JP5587695B2 - Encoder with noise state detection function - Google Patents

Description

  The present invention relates to an encoder having a function of detecting an ambient noise environment.

  In recent years, the environment in which an encoder is used tends to be severe for accurate position detection due to the increase in speed and output of a motor that is a power source. Furthermore, due to the high-speed switching of the servo amplifier that drives the motor, the encoder may be affected by noise depending on the grounding status of the machine, etc., and the position may not be detected correctly, or an abnormality may be detected and the machine may be stopped. .

  FIG. 1 shows an example of a system in which an encoder is used. The control device 10 receives position information from the encoder 14 received by the servo amplifier 12 via the communication cable 16 via the communication cable 18 and controls the rotation of the servo motor 20 via the servo amplifier 12 based on the information.

  The encoder 14 includes a plurality of abnormality detection circuits therein, and when any abnormality is detected, notifies the control device 10 via the servo amplifier 12 as abnormality information. When recognizing that there is an abnormality in the encoder, the control device 10 stops the servo motor 20 and stops the machine 22.

  Depending on the grounding environment of the machine and the wiring conditions of the cables 16 and 18, the encoder 14 may be easily affected by noise. If the encoder 14 detects an abnormality due to the influence of noise, the machine 22 is operated as a result. It will stop inside. Therefore, it is desired that a noise state can be detected and notified to the outside before such a state is reached, and a countermeasure can be promoted.

  Japanese Patent Application Laid-Open No. 2004-151858 describes that noise superimposed on a detection signal in an encoder is directly detected via a coupling capacitor and waveform data of the detected noise is output.

JP 2005-172523 A

  An object of the present invention is to provide an encoder with a noise state detection function that detects a noise state of a signal with a simple and novel configuration and notifies the signal to the outside.

According to the present invention, a signal detection unit that outputs two signals having different phases in response to a change in the position of a moving body, and a time interval between zero cross points or peak points of the two signals output by the signal detection unit. A local phase difference detection unit for detecting a local phase difference on a time scale of two signals;
With a noise state detection function comprising a noise state detection unit that determines whether the local phase difference detected by the local phase difference detection unit exceeds an upper limit value or less than a lower limit value and outputs the result as warning information An encoder is provided.

  By notifying the control device or the like of the influence of noise as warning information, the influence of the noise can be grasped, and the necessity of noise countermeasures can be determined before the encoder detects an abnormality and the machine stops. Furthermore, it is possible to confirm the effect after noise countermeasures.

It is a figure which shows an example of the system by which an encoder is used. It is a block diagram which shows the structure of the encoder with a noise state detection function which concerns on the 1st Embodiment of this invention. It is a wave form diagram which shows a signal waveform when there is no noise, and demonstrates determining a local phase difference from the space | interval of a peak point. It is a wave form diagram which shows the space | interval of the peak point in the signal containing noise. It is a wave form diagram explaining determining a local phase difference from the space | interval of a zero crossing point. It is a wave form diagram which shows the space | interval of the zero crossing point in the signal containing noise. It is a block diagram which shows the structure of the encoder which concerns on the 2nd Embodiment of this invention. It is a figure which shows the binarization signal corresponding to the signal containing noise. It is a block diagram which shows the structure of the encoder which concerns on the 3rd Embodiment of this invention. It is a figure explaining Tsamp and Pn, Pn + 1 for determining an upper limit and a lower limit.

  FIG. 2 is a block diagram showing a configuration of an encoder with a noise state detection function according to an embodiment of the present invention. The encoder with a noise state detection function of the present invention is used as the encoder 14 in the system described with reference to FIG.

  In FIG. 2, the signal detector 30 outputs two sinusoidal signals having different phases in response to, for example, rotation of the shaft of the servo motor 20 (FIG. 1). The sine wave signal is compared with a predetermined threshold value in the comparators 32 and 34 and converted into a binarized signal (rectangular wave signal), and digitally transmitted through the amplifiers 36 and 38 and the A / D converters 40 and 42. The signal is converted into a signal and input to the signal processing unit 44. The position detection unit 46 of the signal processing unit 44 performs position detection according to a known method based on these signals, and the result is converted into data as position information and output.

  The local phase difference detection unit 48 calculates a local phase difference on the time scale (hereinafter referred to as local phase difference) based on the two sinusoidal signals converted into digital signals, and a noise state detection unit. In 50, the local phase difference calculated by the local phase difference detecting unit 48 is compared with predetermined upper and lower limit values, and warning information is output based on the result.

  When the shaft of the motor 20 (FIG. 1) rotates at a constant speed, a waveform as shown in FIG. 3 is obtained as an encoder internal signal. The local phase difference on the time scale between signals is represented by the interval Tabn (n is 1, 2, 3, and 4) of the peak points of each signal, and is constant when there is no influence of noise. On the other hand, as shown in FIG. 4, when noise 52 is included in the signal, the value of Tabn fluctuates due to the influence. Therefore, if the upper limit specified value and the lower limit specified value are set in advance and a warning is issued when the value of Tabn exceeds the upper limit specified value or less than the lower limit specified value in the noise state detection unit 50, it is provided inside the encoder. The detected abnormality detection circuit (not shown) can detect the noise state before detecting the abnormality and stopping the servo motor.

  The lower limit prescribed value of the local phase difference is determined according to the highest response frequency of the encoder, for example. For example, when the maximum response frequency is 100 kHz, the lower limit specified value of the local phase difference is assumed to be a double frequency 200 kHz, and in this case, the lower limit specified value is determined to be 1/200 kHz / 4 = 1.25 μsec. This lower limit specified value is effective even when the motor is stopped.

