JP2008096333A - Encoder controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce power consumption in an optical encoder. <P>SOLUTION: Situation for the transmission and cut-off of light by a pulse plate is indicated by Fig.(a), terminal voltage to be fed to a light-emitting element is indicated by Fig.(b), and detection pulse to be input to a control means is denoted by Fig.(c). A power supply voltage is applied to the light-emitting element in synchronization with the rotation of the pulse plate. Energization is continued, because the time until the first edge rises of to Fig.(a) is unpredictable. Since the pulse speed is very slow during the several succeeding edges and is difficult to bepredict, power feeding to the light-emitting element is continued, wherein only the history of a pulse width is stored. Thereafter, energization to the light-emitting element and a light-receiving element is stopped by a time which is shorter than the pulse width of dark pulse, in accordance with unnecessary time for edge detection calculated by the control means. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optical encoder control device.

  Optical encoders are very widely used for motor rotation detection. For example, as shown in FIG. 7, the light transmitting portion 2 and the light shielding portion 3 are formed at equal intervals on the circumference of the circular pulse plate 1 and are positioned between the light emitting element 4 and the light receiving element 5.

  The light emitted from the light emitting element 4 enters the light receiving element 5 through the light transmitting portion 2, and a photoelectrically converted signal is output. The output waveform at this time is a sine wave shown in FIG. 8, and a signal obtained by comparing the output waveform with a predetermined threshold is detected as a pulse signal. However, in the conventional example, since a constant voltage is constantly applied to the light emitting element 4, there is a problem that current continues to flow and power consumption is large.

  In order to solve this problem, for example, in Patent Document 1, the light emitting element is PWM-driven (intermittently driven), and the output is received by a low-pass filter to reduce power consumption. In Patent Document 2, a photo IC is used as the light receiving element, and the increased power consumption is reduced by PWM driving the light receiving element.

JP-A-5-296798 JP 2001-296147 A

  However, in the PWM drive as disclosed in Patent Documents 1 and 2 described above, there is a high probability of reaching the edge of the pulse while the power source of the light emitting element or the light receiving element is off, and an accurate detection result is not necessarily obtained. . Further, if the ON time is made shorter than the OFF time by changing the PWM duty ratio in order to reduce the power consumption, there is a problem that the detection error increases.

  An object of the present invention is to provide an encoder control apparatus that solves the above-described problems and can perform accurate detection with low power consumption.

  In order to achieve the above object, the technical feature of the encoder control device according to the present invention is that a light receiving element that intermittently receives light from the light emitting element via a light blocking portion that moves relative to the light emitting element, and the light receiving element An rising edge and an edge detector for detecting rising and falling edges of the output pulse, and stopping the power supply to the light emitting element during an edge detection unnecessary time of the edge detector. And a pulse width measuring unit that measures the time between the falling edges as a pulse width and a pulse width predicting unit that predicts the next pulse width.

  According to the encoder control device of the present invention, since power to the light emitting element is stopped at a time when light from the light emitting element is predicted not to be input to the light receiving element, a special detection method is not used on the light receiving side. Thus, the power consumption of the light emitting element can be substantially halved.

  The present invention will be described in detail based on the embodiments shown in the drawings.

  FIG. 1 is a schematic block circuit configuration diagram of the first embodiment. The light emitting element 11 and the light receiving element 12 are connected to a power source 14 via a switching element 13 formed of a transistor. The output of the light receiving element 12 is connected to the control means 16 via the comparator 15 and the input port 16a, and the output of the control means 16 is connected to the switching element 13 via the output port 16b.

  A pulse plate 21 shown in FIG. 2 is interposed between the light emitting element 11 and the light receiving element 12. In the pulse plate 21, light transmitting portions 22 and light shielding portions 23 are alternately formed at equal intervals. By rotating the pulse plate 21, a sine wave is obtained as an output signal from the light receiving element 12.

