JP3542199B2 - Absolute encoder - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a multi-turn absolute encoder having a battery (internal power supply) backup function. More specifically, the present invention relates to a technique for preventing a malfunction that occurs in a transient state where power is switched from energization to power failure. More specifically, the present invention relates to an energization / power failure switching technique that does not cause an error in multi-rotation detection even during high speed rotation.
[0002]
[Prior art]
FIG. 10 shows a general configuration of a conventional absolute encoder. A plurality of tracks 102 to 105 are formed concentrically on the surface of the rotary slit plate 101. Each track has a code pattern that is bit-coded according to a digital code indicating the absolute position of the rotary slit plate 101. A light receiving element array 106 is arranged on one side of the rotary slit plate 101, and a light emitting element, for example, an LED 108 is arranged on the other side via a fixed mask 107. The light emitted from the LED 108 is transmitted or blocked by the code pattern on the rotating slit plate 101, and the light receiving element array 106 outputs a periodic signal according to the amount of light received for each track. By processing this periodic signal, the absolute angular position (address) of the rotary slit plate 101 can be read. That is, this address corresponds to the digital code described above.
[0003]
Various systems are known as digital codes representing addresses. FIG. 11 shows a code pattern formed according to a pure binary system as an example of a digital code. In this pattern diagram, the track numbers are shown in the vertical columns, and the addresses are shown in the horizontal columns. The code pattern of each track is binary-coded, and includes a transparent portion and a non-transparent portion along the rotation direction. In this example, tracks for 4 bits are provided, and 2 4 = 16 absolute addresses are represented.
[0004]
In the conventional absolute encoder, in addition to the absolute address of the rotary slit plate (one-rotation absolute output), the number of rotations of the rotary slit plate (multi-rotation absolute output) can be read by counting the periodic signal obtained from the uppermost track. . Further, an absolute encoder having a backup battery (internal power supply) has been developed so that it can operate continuously even in the event of a power failure, in addition to power supply when an external power supply voltage is supplied. In order to suppress the power consumption of the backup battery, the absolute address is not read at the time of a power failure, and only the rotation speed is read. A battery-backup type multi-turn absolute encoder having such a configuration is disclosed in, for example, Japanese Patent Laid-Open No. 6-235645 and has a configuration as shown in FIG. A rotary slit plate 202 is attached to the input shaft 201. A light emitting element 203 is arranged on one surface side, and a plurality of light receiving elements LSB-1, LSB-2,..., LSB-n and MSB are arranged on the other surface from the lower track to the upper track. ing. At the time of normal energization, the change timing of the periodic signal of each bit output from each light receiving element is synchronized with the change timing of the periodic signal of the lower bit by the synchronizing circuit 205, and then the absolute signal of the periodic signal of each bit is output once. , And supplies the cycle signal of the most significant bit to the multi-rotation counter 213 via the synchronization circuit 210 and the OR gate 211 to obtain a multi-rotation absolute output. At the time of a power failure, the switch 207 switches the periodic signal from the highest-order light receiving element MSB from the path during normal power supply to the path during a power failure according to a detection signal from the power failure detection unit 206, and the periodic signal of the most significant bit It is sent directly to the multi-rotation counter 213 without passing through. Thereby, at the time of a power failure, an extra circuit such as a synchronous circuit is stopped to suppress the current consumption of the backup battery.
[0005]
[Problems to be solved by the invention]
The multi-rotation absolute encoder of the battery backup type as shown in FIG. 12 generally includes a power failure detection unit that monitors an external power supply voltage and outputs a detection signal corresponding to a change from a time of energization to a time of power failure. The driving current supplied to the light emitting element is switched from a normal level to a minute level in response to the detection signal, thereby suppressing current consumption. At the same time, the load resistance of the light receiving element corresponding to the light emitting element is switched from the low level to the high level, and the necessary detection sensitivity is maintained. That is, at the time of a power failure, a countermeasure is taken by lowering the driving current of the light emitting element and simultaneously increasing the load resistance of the light receiving element. However, when the load resistance of the light-receiving element changes instantaneously from a low level to a high level when the power supply changes to a power failure degree, it takes a long time to discharge the electric charge remaining in the light-receiving element, and the steady state at the time of the power failure occurs. Unstable transients intervene. For this reason, there is a problem that noise is added to the multi-rotation absolute output, which causes erroneous detection. In particular, when the slit plate is rotating at high speed, there is a problem that erroneous operations frequently occur due to the influence of the above-mentioned transient state.
