Variable speed drive

A mechanically adjustable variable speed drive includes an electric actuation apparatus which can be controlled by an analog embodiment or a digital circuitry embodiment. A speed change actuator is automatically and mechanically adjustable, such as with a controlled servomotor. A tachometer determines the actual rotational speed of a drive shaft, which is compared in a digital controller with a manually set desired rotational output speed. The digital controller (or an analog circuit in the case of the analog embodiment) controls the servomotor to adjust the mechanically adjustable variable speed drive. An automatic deadband means inhibits driving of the servomotor whenever the tachometer signal and the desired speed setting signal is within a predetermined deadband, which deadband is adaptively changed responsive to various conditions. The rotational information, both desired and actual, may be displayed, with display of the desired speed prior to actual operation of the drive being used to accurately preset the desired speed.

BACKGROUND OF THE INVENTION 
Heretofore, variable speed drives have normally included a drive motor 
which operated at a constant output speed. Positioned on the output shaft 
of the drive motor was a pair of disks which were axially displaceable. An 
output drive shaft was spaced from the output shaft of the motor and had 
another pair of axially displaceable disks provided thereon. A belt 
extended between the pair of disks carried on the output shaft of the 
drive motor and the disks carried on the output shaft of the variable 
speed drive. In order to vary the coupling between the output shaft of the 
motor and the output shaft of the variable speed drive, a cam arrangement 
was used for axially displacing one of the disks carried on the output 
shaft of the motor. This in turn caused the belt extending between the two 
pair of disks to be radially displaced so as to vary the output speed of 
the output shaft of the variable speed drive. In one particular 
application such as being manufactured by Reliance Electric and referred 
to as Reeves XV Motor Drive, a hand wheel was coupled through gears to the 
cam for rotating the cam in order to displace the axially displaceable 
disk carried on the output shaft in order to adjust the output speed of 
the variable speed drive. 
Automatic closed loop drive systems have also been used in the past and one 
such device is manufactured by Reliance Electric and is referred to as an 
ERC Package Control System. In that particular device, there is a magnetic 
pulse pickup for sensing the RPM of the output shaft of the variable speed 
drive. These pulses indicating the RPM of the output shaft of the variable 
speed drive are fed to a transmitter which in turn transmits a signal to a 
customer computer control center. At the customers' computer control 
center, a signal indicating the desired output speed of the variable speed 
device is generated and fed to an amplifier which is used for controlling 
an electronic remote control (ERC) for the variable speed drive. The ERC 
is equipped with a control motor that by rotating in one direction makes 
the output shaft of the variable speed drive go faster and rotating in the 
other direction go slower. A potentiometer is physically connected to the 
control motor shaft that is used for adjusting the output speed of the 
variable speed drive and generates a signal indicating the physical 
position of the arm. The potentiometer in turn is connected to the 
amplifier for making correction signals for the variable speed drive. 
Another drive system is manufactured by T. B. Woods Sons Company of 
Chambersburg, Pa. In the Woods' device, there is a control motor 
associated with the variable speed drive for physically moving the input 
drive motor relative to the output drive shaft of the variable speed 
device for varying the output speed of the variable speed drive. The 
control motor is connected to a screw which upon being rotated physically 
moves the input drive motor back and forth to vary the output speed of the 
drive. A correction signal is produced by a circuit for driving the 
control motor for physically shifting the coupling between the input drive 
motor of the variable drive and the output shaft of the variable drive. 
While the Woods' device does disclose an automatic circuit for maintaining 
the desired speed of the output signal, there is no dead band adjustment 
in the Woods' drive system. 
SUMMARY OF THE INVENTION 
Accordingly, an important object of the present invention is to provide a 
speed sensitive variable speed drive. 
Another important object of the present invention is to provide a variable 
speed drive that automatically maintains a desired output speed regardless 
of variations in loads and minor variations in line voltage. 
Still another important object of the present invention is to provide a 
speed sensitive variable speed drive that is quite stable as a result of 
utilizing a dead band circuit that only permits variations in the output 
speed of the drive when a predetermined correction is required. 
Still another important object of the present invention is to provide a 
speed sensitive variable speed drive that is equipped with circuitry that 
limits the maximum and minimum correction signal that is used for 
adjusting the output speed of the variable speed drive to correspond with 
the desired output speed of the variable speed drive. 
Still another important object of the present invention is to provide an 
automatic control for an adjustable speed belt drive that is a closed loop 
system that has an internal feedback signal associated therewith. These 
and other objects may be more fully understood from the following. 
Yet another important object of the present invention is to provide an 
improved controller for controlling a variety of types of 
mechanically-adjustable variable speed drives. The precision of such a 
controller in an improved digitally-based embodiment thereof further 
disclosed herein generally addresses and improves the sometimes slow and 
slightly unstable performance of mechanically-adjustable variable speed 
drives, as more particularly discussed herein below. 
One variable speed drive in accordance with the present invention includes 
an electric motor having a substantially constant speed on its output 
shaft. A first pair of spaced disks are carried on the output shaft of the 
motor with one of the disks being fixed to the output shaft and the other 
disk being axially adjustable on the shaft. An output drive shaft is 
spaced from the output shaft of the motor and has a second pair of spaced 
disks carried thereon with one of the disks being fixed to the output 
drive shaft and the other disk being axially adjustable on the output 
drive shaft. The distance between the axis of the output shaft of the 
motor and the output drive shaft of the drive is fixed and a drive belt 
extends between the two pair of disks for driving the output drive shaft 
from the output shaft of the motor. Means is provided for varying the 
spacing between the disks of each respective pair of disks for varying the 
output speed of the output drive shaft by radially shifting the drive belt 
between the two pair of disks. In one particular embodiment the means for 
varying the spacing between the disks of the first pair of spaced disks 
includes a cam member carried on the end of the shaft that is in turn 
driven by an electric control motor for rotating the cam. As the cam is 
rotated, the axially adjustable disk carried on the output shaft of the 
motor is shifted for radially displacing the belt between the two pair of 
disks. 
Means is provided for generating a signal indicating the actual RPM's of 
the output drive shaft. In one particular application this means includes 
a magnetic pickup that generates a frequency corresponding to the output 
speed of the output drive shaft. This frequency is converted to a voltage 
and is in turn fed to one input of a controller. The controller has 
another input to which a signal indicating the desired output speed of the 
output shaft is supplied. The controller means generates a correction 
signal responsive to the signal indicating the RPM's of the output drive 
shaft and the signal indicating the desired output speed of the output 
drive shaft. This correction signal is supplied to a speed control motor 
which rotates the cam for adjusting the drive belt to adjust the output 
RPM's of the output drive shaft to the desired speed of the output drive 
shaft. 
The controller includes a first and second control circuit for energizing 
and driving the electric speed control motor in different directions 
responsive to the correction signal. A dead band circuit is connected to 
the first and second control circuit for inhibiting the driving of the 
electric speed motor when the correction signal is within a predetermined 
amplitude range so that the control motor is not energized and driven 
unless the correction signal is outside the predetermined amplitude range. 
The controller also includes electrical means for setting a maximum speed 
adjustment of the output drive shaft and a minimum speed adjustment for 
the output drive shaft. The controller means includes a comparator that is 
used for producing the correction signal responsive to the signal 
indicating the desired output speed of the output drive shaft and the 
signal indicating the actual output speed of the output drive shaft. 
The circuit is also provided with means for producing biasing voltages for 
setting the maximum and minimum speed adjustments for the output shaft of 
the variable speed drive. These biasing voltages may be combined in a 
summing junction with the signal indicating the desired output drive shaft 
speed prior to that signal being input to the comparator for producing the 
correction signal. 
In general, both the presently disclosed analog embodiment and the 
digitally-based embodiments of the present invention may be used with 
different types of mechanically-adjustable variable speed drives. In 
particular, FIG. 1, discussed herein below, illustrates a V-belt type 
cariable speed drive. A control motor (or equivalent controllable actuator 
means) associated therewith physically actuates elemetns which in turn 
change the speed ratio between an input and output shaft thereof. In a 
similar fashion, another variable speed drive (for example, the "DISCTRAC" 
disc-type drive distributed by the Reliance Electric Company) also has 
actuable elements which vary the speed ratio between an input and output 
shaft of the variable speed drive. In such instance, the power flow 
between such shafts is variably provided with opposing pairs of friction 
discs and rings, the radius of the contact areas of which are varied to 
determine the output to input speed ratio of the drive. 
A generic mechanically-adjustable variable speed drive in combination with 
a digital controller in accordance with the present invention may include: 
a mechanically-adjustable variable speed drive, having an input shaft and 
an output shaft drivingly coupled thereto, and an actuable member 
operatively associated with such shafts for mechanically adjusting the 
drive ratio therebetween; power input means for rotatably driving such 
variable speed drive input shaft at a substantially constant speed; 
actuator control means for controllably adjusting the position of the 
variable speed drive actuable member so as to mechanically adjust the 
output speed of the output shaft thereof relative the substantially 
constant speed of the input shaft thereof; tachometer feedback means for 
sensing the rotational speed of the variable speed drive output shaft and 
providing a tachometer signal corresponding to same; speed setting means 
for providing a speed signal corresponding to a user-defined desired speed 
for the variable speed drive output shaft; and digital controller means, 
responsive to the tachometer signal and the speed signal, for driving the 
actuator control means so as to maintain the variable speed drive output 
shaft at the desired speed thereof. 