  The output signal of the light receiving element 12 is converted into an on / off digital signal by the comparator 15 and input to the control means 16 via the input port 16a. The control means 16 generates a control signal for the switching element 13 based on the signal input to the input port 16a, and outputs it to the switching element 13 via the output port 16b. The switching element 13 is turned on / off in synchronization with the control signal, and power from the power source 14 is intermittently supplied to the light emitting element 11 and the light receiving element 12.

  FIG. 3 is a block circuit configuration diagram showing the internal structure of the control means 16. The input port 16 a for inputting the output of the light receiving element 12 is connected to the pulse width measurement unit 32 and the error determination unit 33 via the edge detection unit 31. The output of the pulse width measurement unit 32 is connected to the storage unit 34, the comparison unit 35, and the control signal generation unit 36, respectively. The output of the storage unit 34 is connected to the control signal generation unit 36 via the pulse width prediction unit 37, and a part of the output of the pulse width prediction unit 37 is connected to the comparison unit 35. The output of the comparison unit 35 is connected to the control signal generation unit 36.

  The output of the error determination unit 33 is connected to the control signal generation unit 36 and the counting unit 38, and the output of the counting unit 38 is further connected to the control signal generation unit 36. The output of the control signal generator 36 is connected to the switching element 13 through the output port 16b.

  The rising / falling edge of the signal from the comparator 15 input to the input port 16a of the control means 16 is detected by the edge detection unit 31. Here, in order to simplify the following description, the rising edge is detected when the light beam enters the light receiving element 12, and the falling edge is detected when the light is blocked, and the pulse between the rising edge and the falling edge is detected. This is called a bright pulse. Similarly, a pulse between a falling edge and a rising edge is called a dark pulse.

  The pulse width measuring unit 32 measures each pulse width of the bright pulse and the dark pulse, and the measured pulse width is accumulated in the storage unit 34. Then, the pulse width prediction unit 37 predicts the pulse width of the next dark pulse based on the pulse width history stored in the storage unit 34. At this time, the pulse width of the next dark pulse may be predicted based on the pulse width history of both the light pulse and the dark pulse, or the pulse of the next dark pulse may be predicted based only on the dark pulse history. The width may be predicted. As a result, the pulse width can be accurately predicted.

  The pulse width predicted by the pulse width prediction unit 37 is multiplied by a predetermined value by the control signal generation unit 36, and is calculated as an edge detection unnecessary time. Here, the predetermined value is a constant equal to or less than 1, and a time shorter than the pulse width predicted by the pulse width prediction unit 37 by a predetermined ratio is calculated as the edge detection unnecessary time.

  Further, the value may be an invariant constant, or may be variable depending on the state of the pulse as described later. During the edge detection unnecessary time, the output of the output port 16b is turned off, and power supply to the light emitting element 11 and the light receiving element 12 is stopped.

  Note that since the prediction result in the pulse width prediction unit 37 is not always correct, a means for always verifying whether the prediction result is valid or not is necessary.

  As a first means, the comparison result is compared between the prediction result of the pulse width prediction unit 37 and the result actually measured by the pulse width measurement unit 32. If the prediction result is larger than the measurement result by a predetermined ratio or more, the control signal generator 36 reduces the predetermined value multiplied by the pulse width prediction result, and if the prediction result is smaller than the measurement result by a predetermined ratio or more. Increase the predetermined value. Thereby, more accurate pulse detection becomes possible.

  Further, as a second means, when the error determination unit 33 determines that the detection result of the edge detection unit 31 is different from the predicted value, energization of the light emitting element 11 is continued at least for the next one cycle. For example, if a rising edge should be detected this time but a falling edge is detected, the edge detection unnecessary time based on the prediction result is too long, so the pulse width for the next one cycle is measured again. The operation of resetting the pulse width prediction is performed. This operation will be described in more detail in the second embodiment.

