Variable speed drive

• US 4,770,065 A
• Filed: 12/02/1986
• Issued: 09/13/1988
• Est. Priority Date: 07/22/1985
• Status: Expired due to Term

• Current Assignee: Reliance Electric Company (ABB Limited)
• Original Assignee: Reliance Electric Company (ABB Limited)
• Inventors: Woyton, Joseph
• Primary Examiner(s): Braun, Leslle A.
• Assistant Examiner(s): Macris, Harold F.
• Application Number:
  US06/936,999
• Time in Patent Office: 651 Days
• Field of Search: 474/8, 474/11, 474/19, 474/29, 474/30, 474/31, 474/37, 474/12, 474/17, 474/18, 474/28, 474/70, 74/866, 318/624, 318/678, 318/681, 318/490, 318/434, 364/424.1, 371/62
• US Class Current: 477/44
• CPC Class Codes: F16H 61/66236 using electrical or electronical sensing or control means

Abstract

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.

Claims

1. A variable speed drive, comprising:

an electric motor providing a substantially constant speed on an output shaft thereof;

a first pair of spaced disks carried on said output shaft of said electric motor, one of said disks being fixed to said output shaft and the other disk being axially adjustable on said shaft;

an output drive shaft, having its axis rotatably mounted and spaced a substantially fixed distance from said output shaft of said electric motor, said output drive shaft being adapted for powering a selected load;

a second pair of spaced disks carried on said output drive shaft, one of said disks being fixed to said output shaft and the other disk being axially adjustable on said output drive shaft;

a drive belt extending between said two pair of disks for drivingly coupling said output drive shaft with said electric motor;

control motor means for varying the spacing between said disks of each responsive pair of disks so as to correspondingly radially shift said drive belt between said disks and thereby controllably vary the output speed of said output drive shaft;

tachometer means for generating a signal indicating the actual RPM'"'"'s of said output drive shaft;

speed setting means for providing a signal corresponding to a manual setting indicating a desired rotational output speed of said output drive shaft;

digital controller means, for generating a correction signal responsive to said tachometer means and said speed setting means, and for supplying said correction signal to said control motor means to control same to adjust said spacing of said disk pairs and said shift of said drive belt so as to adjust the output speed of said output drive shaft to said desired speed;

said digital controller means including,

relay means for selectively and alternately driving said control motor means in alternating rotational directions responsive to asid correction signal,

automatic dead band means for inhibiting driving of said control motor means when the relationship between said tachometer means signal and said speed setting means signal is within a predetermined dead band, said predetermined dead band being adaptively changed responsive to operation of said relay means so as to automatically prevent excessive hunting of said digital controller means,

display means for displaying rotational speed information determined by said digital controller means concerning said output drive shaft, and

preset means, selectively operative in one of a defined normal mode and a defined preset mode, operative in said normal mode for causing actual output drive shaft rotational speed information to be displayed by said display means, and operative in said preset mode for inhibting operation of said relay means while causing desired output drive shaft rotational speed information as determined by said speed setting means to be displayed by said display means, said controller means and relay means thereof thereafter, upon return to said normal operative mode, automatically driving said control motor means so as to establish said actual speed in accordance with said desired speed.

2. The variable speed drive as in claim 1, further comprising:

electrical means for indicating to said digital controller means maximum and minimum speed adjustments of said output drive shaft; and

wherein

said digital controller means further includes limit means, adapted to be responsive to a user-determined setting and a load signal from said control motor means, for automatically operating in a limiting mode to limit driving of said motor control means in accordance with said user-determined setting.

3. The variable speed drive as in claim 1, wherein:

said control motor means includes,

(i) a shaft;

(ii) a cam member carried on said shaft; and

(iii) a servo motor for rotating said cam so as to axially shift at least one of said disks of said first pair of disks for varying the spacing therebetween.

4. A variable speed drive as in claim 2, wherein said digital controller means further includes:

feedback loss protection means, responsive to said tachometer means signal, for automatically operating in a fail-safe mode to drive said control motor means to said minimum speed adjustment if said tachometer means signal falls below a predetermined threshold; and

message function means for causing said display means to provide user-identifiable indications whenever said limit means is operative in its limiting mode, or whenever said feedback loss protection means is in its fail-safe mode.