In general, the present digital controller comprises an improved version of 
the presently disclosed analog controller, and more particularly addresses 
further prior art disadvantages concerning the control of 
mechanically-adjustable variable speed drives. For example, making speed 
adjustments with such drives may be relatively slow. In some instances, as 
much as 40 seconds or more may be required to mechanically vary a drive 
between its minimum and maximum speeds. Thus, changing the speed settings 
on such a drive can require long waits between adjustments and guess work 
resulting in multiple adjustments to achieve a desired output speed. One 
aspect of the present invention particularly addresses such prior art 
disadvantage by providing the above-mentioned digital controller means 
with a further preset means for operating the controller means in a preset 
mode for inhibiting driving of the actuator control means, while a newly 
desired speed setting is accurately established, and without guess work. 
Another known disadvantage of mechanically-adjustable variable speed drives 
is that they are relatively unstable. In other words, they are known to 
continuously have slight variations in the output speeds thereof. If a 
control system were too precise in responding to such variations, it might 
undesirably hunt about the desired speed setting. While control systems in 
general are known to have response dead bands to reduce hunting problems, 
the present invention as a further aspect thereof includes an improved 
dead band feature by providing the digital controller means with an 
automatic dead band means for adapting to changes in the relationship 
between a tachometer feedback signal and a desired speed signal by 
automatically adjusting the width of a response dead band used by the 
controller means in driving the variable speed drive. 
Also, different embodiments of the present invention are not limited to 
only an electronic controller in combination with a 
mechanically-adjustable variable speed drive, but also include embodiments 
of such controllers adapted for use with such variable speed drives. 
These and many other features of the present invention, including both the 
analog and digitally-based embodiments thereof, are set forth more 
particularly in the flowing specification.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 there is illustrated an electric drive motor 10 having 
an armature 12 with an output shaft 14 projecting outwardly therefrom. The 
electric motor is bolted to a housing 16 which surrounds the entire 
variable speed drive. The motor is an alternating current fixed speed 
motor. A first disk 18 is secured to the outer end of the output shaft 14 
by means of a lock collar 20 which extends about an axially extending 
flange provided on the disk 18. Disk 18 is fixed to the shaft 14 by any 
suitable means such as a key. Another coupling shaft 20a has one end 
projecting into and fixed by means of a key to a bore provided in the disk 
18. The other end of the shaft 20a projects outwardly therefrom. The shaft 
20a is merely an extension of the output shaft 14 of the motor and is 
hereinafter referred to as the output shaft of the motor. Spaced from the 
disk 18 is an axially adjustable disk 22 which in cooperation with disk 18 
forms a pair of disks that are used for driving a coupling driving belt 
24. The disk 22 can be adjusted axially on shaft 20a by pressing against a 
yolk 24a that has a lower end 26 extending on opposite sides of the shaft 
20a. The lower end 26 of the yolk 24a pushes against a housing of a 
bearing 28 which is in engagement with a flange 32 carried on the disk 22. 
The upper end of the yolk 24a is connected by a pivot pin 34 extending 
between a pair of spaced arms 36. The arms 36 are in turn fixed to the 
housing 16. The yolk 24a is pivoted about pin 34 by means of an 
eccentrically mounted cam 40. The cam 40 is carried on the lower end of a 
vertically extending shaft 42. 
The shaft 42 and the cam 40 are driven in one or the other direction by 
means of a control motor 44. Suitable gearing 46 is provided between the 
output shaft of the control motor 44 and the upper end of the vertical 
shaft 42. The control motor merely rotates the cam 40 a predetermined 
number of degrees for selectively forcing the yolk 24a in and out. As yolk 
24a is forced in and out such causes the disk 22 to be axially displaced 
relative to the fixed disk 18. When this occurs, the belt 24 extending 
between the first pair of disks 18 and 22 is radially adjusted. 
Of course, control motor 44 and gearing 46 thereof may be used in 
conjunction with actuating other types of mechanically-adjustable variable 
speed drives, such as the "DISCTRAC" drive discussed above. The principles 
involved are substantially the same, in that an actuator control means 
(for example, control motor 44) is controllably driven by a controller 
means, such as controller 74 discussed herein below (or other equavalent 
embodiments thereof), to adjust the variable speed drive to obtain the 
desired output on the output shaft thereof. Controller 74 discussed below 
is exemplified by the basically analog circuitry of present FIG. 2. Of 
course, other embodiments of the present invention, including 
digitally-based controllers, may be substituted for controller 74. 
In order to limit the maximum and minimum amount that the yolk 24a can be 
moved by the cam 40, radially projecting pins 48 and 50 are positioned on 
collars 52 and 54 respectively. The angular spacing between the pins 48 
and 50 controls the maximum amount of movement that can be imparted to the 
axially adjustable disk 22. The pins 48 and 50 strike abutments (not 
shown) for limiting the rotation of the cam 40. 
Spaced a fixed distance from the output shaft 14 of the motor 10 is an 
output drive shaft 60 for the variable speed drive. Positioned on the 
output shaft 60 is a second pair of disks which includes disk 62 that is 
fixed to the output shaft 60 and an axially displaceable disk 64. The 
axially displaced disk 64 is forced towards the fixed disk 62 by means of 
a conventional concentrically wound compression spring 66. The fixed disk 
62 has a flange 68 provided thereon through which the output shaft 60 
extends. The flange 68 abuts against a bearing 70 extending around and 
supporting an outer end 72 of the output shaft 60. Any suitable device can 
be coupled to the output shaft 60 and in one particular instance a gear 
reduction box is coupled to the output shaft 60. Such is not further 
discussed since such is conventional. 
The belt 24 which passes between the first pair of disks 18 and 22 also 
extends between the second pair of disks 62 and 64 and is in driving 
relation thereto. As a result, the output speed of electric motor 10 is 
imparted to the output drive shaft 60 through the drive belt 24. The 
degree of coupling can be adjusted by axially shifting the disk 22 of the 
first pair of disks. When this happens, the belt 24 is shifted radially. 
The disks 18, 22, 62 and 64 have inclined inner surfaces so that when the 
disk 22 is shifted axially towards the fixed disk 18, the belt extending 
therebetween is shifted radially outward. This, in turn, causes the belt 
extending between the second pair of disks which includes disks 62 and 64 
to be shifted radially inward. As a result, the output speed of output 
drive shaft 60 is varied responsive to the axial movement of the disk 22. 
The spacing between disks 62 and 64 of the second pair of disks is shifted 
by the force of the belt 24 pressing against the inner surfaces thereof 
against the compression spring 66. 
The variable speed drive discussed in connection with FIG. 1 up to this 
point is conventional and similar to the variable speed drives being sold 
by Reliance Electric discussed above. 
One of the presesnt improvements to the variable speed drive includes 
placing a controller 74 between a means 76 for generating a frequency 
signal indicating the actual RPM's of the output drive shaft 60 and the 
control motor 44. A mechanically manipulatable knob 78 is provided on one 
embodiment of the controller for setting the desired speed for the output 
drive shaft 60 of the variable speed drive. The frequency signal produced 
by the signal generating means 76 is fed to the controller which in turn 
compares the signal which indicates the actual output speed of the output 
shaft 60 with a signal that is produced by manipulating the knob 78 
representing the desired output speed of the shaft 60. If the two signals 
don't come within a predetermined range, then a correction signal is fed 
to the electric speed control motor 44 which rotates in one or the other 
direction to rotate the cam 40 to adjust the coupling between the output 
shaft 14 of the motor and the output drive shaft of the variable speed 
drive to bring the speed of the output drive shaft 60 to the desired 
speed. 
The means for sensing the actual output speed of the shaft 60 includes a 
wheel 82 which has teeth thereon. A magnetic pickup 84 generates a 
frequency signal corresponding to the RPM's of the gear wheel 82. Any 
other suitable signal generation means could be used for generating the 
frequency signal. The magnetic pickup and gear wheel 82 is enclosed in a 
housing 86 so that all of the moving parts of the variable speed drive are 
enclosed. 
Referring now to FIG. 2 of the drawing, there is illustrated schematically 
an electrical diagram of one embodiment of the controller 74. The electric 
speed control motor is represented by the windings 44a and 44b shown in 
the left hand lower corner of FIG. 2. Depending upon which of these 
windings is energized the speed control motor 44 will be rotated in one or 
the other direction. 
The frequency signal produced by the magnetic pickup 76 representing the 
actual speed of the output shaft 60 is fed to terminal 90 on the terminal 
block 92 located in the upper left of FIG. 2. This signal is in the form 
of a plurality of serial pulses, the frequency of which is directly 
proportional to the output RPM of the output drive shaft 60. Also carried 
on terminal block 92 is a common line terminal 94 and terminals 96 and 98 
which are indicated by the plus and minus signs which are provided for 
receiving signals from an external source when it is desired to control 
the speed of the output drive shaft 60 from external signals rather than 
by manipulating the knob 78 shown in FIG. 1. 
