay typically occurs
before the switch actually closes or opens subsequent to receiving
the corresponding activation signal from the switch driver. With
the use of a transistorized switch, the motor/brake controller can
effectively close or open the switch S1 within an activation time
which is negligible (of the order of a tenth of a millisecond)
compared to the relatively larger activation times (of the order of
tens of milliseconds) for conventional switches.
In the control arrangement of FIG. 10, a tank capacitor CT is
provided for boosting the activation current for the two brakes 308
and 310 in order to counteract the standard activation delay
associated with the brakes; the standard delay generally results
from a combination of the delay due to current buildup time and due
to the armature movement time. More specifically, the voltage
signal U1 is connected through a second switch S2 and a diode D1 to
the tank capacitor CT. The operation of switch S2 is controlled by
a switch driver SD-2 which, in turn, is activated by the brake
status signal SB supplied as the second input to the motor/brake
controller 412 (see FIG. 9).
The diode D1 effectively rectifies the a.c. signal at its input so
that a d.c. signal having a value equal to the peak value of the
unrectified signal is applied to the capacitor CT. More
specifically, a voltage U2 equal to 120 V*[2]1/2, i.e., 170 V, is
applied to the capacitor CT. The tank capacitor CT, thus, gets
charged by this high voltage signal U2 which is high enough,
compared to the steady state brake operating voltage of 12 V, to
provide the necessary boosting required for counteracting the
activation delays of both the brakes and neutralize in disparities
therebetween.
The cathode of the diode D1 is connected through a third switch S3
and a diode D2 to the brakes 308 and 310 for application of a
discharge signal from the capacitor CT. The operation of switch S3
is controlled by a switch driver SD-3 which, in turn, is activated
by the brake status signal SB.
The steady state operation of the motor brake 308 and the disc
brake 310 is realized by a third voltage signal U3 which
corresponds to the standard operational d.c. voltage of 12 volts
required to maintain the brakes 308 and 310 in an activated state.
More specifically, the voltage signal U3 is applied to the brakes
308 and 310 through a switch S4 and an isolating diode D3. The
operation of switch S4 is controlled by a switch driver SD-4 which
is also activated by the same brake status signal SB used as the
basis for activating switches S2 and S3.
Prior to initiation of the braking sequence, i.e., when the brake
status signal SB is inactive, the switch driver SD-2 is used to
close the switch S2, thereby applying the 120 VAC signal U1 through
the diode D1 to the tank capacitor CT. At the same time, the switch
driver SD-3 is activated so as to open the switch S3. Under these
conditions, the high voltage signal U2 resulting from rectification
of the signal V1 charges the capacitor CT.
When it is desired that the brakes be activated, i.e., when the
brake status signal SB becomes active, the switch S2 is opened and
the switch S3 closed, thereby establishing a discharge path for the
energy stored in the tank capacitor CT to be supplied to the
brakes. Since the switch S4 is effectively controlled by the brake
status signal SB, the switch S4 also closes when the brake status
signal becomes active. Accordingly, the 12 VDC signal U3 is applied
to the brakes 308 and 310 simultaneously with the discharge voltage
VB from the tank capacitor CT.
The opposing connections of the diodes D2 and D3 effectively act as
a logical OR for the signals applied thereto. Thus, while both the
discharge voltage and the U3 voltage signal are simultaneously
linked to the brakes, the larger of the two voltages is in fact
applied to the brakes at any given instant. More specifically,
immediately upon the brake status signal SB becoming active, i.e.,
as soon as the system brakes are activated, the discharge voltage
VB from capacitor CT and the U3 voltage signal are both connected
to the brakes. At that time, however, the discharge voltage, which
is a gradually decaying voltage having an initial value of 170 VDC
prevails over the U3 voltage of 12 VDC.
