GB2057119A - Fibre optic digital positional encoder - Google Patents

Abstract

In a digital encoder for registering the position of a member moving randomly in a fixed rotary or linear path, e.g. a disc on a rotating shaft, the member is provided with a series of apertures 2 which expose a pair of optical fibres 3, 4 to a light source, the fibres being staggered so as to produce a sequence of optical signals when the disc rotates. These signals are detected at the remote ends of the fibres and decoded by logic to provide positional data. In a modified arrangement a third fibre (not shown) is used to derive up to three fixed reference points around the disc. <IMAGE>

Description

SPECIFICATION Fibre optic digital positional encoder This invention relates to an arrangement for transmitting analogue positional information by digital optical means and is suitable for either rotary or linear movements.

The use of optical arrangements to encode the position of a moving member are known.

Generally these utilise a binary encode reticle, requiring the use of a comparatively large number of optical devices, e.g. photodetectors. For example, simple binary encoding requires nine devices to encode up to 512 positions. A binary encoder transmits one position displacement per hole, in the case of an apertured reticle. Hole size may be a limiting factor in small apparatus. Also there is a need for the same number of signal paths between the photodetectors and the processing electronics as the number of photodetectors. An example of a position encoder using a coded reticle is disclosed in British Patent Specification No. 1,482,593. Furthermore, the binary encoded output may then have to be converted into a decimal representation if a visual display of position is required.

According to the present invention there is provided an arrangement for transmitting positional information relating to a moving member provided with a series of apertures placed so as to pass sequentially and regularly a given position during movement of the member, the arrangement including one or a pair of light sources located on one side of the member at the given position, a pair of optical detecting means on the other side of the member at the given position, the positioning of the detecting means and the dimension and spacing of the apertures being such that during continued movement of the member the following repetitive sequence of shading and/or exposure of the detecting means occurs:: P both means shaded Q first means exposed, second means shaded R both means exposed S first means shaded, second means exposed, logic means responsive to the foregoing sequence of outputs from the detecting means to translate the output sequence into binary encoded signals indicative of the order of the sequence, and up/down counting means responsive to the binary encoded signals.

Embodiments of the invention will now be described with reference to the accompanying drawings, in which: Fig. 1 illustrates an arrangement having a simple apertured disc and a pair of optical fibres for transmitting direction and position information for a rotating shaft, Fig. 2 illustrates the sequence of outputs obtained from the fibres of Fig. 1 for one direction of movement, Fig. 3 illustrates logic for translating the output sequence into binary coded driving signals for an up/down counter, Fig. 4 shows the sequence of logic states required in the logic of Fig. 3, Fig. 5 illustrates a simple up/down counter and display arrangement for use with the logic of Fig.

3, Fig. 6 is a flow chart for the operation of the logic of Fig. 3, Fig. 7 illustrates a modified arrangement for transmitting direction and position information with a "coarse" reading, and increased resolution, for a linearly moving member, Figs. 8 to 10 are flow charts relating to the modified arrangement of Fig. 7, and Figs. 11 and 12 taken together illustrate a logic arrangement for use with the modified arrangement of Fig. 7.

The arrangement shown in Fig. 1 comprises a disc 1 having a number of regular spaced apertures 2, which may be in the form of slits in the edge of the disc as shown in Fig. 1 or holes wholly within the periphery of the disc (similar to those shown in the linear arrangement of Fig. 7).

During rotation of the disc the apertures pass a fixed optical station at which a pair of optical fibres 3,4 terminate on one side of the disc and a pair of light emitting diodes (not shown) are placed on the other side of the disc, each diode illuminating a respective one of the optical fibres when an aperture is between the diode and the fibre, otherwise the fibres are shaded from the diodes. The two fibres are staggered radially relative to the disc so that during rotation of the disc in one direction the following repetitive sequence occurs: P both fibres are shaded, 0 fibre 3 is exposed to light from its diode and fibre 4 remains shaded, R both fibres are exposed, and S fibre 3 is shaded and fibre 4 remains exposed.

This sequence is reversed when the direction of rotation is reversed.

Each fibre is connected to a photodetector to provide electrical outputs which, for the sake of convenience, are designated '0' when the fibre is shaded from, and 'I' when the fibre is exposed to, the light from a diode.

Fig. 2 shows the five conditions in the sequence as a slit 2 moves from left to right past the fibres.

