GB2131163A

GB2131163A - Monitoring rotational movement

Info

Publication number: GB2131163A
Application number: GB08233940A
Authority: GB
Inventors: Robert Frederick Gardner
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-11-29
Filing date: 1982-11-29
Publication date: 1984-06-13
Also published as: GB2131163B

Abstract

A system for monitoring the angular position of a rotary element CS, such as a manual control shaft in a lathe or other machining apparatus, includes means for generating two phase- displaced trains of pulses in accordance with rotation of the element, means for sampling the states of the two trains at intervals and, in response to a change in state of one or other train comparing (on the one hand) the new states and the previous states of the two trains against (on the other hand) stored references in order to identify transitions in the pulse trains. Predetermine identified transitions are counted to determine the magnitude and direction of rotary displacement of the element. <IMAGE>

Description

SPECIFICATION Monitoring rotational movement This invention relates to a system for monitoring the angular position of a rotary element, for example but not exclusively a manual control shaft in machining equipment (e.g. a lathe).

For example in machining equipment (and including numerically controlled equipment), a manual control for the working tool often comprises a shaft which is turned manually by a control knob secured to it, in order to move the working tool along a given axis. Typically there may be a multiplicity of such controls for adjusting the tool position along a corresponding multiplicity of axes. In order to monitor the angular position of each shaft (and hence the position of the tool along the respective axis), it is known to provide the shaft with a coded disc and to provide an optical sensor co-operating with an alternately dark and light annulus on the coded disc to generate a train of pulses as the shaft is rotated.It is further known to provide two optical sensors generating two pulse trains slightly differing in phase (either from the one coded track or from two relatively staggered such tracks): a decoding circuit arrangement receives the two pulse trains and provides an output indicating the direction of rotation of the shaft from a datum, and the magnitude of the angular displacement from that datum. The decoding circuit arrangement has however hitherto been complex.

In accordance with this invention, there is provided a system for monitoring the angular position of a rotary element, including means for generating two trains of pulses in accordance with rotation of said element but differing in phase, means for sampling the states of the two trains at intervals and, in response to a change in state of one or other train, comparing (on the one hand) the new states and the previous states of the two trains against (on the other hand) stored references in order to identify transitions in the pulse trains. By identifying and counting the transitions in this manner, both the direction and magnitude of displacement of the rotary element may be determined.

An embodiment of this invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure lisa schematic diagram of a system in accordance with this invention; and Figure 2 is a wave-form diagram of the two pulse trains produced according to rotation of the element being monitored.

A and B (Figure 2) show the two phase-displaced trains of pulses generated by two optical sensors 5A, 5B (Figure 1) co-operating with a coded disc D rotating with the control shaft CS of machining equipment (e.g. a lathe). A monitoring system in accordance with this invention comprises a microprocessor M serving periodically to sample the states (high -logic 1, or low - logic 0) ofthe two trains. The system comprise & register R for storing the previous pair of states: the system is arranged.so that at each sampling the new pair of states are compared with the stored, previous pair of states.The system is further arranged so that when the newly sampled pair exhibits a change from the stored, previous pair, the 4 bits (2 bits relating to the stored, previous pair of states and 2 bits to the newly sampled pair of states) are compared with stored 4 bit references in a look-up table T to establish a match in order to identify the direction of rotation and pulse transition which has taken place.

Thus, at the position Po (Figure 2) the states of the A and B trains can be expressed as 00. Then assuming say a clockwise rotation and represented by the arrow CW in the drawing, at transition 1 the states will become 10, at transition 2 the states will become 11, at transistion 3 the states will become 01, and at transition 4they will become 00, etc. At position Po the states 00 are stored in the register and this storage is maintained until transition 1 occurs. At the first sampling after transition 1, the new states 1-0 are found to differ from the currently stored previous states 00 and these previously stored bits are shifted two places in the register, say to the left, and the new states are stored in their place, forming the 4 bits 0010.This is representative of the transition 1, and the following table gives the corresponding representatives of the transitions 1-6: Register Contents Transition 0010 1 1011 2 1101 3 0100 4 0001 5 0111 6 1101 7 1000 8 The transitions 1-4 have already been explained and relate to a clockwise rotation and represented by arrow CW. Transitions 5-8 relate to a counterclockwise rotation as represented by arrow CCW, transition 5 being the change from logic states 00 to 01, transition 6to 11, transition 7 to 10 and transition 8 to 00.