[0006]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION In view of the above-described problems of the conventional technology, an object of the present invention is to provide a multi-rotation absolute encoder using a battery backup method that does not cause an error in multi-rotation absolute output even during high-speed rotation. The following measures were taken to achieve this purpose. That is, the absolute encoder according to the present invention includes, as a basic configuration, a rotary slit plate, a light emitting element, a light receiving element, a processing circuit, and a counting circuit. The rotating slit plate has a code pattern in which transmitting portions and non-transmitting portions are periodically arranged along the rotation direction. The light emitting element is arranged on one surface side of the rotary slit plate and emits light according to the drive current. The light receiving element is disposed on the other side of the rotary slit plate, receives the light transmitted through the code pattern, and outputs a periodic signal corresponding to a change in intensity through a load resistor. A processing circuit reads the absolute position of the rotating slit plate by processing the periodic signal. The counting circuit reads the number of rotations of the rotary slit plate by counting the periodic signal. When the absolute encoder is energized, it receives an external power supply voltage to read the absolute position and the number of revolutions, and when a power failure occurs, it receives the internal power supply voltage to read only the number of revolutions. In this configuration, the absolute encoder includes a power failure detection unit, a first switch, a delay circuit, and a second switch as a power supply / power failure switching mechanism. The power failure detection unit monitors the external power supply voltage and outputs a detection signal corresponding to a change from power supply to power failure. The first switch operates in response to the detection signal and switches a drive current supplied to the light emitting element from a normal level to a minute level. The delay circuit generates a delayed control signal from the detection signal. The second switch operates in response to the delayed control signal and switches the load resistance of the light receiving element corresponding to the light emitting element from a low level to a high level.
[0007]
In one embodiment of the present invention, a monitor light-receiving element is provided separately from the light-receiving element, and an output signal of the monitor light-receiving element is used for temperature compensation of the light-emitting element during energization. The signal is used for temperature compensation of the periodic signal input to the counting circuit. In another aspect, a plurality of the light emitting elements are arranged corresponding to a code pattern provided from a lower digit to an upper digit, and the first switch means performs only reading of an absolute address according to the detection signal. The supply of the driving current to the necessary lower-order light emitting element is cut off. According to another aspect of the present invention, a driving unit that supplies a driving current to the light emitting element is provided, and the light emitting element is intermittently driven at the time of a power failure to set the driving current to a minute level on average.
[0008]
[Action]
According to the present invention, the first switch means is first switched by the power failure detection signal to switch the drive current from the normal level to the minute level. Next, a delay circuit delays the timing of the power failure detection signal to generate a control signal, and switches the second switch means to change the load resistance of the light receiving element from a low level to a high level. In the present invention, the delay circuit intentionally creates a state in which the drive current of the light emitting element is at a very low level during a power failure and the load resistance of the light receiving element is at a low level during energization. As a result, the electric charge remaining in the light receiving element during energization is quickly discharged with a low level load resistance. When the load resistance of the light receiving element switches to a high level, the voltage across the load resistance rapidly changes from substantially zero to a steady state, and the noise pulse generated in the conventional transient state disappears.