5. A variable speed drive as in claim 1, wherein:

said digital controller means further includes a user-selectable input mode selector for adapting said controller means to accept input signals with differing ranges; and

said digital controller further provides a predetermined output signal, the presence of which indicates that said controller means is operating properly; and

further wherein

said drive further includes auto reset means, responsive to said controller means predetermined output signal, for operating in a reset mode to restart operation of said controller means whenever said controller means is not operating properly.

6. A variable speed drive apparatus, comprising:

a mechanically-adjustable variable speed drive, having an input shaft and an output shaft drivingly coupled thereto, and an actuable member operatively associated with said shafts for mechanically adjusting the drive ratio therebetween;

power input means for rotatably driving said variable speed drive input shaft at a substantially constant speed;

actuator control means for ocntrollably adjusting the position of said variable speed drive actuable member so as to mechanically adjust the output speed of said output shaft thereof relative the substantially constant speed of said input shaft thereof;

tachometer feedback means for sensing the rotational speed of said 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 said variable speed drive output shaft;

digital controller means, responsive to said tachometer signal and said speed signal, for driving said actuator control means so as to maintain said variable speed drive output shaft at said desired speed thereof;

wherein

said digital controller means further includes automatic dead band means for adapting to changes in the relationship between said tachometer and speed signals by adjusting automatically the width of a response dead band used by said controller means in driving said actuator control means, whereby excessive hunting of said controller means is adaptively prevented; and

further wherein

said controller means further includes manually-selectable dead band means for adjusting said width of said response dead band, subject to automatic adjustment thereof by said automatic dead band means; and

said automatic dead band means functions to incrementally increase said width of said response dead band from the setting thereof established by said maually-selectable dead band, responsive to the occurrence of said actuator control means being driven in reverse actuations by asid controller means a given number of times within a predetermined period of time, with subsequent incremental decreases from such increased dead band widths as the number of such actuation reverses decreases below said given number in said predetermined period of time.

7. An apparatus as in claim 6, wherein said mechanically-adjustable variable speed drive includes:

a first pair of spaced disks carried on an output shaft of said power input means, with one of said disks being fixed on such output shaft and the other disk bieng axially adjustable thereon;

a second pair of spaced disks carried on said variable speed drive output shaft with one of such disks being fixed to such output shaft and the other being axially adjustable relative thereto; and

a drive belt extending between said two pair of disks for drivingly coupling said variable speed drive input shaft and output shaft at variable ratios, with said drive belt being adapted for positioning by said variable speed drive actuable member.

8. An apparatus as in claim 6, further comprising display means, drivable by said digital controller means, for selectively displaying variable speed drive output shaft speed information and messages from said digital controller means.

9. An apparatus as in claim 8, wherein said digital controller means operates in a normal mode to drive said display means to display output shaft actual rotational speed information as derived from said tachometer signal, and wherein said digital controller means further includes:

preset means for operating said controller means in a preset mode to inhibit driving of said actuator control means and to cause said display means to display desired speed settings for said output shaft as determined by said speed setting means, with said controller means upon returning to said normal mode thereof subsequently driving said actuator control means to achieve the most recently displayed desired speed setting;

feedback loss protection means, responsive to loss of said tachometer signal by said controller means, for operating said controller means in a fail-safe mode to drive said actuator control means so as to lower said output shaft speed to a predetermined minimum speed; and

message function means for causing said display means to display user-identifiable indications that said controller means is operating in said fail-safe more.

10. An apparatus as in claim 9, further comprising:

limit setting means for providing a threshold signal corresponding to a user-defined limit for a load characteristic of a device or process adapted to be driven by said variable speed drive output shaft; and

wherein

said digital controller means further includes limit means, responsive to said threshold signal and further adapted to be responsive to a load characteristic signal from such device or process being driven by said output shaft, for driving said actuator control means so as to limit the rotational speed of said output shaft whenever said threshold signal is exceeded by such load characteristic signal; and

wherein

said message function means of said controller means further operates to display a user-identifiable indication whenever said limit means is driving said actuator control means.

11. An apparatus as in claim 6, wherein said digital controller means further includes:

a selectable low reference voltage for adjusting said controller means to accept input signals from existing devices having different output signal ranges;

follower outputs and external inputs for providing and accepting, respectively, variable speed drive control signals with other like controller means configured in a master/slave arrangement with said digital controller means; and

an operation characteristic output signal indicative of proper operation of said digital controller means; and

said apparatus further includes automatic reset means, responsive to said operation characteristic output signal from said digital controller means, for automatically resetting said digital controller means upon improper operation thereof.