The series of pulses, frequency of which represent the RPM of the output 
shaft 60, coming in terminal 90 are fed through a resistor 100 to an input 
terminal 102 of a frequency to voltage converter 104. The frequency to 
voltage converter 104 in turn generates a signal on output terminal 106 
having a voltage which corresponds to the frequency of the input signal 
applied to the input terminal 102. Limiting diodes 108 and 110 are 
connected between leads 112 and 114 for limiting the voltage that can be 
applied to the input of the frequency to voltage converter 104 so as to 
minimize the damage to such in case there is an excessive voltage applied 
to the input terminal. 
The output voltage from the frequency to voltage converter 104 is fed 
through resistor 116 which is connected to a potentiometer 118. The wiper 
arm 120 of potentiometer 118 is connected to a resistor 122 that is in 
turn connected to the positive input 124 of an operational amplifier 126. 
An input filter capacitor 128 is connected between the positive input 
terminal 124 and ground. A feedback circuit is connected to the output 
terminal 130 of operational amplifier 126 and includes a shorting lead 132 
which is connected back to the negative input terminal 134 of the 
operational amplifier 126. The purpose of the operational amplifier 126 is 
primarily for impedence matching. 
When there is a high impedence on the input side of the operational 
amplifier 126 the operational amplifier 126 matches the high impedence on 
the input side with a high impedence on the output side so that components 
of a smaller size can be used in the circuit. The output voltage from the 
operational amplifier 126 is applied to a negative terminal 138 of 
operational amplifier 140 through a phase compensation network consisting 
of capacitor 142 and resistor 144. The operational amplifier 140 acts as a 
comparator means for comparing the signal indicating the actual speed of 
the output drive shaft 60 with a signal produced to indicate the desired 
output speed of the output drive shaft 60 and produces a correction signal 
on the output terminal 146 corresponding to the difference therebetween. 
The signal being produced by the magnetic pickup 76 is fed to the feedback 
leg 138 of the operational amplifier 140 to be compared as previously 
mentioned with a signal produced by the summation of a signal produced by 
the manually operated knob 78, that in fact is the wiper arm 148 of speed 
pot 150, and a biasing voltage produced by the wiper arm of pot 223. The 
signal produced by the speed pot 150 indicating the desired operational 
speed of the output shaft 60 is fed through switching element 152 over 
lead 154 through resistor 156 to the positive input terminal 158 of 
operational amplifier 140. Summation of the speed pot signal with the 
biasing voltage of pot 223 occurs at a summing junction just prior to the 
input of the speed pot signal to positive terminal 158. The resistor 
element 160 of the pot 150 has one side connected to ground and the other 
side connected to a lead 162 through lead 163 which acts as a fixed 
voltage source. This fixed voltage source is produced by transformer 166, 
voltage regulator 168 and associated filter capacitors 170. The input of 
transformer 166 is connected to a conventional 115 volt ac supply across 
terminals 172 and 174. 
The transformer 166 steps down the 115 volts to approximately 18 volts in 
one particular application and the regulator causes it to be approximately 
12 volts dc on line 162. The signal produced by the setting of knob 78 
associated with the wiper arm is fed by means of lead 152 to the positive 
terminal of operational amplifier 140 as previously discussed. 
The operational amplifier 140 compares the signal on the input terminal 158 
with the signal appearing on the input lead 138 and generates an error or 
correction signal on output lead 176. This error signal is fed back 
through feedback network 178 to terminal 138. The error or correction 
signal is also fed through resistor 180 over lead 182 to operational 
amplifiers 184 and 186 which forms part of a first and second control 
circuit respectively. A positive terminal 188 of operational amplifier 184 
is tied to the negative input terminal 190 of operational amplifier 186 
through junctions 191 and 192. A divider network consisting of resistor 
194 and capacitor 196 is provided for limiting the output voltage of 
operational amplifier 140 to an operating range for the operational 
amplifiers 184 and 186. 
The two operational amplifiers 184 and 186 are provided for generating 
signals for operating the control motor 44 to rotate such in one or the 
other direction in order to displace the drive belt 24 for varying the 
output speed of output drive shaft 60. 
The negative input terminal 198 of operational amplifier 184 and the 
positive input terminal 200 of operational amplifier 186 are fixed to 
different voltage reference points. Voltages under control of 
potentiometer 201 are applied to junctions 202 and 204. The purpose of the 
potentiometer 201 is to vary the dead band range of operational amplifiers 
184 and 186. If the potential of junction 204 is the same potential as 
junction 202, then the dead band range is zero. 
Of course, it is desireable to have some differences in the potential 
between the two junctions 202 and 204. The purpose of this is to prevent 
hunting when it is desired to either increase or decrease the speed of 
rotation of the output drive shaft 60 responsive to an error signal 
appearing at the output of comparator 140. This produces a more stable 
performance for the variable speed drive. 
Depending on the error signal coming in on lead 182, it will either cause 
the operational amplifier 184 or 186 to be energized. It is one or the 
other, but not both. Assuming that operational amplifier 184 is energized, 
a signal will be supplied to output lead 206 through resistor 208 to lamp 
210 indicating that the speed is to be increased. When the lamp 210 is 
energized, the correction is taking place. The signal being fed over lead 
206 is in turn fed to a solid state relay control device 212 that is 
connected to the control winding 44b of the control motor 44. Depending on 
whether winding 44a or 44b is energized, the motor will be driven in one 
or the other direction for making the speed adjustment. 
If the operational amplifier 186 is energized, a signal is produced on its 
output 214 through resistor 216 and lamp 218 to a solid state relay 
control device 221 for supplying current through the winding 44a in an 
opposite direction from when the solid state relay control device 212 is 
energized. The dead band circuit 211 which is interposed between the 
voltage comparator means 140 and the first and second control circuits 
which includes operational amplifiers 184 and 186 is provided for 
activating either the operational amplifier 184 or 186 only when the 
correction voltage is outside a predetermined range. This range is set by 
the wiper arm of the potentiometer 201. 
Another advantage of this exemplary circuit constructed in accordance with 
the present invention is that an external signal can be applied to the 
terminals 96 and 98. The external signal can be used for varying the 
output speed of the drive rather than using the manually manipulatable 
knob 78. 
When it is desired to use an external signal, the signal is connected as 
previously mentioned to the terminals 96 and 98. The switch 164 is placed 
in the automatic mode as shown in FIG. 2. This disconnects the manual 
speed pot 150 from the fixed internal reference voltage lead 162. The 
resistor portion 160 of the pot 150 is then connected to the terminal 98. 
In other words, the pot 150 is either connected to the fixed voltage lead 
162 or the external terminal 98 depending on the mode that the switch 164 
is placed. 
When the switch 164 is appropriately manipulated, switching elements 152 
and 153 are switched to the position shown in full lines. When in this 
automatic mode, the external signal is fed over lead 220 through switch 
153, wiper arm 222 of pot 224, the switch contact 152 to terminal 158 of 
the comparator which includes the operational amplifier 140. As a result, 
signals from any suitable external source can be supplied to the 
comparator 140 for being compared with the signals being generated by the 
magnetic pickup 76 for controlling the output speed of the variable speed 
drive. When in the automatic mode, the switching terminals 152 and 153 are 
in the "up" position and the wiper arm 140 of the potentiometer 150 is 
completely disconnected from the circuit. 
The circuit has a maximum speed adjustment which includes the wiper arm 222 
forming part of the pot 224 which includes the resistor element 225. The 
resistor element 225 of the pot 224 is connected between lead 163 and the 
external signal coming in on terminal 98 through lead 220. The pot 224 
sets the maximum value of the voltage that can be applied to terminal 158 
of the operational amplifier 140. This in turn controls the maximum 
correction that can be applied to the motor 44 and in turn the output 
speed of the drive shaft 60. 
A similar pot 223 is provided for setting the minimum correction that can 
be produced by the error signal and in turn the minimum correction applied 
to the output speed of the output shaft 60 of the variable speed drive. 
The signal produced by the pot 223 is also connected to the positive 
terminal 158 of operational amplifier 140. 
In both the automatic and manual mode, the signal comes either from an 
external source 98 or a signal produced by the variable knob 78 and is 
connected to the terminal 158 of the comparator 140 through pot 224. 
The purpose of the pot 223 is to place a minimum voltage on the terminal 
158 of the operational amplifier 140 so that regardless of whether the 
knob 78 is set to zero or the input signal coming in on terminal 98 is 
zero, there will be a minimum voltage applied to the operational amplifier 
140 causing the drive to be driven at a minimum speed. In this circuit, 
you cannot reduce the output below this minimum speed. 
A visual display panel can be mounted in any suitable position to indicate 
the speed being registered by the magnetic pickup 76 and is shown in the 
schematic diagram by the display screen labeled tachometer in FIG. 2. 
One of the advantages of the circuit disclosed above is that it provides a 
variable speed drive that includes a self-contained feedback loop wherein 
a frequency signal is produced that is directly proportional to the output 
speed of the variable speed drive output shaft 60 for making corrections 
to the output speed responsive to an error signal being produced. The 
error signal is produced by comparing a signal representing the desired 
output speed of the output shaft with the voltage corresponding with the 
frequency indicating the actual output speed of the output drive shaft 60. 