  The upper limit value of the local phase difference is valid under the condition that the encoder is rotating at a predetermined speed or higher. For example, when the maximum response frequency is 100 kHz, the upper limit specification value is effective when the signal frequency exceeds 10 kHz, which is 1/10 of the maximum response frequency, and the upper limit specification value is 1 / 10 kHz / 4/2 × 3 = 37.5 μsec.

  In this case, in the example of FIG. 4, when Tab2 <12.5 μsec is detected, or when Tab1 + Tab2 + Tab3 + Tab4 <100 μsec, that is, the frequency of the signal exceeds 10 kHz and Tab3> 37.5 μsec is detected, a warning is given. Information is output.

  Note that there are some encoders having a plurality of sinusoidal signals with different periods, such as an absolute type encoder. In such a case as well, the lower limit specified value and the upper limit specified value are similarly determined by the period of the signal.

  In the local phase difference detection unit 48, instead of detecting the local phase difference from the peak interval, the local phase difference can be similarly detected from the zero cross point interval and a warning can be issued. As shown in FIGS. 5 and 6, when normal, the intervals are equal as shown in FIG. 5, and when noise 52 is present, as shown in FIG. 6, the lower limit specified value and the upper limit specified value are the same as described above. By comparing with Tabzn (n = 1, 2, 3, 4), it is possible to detect the mixing of noise and issue a warning in the same manner.

  FIG. 7 shows a configuration of an encoder according to the second embodiment of the present invention. 2 is different from the embodiment of FIG. 2 in that the local phase difference detector 48 detects the local phase difference based on the digitized sinusoidal signals output from the A / D converters 40 and 42, instead of detecting the local phase difference. The phase difference is detected on the basis of the binarized signal (rectangular wave signal) output by 34.

  In the example shown in FIG. 6, the binarized signal is as shown in FIG. 8, so that the locality is obtained from the time interval Tabzn (n = 0, 1, 2, 3) of the conversion point from 0 to 1 or 1 to 0. The phase difference can be detected, and the abnormality can be detected by setting the lower limit specified value and the upper limit specified value in the same manner as described above. The same applies to the absolute type encoder.

  FIG. 9 shows the configuration of an encoder with a noise state detection function according to the third embodiment of the present invention. In this embodiment, the upper limit value and the lower limit value of the local phase difference are not determined in advance according to the maximum response frequency, but based on the change amount per predetermined time of the position detected by the position detection unit 46 in the upper / lower limit calculation unit 52. It is determined.

As shown in FIG. 10, if the position changes from Pn to Pn + 1 during a predetermined time Tsamp, if the movement amount corresponding to one signal period is λ, the time required for one signal period is λ / (Pn + 1 −Pn) × Tsamp
Can be calculated from When the phase difference of the signal is 90 °, the phase difference Tpdif on the time scale when there is no noise is Tpdif = λ / (Pn + 1−Pn) × Tsamp / 4
Based on the value, for example, the lower limit specified value: Tpdif / 2
Upper limit specified value: Tpdif × (3/2)
Can be determined as follows.

Instead of calculating the time required for one signal cycle from Tsamp and (Pn + 1−Pn) as described above, it is also possible to determine from a time Tbz required for a predetermined position change, for example, movement of nλ (n is an integer). In this case, Tpdif is Tpdif = Tbz / n / 4
The subsequent processing is the same as described above.

  In this way, by determining the lower limit set value and the upper limit set value based on the average phase difference or moving speed, it is possible to detect sudden fluctuations such as noise, and the lower limit set value of the local phase difference. The warning information derived from the upper limit setting value can inform the worker of the noise environment at the time of starting up the machine, and the worker can improve the environment to detect false alarms and alarms due to the influence of noise. It is possible to prevent the machine from being stopped due to occurrence.

  Furthermore, even when the machine is operating in a good noise environment, it is possible to accurately determine changes in the noise environment due to changes in external devices and wiring, etc. It is possible to prevent erroneous detection of the position due to the influence and stop of the machine in operation due to an alarm.

  Note that when noise countermeasures are used, it is possible to identify conditions and noise sources that are susceptible to noise depending on the accuracy, frequency, and timing with which warning information is notified. Judgment is based on a decrease in frequency and a change in timing.

  The number of times that the local phase difference between the signals falls below the lower limit specified value, the number of times that the upper limit specified value has been exceeded, or the sum of those times is output from the encoder as warning information, and the number of times is output from the control device 10 (FIG. 1). It can also be confirmed on the screen.

  Depending on the degree of change in this value and the output timing, the operator can specify conditions and noise sources that are easily affected by noise, and the effect after noise countermeasures is also determined by the degree of change and timing of this value. Is done.

Claims (4)

A signal detector that outputs two signals having different phases in response to a change in the position of the moving body;
From the time interval between the zero cross points or peak points of the two signals output by the signal detector, a local phase difference caused by noise superimposed on both or one of the two signals for a very short time with respect to the signal period A local phase difference detection unit for detecting
With a noise state detection function comprising a noise state detection unit that determines whether the local phase difference detected by the local phase difference detection unit exceeds an upper limit value or less than a lower limit value and outputs the result as warning information Encoder.   The encoder according to claim 1, wherein the upper limit value and the lower limit value are determined based on a change amount of the position of the moving body per predetermined time or a time required for a position change of the predetermined amount of the moving body.   The encoder according to claim 1, wherein the upper limit value and the lower limit value are determined based on a maximum response frequency of the encoder, and the upper limit value is effective only when a position change speed of the moving body is equal to or greater than a predetermined value.   The noise state detection unit is configured to calculate a first number of times that a phase difference in the time scale exceeds the upper limit value, a second number of times that is less than the lower limit value, or the first number and the second number of times. The encoder according to claim 1, wherein a sum is output as the warning information.

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