[0009]
【Example】
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a circuit diagram showing a basic configuration of an absolute encoder according to the present invention. As shown in the drawing, the absolute encoder includes a rotary slit plate 1 and rotates at high speed around an input shaft 2. The rotating slit plate 1 has a code pattern in which transmitting portions and non-transmitting portions are periodically arranged along the rotation direction. A light emitting element 3 composed of an LED or the like is arranged on one surface side of the rotary slit plate 1 and emits light according to a drive current. A light receiving element 5 is disposed on the other surface of the rotary slit plate 1 to receive the light that has passed through the code pattern of the rotary slit plate 1 and output a periodic signal according to the intensity change via a load resistor. I do. In this example, a plurality of light receiving elements 5 are arranged corresponding to the code pattern provided from the lower digit to the upper digit. Among them, a pair of light receiving elements A and B corresponding to the most significant digit are also used for detecting the rotation speed. The remaining light receiving elements on the lower digit side are used exclusively for reading absolute addresses. The pair of light receiving elements A and B corresponding to the most significant digit output periodic signals having phases different from each other by 90 ° so that not only the rotation speed but also the rotation direction can be detected.
[0010]
Although not shown, a processing circuit is connected to the plurality of light receiving elements 5 and processes each periodic signal output from the light receiving elements 5 to read the absolute position of the rotary slit plate 1. Similarly, although not shown, a counting circuit for counting the periodic signals output from the pair of light receiving elements A and B and reading the number of rotations of the rotary slit plate 1 is provided. The absolute encoder having such a configuration receives power supply voltage from an external power supply to read the absolute position and the number of revolutions when energized, and reads only the number of revolutions when supplied with the internal power supply voltage from the backup power supply 6 during a power failure. Perform A power failure detection unit 7 is provided to control mode switching between power supply and power failure, and monitors an external power supply voltage to output a detection signal DT corresponding to a change from power supply to power failure. A first switch 8 is connected to the power failure detection unit 7, and switches a drive current supplied to the light emitting element 3 from a normal level to a minute level according to a power failure detection signal DT. The state shown in FIG. 1 represents the state during energization. At this time, the low resistance RL1 is connected to the light emitting element 3 via the first switch 8, and the driving current is at the normal level. On the other hand, at the time of a power failure, the first switch 8 is opened and the light emitting element 3 is connected only to the high / low resistance RL2. Thereby, the drive current supplied to the light emitting element 3 is switched to a minute level. Further, a delay circuit 9 is connected to the power failure detection unit 7, and generates a control signal CTL delayed by a predetermined time from the power failure detection signal DT. A pair of complementary second switches 41 and 42 are connected to the delay circuit 9. At the time of energization, one second switch 41 is in a conductive state, and the other second switch 42 is in a non-conductive state. At the time of power failure, the conductive state / non-conductive state is switched according to the control signal CTL output from the delay circuit 9. The pair of second switches 41 and 42 are commonly connected to the output terminal of the light receiving element A, and switch the load resistance of the light receiving element A from a low level to a high level according to the delayed control signal CTL. Specifically, one of the second switches 41 is in a conductive state when the power is supplied, and the low load resistance RA1 is connected to the output terminal of the light receiving element A. At the time of a power failure, the other second switch 42 becomes conductive, and the output terminal of the light receiving element A is connected to the high load resistance RA2. Note that the terminal voltage of the low load resistor RA1 is taken out as an energization A output via the waveform shaper 10. On the other hand, the terminal voltage of the high load resistor RA2 is similarly extracted as the power outage A output via the waveform shaper 10. The energized A output and the power outage A output pass through an OR gate (OR) 11A, and a final A output is obtained. Similarly, another pair of complementary second switches 43 and 44 are connected to the delay circuit 9 and open and close in response to the control signal CTL. The pair of second switches 43 and 44 are commonly connected to the output terminal of the light receiving element B. At the time of energization, one of the second switches 43 is in a conductive state, and the terminal voltage of the low load resistor RB1 is taken out as an energized B output via the waveform shaper 10. At the time of a power failure, the other second switch 44 is in a conductive state, and the terminal voltage of the high load resistance RB2 is taken out as a power failure B output via the waveform shaper 10. The energized B output and the power outage B output pass through an OR gate (OR) 11B, and a final B output is obtained. As described above, the A output and the B output are input to the counting circuit, and the rotation speed of the rotary slit plate 1 is read. The A output and the B output are further input to the direction discriminator, and the rotation direction of the rotary slit plate 1 is discriminated.