The remainder of the specification more particularly concerns the 
digitally-based controller embodiment represented by present FIGS. 3-8. 
FIG. 3 illustrates a structure 300 essentially defining a housing for a 
controller in accordance with this invention. A similar such housing may 
be used to receive either an analog or a digital controller embodiment of 
this invention. different embodiments of this invention may have a number 
of adjustment features, with access to various of such features being 
within housing 300 (requiring opening thereof) and outside of housing 300. 
The present embodiment is only one example of the placement of such 
adjustment features, other placements of which are included aspects of 
this invention. 
Control board 310 of housing 300 supports a display means 320, which in 
this instance comprises a four digit display of LED's or the like (more 
fully discussed below). Two toggle switches 330 and 340 respectively 
concenr PRESET and RUN/IDLE functions of the present invention. While such 
functions and other aspects of this embodiments are discussed more fully 
below, in s ummary the preset switch functionally permits a user to select 
with speed knob 350 a newly desired rotational speed for output drive 
shaft 360 of the generic representaiton of variable speed drive 362 
without yet beginning to make such change. In an established preset mode, 
obtained by switching toggle switch 330 momentarily towards the present 
indice, the controller within housing 300 is temporarily inhibited from 
driving control motor 364 with combined power and control line 366 
therefor. Control motor 364 is substantially analogous to control motor 44 
of present FIG. 1, while the controller within housing 300 of FIG. 3 is 
generally analogous with control motor 74 thereof. Likewise, the output 
speed feedback 368 from variable speed drive 362 is substantially 
functionally equivalent with the actual rotational speed tachometer 
indication 76 which forms a feedback input to controller 74 of present 
FIG. 1. 
While inhibiting driving of a control motor 364 in a defined preset mode, 
drive motor 370 (analogous to armature 12 of present FIG. 1) continues to 
provide a power input means for rotatably driving input shaft 372 of 
variable speed drive 362. Such input power means defined by drive motor 
370 is distinguished, as understood by one of ordinary skill in the art, 
from the AC input power 380 supplied to the circuitry within housing 300. 
As further understood herein below, such AC input power on line 380 is 
also selectively output along line 366 so as to controllably drive control 
motor 364 (which forms substantially an actuator control means) for 
adjusting the drive ratio of output shaft 360 of variable speed drive 362 
relative input shaft 372 thereof. 
The controller within housing 300, during such preset mode, further causes 
a newly desired speed indication selected by a user with speed knob 350 to 
be shown on display means 320. Thus, the user can know exactly what new 
speed is being input. Upon release of momentary switch 330, the controller 
within housing 300 returns from the preset mode of operation thereof to 
its normal mode of operation, in which the control motor 364 is 
controllably driven so as to establish an output speed on output drive 
shaft 360 in accordance with the newly desired speed established with 
speed knob 350. Thus, the user accurately and efficiently changes the 
output speed with one simple rigorous (i.e. no guess work) procedure. 
Such preset function therefore greatly enhances the ability of on-sight 
user to select and change the desired speed of a mechanically-adjustable 
variable speed drive. As discussed above, such variable speed drives can 
take relatively long times to adjust to desired speed settings. Hence, a 
user might need to wait for an extended period of time, for example 15 to 
30 seconds, while the variable speed drive changes towards the newly 
desired speed setting. If a display only shows actual tachometer feedback, 
the user can never know exactly what new speed is being set, and multiple 
attempts to reach a specific speed can result. Each such attempt takes 
more time. 
It is particularly important to keep in mind that throughout such attempts, 
the variable speed drive might be providing drive power to a large 
commercial load or process which requires a particular drive input. During 
the time that a required speed is not provided or maintained, the ultimate 
product being produced with such commerical processes may constitute waste 
to the manufacturer. Thus, multiple delays of 15 to 30 seconds simply to 
attempt to adjust the drive speed for the process can be very costly to 
the manufacturer. 
Particular circuitry discussed herein below more specifically sets forth 
explains how such preset function is achieved in one exemplary fashion. 
Toggle switch 340 when placed in its run position (upward in the FIG. 3 
illustration) causes the controller within housing 300 to respond to the 
desired speed setting on speed knob 350. When placed in a downward 
position towards the idle indice, the desired speed indication from speed 
knob 350 is replaced with an internally-defined (i.e. board programmable) 
minimum speed setting. In other words, during an idle setting control 
motor 364 is selectively driven so as to automatically reduce the output 
speed of output drive shaft 360 to a predetermined minimum, without having 
to disrupt or change the setting on speed knob 350. 
Limit knob 390 also relates to practical concerns associated with variable 
speed drive 362 providing input power to a real world load or process. 
Such real world process may have inherent or natural limits which are 
unrelated to inherent limits of variable speed drive 362, control motor 
364, or the controller within housing 300. To account for such limits, a 
special load characteristic signal as defined by the user may be provided, 
and accepted by the present invention so as to maintain process activity 
within such established limits. Essentially, such user-defined load 
characteristic signals are input through limit knob 390, which essentially 
scales the user-defined process feedback signal so as to establish a limit 
threshold which the controller within housing 300 uses to prevent variable 
speed drive 362 from exceeding the desired process limits. This paragraph 
only summarizes the function behind limit knob 390, which is more 
particularly set forth and explained below. 
FIG. 3 is a schematic representation only, and is not intended as drawn to 
scale. For example, housing 300 can normally form one of the smaller 
components of an overall system illustrated. However, from a schematic 
representation view point, FIG. 3 is highly useful to understand the 
significance of the control features of the present invention in 
interfacing with a mechanically-adjustable variable speed drive, and even 
special concerns (as alluded to above) of the process or load which may be 
powered by such drive. 
FIG. 4 illustrates an exemplary board layout of elements which may be 
mounted within a housing, such as housing 300 of FIG. 3, for providing a 
digitally-based controller in accordance with the present invention. In 
general, digital circuits themselves and board mounting thereof are 
well-known to those of ordinary skill in the art. Particular placement and 
mounting of such circuit elements are also subject to numerous design and 
aesthetic considerations. Hence, mere exemplary interconnections of the 
elements and features illustrated in FIG. 4 are omitted to more clearly 
illustrate the elements themselves. Likewise, all pin connections or 
representations thereof related to microprocessor 400 are omitted for 
clarity. 
Micro-processor 400 is a multi-pin digital chip device which is typically 
mounted on a board 402, along with other peripheral circuitry elements 
which are associated therewith. Enlarged detail of microprocessor 400 is 
more particularly set forth and discussed with FIG. 5, below. 
Essentially, microprocessor 400 controls respective up and down solid state 
relays 404 and 406, which in turn control the application of AC power to 
an actuator control means such as control motor 364. Motor 364 may 
comprise a servo motor (like 44) or other bi-directional motor which 
reverses depending on the polarity of power applied thereto. Relays 404 
and 406 are also analogous to relays 212 and 221 of the analog circuitry 
of present FIG. 2. A terminal board or terminal strip 408 generally 
illustrates the board layout for interconnections with such motor 364. In 
particular, connections 2-4 of terminal board 408 may be connected to 
control motor 364 so as to selectively provide AC power thereto of 
selected polarity for alternately driving the motor in one of its two 
rotational directions. As understood by those of ordinary skill in the 
art, such rotational driving of control motor 364 in either upward or 
downward speed changes for output drive shaft 360 of variable speed drive 
362. 
For completeness, terminal strip 408 further illustrates on pins 5-8 
thereof the incoming connections for AC input power, such as on line 380 
of present FIG. 3. Further, alternatively, an AC line fuse 410 may be 
mounted on board 402 and wired between such AC power and the components on 
board 402 (as understood by those or ordinary skill in the art) for the 
protection of all such components. In particular, AC line fuse 410 may be 
interposed between the AC input power and a power transformer 420, which 
may be of various known designs. A schematic representation of an 
exemplary embodiment of such design is illustrated in present FIG. 8, 
discussed below. 
One of the chief characteristics concerning power transformer 420 is that 
the power supply provided therewith (as more fully discussed with 
reference to FIG. 8) outputs several different voltage levels for 
supporting a variety of input voltage needs for the circuitry of FIG. 4. 
For example, microprocessor 400 and other chip elements on board 402 are 
typically powered by a five (+5) volt source. Power requirements for the 
various elements and circuitry mounted on board 402 are more particularly 
illustrated in present FIGS. 5-7, and discussed more fully herein below. 
Element 422 is intended to be a general representation of the normally 
relatively large capacitor which would be associated with power supply of 
FIG. 8. For example, a capacitor of 6800 microfarads could be used in one 
exemplary embodiment, and mounted on board layout 402 in the position 
illustrated in FIG. 4. 
The auto reset device 424 may comprise an optional component of the 
illustrated embodiment of the present invention, and essentially be 
provided on a single chip which may be plugged in and out of board 402. As 
discussed more fully below, a particular output signal of microprocessor 
400 may be monitored for indications of whether such microprocessor is 
operating properly. Upon indications of malfunction, auto reset device 424 
would then automatically initiate reset functions for microprocessor 400. 
An exemplary embodiment of such optional auto reset device is more fully 
disclosed with FIG. 6, below. 