  As a third means, the number of times determined as an error by the error determination unit 33 is counted by the counting unit 38, and when the result exceeds the predetermined number, the control signal generation unit 36 reduces the predetermined value multiplied by the pulse width prediction result. To do. In this way, the calculation error of the edge detection unnecessary time is counted as an error, and the prediction accuracy is changed when there are many errors, so that more accurate pulse detection is possible.

  Further, as a fourth means, when the pulse width measurement result in the pulse width measurement unit 32 becomes smaller than a predetermined pulse width, the edge detection unnecessary time in the control signal generation unit 36 is set to 0, and the power supply to the light emitting element 11 is performed. continue. This is because in consideration of reaction delay and prediction error of the control means 16 when the pulse becomes high speed, when the pulse becomes too high speed, the power supply to the light emitting element 11 is continued to maintain measurement accuracy. Is the action. Therefore, it is not necessary to use a microcontroller that can be controlled at high speed by the control means 16 or a detection system in which the pulse is not so fast. Thereby, degradation of detection accuracy with respect to a high-speed pulse can be limited.

  FIG. 4 is a timing chart in the first embodiment. (A) shows how light is transmitted and blocked by the pulse plate 21, where H indicates the case where light is transmitted and L indicates the case where light is blocked. (B) shows a terminal voltage for supplying power to the light emitting element 11, which is synchronized with a control signal given from the control means 16 to the switching element 13. (C) shows the detection pulse input to the control means 16 from the input port 16a.

  In synchronization with the start of driving of an operation detection target such as a DC motor (not shown) by the pulse plate 21, the switching element 13 is turned on by the output of the control means 16, and the power supply voltage is applied to the light emitting element 11. Since the time until the first edge in FIG. 4A rises is unpredictable, energization is continued. During the subsequent few edges, the pulse speed is very slow and it is difficult to predict, so power supply to the light emitting element 11 is continued only by storing the history of the pulse width.

  Here, the power supply is continued for the first four edges, but the present invention is not limited to this and may be further shortened depending on conditions. Thereafter, the switching element 13 is turned off in accordance with the edge detection unnecessary time calculated by the control means 16, and power supply to the light emitting element 11 and the light receiving element 12 is stopped for a time shorter than the pulse width of the dark pulse.

  FIG. 5 is a timing chart in the second embodiment. In the second embodiment, when a pulse edge is mainly detected, power supply to the light emitting element 11 is stopped except for the predicted time, thereby further reducing power consumption. The basic configuration is the same as that of the first embodiment, and the difference from the first embodiment is that the power supply to the light emitting element 11 is stopped only during the dark pulse time in the first embodiment. The power supply to the light emitting element 11 is stopped even during the time of the bright pulse.

  According to the edge detection unnecessary time calculated by the control means 16, the switching element 13 is turned off, and the power supply to the light emitting element 11 and the light receiving element 12 is stopped for a time shorter than the pulse width of the bright pulse and the dark pulse. Thereby, power supply to the light emitting element 11 is stopped except for the time when the pulse edge is predicted to be detected, so that the power consumption of the light emitting element 11 can be greatly reduced.

  FIG. 6 is a timing chart of the operation when the error determination unit 33 of the control means 16 determines that an error has occurred. When the power supply to the light emitting element 11 is stopped and the power supply is started again for the time calculated as the edge detection unnecessary time of the bright time, if the original prediction is correct, the pulse plate 21 that should have been in the bright state goes into the dark state. In such a case, it is determined as an error.

  In this case, the detection pulse detects a pulse width longer than the original pulse width in order to output a falling edge when power supply to the light emitting element 11 is resumed. For this reason, an inaccurate value is used for the prediction of the next pulse width. Therefore, the power supply to the light emitting element 11 is continued at least for the next one cycle, and the accurate pulse width is measured again before the prediction. To do.

