AU619472B2 - Indexing system for stepper motors - Google Patents

Description

COMMONWEALTH OF AUSTRALIA Patents Act 1952 COMPLETE SPECIFICATION (Original) FOR OFFICE UJSE Application Number: P12925 Class Lodc,ed: 3rd July 1987 6197 Int. Class Complete Spec:-ification Lodged: Accepted: Published: Priority; Related Art: TO BE COMPLETED BY APPLICANT Name of Applicant: ACKMAR NOMINEES PTY LTfl.

LTD.

£Ct cC C Address of Applicant: 1 brewer Street, East Perth, in the State of Western Australia, Commonwealth of Australia Actual Inventor: Addrhess for Service:- Wray Associates Primary Industry House 239 Adelaide Terrace Perth Western Australia 6000.

Complete Specification for the invention entitled: "Indexing System for Stepper Motors" P0C)0 7 61e 001bOLZde~atement is a full description of this invention, including the best method of performningi it known to me:- 1- 2 THIS INVENTION relates to an indexing system for indexing a plurality of stepper motors in a controlled manner.

Stepper motors are employed to effect movement of machine parts in various directions in a controlled manner. In some applications, it is important to control not only the starting and finishing points of the machine part during each movement, but also the path followed by the machine part in moving between the starting and finishing points.

Precision equipment such as plotters, profilers, cutters and engraving machines are examples of such machines.

There is a difficulty in precisely controlling the stepper motors, particularly during starting and stopping thereof where pulses which drive the stepper motors are required to be delivered to each stepper motor at progressively increasing or piogressively decreasing rates as the case may be. During starting of a stepper motor, it is necessary to deliver pulses to the motor in a progressively increasing fashion for otherwise the motor .e may miss pulses or not start at all. Similarly, during stopping of a stepper motor, it is necessary to deliver pulsus at a progressively decreasing rate for otherwise the motor may over-run owing to inertia in the machire components.

In machines where a plurality of stepper motors are controlling movement of a machine part, it is important to accelerate and decelerate the steppjr motors at proportional rates so as to attain their respective terminal velocities at the same time for otherwise there is a loss of precision of movement of the machine part.

The present invention seeks to provide a novel and useful indexing system for controlled inCdxing of a plural3ty of stepper motorss.

9 n L I I 3 In on? form the invention resides in an indexing system for indexing a plurality of s'epper motors, said indexing system comprising oeans for generating a train of pulses at a substantially constant rate, means for manipulating the train of pulses to selectively vary the pulse rate and de-iver the pulses so varied to a plurality of counters one corresponding to each stepper motor, the counters being provided for counting and regulating pulses delivered to the respective stepper motor, and management means for controlling the manipulating means to regulate the common pulse rate delivered to the counters and for further controlling each counter independently of the *other counters to govern the number of pulses delivered to I ',the respective stepper motor.

With this arrangement, the manipulating means i.der the control of the management means can vary the speed of the SI stepper motors in unison by varying the common pulse rate delivered to the counters. Additionally, the management j system can control the number of steps throuJh which each j stepper motor indexes independently of the other stepper motors by governing the 'number of pulses delivered to the stepper motor. In this way, precision control of a machine part driven by the stepper motors can be achieved.

Preferably, a multiplier is provided for multiplying the pu'.Xse r&te veried by said manipulating means.

Preferably, the management system is in the form of a microprocesaor, Preferably, the manipulating means is in the form of a pre-counter.

Preferably, a speed table is maintained within a control program and contains a series of counter values which can I- 4 be sequentially applied to the pre-counter to progressively increase or progressively decrease the pulse rate as necessary.

The invention will be better understood by reference to the following description of one specific embodiment thereof as shown in the accompanying drawing which is a diagrammatic representation of the indexing system.

The indexing system according to the embodiment comprises a frequency source 11 for generating a pulse stream at a i I 10 substantially constant rate. The pulse stream emanating from the frequency source 11 is applied to a software t' programmable pre-co iter 13. The output of the pre-counter 13 is multiplied in frequency by a soft::.'re programmable multiplier 15. The ep ut of the multiplier provides a basic counting unit and is applied to a plurality of counters 17, one corresponding to each t* stepper motor. The outputs of the counters 17 are the driving pulses which are applied to the stepper motors.