The discharge voltage is thus applied to both the brakes
immediately upon activation of the brake status signal SB, thereby
providing the booster voltage necessary to instantaneously generate
the high saturation current required for activating both the brakes
in a substantially instantaneous manner. Since the switch S2 is
closed at this time, the capacitor voltage subsequently decays
gradually to a point where it corresponds to the level of the
voltage signal U3. At that point, the voltage signal U3 becomes
actively connected to the brakes 308 and 310, thereby continuing to
maintain the brakes in their steady state operation condition until
both the motor 402 and the coin disc 406 are brought to a stop.
Once the voltage signal U3 comes into play, the switch driver SD-2
is activated to close the switch S2 while the switch driver SD-3 is
activated to open the switch S3. Thus, the high voltage signal U2
again becomes available to initiate the recharging of the tank
capacitor CT.
Referring now to FIG. 11, there is shown a graphical representation
500 of the various control and status signals associated with and
illustrating the operation of the control system of FIG. 10 in
achieving the synchronous braking sequence according to the present
invention. As shown therein, the brake signal 502 is used for
activating the switches in its inverse state. Thus, the signal
remains high until the synchronous braking sequence is initiated at
point A, when the signal goes low and initiates the activation of
the brakes. In FIG. 11, the point B marks the moment when both the
motor and the coin disc have been brought to a halt and there no
longer exists the need to keep the brakes activated. Thus, at point
B, the brake signal returns to its inactive high status.
The motor signal 504 is also active in its inverse status and,
accordingly, remains low prior to the point A when the braking
sequence is initiated. In other words, the motor remains activated
prior to the point A and the motor signal goes inactive or high at
point A so as to deactivate the motor.
The waveform designated as 506 corresponds to the signal at the
brake terminals. As shown, this signal is boosted up to the charge
value (170 VDC) of the tank capacitor CT upon initiation of the
braking sequence at point A. At this point, the switch S2 is opened
and the switch S3 closed in the illustrative control system of FIG.
10. Thus, the discharge voltage VB is applied through the switch S3
and the diode D2 to the brakes 308 and 310. It should be noted
that, at the same time, the voltage signal U3 is also applied to
the brakes by closing the switch S4. However, because the discharge
voltage VB predominates, the waveform 506 does not reflect the
effect of the signal U3 until the discharge voltage VB has decayed
to a level V-HOLD equivalent to the voltage level of the signal
U3.
The time delay TB required for the discharge voltage VB to decay to
the level V-HOLD represents the time period for which the discharge
voltage acts as a booster voltage for instantaneously activating
the two brakes 308 and 310. For the remaining period for which the
brakes remain activated, i.e., up until the point B in FIG. 11, the
brakes remain activated by the 12 VDC signal U3. At point B, the
switch S4 is opened so that the voltage signal U3 is removed from
the brakes, thereby deactivating the brakes completely. Thus, at
point B, the brake driver output 506 drops to zero.
The brake current 508 essentially tracks the brake driver output
signal 506. More specifically, the brake current is boosted up when
the braking sequence is activated at point A as a result of
application of the discharge voltage VB to the brakes. During the
delay period TB, the brake current continues rising and at the end
of that period, the brake current drops down to a level I-HOLD
which corresponds to the voltage V-HOLD necessary for steady state
activation of the brakes. At the end of the braking sequence, i.e.,
at point B, the brake current drops exponentially to zero from the
steady state value I-HOLD.
In FIG. 11, the waveform 510 represents the brake engagement status
of the two brakes. As shown, the brakes remain inactive prior to
initiation of the braking sequence at point A. The brakes also
remain inactive for an additional delay period TD following
activation of the brakes at point A; this delay TD corresponds to
the finite brake activation delay required for armature activation
and current saturation despite the application of the high
discharge voltage. This inherent brake delay TD is, however,
negligible in comparison with the brake delay that would otherwise
occur if the discharge or booster voltage VB were not used.
Following the brake delay TD, the brakes move into their active or
engaged status until the end of the braking sequence at the point
B, whereupon the brakes revert to their inactive status.