[0011]
FIG. 2 is a circuit diagram showing a reference example of the absolute encoder. This reference example has a configuration basically similar to that of the absolute encoder according to the present invention shown in FIG. 1, and corresponding portions are denoted by corresponding reference numerals to facilitate understanding. The difference is that in this reference example, the delay circuit is omitted, and the detection signal DT output from the power failure detection unit 7 is directly input to the second switches 41 to 44. In other words, the first switch 8 and the second switches 41 to 44 are simultaneously opened and closed. As described above, there is a relation of RL1 <RL2, RA1 <RA2, RB1 <RB2. At the time of a power failure, the switches 8, 41 to 44 operate simultaneously in response to the power failure detection signal DT, thereby lowering the drive current of the light emitting element 3 and increasing the load resistance of the light receiving elements A and B. The A output and the B output, which are multi-rotation period signals of one rotation and one pulse having a phase difference of 90 ° that can be discriminated in the direction, are obtained by OR-combining the outputs during energization and during a power failure.
[0012]
FIG. 3 is a timing chart showing switching from energization to power outage while the input shaft is rotating. Immediately after the switching, it takes time until the voltage between both ends of the high load resistors RA2 and RB2 reaches a steady state, and a pulse as shown by a dotted line may be generated in the A output after OR and the B output after OR, and the rotation speed is read ( An error occurs in multi-turn count).
[0013]
This will be described with reference to FIG. (A) is a graph showing the relationship between the load resistance of the phototransistor and the switching time. (B) illustrates a circuit for measuring the switching characteristics shown in (A). In order to reduce the current consumption during a power failure as much as possible, it is necessary to increase the resistance values of the load resistors RA2 and RB2 of the light receiving element and set the driving current of the light emitting element small. However, as shown in the graph of FIG. 4A, the response time of the phototransistor constituting the light receiving element is delayed as the load resistance increases, and the delay time ts and the fall time tf when the incident light is turned off are reduced. become longer.
[0014]
FIG. 5 shows a transient state when switching is performed from the time of energization to the time of power failure. As shown in FIG. 3, at the moment of switching from the time of energization to the time of power failure, electric charges generated by light irradiation during energization remain immediately before in the phototransistor, and flow through the high load resistors RA2 and RB2. Therefore, as shown in FIG. 5, the voltage across RA2 and RB2 jumps immediately after a power failure and has a long transient state gradually approaching a steady value. Therefore, an erroneous pulse may be generated immediately after switching to the A output and the B output depending on the relative relationship with the comparison voltage of the waveform shaping unit. If the width of the erroneous pulse is longer than the time required for the code pattern at the rotation speed at the time of the power failure switching to make 1/4 turn, an error occurs in the multi-turn count. In the reference example shown in FIG. 2, in order to prevent this error, the rotational speed is necessarily limited.
[0015]
Therefore, a problem arising in the reference example is solved by introducing a delay circuit as shown in FIG. The first switch for lowering the drive current of the light emitting element is first switched by the power failure detection signal DT, and the second switch for delaying the timing by the delay circuit and setting the load resistance of the light receiving element to a high level is switched. FIG. 6 shows a transient state in this switching. The drive current of the light-emitting element such as an LED is at a very low level at the time of a power failure, and the load resistance of the light-receiving element such as a phototransistor is at a low level at the time of energization. The accumulated residual charge of the phototransistor is quickly discharged with a low load resistance. When the load resistance of the phototransistor is switched to a high level, the voltage across the phototransistor rapidly changes from substantially zero to a steady state, and there is no pulse generated in the conventional transient state.