At condition P both fibres being shaded the outputs are 00. At 0 fibre 3 is exposed and fibre 4 is shaded, the outputs now being 10, and so on.

These outputs are fed to the logic shown in Fig. 3.

The logic will accumulate a series of pulses, which are subsequently automatically counted up or down, by detecting changes in the input sequence direction. The input must be in the form of three distinguishable signals, repeated in rotation. If these signals are labelled A, B and C, transitions of the form. A to B, B to C, C to A represent counting in the down mode and result in one down-count per transition.

The logic detects these transitions by storing the former input type (as A', B' or C') and when the subsequent input is read, it is compared to the stored or previous input: then according to the mode of the transition (i.e. 'up' or 'down') an up or down-count is recorded by the subsequent counter.

The signals A, B and C take the form of binary coded inputs. Thus two lines are required to code the three types and the input data on these lines is decoded as follows: OUTPUTS DECODED DATA Fibre 3 Fibre 4 A B C 0 O L L L 1 0 H L L 1 1 H H L 0 1 L L H L = Low state H = High state The logic uses three AND gates 5, 6 and 7 and two exclusive OR gates 8 and 9 to decode the fibre outputs to the appropriate data A, B or C, as shown in Fig. 3. The arrangement employed ensures that the propagation delay for each decoding process is the same. The function of the AND gates 5 and 7 is primarily to act as followers to delay the outputs. As each signal A, B or C goes high each triggers a corresponding monostable 10, 11 and 12, to provide the necessary "edges" in the circuit for counting purposes.Two AND-OR-INVERT Gates 13, 14 are arranged to detect the six possible transitions (A'B, B'C, C'A and A'C, C'B, B'A) from the store 1 5 and the three monostables and they categorise the type of transition as 'up' or 'down' mode. Thus the 'oneshot' is passed at only one AND gate and this pulse is read by either the up or the down input of the counter.

On the returning edge of the count pulse, the store is refreshed and the appropriate signal A, B or C, having triggered its monostable can now be stored. The store 1 5 consists of three latches which follow the input data when the enable G is high but retain the incident input when the enable is made low. The enable is controlled by a fourth monostable 1 6 which is triggered either by a returning count pulse as above or by the clear signal. This latter is an input independent of the signals from the fibres 3, 4 which is required to clear the display and pre-load the store on the initial cycle. Fig. 4 shows the sequence of triggering states, inversions etc.

The counter, Fig. 5, uses three cascaded up/down decade counters 17, 18 and 19 which control three B.C.D. decoder/drivers 20, 21 and 22 driving seven segment light emitting diodes.

The up and the down inputs are each filtered through variable pulse-length monstables 23, 24 so that the maximum input pulse repetition rate can be controlled. These monstables give a preselected pulse length to each input pulse and any further pulses during that pulse time are ignored.

In this way, spurious pulses due to mechanical vibration at the logic input are filtered out. Fig. 6 gives a flow chart for the operation of the logic. If the P condition is utilised as a fourth distinguishable signal, with suitably altered logic, improved resolution can be obtained.

In a modification of the invention a third optical fibre, (not shown) together with its light source, is located at the fixed position. This fibre is shaded at a limited number of positions, say 3, of the disc, henceforth referred to as reference points. If the fibre is exposed instead being shaded the logic would then require inversion at the input.

However, if the three fibres are required to indicate more than one reference point then a circuit such as that shown in Figures 11 and 12 (described below) must be used.

As before, the fibres transmit a sequence of outputs which are detected by photodetectors and decoded. However, the inclusion of the third fibre enables the reference points to be detected so that counting can begin from a reference point.

The signal from the third fibre is simply fed into the circuit of Fig. 3 via an exclusive OR gate 25 to the clearing monostable 1 6. The signal from the third fibre also acts as an automatic clearing signal for the display.

A further refinement is the inclusion of a "coarse" counter to obviate the necessity for the disc to rotate a reference point past the fixed position. This will display the position of the disc to the nearest segment, a segment being bounded by two successive reference points. In this way, at power-on the initial display will indicate the location of the disc as one of the three segments.

This is accompanied by a coarse position warning.

Once a segment boundary i.e. a reference point has been crossed the exact position is then transmitted and the coarse warning is inhibited.