The frequency to voltage converter device 426 is used in accordance with 
the present invention to convert frequency tachometer feedback signals 
(such as might be found on line 368 of FIG. 3) to voltage levels for use 
by microprocessor 400. Alternately, the output speed feedback signal 
itself may characteristically be a changing voltage level which may be 
directly accepted by microprocessor 400, without requiring conversion by a 
frequency to voltage converter 426. 
TB 2 generally represents a second terminal board strip 428 which may 
receive and output various control signals for use with the circuitry 
mounted on board 402. In contrast, terminal strip 408 essentially 
concerned AC power connections. An example of the control signals with 
which terminal strip 428 is concerned is pin 5 thereof, which corresponds 
to the feedback signal just discussed with reference to frequency to 
voltage controller 426. 
In particular, line 368 of FIG. 3 may be directly connected with pin 5 of 
terminal strip 428, with pin 6 thereof serving as a ground for such 
signal. Essentially, pins 2, 4, 6, 8, and 10 serve as signal grounds for 
respective signals indicated on pins 1, 3, 5, 7, and 9 of such terminal 
board. An optional jumper 430 may be utilized to connect pin 1 of terminal 
strip 408 (AC ground) with one of the signal ground pins of terminal strip 
428 (eg. pin 10), all of which such signal ground pins may be connected 
with one another so that a common ground is conveniently achieved. Of 
course, the presently illustrated terminal strip layouts form merely 
exemplary layouts for one embodiment in accordance with the present 
invention, which invention need not be limited to such example. 
The remainingg structures or features on board 402 not yet discussed may 
essentially be collectively referred to as "board programmable" features 
since they constitute board-mounted adjustable elements. The adjustments 
usually take the form of switches, trim pots, or jumper connections. For 
example, four switches, S1-S4 are used to provide inputs to microprocessor 
400 which select the width of a response dead band used by the controller 
(switches S1, S2, and S3 corresponding respectively to DB1, DB2, and DB4) 
and additionally to select whether display means 320 of FIG. 3 displays 
data in a time mode or an inverse time mode. 
The remaining circuit jumper clips and trim pots ultimately also affect 
inputs for microprocessor 400, but are nore directly associated with 
analog circuitry features such as illustrated in present FIG. 7. Inasmuch 
as all such features are discussed fully below with respect to such 
analog, circuitry, it suffices for the purposes of FIG. 4's illustration 
of an exemplary board layout of the present invention to merely indicate 
at this point that elements 432-440 concern trim pot mountings on board 
402 while lemenets 442-450 constitute jumper elements on board 402. 
Also, the remaining control signals shown on terminal board 428 are 
respectively associated with the signals delineated therein. For example, 
pin 9 of terminal board 428 is adapted to receive a user-provided 
characteristic load signal related to the limit function described iwth 
reference to limit knob 390 of FIG. 3. Pins 7 and 3 of terminal board 428 
relate to external control signal inputs and control signal follower 
outputs for use with other similar controller devices in a master/slave 
configuration, as discussed more fully below with respect to FIGS. 5-7. 
Lastly, the COP signal of pin 1 of terminal board 428 related to an output 
signal for microprocessor 400 delineated as "computer operating properly", 
which as more fully described below is forwarded to auto reset device 424 
for monitoring thereof so as to reset microprocessor 400 whenever same is 
not operating properly. 
The remaining disclosure more particularly concerns FIGS. 5-8, which 
illustrate details of the digitally-based preferred embodiment represented 
by present FIG. 4. Referring first to FIG. 8, an exemplary schematic of a 
power supply, as referenced by power transformer 420 of present FIG. 4, is 
illustrated. 
As shown, four discrete voltage levels are established by the power supply, 
those being 4.7 volts, 5 volts, 7.5 volts, and 10 volts. AC power inputs 
500 and 502 are drawn from pins 7 and 8 of terminal strip 408 of FIG. 4, 
with the hot side thereof fed through a fuse 504 representing AC line fuse 
410 (of approximately 1 amp). Such fuse-protected line may also be 
returned to pin 4 of terminal strip 408 as illustrated by connector 506, 
to serve as an AC common line for motor 364 (FIG. 3). AC input lines 500 
and 502 are conventionally fed to a transformer 508, whose output is fed 
through rectifying diodes 510 and 512 for rectification. Filter capacitor 
514, which goes to ground as does the secondary center tap of transformer 
508, may comprise the relatively large capaciotr 422, referred to in 
conjunction with FIG. 4. 
The DC output from rectifying diodes 510 and 512 is variously handled by 
the remaining circuitry of FIG. 8 so as to provide the four discrete 
voltage levels earlier discussed. For purposes understood herein below, 
the 7.5 volts and 10 volts references need not be highly regulated, and 
hence may be directly drawn from such rectifying diodes, as illustrated. A 
reducing resistor 516 is representatively used for dropping the 10 volt 
output to the desired 7.5 volts. 
A known regulator circuit, including a regulator chip 518 and smoothing 
capacitor 520 may be used, as known, to provide the regulated 5 volt 
supply. The regulator chip MC68M05CT is one example of a conventional 
regulator chip known to those of ordinary skill in the art. In contrast, a 
zener diode circuit may be used to produce a highly-regulated 4.7 volt 
output, comprising zener diode 522, a pair of capacitors 524 and 526, and 
a resistor 528. While values for several of the cirucit elements 
illustrated in FIG. 8 have not been specifically provided, those of 
ordinary skill in the art will fully understand the representative power 
supply of FIG. 8, details of which do not form particular features of the 
present invention. 
In comparison, present FIGS. 5-7 illustrate numerous features, which may be 
variously combined to comprise different emobidments of the present 
invention. 
Referring now to such figures, microprocessor 550 may actually comprise a 
number of different embodiments, but preferably is a programmable 
micro-controller, such as the Motorola chip MC68705R35. Such 
micro-controller essentially comprises a combination of a microprocessor, 
further including an input section for directly receiving analog signals 
(with an internal a/D converter for handling same, as well as a separate 
input section for receiving more conventional digital inputs, and internal 
means for directly driving a display means. Of course, different chips 
could be used, as well as a separate A/D converter for inputs and driving 
means for a display. To the extent possible, FIGS. 5-7 are labeled with 
pin numbers and inter-connection identifications so as to be 
self-explanatory to one of ordinary skill in the art as to the structures 
and workings thereof. With clarity of the present description in mind, pin 
numers of micro-controller 550 (illustrated within circles on such 
micro-controller) are not separately provided with further reference 
characters. 
Referring to FIG. 5, pin 9-16 and 33-40 of micro-controller 550 are 
directly associated with driving display means 320 of FIG. 3, and as 
illustrated are directly connected with jumper pins J1-1 through J1-16 
(which were omitted from FIG. 4 for the sake of clarity). As illustrated, 
a four digit display 320 is driven, with four of such pins 9-16 and 33-40 
being respectively grouped for each one of the four digits. As understood 
by those of ordinary skill in the art, micro-controller 550 outputs a 
binary coded decimal (BCD) signal on such grouped four lines, which are 
used to drive display means 320. While such display may assume different 
embodiments in accordance with the present invention, one typical 
embodiment thereof may include a family of so-called "four-line decoders" 
such as known decoder chips 74LS247, which in turn drive 7-segment display 
suchas known devices MAN6760. Such display elements may as a further 
feature of the present invention be associated with decimal jumper points, 
to permit manual adjustment of the decimal point of display means 320. 
Also, the decoder chips and segmented display devices may optionally be 
completely removed form a controller in acordance with the present 
invention, which does not require a display for providing a most of the 
features of this invention. 
Throughout FIG. 5-7, the +5, +4.7, +7.5, and +10 designations are intended 
to indicate connections with the respective volatge outputs established by 
the power supply of FIG. 8, and further illustration of the 
inter-connection therebetween is not required for an understanding thereof 
by those of ordinary skill in the art. 
Pins 29-32 of micro-controller 550 all concern output control signals from 
micro-controller 550. For example, pin 30 (marked "INC" for "increase") 
powers an "up" solid state relay 552, while pin 29 (marked "DEC" for 
"decrease") provides a control input to "down" solid state relay 554. Such 
relays may Comprise various chips know to those of ordinary skill in the 
art, with chips P/B OZ1665 providing one example thereof, with SIGMA 
230E2-5 being alternates therefor. Connectors 556, 558, and 560 are 
clearly marked for correspondence with the control motor up and down and 
AC neutral pins of terminal board 408 of FIG. 4. Thus, solid state relays 
552 and 554 directly correspond with relays 404 and 406 illustrated on the 
board layout of FIG. 4, and are analogous to relays 2I2 and 221 of FIG. 2. 
Pins 32 and 31 correspond to increase and decrease annuciators (i.e. 
lights), respectively, with LED's 562 and 564 being automatically lit to 
illustrate driving of control motor 364 in either the respective up or 
down direction, with the understanding that up/down refers to the output 
speed of output drive shaft 360 of variable speed drive 362, while the 
actual control inputs to motor 364 correspond to selection of the 
rotational direction of output shaft 365 thereof. LED's 562 and 564 may be 
externally mounted on control plate 310 of housing 300 (e.g. next to 
display means 320) so that a user may readily monitor whenever variable 
speed drive 362 is being controllably driven in either the increasing or 
decreasing speed direction. It is understood that the paired outputs 30 
and 29, and 32 and 31 of micro-controller 550 are mutually exclusive, so 
that control motor 364 will be driven in only one rotational direction at 
a given time. The qeneration of outputs on such pins are subject to the 
various features and aspects of the present invention further discussed 
below. 