12. An apparatus as in claim 6, wherein said digital controller means outputs variable speed drive control signals for driving said actuator control means, the width of which control signals is automatically varied in proportion with the amount of difference between said tachometer signal and said speed signal.

13. An apparatus as in claim 8, wherein said digital controller means further includes user-actuatable run/idle means for selectively operating said controller means in a run mode where said controller means drives said actuator control means in accordance with said tachometer and speed signals, and an idle mode where said controlled means drives said actuator control means in accordance with said tachometer signal and a minimum speed signal, without disturbing said speed signal as established by said speed setting means.

14. A variable speed drive apparatus, comprising:

a mechanically-adjustable variable speed drive, having an input shaft and an output shaft drivingly coupled thereto, and an actuable member operatively associated with said shafts for mechanically adjusting the drive ratio therebetween;

power input means for rotatably driving said variable speed drive input shaft at a substantially constant speed;

actuator control means for controllably adjusting the position of said variable speed drive actuable member so as to mechanically adjust the output speed of said output shaft thereof relative the substantially constant speed of said input shaft thereof;

tachometer feedback means for sensing the rotational speed of said 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 said variable speed drive output shaft;

digital controller means, responsive to said tachometer signal and said speed signal, for driving said actuator control means so as to maintain said variable speed drive output shaft at said desired speed thereof; and

display means, driven by said digital controller means, for displaying rotational speed information concerning said variable speed drive output shaft;

wherein

said digital controller means in a normal mode drives said display means to display output shaft actual rotational speed information as derived from said tachometer signal, and said digital controller means further includes a user-actuable preset means for operating said controller means in a preset mode to inhibit driving of said actuator control means and to cause said display means to display desired speed settings for said output shaft as determined by said speed setting means, whereupon return to said normal mode from said preset mode said controller means drives said actuator control means so as to attain the most recently displayed desired speed setting;

said apparatus further comprising

limit setting means for providing a threshold signal corresponding to a user-defined limit for a selected load characteristic of a device or process adapted to be driven by said variable speed drive output shaft; and

wherein said digital controller means further includes

limit means, responsive to said threshold signal and a load characteristic signal form such device or process being driven by said output shaft corresponding to said selected load characteristic, for driving said actuator control means to limit the rotation speed of said output shaft whenever said threshold signal is exceeded by such load characteristic signal;

adjustable dead band means for permitting a user to manually select the width of a response dead band in which said controller means will not respond to differences between said tachometer signal and said speed signal to drive said actuator control means;

automatic dead band means, operative whenever the smallest response dead band width is selected and responsive to predetermined characteristics of said driving of said actuator control means by said digital controller means, for automatically increasing and subsequently decreasing said selected response dead band width so as to prevent excessive hunting of said controller means;

feedback loss protection means, responsive to loss of said tachometer signal by said controller means, for operating said controller means in a fail-safe mode to drive said actuator control means so as to establish a predetermined minimum speed for said variable speed output shaft; and

message function means for driving said display means to indicate respective user-indentifiable indications whenever said controller means is operating in said fail-safe mode thereof, and whenever said limit means is driving said actuator control means.

15. An apparatus as in claim 14, wherein said digital controller means provides a variable pulse width drive signal for driving said actuator control means, with the width thereof being proportionately controlled responsive to the proportional amount of error between said tachometer signal and said speed signal;

and wherein

said digital controller means further outputs a signal indicative of proper operation by said controller means; and

wherein said apparatus further includes automatic reset means, responsive to such proper operation output signal from said controller means, for automatically resetting said controller means during improper operation thereof.

16. An apparatus as in claim 14, wherein said digital controller means further includes:

a user-selectable multiplying scale factor by which the output of said display means may be scaled for correspondence to selected engineering units;

a user-selectable display mode for selecting display of such units in a time mode or in an inverse time mode; and

follower outputs and external inputs for operation with a plurality of other like controller means in a master/slave configuration.