Figure 7 shows an arrangement for a linear (or a disc of infinite radius) movement position indicator in which separate apertures 2a, 2b are provided for the two fibres 3, 4 and shading projections 2c are provided for the third fibre 26, there being one such projection at each coding position but the precise positioning of the shading projections being different in each segment, as will now be explained. Each segment is designated according to the step of the sequence of outputs from fibres 3 and 4, as previously shown in Figure 2. Step P is not used in the present example, the three segments being designated 3Q, 3R and 3S.

In segment 3Q the projections 2c are aligned with the apertures 2a, 2b in such a way that fibre 26 is shaded when step Q of the sequence occurs. Thus the total output of the three fibres 3,4 and 26 when the projections 2c in this segment move past the fixed position is 010. In the next segment the projections 2c are aligned with the apertures when step R of the sequence occurs, the outputs then being 011. In the final segment the fibre 26 is shaded when step S occurs, the outputs now being 001.

When movement of the apertured member occurs counting proceeds as follows:- (a) A reference point is transmitted from the member. The reference point is detected when a transition from one segment to the next occurs.

(b) Each aperture position transmits and the counter is incremented (or decremented).

(c) Each count is added to (or substracted from) a reference value.

However, before a reference point has been detected, the segment input types are analysed and displayed as the coarse position of the member, to the nearest segment. This coarse reader is inhibited once the segment input type changes, i.e. a transition from one segment to another must have occurred and a reference point detected. The coarse reader is only enabled when the reference value is lost i.e. at power-off.

Once counting has been initiated, at subsequent segment transitions (reference points) the accumulated'count value should equal that reference point value. However, as a safeguard against (unlikely) stray counts the reference values will continue to be loaded into the display and counting re-started, from that value.

The signal of fibre 26 shaded in coincidence with a P input type is used as a transmission failure warning. This state is coded by all three fibres being shaded and it automatically "clears" the display to zero. This requires an extra projection from the member, as illustrated by the dashed outline in- Figure 7, in the (3S) segment, the extra projection being located preferably at the end of the segment. The signal transmitted from this position can also define a zero mark on the member.

If the third fibre is used in conjunction with a disc then by locating the extra projection where the third fibre is shaded simultaneously to a P input type at the beginning of the 30 segment this position will conveniently occur at the end of a previous segment, e.g. it will be at the end of the 3S segment and will provide a reference transition from first third segment.

Figure 8shows a flow chart for the basic operation of the apparatus using a member such as that shown in Figure 7. Figure 9 shows a flow chart for the reference points detection and coarse reading process and Figure 10 shows a flow chart for the direction detection and counting process.

Figures 11 and 12 taken together illustrate the circuit for preforming the operations given in the flow charts. Light activated switches with T.T.L.

outputs are used to provide the opto-electronic conversion at the fibre ends. Fibres 3 and 4 and decoded into the current P, Q, R or S at a two-to four line INPUT TYPE DECODER 30. The DECODER ENABLE from switch S3 is employed to inhibit the inputs at switch on until the warning circuits have been set. The four decoder outputs are fed to two sets of monostables 31,32 (corresponding to the store 1 5 and monostables 10, 11 and 12 of Fig. 3). The following convention is used to indicate particular types of monostable:- = = negative edge triggered monostable t = positive edge triggered monostable.

The outputs of the two sets of monostables are used, via AND gates 33--40 and exclusive OR gates 41, 42 to increment/decrement the counters 4345 as in Figure 3.

After each count it is necessary to renew the information in the store. An AND gate 46 connected to the "UP" and "DOWN" outputs (gates 41 and 42) will go low when either an up or down count is transmitted to the counters. The output from gate 46 is connected to the positive edge triggered input of a monostable 47 and when the UP or DOWN count pulse terminates the AND gate will also return high and this positive edge will trigger monostable 47. The output pulse (STORE ENABLE) from monostable 47 is connected to the enable inputs of the store monostables 31. When this pulse goes high the states of the four outputs from decoder 30 are transferred into the INPUT TYPE STORE 31, the present input type appearing at the 5 output of the relevant store monostable as a high output.

Once the pulse from monostable 47 ceases the contents of the store monostables remain unaltered by any changes in the decoder outputs.