In FIG. 11 the waveform 512 represents the velocities V1, V2
respectively of the motor and the coin disc in relation to the
synchronous braking sequence. These velocities initially remain at
their operational level corresponding to the motor being active
during the standard coin sorting operation. These velocities are
maintained for a period corresponding to the brake delay TD
following the activation of the braking sequence at point A. As the
brakes are actively engaged, the velocities V1 and V2 gradually
drop to zero. The time period TV required for the motor and disc
velocities to drop to zero is somewhat less than the brake
activation period TA.
In FIG. 11, the waveform 514 represents the voltage level of the
tank capacitor CT in relation to the braking sequence. Prior to
initiation of the sequence at point A, the capacitor CT is in its
ready or charged state which, in the illustrative embodiment,
corresponds to the 170 VAC level. At point A, discharging of the
capacitor is initiated and the capacitor voltage VB gradually drops
down to the level corresponding to the voltage signal U3, i.e., 12
VDC. At this point, the discharge potential for the capacitor is
effectively neutralized and the capacitor voltage VB is essentially
maintained at the level of the signal U3. After the passage of a
time period TC, which insures that the steady state voltage level
for the brakes has been established by directly connecting the
voltage signal U3 thereto, the tank capacitor starts charging again
as a result of the charging switch S2 being closed. This charging
continues until the tank capacitor attains its fully charged or
ready status.
It should be noted that the above-described control system can
operate effectively despite the fact that the brake activation
times for the motor brake and the disc brake may be somewhat
different in practice. For instance, because of the lower torque
factor at the motor end, the motor brake typically engages in about
0.3 milliseconds, whereas the disc brake, by virtue of its
correspondingly higher torque factor, engages in about 1.0
milliseconds. However, differences of the magnitude of 0.1-0.5
milliseconds are negligible in terms of synchronized brake
operation. As described above, it is important that the
dual-braking system operate in such a manner that one of the brakes
does not operate alone for a substantial amount of time relative to
the other brake. Thus, the effective torque displacement on either
end of the speed reducer, and, hence, the shockload appearing on
the gear train of the speed reducer, are maintained within
manageable levels as long as the activation and braking times for
the two brakes substantially correspond to each other.
Using a synchronized dual-brake system of the foregoing type, the
coin disc can be brought to a complete stop, even under fully
loaded conditions, within an angular movement of the disc of only
about eight (8) degrees. This restricted angular rotation of the
disc corresponds to stopping times of about ten (10) milliseconds
and is sufficient to completely prevent discharge of any additional
unwanted coins once the synchronized braking sequence has been
initiated following the counting of the preselected number of
coins.
In a practical implementation of a synchronized braking system of
the above-described type, it is important not only that the motor
and coin disc brakes operate in a synchronous fashion, but that
each of the brakes operate only when the other brake is also
activated. In other words, it is important that when one of the
brakes fails for any reason, the other brake be immediately
deactivated. Otherwise, the resulting disparity in torque
displacement on either end of the speed reducer could easily lead
to destruction of the gear train disposed therein. Accordingly,
some form of signal monitoring device (not shown) is associated
with the input signals to each of the two brakes so that when one
of the input signals is found to be non-existent, the other input
signal is immediately deactivated.
Using the above-described illustrative arrangement, the
microprocessor-based motor/brake controller used for controlling
the synchronized operation of the two brakes can also be used, in
conjunction with a monitoring device associated with the drive
voltage currents for the two brakes, so that the voltage applied to
the brake coils may be independently varied (for instance, by
correspondingly varying separate serially connected variable
resistances) to compensate for torque and other variations between
the two brakes over the lifetime of the coin sorter system. Such an
arrangement can effectively counteract any deviation in the
synchronous operation of the motor and coin disc brakes resulting
from variations in torque and other parameters over prolonged use
of the braking system during in-field use of the coin sorter.
* * * * *