The counters 17 need to be of sufficient size to allow the desired maximum number of steps by any one or more stepper motors while allowing fewer steps (as low as one) by other stepper motors. Factors to be considered in the selection of a counter include the physical limits of the multiplier, the desired maximum speed which the stepper motors are to be capable of attaining, and the desired resolution between the stepper motors. For example, 24 bit counters will allow a maximum of 32,000 steps by one stepper motor and one step by any other stepper motor.

Because the output frequency from the multiplier is common 3 0 to each counter, the system can accommodate slight variation in the output frequency, as a missed pUlse or a slightly mis-timed pulse will have little effect.

5 A management means in the form of a microprocessor 21 is provided for controlliig the pre-counter 13 and also the i various counters 17. In controlling the pre-counter, 13, the microprocessor regulates the pulse rate delivered to the counters 17 and can thereby regulate the speed of the stepper motors. The pulse rate can be progressively increased to accelerate the stepper motors at a unifurm rate, or progressively decreased to decelerate the stepper Smotors at a uniform rate. A speed table is provided in I" 10 control program and the microprocessor can sequentially change the control value in the pre-counter to the next value (either upper or lower) in the speed table to vary the pulse rate in the manner described.

.ccc In controlling each counter independently of the other counters, the microprocessor can control the speed relationship between the stepper motors. This control is achieved by regulating the number of pulses issuing from S each counter relative to the number of pulses delivered to the counter, For example, the control exerted on one counter may be such that it allows every pulse delivered to the counter to in turn be delivered to the stepper motor associated with that counter, while the control exerted on another counter may be such that it allows only every, say, third. pulse delivered to the counter to be delivered to the stepper motor associated with that i counter. In this way, the stepper motor corresponding to the first-mentioned counter would opelate at a higher rotational speed than the stepper motor corresponding to e, 30 the -econd-mentioned counter.

If desired, the multiplier may be of a programmable nature so that the multiplying value can be selectively varied.

This allows the dynamic range of the indexing system to be varied by changing the multiplier value.

I- 6 From the foregoing, it is evident that the present invention provides an indexing system in which acceleration and deceleration of stepper motors can be controlled in a uniform manner and in which the speed relationship between the motors can also be controlled.

In this way, a machine part operated by the stepper motors can be precisely controlled.

It should be appreciated that the scope of the invention is not limited to the scope of the embodiment described.

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Claims (6)

1. An indexing system for indexing a plurality of stepper motors, said indexing system comprising means for generating a train of rulses at a substantially constant rate, means for manipulating the train of pulses to selectively vary the pulse rate and deliver the pulses so r varied to a plurality of counters one corresponding to each stepper motor, the counters being provided for counting and regulating pulses delivered to the respective stepper motor, and management means for controlling the manipulating means to regulate the common pulse rate delivered to the counters and for further controlling each counter independently of the other counters to govern the number of pulsers deliverea to the respective stepper motor.

2. An indexing system according to claim 1 wherein a multiplier is provided for multiplying the pulse rate I varied by said manipulating means.

3. An indexing system according to claim 1 or 2 wherein the management system is in the form of a microprocessor.

4. An indexing system according to claim 1, 2 or 3 wherein the manipulating means is in the form of a pre-counter. An indexing system according to any one o€ the AA preceding claims further comprising a speed table maintained within a control program and containing a series of counter values which can be sequentially applied to the pre-counter to progressively increase or progressively decrease the pulse rate as necessary. I V

8- 6. An indexing system substantially as herein described with reference to the acciompanying drawing. DATED this FIRST day of JULY

1988. ACKMAR NOMINEES PTY. LTD. Applicant J 4- ,.tI~ *4 I.. I I I WRAY Ae8OCIATES Perth, Western Australia Patent Attorneys f or Applicant 7