To initiate the cycle, the present input type must be stored. Once a reference point has been detected, the COUNT ENABLE gate 48, the output of which is connected to the negative edge triggering input of the STORE ENABLE monostable 47, will go low and this negative edge will trigger this monostable causing the present input type to be stored as above. Successive inputs of the same input type will not have any effect since the transitions P'P, Q'O etc. are meaningless and not detected. Single transitions of P to R, O to S etc.

never occur.

To initiate the direction detector process two AND gates 49, 48 are arranged serially with their remaining inputs connecting to the 3Q'3R, 3R'3S.

3S'3R and 3R'30 outputs of the SEGMENT TRANSITION READER 50 and through an inverter gate 51 to the 3P output of the SEGMENT INPUT TYPE READER 52. When any one of these five outputs above changes state to indicate that a reference point has been crossed the COUNT ENABLE output from AND gate 48 will go low and this negative edge will trigger the INPUT TYPE STORE ENABLE monostable 47, starting the direction detection and counting process as described.

The counter consists of three cascaded decade counters 43, 44, 45. Each decade counter is cascaded to the next higher decade by connecting its CARRY output to the UP input of the higher one and its BORROW output to the DOWN input. The UP input of the units decade counter 43 (the least significant digit or LSD) is used as the UP input to the whole COUNTER and, similarly, the DOWN input of the units decade counter 43 is the DOWN input to the whole COUNTER.

The CLEAR inputs to each decade are connected together and making this input high will clear the outputs of the counter to 000.

The LOAD inputs to each decade counter are connected together and making this input low will set the outputs of the counter to the value present at the preset inputs.

There are four preset inputs to each decade counter, A, B, C and D. A Binary number from 0 to 1001 may be set up across these four inputs, A being the 'units' input and D being the 'eights' input. In this way numbers from 000 to 999 may be set up across all twelve preset inputs, the inputs to the least significant digit decade counter (LSD) being the decimal 'units', the next significant digit decade counter (NSD) receiving the decimal 'tens', and the most significant digit (MSD) receiving the 'hundreds' preset inputs, Operating the load facility will transfer this number to the twelve outputs of the counter, still as a Binary Coded Decimal (B.C.D.) number. Further counting will be from this preset number.

Before a reference point is detected, the coarse position of the member is displayed. The coarse position is transmitted at every shuttering of the third fibre 26. In any given segment the third fibre is only shuttered simultaneously to every transmission of one particular input type (0, R, or S). For instance, in the first segment every time a 0 type is transmitted, the third fibre is cut off.

Similarly, in the second segment the third fibre is cut off simultaneously to each R type transmission. In this way each segment may be labelled 3Q, 3R or 3S . . . When the position traverses from one segment to another therefore, the input type transmitted simultaneously to each shuttering of the third fibre 26 will be different to that transmitted in the previous segment. For instance a shift from the 30 to the 3R segment will be marked by a change from fibre 26 being cut off together with 0 types to fibre 26 being cut off together with R types. This change in information implicitly marks the boundary of two segments, and can therefore be decoded as an implicit reference point.It must be noted that in the change from any segment to another e.g. 3Q to 3R, the different input types (Q and R) occur successively thus fibre 26 is shuttered continuously over these two digits and the reference point will be registered immediately the input type changes from 0 to R.

Thus the first time fibre 26 is cut off, the segment type is read (e.g. 30) and the preselected value of that segment displayed. When, after this, fibre 26 is cut off and a different input type is read (e.g. 3Fl), this segment transition is decoded to its implicit positional value and displayed, the coarse warning being removed. One exception is the 3P input. Since the 3P input is coded by all 3 fibres being blanked off it will be transmitted in the event of light failure, and will cause the display to register 000. Thus it may also be employed to code the zero reference point.

Therefore the 3p input may be treated as a segment of width one digit and movement either side of this point will implicitly mean a transition into a different segment. For that reason it is unnecessary to decode a transition from an adjacent segment into the 3P 'segment' since on arriving in the 3P 'segment' the counter will automatically clear the 000 reference. Similarly, if the counter is switched on in the 3P 'segment' it is unnecessary to transmit a coarse position, thus the COARSE READER 53 will be immediately inhibited once the 000 reference is decoded.

At power On switch S2 must be operated which triggers a monostable 54, the output pulse of which is used to preset the warning circuits to their initial conditions. Then S3, the input decoder enable, can be operated to allow data from the fibres to be input into the circuit.