[0016]
FIG. 7 shows a specific configuration example of the absolute encoder according to the present invention. To facilitate understanding, parts corresponding to those of the absolute encoder shown in FIG. 1 are denoted by corresponding reference numerals. As shown in the figure, two sets of upper and lower LEDs 3H and 3L and light receiving element groups 5H and 5L are arranged to face each other for one-rotation absolute detection with the rotary slit plate 1 and the fixed mask 21 interposed therebetween. First, the configuration and operation during energization will be described. One of the light receiving elements M1 and M2 of the light receiving elements 5L and 5H is used as a monitor light receiving element for compensating the temperature characteristics of the lower LED 3L and the upper LED 3H. The pattern of the rotary slit plate 1 corresponding to these monitor light receiving elements M1 and M2 is such that transmitted light of a certain area enters the light receiving elements M1 and M2 over one rotation. The corresponding lower LEDs 3L and upper LEDs 3H are energized by the LED driving units 22L and 22H so that the output signals of M1 and M2 are always constant. The periodic signals output from the remaining light receiving elements are input to a code generation unit (processing circuit) 23 and are converted into one-turn n-bit absolute outputs (absolute addresses). The code generator 23 is configured by a method disclosed in, for example, Japanese Patent Application Nos. 6-72779 and 6-72780. The outputs of the two light receiving elements A and B included in the higher order light receiving element group 5H are periodic signals having a 90 ° phase difference of one cycle per rotation, and are input to the code generator 23 and used for generating one rotation absolute signal. At the same time, it is converted into two pulse signals TA and TB having a 90 ° phase difference of one pulse per rotation. TA and TB pass through the corresponding OR gates 11A and 11B, respectively, and are input to the direction discriminator 24 to obtain a count pulse and an up / down signal. The multi-rotation m-bit absolute output (rotation speed) is obtained by counting up and down the count pulse by a counter (counting circuit) 25.
[0017]
Next, the configuration and operation at the time of power failure switching will be described. A drop in the external power supply voltage is detected by the power failure detection unit 7, and a power failure detection signal DT is generated. The power failure detection signal DT is input to the first switch 8L that cuts off the drive current of the lower LED 3L, and at the same time, is input to the first switch 8H that switches the upper LED 3H from normal energization to microcurrent drive set by the resistor RL. The power failure detection signal DT is also input to the delay circuit 9 to obtain a control signal CTL that is delayed by a certain time from the power failure detection signal. This control signal CTL is input to the second switch 4 for switching the load resistance of the phototransistor. The second switch 4 opens and closes in response to the delayed control signal CTL, and switches the load of the light receiving elements A, B, and M2 to a high load resistance in a power failure state. The voltages output from A, B and M2 are input to comparators (comp) 26A and 26B. One comparator 26A compares the voltages output from A and M2 with each other to generate a multi-rotation detection pulse TAX. By using the output of M2 as a reference voltage for comparison, the temperature of the light receiving element output can be equivalently compensated. The other comparator 26B compares the voltages output from B and M2 with each other to generate a multi-rotation detection pulse TBX. TAX and TBX have a phase difference of 90 ° from each other. TAX and TBX pass through the corresponding OR gates 11A and 11B, are discriminated in the same direction as when energized, and the number of revolutions is read by the counter 25.
[0018]
FIG. 8 shows operation waveforms of each unit at the time of power failure switching. As shown, the output voltages of A, B, and M2 have a short transient state at the time of switching, and no erroneous pulses are generated. Therefore, the inputs TAORTAX and TBORTBX of the direction discriminator 24 can accurately detect multiple rotations without generating erroneous pulses due to mode switching.
[0019]
If there is no delay circuit and the load resistance of the light receiving element is switched at the same time as the light emitting element by the power failure detection signal DT, the operation shown in FIG. 9 is performed. Such erroneous pulses are generated. In the embodiment shown in FIG. 7, the drive current at the time of power failure is switched to a small current, but the present invention is not limited to this. Even in the case of a method in which power consumption during a power failure is suppressed by pulse driving, it is similarly effective to reduce the transient state of the phototransistor by using a delay circuit.
