GB2133541A

GB2133541A - Movement detecting apparatus

Info

Publication number: GB2133541A
Application number: GB08334142A
Authority: GB
Inventors: D A Straw
Original assignee: Plessey Co Ltd
Current assignee: Plessey Co Ltd
Priority date: 1983-01-07
Filing date: 1983-12-22
Publication date: 1984-07-25
Also published as: GB8334142D0

Abstract

A very sensitive indicator for a winding drum used at collieries consists of a toothed wheel rotating between a light emitter and a light detector. The pulses of light received by the detector are counted until a preprogrammed count is reached when the speed of the winding drum is reduced prior to stopping it with the lift at a certain level. Two detectors 10, 12 located side by side are used and positioned so that one of the detectors is always fully off or on whenever the other is in an intermediate state. The detector circuit looks for a change in state of both detectors to protect against vibrations causing a count, and determines the sense of movement by detecting which of the detectors changes state before the other. <IMAGE>

Description

SPECIFICATION Movement detecting apparatus This invention relates to movement detecting apparatus and more particularly but not exclusively to apparatus for detecting rotational movement of a member such as the winding engine drum for lift cages used in mines. The direction of movement of a lift cage in a mine is required to be known and its position needs to be accurately determined for stopping it at predetermined positions.

It is an object of the present invention therefore to provide movement detecting apparatus which will indicate movement of a member, its direction of movement and which is able to accurately determine its relative position.

According to the present invention movement detecting apparatus comprises a movable member having a plurality of equally spaced windows formed therein, a light source located on one side of the member and two light detectors located on the opposite side of the member to receive light from the light source through the windows, the light detectors being spaced such that when the member is stationary one of the detectors receives either full light or no light from the light source, and the other detector receives a partial amount of light from the light source, an electrical circuit for receiving signals from the light detectors and adapted to detect changes in state of the light detectors to detect movement of the member, which of the light detectors change state before the other to determine the direction of movement of the member, the electrical circuit also including counter means for counting the number of windows which have traversed the light detectors for determining the distance moved by the member.

In this specification the term "light" also includes light invisible to the human eye such as infra-red and ultra-violet rays.

Preferably the electrical circuit includes clock means to determine the speed of movement of the member.

The electrical circuit may also determine when a predetermined speed of the member has been exceeded.

The movable member preferably comprises a rotatable wheel.

The windows preferably comprise a series of slots formed in the periphery of the wheel.

An embodiment of the invention will now be described with reference to the accompanying drawings in which Figure 1 is a scrap view of a slotted wheel for use in a rotation sensor constructed in accordance with the present invention and Figure 2 is an electrical circuit for the rotation sensor The rotation sensor is designed to give indication and direction of movement of the lift winding engine drum used at colleries. It was designed as a direct replacement for a mechanical device currently in use. The main advantage over the mechanical device is the sensitivity, the new device being capable of detecting down to 3" of rope movement on the winding drum, whereas its mechanical counterpart has nothing like this performance.

The sensor is adapted to detect the position of the drum, whether the drum is stationary or rotating, the direction of rotation of the drum and also detects when a predetermined rate of rotation of the drum has been exceeded. The system can be used merely to indicate these conditions or signals can be produced to affect the actual mine signalling system or the drum operating control system itself.

It is not limited to colliery use, since a belt drive to a pulley may be driven from any available shaft where detection of any movement is required.

Electronic pulses are generated by the rotation of a wheel 14 having a plurality of teeth 1 6 in its periphery between a light source (not shown) and two detectors 10, 1 2 mounted side by side. The teeth 1 6 of the wheel prevent light from passing between the light source and the light detectors 10 and 1 2 while the slots permit passage of light, thus creating on-off states in the light detectors.

As the wheel 1 4 rotates at a fairly high speed the detectors 10, 1 2 switch on and off, and the pulses produced are counted by a high speed electronic circuit. If the number of pulses in a preset scan time exceeds a preprogrammed count the sensor indicates that the drum is operating normally. When the wheel slows down to a speed below the preprogrammed count a slow speed circuit activates and slow speed is indicated by the sensor.

Both circuits are reset when the wheel comes to rest.

By monitoring which of the two light detectors 10, 12 changes state before the other, then the direction of rotation is detected.

The spacing of the two opto devices is such that when the wheel is stationary, one of the detectors is guaranteed to be fully off or fully on (e.g. detector 12), whereas the other detector can be in an intermediate state i.e. just on the verge of being on or off (e.g. detector 10). The input circuitry is arranged to look for a change in state of both detectors thus protecting against vibrations causing a 'count' (slow movement) from being detected.