The system is arranged such that when, as explained above, the register has its 4 bit contents, these contents are compared with each of the references shown in the above table (and stored in the look-up table T of the system) until a match is found, indicating the corresponding transition. Such transitions are counted as a measure of the angular displacement of the shaft, and the direction of displacement is indicated according to whether transitions 1-4 or 5-8 are detected. If there is no match, the transition is regarded as spurious and not counted: the register is reset with its previous 2 bits.

The system preferably has selectable resolution as follows: Thus, the system counter may be selectively set to count each and every one of the transitions 1-4 then being 4. However, the system counter may be selectively set instead to count transitions 1 and 3 only (or 6 and 8 only), the resolution factor then being 2, and again the system may be selectively set instead to count transitions 1 only (or 6 only) for a resolution factor of Unity. In any event the system is arranged to provide a multi-bit output which, in addition to giving the sum of the counted transitions, indicating which resolution factor is operative and also includes a bit indicating direction (say 0 for clockwise and 1 for counterclockwise).

The microprocessor control gives the facility to respond to an externally supplied command signal for the counter to reset to zero (or to some preset count) upon detection of a predetermined marker pulse generated from the coded disc.

The system may be arranged for monitoring a multiplicity of indpendently controlled shafts (e.g. in a multi-axis machine).

CLAIMS (Filed on 21 Nov 83) 1. A system for monitoring the angular position of a rotary element, including means for generating two trains of pulses in accordance with rotation of said element but differing in phase, means for sampling the states of the two trains at intervals and, in response to a change in state of one or other train, comparing (on the one hand) the new states and the previous states of the two trains against (on the other hand) stored references in order to identify transitions in the pulse trains.

2. A system as claimed in claim 1, further comprising means for counting predetermined identified transitions to determine the magnitude and direction of rotary displacement of said element.

3. A system as claimed in claim 2, in which said counting means is selectably controllable to count every transition of the two pulse trains, every transition of one pulse train only, or alternate (like) transitions of one pulsetrain only, to provide for selectable resolution.

4. A system as claimed in any preceding claim, including a register which stores the previous and previous but-one states of the two pulse trains and which in response to a change in state of one pulse train stores the new states in place of the previous states and stores said previous states in place of the previous-but-one states.

5. A system as claimed in claim 4, arranged sa that if the new and previous states fail to match, upon said comparing step, with any of the stored references, no transition is identified or counted and the register is reset with the previous and previous but-one-states.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. representative of the transition 1, and the following table gives the corresponding representatives of the transitions 1-6: Register Contents Transition 0010 1 1011 2 1101 3 0100 4 0001 5 0111 6 1101 7 1000 8 The transitions 1-4 have already been explained and relate to a clockwise rotation and represented by arrow CW. Transitions 5-8 relate to a counterclockwise rotation as represented by arrow CCW, transition 5 being the change from logic states 00 to 01, transition 6to 11, transition 7 to 10 and transition 8 to 00. The system is arranged such that when, as explained above, the register has its 4 bit contents, these contents are compared with each of the references shown in the above table (and stored in the look-up table T of the system) until a match is found, indicating the corresponding transition. Such transitions are counted as a measure of the angular displacement of the shaft, and the direction of displacement is indicated according to whether transitions 1-4 or 5-8 are detected. If there is no match, the transition is regarded as spurious and not counted: the register is reset with its previous 2 bits. The system preferably has selectable resolution as follows: Thus, the system counter may be selectively set to count each and every one of the transitions 1-4 then being 4. However, the system counter may be selectively set instead to count transitions 1 and 3 only (or 6 and 8 only), the resolution factor then being 2, and again the system may be selectively set instead to count transitions 1 only (or 6 only) for a resolution factor of Unity. In any event the system is arranged to provide a multi-bit output which, in addition to giving the sum of the counted transitions, indicating which resolution factor is operative and also includes a bit indicating direction (say 0 for clockwise and 1 for counterclockwise). The microprocessor control gives the facility to respond to an externally supplied command signal for the counter to reset to zero (or to some preset count) upon detection of a predetermined marker pulse generated from the coded disc. The system may be arranged for monitoring a multiplicity of indpendently controlled shafts (e.g. in a multi-axis machine). CLAIMS (Filed on 21 Nov 83)

1. A system for monitoring the angular position of a rotary element, including means for generating two trains of pulses in accordance with rotation of said element but differing in phase, means for sampling the states of the two trains at intervals and, in response to a change in state of one or other train, comparing (on the one hand) the new states and the previous states of the two trains against (on the other hand) stored references in order to identify transitions in the pulse trains.

6. A system for monitoring the angular position of a rotary element and substantially as herein described

with reference to the accompanying drawings.

7. A machining apparatus (for example a lathe) which includes at least one manual control shaft and a system as claimed in any preceding claim for monitoring the angular position of that shaft.