Pin 28 of micro-controller 550 refers to the computer operating properly 
(COP) output signal thereof discussed with reference to pin 1 of terminal 
board strip 428 of FIG. 4. During proper opration, micro-controller 550 
outputs a predetermined signal, such as a square wave at an exemplary 
frequency of 75 cps. As illustrated by FIG. 5, such COP signal may be 
output via line 566 to an autoreset means, such as illustrated in present 
FIG. 6. Essentially, such circuit comprises a timer means or 
multi-vibrator chip 568, such as an MC1455P or its equivalent. Use of such 
timer chips for various timing functions is well known to those of 
ordinary skill in the art, and thus the peripheral circuitry of FIG. 6 
need not be discussed in detail. 
As generally illustrated, the COP output signal from micro-controller 550 
is input to pin 4 of timer chip 568. Discontinuance of such signal for any 
appreciable length of time, such as 1/10 or 2/10 of a second is indicative 
of improper operation by micro-controller 550. Timer means 568 is 
responsive to such discontinuance of the input to pin 4 thereof, for 
periodically firing on output pin 3 thereof. Such response and firing can 
occur within less than 1 second, and is conveyed along line 570 to an LED 
572 for enunciation of such reset firing, and further to a transistor 574 
which is thereby driven to pulse reset pin 2 of micro-controller 550 (see 
also FIG. 5). 
Thus, the reset means of FIG. 6 monitors the loss of the COP signal from 
micro-controller 550 and responds thereto be periodically firing at 
approximately 1 second intervals during such loss so as to reset 
micro-controller 550 (if possible). Such resetting function is optional 
with given embodiments of the present invention, but where utilized is 
typically sufficient to reset micro-controller 550 after most causes of 
error therewith. 
Referring again to FIG. 5, a number of pins on micro-controller 550 more 
particularly concern relative housekeeping aspects of such 
micro-controller, without concerning more particular features of this 
invention. For example, pin 1 related to V.sub.ss is merely strapped to 
ground so as to provide ground for micro-controller 550, while pin 4 
related to V.sub.cc is connected to the 5 volt output from the power 
supply of FIG. 8 for providing a power input to micro-controller 550. Pin 
3 on the other hand corresponds to an interrupt input for micro-controller 
550 which is not utilized in the presently preferred embodiment. Hence, 
such input is arbitrarily strapped high and is not changed throughout 
operation of micro-controller 550. 
Furthermore, pin 5 and 6 provide a necessary high frequency clocking input 
for micro-controller 550, as is common to virtually all types of 
microprocessors units. In this instance, the frequency X.sub.f of the 
crystal oscillator 580 is 4 megacycles. Pin 7 related to V.sub.pp concerns 
a control line for initially programming micro-controller 550. By using 
such control line once to "burn in" a program, such program may be 
confidentially preseved within micro-controller 550, as understood by 
those of ordinary skill in the art. Pin 8 refers to an internal timer 
which is similarly strapped high for non-use with the presently preferred 
exemplary emobdiment, similar to the treatment of pin 3. 
The remaining pins of micro-controller 550 more particularly relate to 
circuitry including the switches, trim pots, and jumper pins mentioned 
with reference to FIG. 4. An explanation of all such circuitry, as more 
particularly illustrated in FIG. 7, and the functions collectively 
achieved thereby with micro-controller 550 are set forth more particularly 
below. 
Pins 25-27 of micro-controller 550 are related to manually selectable 
switches S1-S3, respectively, which establish the width of a repsonse dead 
band in a digital count system. In general, micro-controller 550 is an 
eight bit processor, working with counts 0-255. The three bits of inputs 
on pins 25-27 establish eight counts 0-7, with 0 being representative of 
the smallest width dead band. 
Generally in accordance with the present invention, a user is permitted to 
select the psition of such digital switches so as to designate a 
particular dead band width for use by the controller. Just as the analog 
embodiment of present FIGS. 1 and 2 has a comparator 140 which compares an 
actual feedback speed and a desired speed setting, and uses the error 
difference therebetween to control servo motor 44, the present 
digitally-based embodiment of this invention compares the feedback signal 
and the desired speed signal to obtain an error difference which falls in 
the range of counts 0-255. The selected dead band count of 0-7 establishes 
that portion of the error range 0-255 which would be ignored by 
micro-controller 550 in driving either solid state relay 552 or 554 to 
control motor 364 of present FIG. 3. 
While use of a response deasd band with a control circuit is generally 
known, the present invention further provides an automatic dead band means 
feature in addition to the manually-selectable mean band means discussed 
above with reference to switches S1-S3. As discussed above, 
mechanically-adjustable variable speepd drives under load are generally 
known to have at least some small amount of variation (i.e. instability). 
With a digitally-based highly accurate control system, even such slight 
load variations could cause the controller to hunt about the desired 
speed, i.e. constantly reverse the actuating control means (e.g. motor 
364) by jogging between up and down relays 552 and 554. It is one 
objective of the present invention to provide a manually selectable dead 
band width so that the ultimate user of the controller and variable speed 
drive may select his or her own desired dead band based on the conditions 
of their application. However, it is a further object of this invention to 
overcome the difficulties of hunting which would occur with a high 
precision controller operative with a tight dead band setting and a 
slightly unstable mechanically-driven variable speed load. Accordingly, 
the present invention as a further aspect thereof may include automatic 
dead band means for automatically electronically adjusting the dead band 
width (without physically changing the position of switches S1-S3) 
whenever the user has selected the most narrow (i.e. tightest) dead band 
width corresponding to the 0 position. 
In the exemplary embodiment of the present invention, such automatic dead 
band means is conveniently achieved through use of the micro-controller 
550, and is operative to automatically and incrementally increase the 
counts from 0 through 7 as needed to prevent excessive hunting by 
micro-controller 550. While different embodiments of such adaptive control 
may be utilized, a preferred embodiment of automatic dead band means for 
the present invention monitors the number of reverse actuations between up 
and down relays 552 and 554 in a given period of time, and increases the 
width of the response dead band whenever a given number of such reverse 
actuations is exceeded within a given period of time. For example, if the 
user initially sets the dead band position to zero count, the automatic 
dead band means of the present invention automatically increases such 
count from zero to one if there are more than three reverse actuations 
between the up and down solid state relays within a given period of time, 
such as 6.4 seconds. If a succeeding period of time produces still a 
determined excessive number of reverse actuations, the response dead band 
width is again incrementally increased from count one to two. Conversely, 
as the number of reverse actuations falls within an acceptable number for 
a given period of time, any incrementally increased number of counts for 
the response dead band width is likewise decremented one at a time (per 
given period of time) until the zero count width set by the user is again 
achieved. Such automatic dead band means greatly enhances the prevention 
of excessive hunting by micro-controller 550, particularly when used with 
a mechanically adjustable variable speed drive. 
Pins 21-24 of microcontroller 550 are all adapted to accept analog inputs 
thereto. Internally, such inputs are then converted to digital values. 
Respectively pins 21-24 are related to the aforementioned user-defined 
load characteristic signal (LIM), a scale factor (SF) signal for scaling 
the output shown by display means 320, a feedback (FB) signal (such as 
received on line 368 of FIG. 3), and a speed setting signal, such as 
established with speed knob 350 of FIGS. 3. As shown by FIG. 5, the 
circuitry for generating each of such four signals is more specifically 
illustrated in presnet FIG. 7, as discussed below. 
Referring to FIG. 7, limit pin 21 includes a settable potentiometer 600 for 
scaling the user-provided load characterization signal from input 
connector 602, previously described with reference to pin 9 of terminal 
board 428 of FIG. 4. It should be understood that for the sake of clarity 
the signal ground (pin 10 of terminal board 428) for such user-provided 
limit input signal is not specifically illustrated in FIG. 7, through 
understood by those of ordinary skill in the art. For the same reasons, 
similar other signal input grounds throughout such circuit are also 
omitted. Capacitor 604 and dividing resistors 606 and 608 further complete 
the input circuit for such user-prepared limit signal "LIM". 
Functionally, micro-controller 550 responds to the arbitrarily defined and 
user-scaled input on pin 21 thereof to prevent excessive driving of the 
load powered by variable speed drive 362. In other words, once an 
arbitrary load threshold is exceeded (such threshold being established by 
judicious setting of potentiometer 600), the limit means defined by 
digital controller means of FIGS. 5-8 functions to drive control motor 364 
so that the output of output drive shaft 360 once again conforms with the 
limit threshold. For example, the process load or variable in which a user 
is interested may be related to a torque value within the powered load or 
process, or the amount of load being applied to output shaft 360. 
Whenever the limit threshold is exceeded, as initially established in part 
with limit knob 390 of FIG. 3 (corresponding to potentiometer 600 of FIG. 