17. A variable speed drive apparatus, comprising:

a mechanically-adjustable variable speed drive, having an input shaft and an output shaft drivingly coupled thereto, and an actuable member operatively associated with said shafts for mechanically adjusting the drive ratio therebetween;

power input means for rotatably driving said variable speed drive input shaft at a substantially constant speed;

actuator control means for controllably adjusting the position of said variable speed drive actuable member so as to mechanically adjust the output speed of said output shaft thereof relative the substantially constant speed of said input shaft thereof;

tachometer feedback means for sensing the rotational speed of said 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 said variable speed drive output shaft;

digital controller means, responsive to said tachometer signal and said speed signal, for driving relay means for selectively and alternately determining the rotational direction operation of said actuator control means so as to maintain said variable speed drive output shaft at said desired speed thereof;

display means, driven by said controller means, for displaying output shaft speed information and messages from said controller means; and

limit setting means for providing a threshold signal corresponding to a user-defined limit for a selected load characteristic of a device or process adapted to be driven by said variable speed device output shaft; and

wherein

said digital controller apparatus further includes

limit means, responsive to said threshold signal and further adapted to be responsive to a load characteristic signal from such device or process being driven by said output shaft, for driving said actuator control means to limit the rotational speed of said output shaft whenever said threshold signal is exceeded by such load characteristic signal,

automatic dead band means for automatically adjusting to differences between said tachometer and speed signals by making adjustment to the width of a response dead band used by said controller means in driving said actuator control means, so as to adaptively prevent excessive hunting of said controller means said adjustment being responsive to operation of said relay means,

feedback loss protection means, responsive to loss of said tachometer signal by said controller means, for operating said controller means in a fail-safe mode to drive said actuator control means to establish a predetermined minimum speed for said output shaft, and

preset means for operating said controller means in a preset mode to prevent driving of said actuator control means and displaying of actual output shaft speed information while causing display of newly set desired speed information designated with said speed setting means, whereupon exit of said preset mode said controller means drives said actuator control means in accordance with such newly set desired speed.

18. An apparatus as in claim 17, wherein;

said digital controller means operates to proportionally control driving of said actuator control means responsive to a difference ratio between said tachometer signal and said speed signal;

said digital controller means outputs a square wave signal indicative of proper operation of said controller means;

said digital controller means further includes message function means for driving said display means to indicate whenever either said limit means is driving said actuator control means;

or said controller means is operating in said fail-safe mode thereof; and

wherein

said apparatus further includes automatic reset means, responsive to said square wave output signal of said controller means, for automatically resetting said controller means upon loss of said square wave signal for a given period of time.

19. An apparatus as in claim 17, wherein said controller means automatically refreshes outputs thereof driving said display means, and said controller means further includes:

means for selectably accepting either a frequency-based or dc-based tachometer signal from differing types of tachometer feedback means; and

maximum and minimum speed settings for establishing a permissable range of speed settings for said speed signal by said speed setting means; and

further wherein

said power input means comprises reversible servo motor means; and

said relay means includes respective up and down relay means controlled by said digital controller means for driving said servo motor means respectively up and down to effect desired changes in the output speed of said variable speed drive output shaft; and

respective up and down control indicators for indicating actuation of said up and down relays by said digital controller means.

20. A controller apparatus for controlling a variable speed drive apparatus, including 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 the 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 actual rotational speed of the variable speed drive output shaft and providing a tachometer speed signal corresponding to same; and

display means, adapted to be driven for displaying rotational speed information concerning the variable speed drive output shaft, said controller apparatus comprising;

command speed setting means for providing a commanded speed signal corresponding to a user-determined desired speed for the variable speed drive output shaft;

digital controller means, selectively operative in one of a normal mode and a preset mode, and adapted to be responsive to the tachometer speed signal and said commanded speed signal, for producing in said normal mode thereof drive command signals based on differences between such tachometer speed signal and said commanded speed signal, said drive command signals adapted for driving the actuator control mens so as to adjust the output speed of the variable speed drive output shaft into conformance with said desired speed thereof;

relay means responsive to said digital controller means for selectively and alternately determining rotational direction operation of said actuator control means so as to adjust said output shaft output speed as desired;

automatic dead band means for inhibiting driving of said actuator control means when the relationship between said tachometer speed signal and said commanded speed signal is within a predetermined dead band, said predetermined dead band being adaptively changed responsive to operation of said relay means so as to automatically prevent excessive hunting of said digital controller means; and

preset means for selectively placing said digital controller means in said preset mode thereof, during which said controller means is inhibited from producing said drive command signals, but instead is adapted for driving said display means to display desired speed information as determined by a user with said command speed setting means, whereupon return to said normal mode said controller means resumes producing said drive command signals responsive to said desired speed, whereby said preset mode of operation permits a user to accurately and rapidly preset a desired output shaft speed before actually commanding the variable speed drive in accordance with such desired speed.