  Thus, when the encoder output when power supply to the light emitting element 11 is restored is different from the predicted value, it is determined that the calculation of the edge detection unnecessary time is incorrect. Then, during the next one cycle, power supply to the light emitting element 11 is continued to correct the pulse, thereby enabling more accurate pulse detection.

  In the above description, preferred embodiments of the present invention have been described. However, it goes without saying that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the present invention.

1 is a schematic block circuit configuration diagram of Example 1. FIG. It is a front view of a pulse plate. It is a block circuit block diagram of a control means. 4 is a timing chart of Example 1. FIG. 6 is a timing chart of Example 2. FIG. FIG. 10 is a timing chart of the operation of the error determination unit according to the second embodiment. It is explanatory drawing of the optical encoder of a prior art example. It is a graph figure of the output signal from the light receiving element of an optical encoder.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light emitting element 12 Light receiving element 13 Switching element 14 Power supply 15 Comparator 16 Control means 16a Input port 16b Output port 21 Pulse plate 22 Light transmission part 23 Light-shielding part 31 Edge detection part 32 Pulse width measurement part 33 Error determination part 34 Storage part 35 Comparison unit 36 Control signal generation unit 37 Pulse width prediction unit 38 Counting unit

Claims (8)

  A light-receiving element that intermittently receives light from the light-emitting element via a light-blocking part that moves relative to the light-emitting element, and an edge detector that detects rising and falling edges of the output pulse from the light-receiving element, respectively. A pulse width measuring unit that measures the time between the rising edge and the falling edge as a pulse width in an encoder control device that stops power supply to the light emitting element during an edge detection unnecessary time of the edge detection unit; An encoder control device comprising: a pulse width prediction unit that predicts a next pulse width.   A control signal generation unit that calculates the edge detection unnecessary time by multiplying the estimated pulse width by a coefficient, and predicts a first time when light from the light emitting element is not incident on the light receiving element by the pulse width prediction unit. 2. The encoder control according to claim 1, wherein power supply to the light emitting element is stopped during the edge detection unnecessary time after an edge indicating the start of the first time is detected by the edge detection unit. apparatus.   A control signal generating unit configured to calculate the edge detection unnecessary time by multiplying the predicted pulse width by a coefficient; and a first time during which light from the light emitting element does not enter the light receiving element and light from the light emitting element The second time incident on the light receiving element is predicted by the pulse width prediction unit, and the edge detection is performed after the edge detection unit detects the start of the first time or the start of the second time. The encoder control device according to claim 1, wherein power supply to the light emitting element is stopped during an unnecessary time.   A storage unit for storing a measurement result of the pulse width measurement unit, wherein the pulse width prediction unit calculates a next pulse width based on a history of the pulse width measurement result stored in the storage unit; The encoder control device according to any one of claims 1 to 3.   The power supply to the light emitting element is continued when the pulse width prediction result by the pulse width measurement unit or the pulse width prediction unit becomes smaller than a predetermined pulse width. The encoder control device according to any one of claims.   A comparison unit that compares a pulse width measurement result by the pulse width measurement unit with a pulse width prediction result by the pulse width prediction unit, and the comparison unit causes the prediction result to be different from the measurement result by a predetermined ratio or more. 4. The encoder control apparatus according to claim 2, wherein the ratio by which the control signal generation unit multiplies the pulse width prediction result is changed.   An error determination unit that determines an output result when power supply is started again after power supply to the light emitting element is stopped during the edge detection unnecessary time. When the error determination unit determines an error, the light emission is performed. 4. The encoder control device according to claim 2, wherein the power supply to the element is continued for at least the next one cycle.   A counter that includes an error determination unit that determines an output result when power supply is started again after stopping power supply to the light emitting element during the edge detection unnecessary time, and counts the number of times the error determination unit determines that an error has occurred. The encoder according to claim 6, further comprising: a control unit configured to change the ratio by which the control signal generation unit multiplies the pulse width prediction result when a counting result of the counting unit exceeds a predetermined number of times. Control device.

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