7), the digital controller means defined by micro-controller 550 and its 
peripheral circuitry operates to suspend normal driving of display means 
320, and instead flashes a message or contorl code on such display means 
to let the user realize that control motor 364 is under the driving 
control of the limit means of the present invention. Such message function 
may be incorporated inot programming of micro-controller 550 as a type of 
diagnostic display multiplexer with different messsages for indicating 
different control modes, and the like. In this instance, a particular 
control code (for example CC1) can be indicated by display means 320 to 
show that the controller means is operating in the load limiting mode and 
is not commanding control motor 364 in accordance with the desired speed 
signal established with speed knob 350. Such messasge function means of 
the present invention and further exemplary control codes and conditions 
thereof are discussed further, below. 
Pin 22 of micro-controller 550 also generally concerns interaction between 
such micro-controller and display means 320. Pin 22 is also adapted to 
directly reeive an analog signal. As illustrated in FIG. 7, SF stands for 
scale factor, and is related to trim pot 434 of FIG. 4. Such trim pot 
directly corresponds with potentiometer 610 of FIG. 7 indicated between 
ultrastable input 4.7 volts and dividing resistor 612, and ground, for 
providing an analog input on lead line 614 to pin 22 of micro-controller 
550. 
The purpose of the scale factor is to provide a multiplier by which 
information to be displayed by display means 320 is scaled or multiplied 
to establish given or desired engineering units to provide a more 
meaningful output by display means 320. All four analog inputs of pins 
21-24 of micro-controller 550 are responsive to a range of voltages 
established by low and high reference voltages for same (pins 20 and 19 
thereof, respectively). The voltage level provided on such analog input 
pins is thus ratiometrically compared with such reference voltages in a 
manner similar to an analog to digital conversion over a count of 0-255. 
Thus, in theory, the multiplying factor which can be established by 
potentiometer 610 is between 1 and 255. However, when only a four digit 
display is used for display means 320, a range of only about 1-50 is more 
than adequate to cover all practical applications. If a higher number of 
digits were used for display means 320, then a wider range of multiplying 
factors might be more practical, and would already be provided with the 
present embodiment. 
FIG. 7 further illustrates that signal information on line 615 is fed to a 
feedback (i.e. FB) pin 23 of micro-controller 550. It should be understood 
that whatever signal information appears on such analog input pin is 
processed as a tachometer signal indicative of the output speed of output 
drive shaft 360 of variable speed drive 362, and as such is automatically 
displayed by display means 320 under the drive of micro-controller 550. 
From FIG. 7, it may be further seen however that input line 616 connects 
with a dual-ganged switch 618 associated with the preset function of the 
present invention, discussed above in conjunction with momentary switch 
330 of FIG. 3, with which 618 corresponds. The upper portion of double 
pole switch 618 causes input line 616 to be switched between two further 
lines 620 and 622. The condition with lines 616 and 620 inter-connected is 
regarded as a normal mode while connection of line 616 with line 622 
occurs during a defined preset mode. 
Considering the lower pole of preset switch 618 with respect to pin 17 of 
FIG. 5, it is understood that input pin 17 of micro-controller 550 is 
either connected with a defined high voltage (+5 volts DC) or a defined 
low voltage (ground). In the normal mode (i.e. lower pole of switch 618 
connected to contact 626), input pin 17 of micro-controller 550 is set to 
such high input, while it is set to ground (i.e. the low input) during the 
preset mode. Hence, contact of the respective poles of switch 618 with 
upper contacts 624 and 626 maintain micro-controller 550 in a normal mode, 
while contact of such poles with respective lower contacts 628 and 630 
cause operation in the defined preset mode. 
During the normal mode, actual output speed information concenring output 
drive shaft 360 is fed via line 620, contact 624, the upper pole of preset 
switch 618, and line 616 into the feedback pin of micro-controller 550. 
Tachometer signal information is present on line 620 from a speed feedback 
means by virtue of connection of a signal from such means with input 
connection 632 (discussed above the reference to pin 5 of terminal board 
428 of FIG. 4). 
The present invention is adaptive to operate with a variety of different 
structures now existing in the field. For example, some of such structures 
concerning feedback means produce signals having a varying frequency 
related to rotational speed, while others produce a varying voltage 
related to such rotational speed. By changing the position of jumper pin 
448 of FIG. 4 (corresponding to jumper pin 634 of FIG. 7), the present 
invention may adapted for use with either of such two basic types of 
feedback means. 
If a feedback signal present on contact 632 is of a varying voltage type, 
then feedback jumper 634 is connected between the center pole and the DC 
pole thereof, so that the incoming varying voltage feedback signal may 
proceed directly along line 636, through a potentiometer defined as 
"standard" (STD), and eventually into pin 23 of micro-controller 550. 
However, should the feedback signal at contact 632 be the varying frequency 
type, then such signal may be fed through a filter circuit 638 and into a 
frequency to voltage converter 640, whereupon the final voltage signal is 
again fed through the trim pot STD and eventually into FB analog input pin 
23 of micro-controller 550. In such instance, jumper pin 634 is set 
between the center contact thereof and the FQ (for frequency) contact 
thereof. Frequency to voltage converter 640 may comprise a number of 
different elements, but in the presently preferred exemplary embodiment 
includes a micro-chip based device known to those in the art as an 
LM2917N. Such chip 642 includes other features as discussed more fully 
herein below. 
The STD potentiometer 644 of FIG. 7 and the filter capacitor 646 thereof 
corresponds wiwth the trim pot 436 of FIG. 4. The purpose of such 
potentiometer (which is essentially in series between the feedback signal 
of contact 632 and the feedback input 23 of micro-controller 550 is to 
standardize such signal to be compatible with the micro-controller display 
range. In other words, the feedback signal is scaled so that the maximum 
rpm of the micro-controller (in the preferred embodiment set arbitrarily 
at 5100 rpm) corresponds to an input voltage of 4.7 volts, i.e. the high 
reference voltage for micro-controller 550 as discussed herein below with 
reference to pin 19 thereof. 
With further regard to function of the preset means, switching of preset 
switch 618 (from contacts 624 and 626 to 628 and 630) causes the 
tachometer feedback signal on line 620 to be removed from feedback pin 23 
of micro-controller 550, and replaced with signal information present on 
line 622. Whenever the jumper for reference set point A (SPA) 650 is set 
to internal (I), a desired speed setting from speed potentiometer 652 is 
forwarded through lline 654, jumper 650, and line 656 onto line 622 for 
input into feedback pin 23 of micro-controller 550. 
Micro-controller 550 automatically causes display means 320 to display 
rotational speed information input on pin 23 thereof. Thus, during the 
preset mode, display means 320 is caused to display the desired speed 
setting data determined by speed potentiometer 652, instead of the actual 
feedback speed data received on pin 632. 
Also as part of the preset mode function, because the lower portion of 
preset switch 618 causes input pin 17 of micro-controller 550 to changes 
states (as described above), the micro-controller recognizes such state 
changing as a sign of the preset mode to inhibit any driving of either 
solid state relay 552 or 554 during such mode. Hence, the preset mode 
temporarily suspends active control of motor 364, and permits a user to 
see on display means 320 an accurate indication of a newly desired speed 
being established with speed knob 350. 
Upon completion of the preset mode and return to the normal operating mode 
(i e. switch 618 being returned to contacts 624 and 626), micro-controller 
550 automatically drives solid state relays 552 and 554 as needed so as to 
obtain an output speed for output drive shaft 360 in accordance with the 
newly selected desired speed thereof established with speed potentiometer 
652 (corresponding to speed knob 350 of FIG. 3). 
In the analog-based embodiment of the present invention illustrated in 
present FIGS. 1 and 2, controller 74 included a manual knob 78 on the face 
thereof for establishing a desired rotational speed for output drive shaft 
60. Micro-controller 550 of the present digitally-based embodiment of this 
invention likewise receives a desired speed signal input. In paritcular, 
an analog representation of such desired speed is received on pin 24 of 
micro-controller 550. As more specifically illustrated in FIG. 7, such 
desired speed signal is forwarded to pin 24 via line 660, pins 662 and 664 
of RUN/IDLE switch 667 (when such switch 667 is set to its "run" 
position), line 656, the internal (I) side of jumper 650, and line 654 
from speed potentiometer 652. Speed potentiometer 652 corresponds directly 
to setting of the speed knob 350 of present FIG. 3. 
Trim pots 432 and 438 of FIG. 4, related to minimum and maximum speed 
adjustment settings, corresponds respectively with potentiometers 670 and 
672 of FIG. 7. Such potentiometers are respectively coupled with reference 
input voltages of 4.7 volts and respective voltage divider resistances 674 
and 676. 
Thus, whenever a user desires to adjust the desired speed for output shaft 
360, the preset mode of doing same (as described above) may be utilized, 
or speed potentiometer 652 may be manipulated for directly changing the 
speed inputs of micro-controller 550. 
Run/idle switch 667, corresponding to toggle switch 340 of FIG. 3, enables 
the user to select the minimum speed operating point defined by 
potentiometer 670 without having to disturb the set point setting 
determined by speed potentiometer 652. In other words, as switch 667 is 
actuated to its idle position so that poles 662 and 678 thereof are in 
contact, line 680 directly in contact with minimum speed adjustment 
potentiometer 670 conducts the setting thereof to input pin 24 of 
micro-controller 550 (instead of the desired speed setting on speed 
potentiometer 652). 