Fig. 1 shows part of the toothed wheel 14 which has twenty four teeth and the relative positions of the optical detectors 10, 1 2.

From this it can be seen that irrespective of which position the wheel comes to rest it is guaranteed that one of the detectors is either completely off or completely on. The spacing of the detectors is controlled very strictly by accurate P.W.B. layout and the toothed wheel is precisely machined.

The outputs from the detectors 10, 1 2 are taken via test switches 18, 20 to clock D type flipflops ML1 and ML2. Before an output can appear at an AND gate ML3 both D types have to be clocked which means that a positive going edge has to be received from both detectors thus preventing false pulses, due to vibrations causing a detector which is at the threshold of being just on (as is detector 10 in Fig. 1) from causing incorrect operation.

Once the wheel 14 has travelled a distance of 1 pitch both detector outputs will have gone from a low to high state and so both D type flip-flops ML1, ML2 will be set, and the AND gate ML3 will be enabled, so that as the wheel continues to rotate, pulses appearing at the AND gate ML3 output are injected into a mono stable ML4. The monostable ML4 gives output pulses of 1 ms into a second monostable ML5, which operates in the retriggerable mode and has an output duration of 1 second. This means that once the wheel has started to rotate the output from the monostable ML5 will stay low until rotation has stopped, when after 1 second of stopping the monostable ML5 output returns to the high state. This output is differentiated by a differentiator D12 to give a narrow reset pulse to both of the D type flip-flops ML1 and ML2.

Output pulses from the monostable ML5 are used to clock a counter ML6 once the reset from the counter ML6 is removed by the monostable ML5. The setting of switches A3 determines the number of pulses required to enable AND gate ML7. Once an output at the AND gate ML7 appears a J/K flipflop ML8 is set, the information being clocked into the flipflop by a free running clock ML11. The flip-flop ML8 output is used to operate a relay SC via a driver ML10. The relay SC remains operated until the flip-flop ML8 is reset when rotation ceases and the stop output from the monostable ML5 goes high.It follows that the relay SC may be operated by 1-1 5 pulses which on the 24 tooth wheel 14 corresponds to between 1 5 and 225 degrees of angular movement. On the most sensitive setting i.e.

position 1 of A3, providing the wheel is rotated at greater than 2.5rum slow speed detection will be achieved.

The relay SC is used to operate a slow speed indicator.

The master clock ML1 1 output is divided down by counters ML12 and ML13 and passed to a monostable ML14 which gives a 1 mSec output every 1.3 seconds. This output is used to apply a reset pulse to counters ML15, ML16 and ML17. The counter outputs ML16 and ML17 are counted via switches A5 and AND gates ML18 and ML19. Pulses from the monostable ML4 are used to clock the counter ML15 and when the pulses are received at a rate equal to or higher than that required to cause an output from the AND gate ML18 within the 1.3 second scan time a flip4lop ML9 will be set. In turn a relay FC will operate via the driver ML1O and will remain operated until rotation has ceased and a stop signal from the monostable ML5 resets the flip-flop ML9.

The relay FC is used to operate a high speed indicator.

By selection of switches A5 the detection speed may be governed between approximately 30RPM and 20û0RPM.

Test switches 18, 20 are included which when operated disconnect the detectors 10, 1 2 from the circuit and connect the D type flip-fiops ML1, ML2 to the master clock output ML1 1. This may be used to determine the health of the main circuit for maintenance purposes and, by elimination, the state of the detector circuit may be also determined.

Claims

1. Movement detecting apparatus comprising a movable member having a plurality of equally spaced windows formed therein, a light source located on one side of the member and two light detectors located on the opposite side of the member to receive light from the light source through the windows, the light detectors being spaced such that when the member is stationary one of the detectors receives either full light or no light from the light source, and the other detector receives a partial amount of light from the light source, an electrical circuit for receiving signals from the light detectors and adapted to detect changes in state of the light detectors to detect movement of the member, which of the light detectors changes state before the other to determine the direction of movement of the member, the electrical circuit also including counter means for counting the number of windows which have traversed the light detectors for determining the distance moved by the member.

2. Movement detecting apparatus as claimed in claim 1 in which the electrical circuit includes clock means to determine the speed of movement of the member.

3. Movement detecting apparatus as claimed in claim 2 in which the electrical circuit determines when a predetermined speed of the member has been exceeded.

4. Movement detecting apparatus as claimed in any preceding claim in which the movable member comprises a rotatable wheel.

5. Movement detecting apparatus as claimed in claim 4 in which the windows comprise a series of slots formed in the periphery of the wheel.

6. Movement detecting apparatus constructed and adapted to operate substantially as hereinbefore described with reference to the accompanying drawings.