A RANDOM DISPLAY WARNING 55 is operative from power ON until the counter is initially 'cleared' and a coarse reading displayed, the initial 'clear' signal being used to override the warning (subsequent 'clear' signals are irrelevant).

The clear signal is taken directly from the clear input on the COUNTER.

A COARSE DISPLAY WARNING 56 is preset to OFF at power ON. When the COARSE READER 53 detects the segment position one of its three outputs will go low to indicate the appropriate segment (3Q, 3R or 3S) and this will cause the output of the COARSE WARN ENABLE AND gate 57 to go low. This will turn ON the COARSE DISPLAY WARNING 56. When the COUNT ENABLE circuit 48 detects an output from the SEGMENT TRANSITION READER 50 or from the 3P output (either implies that a reference point has been crossed) its output will go low. This will cause i) the COARSE DISPLAY WARNING 56 output to turn OFF and ii) the INPUT TYPE STORE ENABLE monostable 47 to be triggered to initiate the direction detector/counting process.

Subsequent outputs from the COUNT ENABLE 48 are irrelevant.

The SEGMENT INPUT TYPE READER 52 comprises four NOR gates 58-61 connected to each of the four outputs from the INPUT TYPE DECODER 30, P, Q, R and S. Each time the third fibre 26 is shuttered its optoelectronic detector will go low. This is connected to all four NOR gates and it is only when fibre 26 is shuttered that the appropriate NOR gate (3P, 3Q, 3R or 3S) will go high indicating the SEGMENT INPUT TYPE.

The COARSE READER 53 includes the STORE READER 62. This is a four input NOR gate connected to all four outputs of the SEGMENT INPUT TYPE STORE 63 and its output is high when the store is empty. (As will be seen, this implies that no previous COARSE or REFERENCE reading can have been made, therefore a coarse reading must be made. Once a COARSE or a REFERENCE reading is displayed, the store will contain data and this will make the STORE READER output low). One NAND gate is connected to each of the 30, 3R and 3S outputs.

The STORE READER output is connected to all three NAND gates. If a coarse reading is to be made then the high STORE READER output will allow the data on the three NAND gates' inputs to appear inverted at the NAND gates' outputs. Thus, if one SEGMENT INPUT TYPE READER output is high indicating the segment position then one COARSE READER output will go low only if a coarse reading is to be made. This output, of coarse, indicates the segment location, depending on which output is low. The 3P segment will not cause a coarse reading since it is implicitly the 000 reference point.

The TRANSITION READER 50 is similar to the direction detection process. It consists of a quad store (the SEGMENT INPUT TYPE STORE 64) and six NAND gates which form the SEGMENT TRANSITION READER itself. Each store is connected to one of the four outputs from the SEGMENT INPUT TYPE READER 52. They record the previous SEGMENT INPUT TYPE as a high output at the 0 output of the appropriate store, e.g. store S is high when segment input type S was high on the previous input. Two NAND gates are connected to each of the outputs from the SEGMENT INPUT TYPE READER except for the 3P output.Each NAND gate is connected also to one of the four stores in order to detect the following six combinations of previous (stored) segment input type and present segment input type: 3P'3Q, 3Q'3R, 3R'3S, 3S'3R, 3R'30, 3P'3S. This is done by connecting one of the NAND gates on each SEGMENT INPUT TYPE output to the store recording the state of the segment input type which occurs before that segment input type in the rotational sequence 3P, 3Q. 3R. 3S. 3P, e.g.

one NAND gate on the 3R line will be connected to the 3Q store. The other NAND gate is connected to the segment input type store which records the state of the segment input type which occurs after that segment input type in the same rotational sequence e.g. the other NAND gate on the 3R line will be connected to the 3S store. Thus if the 3R line goes high and the previous (stored) segment input type is 3Q then the NAND gate in the first example will go low, registering the transition from 3Q to 3R segments. If the previous (stored) segment input type is 3S then the second example NAND gate will go low, registering the transition from 3S to 3R segments. Thus the above six combinations will be detected, one at each NAND gate.The transitions into the 3P segment,3S'3P and 3Q'3P are not detected, since moving into the 3P segment implicitly transmits the 000 reference point Each of the above six transitions represents crossing a known segment boundary (reference point). Thus one of the outputs from the six NAND gates will go low on one particular transition of the above transitions across segment boundaries representing a known reference point on the encoder.