[0020]
【The invention's effect】
As described above, according to the present invention, a delay circuit is added to the related art, and the first switch that lowers the drive current of the light emitting element by the power failure detection signal is first switched, and after the timing is delayed by the delay circuit, the light is received. A second switch for setting the load resistance of the element to a high level is switched. As a result, it is possible to suppress an increase in the transient state time due to a large light-receiving element load resistance at the time of power failure switching, and it is possible to obtain an effect that no error occurs in multi-rotation detection even during power failure switching during high-speed rotation.
[Brief description of the drawings]
FIG. 1 is a block diagram showing a basic configuration of an absolute encoder according to the present invention.
FIG. 2 is a block diagram showing a reference example of an absolute encoder.
FIG. 3 is a timing chart for explaining the operation of the reference example shown in FIG. 2;
FIG. 4 is a schematic diagram showing a graph showing switching characteristics of a phototransistor and an example of a measurement circuit thereof.
FIG. 5 is a waveform chart showing a power-on / power-off switching operation of the reference example shown in FIG. 2;
FIG. 6 is a waveform diagram showing a power-on / power-off switching operation of the absolute encoder of the present invention shown in FIG.
FIG. 7 is a circuit diagram showing a specific configuration example of an absolute encoder according to the present invention.
8 is a waveform chart for explaining the operation of the absolute encoder shown in FIG. 7;
FIG. 9 is a reference waveform diagram for explaining the absolute encoder shown in FIG. 7;
FIG. 10 is a perspective view showing a general configuration of a conventional absolute encoder.
FIG. 11 is a schematic diagram showing an example of a conventional code pattern.
FIG. 12 is a block diagram showing an example of a conventional battery-backup type multi-rotation absolute encoder.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Rotation slit plate 2 Input shaft 3 Light emitting element 5 Light receiving element 6 Backup power supply 7 Power failure detecting section 8 First switch 9 Delay circuit 41 Second switch 42 Second switch 43 Second switch 44 Second switch

Claims (4)

A rotating slit plate having a code pattern in which transmitting portions and non-transmitting portions are periodically arranged along a rotation direction, a light emitting element which is disposed on one surface side of the rotating slit plate and emits light in accordance with a driving current, A light-receiving element disposed on the other side of the rotary slit plate for receiving light emitted through the code pattern and outputting a periodic signal corresponding to a change in intensity through a load resistor; A processing circuit that reads the absolute position of the rotating slit plate, and a counting circuit that counts the periodic signal and reads the number of rotations of the rotating slit plate,
Absolute encoder which receives the supply of external power supply voltage when energized and reads the absolute position and the number of revolutions, but receives the supply of internal power supply voltage and reads only the number of revolutions during a power failure.
A power failure detection unit that monitors an external power supply voltage and outputs a corresponding detection signal when the power supply changes from a power supply to a power failure;
First switch means which operates in response to the detection signal and switches a drive current supplied to the light emitting element from a normal level to a minute level;
A delay circuit for generating a control signal delayed from the detection signal;
An absolute encoder having second switch means which operates in response to the delayed control signal and switches a load resistance of a light receiving element corresponding to the light emitting element from a low level to a high level. A monitor light-receiving element is provided separately from the light-receiving element. An output signal of the monitor light-receiving element is used for temperature compensation of the light-emitting element when energized, and an output signal of the monitor light-receiving element is input to the counting circuit during a power failure. 2. The absolute encoder according to claim 1, wherein the absolute encoder is used for temperature compensation of the periodic signal. A plurality of the light emitting elements are arranged in correspondence with a code pattern provided from a lower digit to an upper digit, and the first switch means is provided in accordance with the detection signal to determine a lower digit side necessary only for reading an absolute address. 2. The absolute encoder according to claim 1, wherein the supply of the drive current to the light emitting element is interrupted. 2. The absolute encoder according to claim 1, further comprising a driving unit for supplying a driving current to the light emitting element, wherein the light emitting element is intermittently driven at the time of a power failure so that the driving current is reduced to a minute level on average.

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