However, whenever switch 667 is set in its run position, a desired speed 
signal set by potentiometer 652 is compared with the speed feedback signal 
on contact 632 (inputs to pins 24 and 23, respectively) for establishing 
driving control signals selectively output to relays 552 and 554. In 
controlling such relays, micro-controller 550 functions (taking into 
account the dead band feature of the present invention discussed above) so 
as to output control pulses to correct for effects between the actual 
speed signal (on contact 632) and the desired speed signal (produced by 
potentiometer 652). To minimize any overshoot or hunting errors, the 
widths of the output control pulses to relays 552 and 554 are 
proportionately controlled with respect to the size of the error between 
the desired and actual speed signals. 
Since a digital embodiment is presently considered, such errors take the 
form of a whole number count falling within the range of 0-255 (with zero 
being the lowest). Any error count up to the amount of a presently 
established dead band width results in no control signals whatsoever being 
output to either of the relays 552 or 554. An error count falling between 
the established dead band width and an arbitrarily defined count number 
(e.g. such as 4) may be defined as low error, which results in designation 
of a particular percentage (low) width control pulse, for example 25%. 
Medium control pulses may be arbitrarily defined, such as 50% duty width, 
and be output responsive to arbitrarily defined medium error, such as 
within a range of 4 to 8 counts of error. A defined class of large error 
signals may result in still larger pulse widths. For example, errors in 
excess of eight counts may be considered as high, and result in a 100% 
pulse width control signal being output to an appropriate one of the solid 
state relays 552 and 554. 
Such overall pulse width scheme is referred to as a proportional control 
move since the degree of control is in proportion to the degree of error. 
Still another feature of the present invention permits further alternative 
establishment of a speed input signal on pin 24. Specifically, X (i.e. 
external) poles 690 and 692 of set point jumpers A and B (650 and 694, SPA 
and SPB respectively) may permit micro-controller 550 to have its speed 
set point input controlled externally in a master/slave configuration. 
Input contact 696 (mentioned above with reference to pin 7 of terminal 
board 438 of FIG. 4) may receive speed set point commands from different 
external sources, such as other drive controllers, which essentiallly 
control processes or loads operating in parallel or in conjunction with 
the loads being driven by respective output shafts of different variable 
speed drives. In such instance, the input signal on external input contact 
696 is input with respect to resistor 698 connected to ground along line 
700 through maximum speed adjustment potentiometer 672, through line 702, 
and ultimately into line 660 which carries the externally-defined speed 
command into the speed pin 24 of micro-controller 550. 
It is readily apparent from present FIG. 7 that placement of jumper set 
point B (SPB) 694 on the internal side (i.e. I) thereof establishes a 
reference of 4.7 volts, which is further variably reduced either through 
potentiometer 672 (SPA jumper 650 set to its X position), or a combination 
of potentiometer 672 and 652 (SPA jumper 650 set to its I position), or a 
combination of all three potentiometers 672, 652, and 670 (with run/idle 
switch 667 set in its idle position). 
In addition to making provision for accepting external control inputs, the 
present invention also provides follower outputs for use in similar 
master/slave configurations, for powering up to eight slave units. In 
particular, follower output connection 710 of FIG. 7 corresponds to pin 3 
of terminal board 428 of FIG. 4, as discussed above. Chip device 642 (as 
described above) also provides in addition to frequency to voltage 
converter device 640 thereof, a follower output amplifier 712 and follower 
transistor 714 for providing the folloer output at contact 710. A negative 
feedback loop for operational amplifier 712 and transistor 714 is 
established with resistors 716 and 718, and further with the follower 
output gain being established by gain (G) potentiometer 720, which 
corresponds with trim pot 440 of FIG. 4. 
As further illustrated in FIG. 7, input line 722 of follower amplifier 712 
may be connected to several different points through selected setting of 
follower output (FO) jumper 724, corresponding with jumper 450 of FIG. 4. 
In the illustrated position of jumper 724, the desired (i.e. commanded) 
speed signal (however established) existing at contact point 726 for 
feeding to speed pin 24 of micro-controller 550 is forwarded via line 728 
into follower amplifier 712. 
Alternatively, jumper 724 may be set to interconnect the center pin thereof 
with feedback pin 730 thereof so as to disconnect the commanded speed 
input side thereof to the follower output amplifier, and instead connect 
through line 732 as the input thereof whatever feedback information 
appears on line 620. Hence, even the follower output on contact 710 is 
selectable to follow either the commanded speed set point of the 
micro-controller 550 or the feedback signal of the master drive. 
Furthermore, the follower gain is adjustable with use of gain pot 720, as 
discussed. Chip device 642 essentially utilizes the higher voltage of 7.5 
volts as its reference. Such higher reference is preferred to establish a 
chip functioning range of at leat 0-5 volts. If only a 4.7 volt reference 
were used, it is known that approximately 1.5 volts or so is lost due to 
voltage drops induced with the frequency to voltage converter so that an 
insufficient voltage range would result between the low and the high 
reference thereof. The remaining inter-connections of device chip 642 are 
understood by those of ordinary skill in the art without further comment. 
With respect to the reference voltages utilized by micro-controller 550 
itself, an ultrastable high reference voltage V.sub.RH of 4.7 volts is 
supplied from the power supply of FIG. 8 to pin 19 of the micro-controler 
(see FIG. 5). However, the low reference voltage V.sub.RL, which is input 
on pin 20 of micro-controller 550 of FIG. 5, is selectable between zero 
and one volts. The purpose of such selection is to permit adaptation of 
the input range of micro-controller 550 between two separate ranges of 
0-4.7 volts or 1-4.7 volts. It is known in the industry that different 
devices sometimes operate on different signal voltage ranges. A selectable 
voltage range for micro-controller 550 permits maximum flexibility for use 
with different types of existing equipment in the field. 
The last feature which is actually selected with respect to 
micro-controller 550 with a switch or the like relates to the switching 
function accomplished with switch S4 on pin 18 (defined as RPM). Such 
switch itself merely interconnects pin 18 with a respective digital high 
or lower. Micro-controller 550 responds to switch S4 for driving display 
menas 320 so as to display subject matter thereon in either a time mode 
(e.g. rpm's) or as inverse time mode. 
With respect to driving of a display means 320 by micro-controller 550, and 
the diagnostic display multiplex or message function operation thereof 
described generally above, additional control codes and the like may be 
output on display means 320 responsive to various operating conditions of 
micro-controller 550. For example, micro-controller 550 may be programmed 
for automatically responding to loss of a feedback signal on contact 632 
(actually lost at pin 23) to automatically drive variable speed drive 362 
down to the minimum defined speed thereof, and alternately flash a message 
(for example "CCO" for "control code zero") to indicate that there has 
been a loss in feedback. In a practical sense, such minimum speed normally 
approximates 200-300 rpm. Without such feedback loss protection means, 
racing or other undesired control of variable speed drive 362 could result 
upon loss of such signal. Hence, the automatic feedback loss protection 
means established with such operation of micro-controller 550 protects 
both the ariable speed drive 362 and any real world load or process being 
driven or managed thereby. 
Also, while specific details of programming for micro-controller 550 have 
not been addressed, those of ordinary skill in the arts concerning 
microprocessors and related devices are in general very familiar with 
programming of same once desired functions are established. The present 
disclosure has provided a full and enabling description of the functions 
of the present invention sufficient to permit one of ordinary skill in the 
art to make and practice such invention. 
Furthermore, while a greater variety of different specific embodiments may 
be provided by those of ordinary skill in the art in order to practice the 
invention presently disclosed, the embodiment generally illustrated in 
present FIGS. 3-8 is preferred, particularly in that because it provides 
maximum flexibility in the field for use with a variety of different 
equipment. For example, the various board programmable jumpers discussed 
throughout the specification permit for example use of different types of 
tachometer feedback signals, and different sources of desired speed input 
signals. 
Similarly, use of a micro-controller in the preferred embodiment of the 
digitally-based embodiment of this invention permits efficient and 
convenient handling of such functions, such as automatic input/output 
refresh, and incorporation of input low pass filters. Such a completed 
system provides an overall control system with a high degree of electrical 
noise immunity to provide reliable operation in industrial environments 
where it is likely the controller will be used to drive processes 
associated with mechanically-adjustable variable speed drives. 
While generally rugged, the present device still maintains adaptability to 
user circumstances. For example, the limit information supplied by the 
user on contact 602 of FIG. 7 may include a variety or signal sources, 
such as the current being drawn by further loads powered by variable speed 
drive 362, or various torque or time-related processing signals from such 
commercial applications. 
It will be understood, of course, that while the form of the invention 
herein shown and described constitutes preferred embodiments of the 
invention, it is not intended to illustrate all possible forms of the 
invention. 
It will be further understood that the present disclosure is directed to 
those of ordinary skill in the art, and thus presumes a corresponding 
level of understanding by the reader concerning common terminology and 
symbols. For example, fixed voltage sources, such as connected to the 
wiper arms of potentiometers 223 and 118 (FIG. 2), and represented by a 
circle and intersecting line, are not discussed in detail. It will also be 
understood that the words used are words of description rather than of 
limitation and that various changes may be made without departing from the 
spirit and scope of the invention herein disclosed.