The SEGMENT INPUT TYPE STORE 64 is refreshed once a reference point has been detected by making the enable input G on the store high. This allows the present segment input type to be stored as the (now) previous segment input type, (the previous store data) is erased. The refresh process is at the end of the CLEAR/LOAD/STORE loop discussed below.

The REFERENCE POINT TO B.C.D. DECODER 65 converts an output from the SEGMENT TRANSITION READER 50 into a reference value or from the COARSE READER 53 into a numerial value representing one of the three segments. It then sets this value in Binary Coded Decimal across the twelve B.C.D. preset inputs to the COUNTER. Since the coarse values selected for representing the three segments are the same as those values of three of the reference points, like values have been paired by three AND gates 66-68. The three outputs from these AND gates together with the remaining three unpaired reference values are now decoded. Each line is connected to the B.C.D. preset inputs to the COUNTER in such a way that when each line goes low (representing a particular value is to be decoded) the inputs to the counter representing that number in Binary Coded Decimal will go high.

For example the representation of the 3S segment is 267 (which is the same as that of the 3R'3S transition). Thus the B.C.D. number 0010 0110 0111 must be set up by making the following counter inputs high 'Hundreds' decade; B; Tens' decade; C, B; 'units' decade; C, B, A. Since different value input lines must be connected to the same outputs to the COUNTER, gates are used to group the connections, and these also provide the necessary low to high logic inversion.

All the selected preset values will make either or both the 'units' (A) or the 'fours' (C) inputs to the units decade counter high. Thus the NOR gate 69, the REFERENCE DETECTOR, connected across both these inputs will go low whenever a reference point or segment has been detected and decoded to B.C.D. This negative edged output of the NOR gate initiates the "Clear", "Load", "Store" loop. In addition, the 3P output is also connected to the NOR gate and this will also cause the NOR output to go low wherever a 3P 'segment' is detected by the SEGMENT INPUT TYPE READER 52.

The negative edge of the NOR output triggers a monostable 70 and the output pulse from this is connected both to the clear input on the COUNTER and to the Random Display Warning 55. Thus the pulse clears the counter and, on the first cycle only, it will override the Random Display Warning. This monostable 70 is also connected to the negative edge triggered input to a second monostable 71. When the clear pulse terminates to low, the second monostable triggers. Its n output sends an inverted (low) pulse to the load input on the counter and this then enters the B.C.D. value from the REFERENCE POINT TO B.C.D. DECODER into the COUNTER. This monostable is further connected by its Q output to a third monostable 72 which is triggered when the load pulse terminates.This is the SEGMENT INPUT TYPE STORE ENABLE monostable and it sends a high pulse to the store enable input G on the SEGMENT INPUT TYPE STORE. This allows the present segment input type to be recorded in its own particular store, erasing the previous stored data in all the stores, and that now becomes the previous segment input type. Once the monostable pulse terminates to low the stored data cannot change until the next cycle.

The cycle is now complete. Successive segment input types will not cause a coarse reading since there is now data in the store i.e. the STORE READER will be low, and a value in the COUNTER. The new input will be compared to the store at the SEGMENT TRANSITION READER and if a transition across segment boundaries has occurred then the transition will be detected, decoded, the counter will be cleared and loaded with this new reference value and the new segment input type will be stored as the previous segment input type. If the previous display was a coarse reading then once a boundary is crossed the coarse display warning will be removed and the reference position displayed. The counting then begins from the new reference position.

Successive inputs of the same segment input type will have no effect on the COUNTER. The 3P input is not 'decoded' to a value since it is 000 i.e. set all counter preset inputs low. When it triggers the REFERENCE DETECTOR NOR gate 69, the Counter Clears and Loads as above but since none of the preset inputs to the COUNTER are high, the number 000 is loaded. The cycle is as normal, with 3P being stored at the end of the loop. The Random Display Warning 55 is inactive from the initial clear signal to the counter onwards.

Whilst reference has been made to remote coupling of the photodetectors via optical fibres, it will be appreciated that the light emitting diodes may be similarly remote coupled, thus enabling the entire electronics equipment to be placed in a remote situation when the moving member is operating in a hazardous environment, e.g. in a potentially explosive atmosphere.

Claims (10)

1. An arrangement for transmitting positional information relating to a moving member provided with a series of apertures placed so as to pass sequentially and regularly a given position during movement of the member, the arrangement including one or a pair of light sources located on one side of the member at the given position, a pair of optical detecting means the other side of the member at the given position, the positioning of the detecting means and the dimension and spacing of the apertures being such that during continued movement of the member the following repetitive sequence of shading and/or exposure of the detecting means occurs:: P both means shaded O first means exposed, second means shaded R both means exposed S first means shaded, second means exposed, logic means responsive to the foregoing sequence of outputs from the detecting means to translate the output sequence into binary encoded signals indicative of the order of the sequence, and up/down counting means responsive to the binary encoded signals.

2. An arrangement according to claim 1 wherein the light source or sources are light emitting diode(s).

3. An arrangement according to claim 1 or 2 wherein the optical detecting means are photodetector diodes.

4. An arrangement according to claim 2 wherein the light emitting diodes are remote from the moving member and each is coupled to the given position by an individual optical fibre.

5. An arrangement according to claim 2, 3, or 4 wherein the photodetector diodes are remote from the moving member and each is coupled to the given position by an individual fibre.

6. An arrangement according to any preceding claim including a third optical detecting means and light source therefor at the given position, the moving member having shading means, less in number than the series of apertures, which are placed so as to pass sequentially and regularly the given position during continued movement of the member to cause shading or exposure of the third detecting means only, the logic means being arranged to be responsive to the output from the third detecting means in conjunction with the outputs from the pair of detecting means to derive signals indicative of predetermined reference points relating to movement of the member.

7. An arrangement according to any preceding claim wherein the moving member is a disc rotatable about its centre.

8. An arrangement according to claim 7 wherein the apertures are slits in the edge of the disc.

9. An arrangement according to claim 7 or 8 wherein the shading means are projections from the edge of the disc.

10. An arrnngement for transmitting positional information relating to a moving member substantially as described with reference to Figs. 1 to 6 or Figs. 7 to 11 of the accompanying drawings.

10. An arrangement according to any preceding claim including means to display visually the count(s) in the counting means.

11. An arrangement according to claim 6 or any one of claims 7-10 when dependent on claim 6 wherein the logic means is arranged to clear the counting means when a signal indicative of a reference point is derived.

12. An arrangement for transmitting positional information relating to a moving member substantially as described with reference to Figs.

1-6 or Figs. 7-11 of the accompanying drawings.

New claims or amendments to claims filed on 27-3-1980 Superseded claims 1, 12 New or amended claims:

1. An arrangement for transmitting positional information relating to a moving member provided with a series of apertures placed so as to pass sequentially and regularly a given position during movement of the member, the arrangement including one or a pair of optical fibres located on one side of the member at the given position and coupled to a remote light source or sources, a pair of optical fibres located the other side of the member at the given position and coupled to a remote pair of optical detecting means, the positioning of the fibres coupled to the detecting means and the dimension and spacing of the apertures being such that during continued movement of the member the following repetitive sequence of shading and/or exposure of the fibres coupled to the detecting means occurs: P both fibres shaded O first fibre exposed, second fibre shaded R both fibres exposed S first fibre shaded, second fibre exposed, logic means responsive to the foregoing sequence of outputs from the detecting means to translate the output sequence into binary encoded signals indicative of the order of the sequence, and up/down counting means responsive to the binary encoded signals.

4. An arrangement according to any preceding claim including a third fibre coupled to a third remote optical detecting means and fibre optic light source therefor at a or the given position, the moving member having shading means less in number than the series of apertures which are placed so as to pass sequentially and regularly the given position of the third fibre during continued movement of the member to cause shading or exposure of the third detecting means only, the logic means being arranged to be responsive to the output from the third detecting means in conjunction with the outputs from the pair of detecting means to derive signals indicative of predetermined reference points relating to movement of the member.

5. An arrangement according to any preceding claim wherein the moving member is a disc rotatable about its centre.

6. An arrangement according to claim 5 wherein the apertures are slits in the edge of the disc.

7. An arrangement according to claim 5 or 6 wherein the shading means are projections from the edge of the disc.

8. An arrangement according to any preceding claim including means to display visually the count(s) in the counting means.

9. An arrangement according to claim 4 or any one of claims 5 to 8 when dependent on claim 4 wherein the logic means is arranged to clear the counting means when a signal indicative of a reference point is derived.