JPH0560571A - Method for detecting abnormality of encoder - Google Patents

Abstract

PURPOSE:To easily detect abnormalities in an encoder when a servo motor and the encoder are used in conjunction with each other by calculating a theoritical pulse counted value during the period of change of polar position level signals if polar position levels stored are changed. CONSTITUTION:An encoder 5 detects the output angle of rotation of a servo motor 1 and the number of pulses generated by the two-phase encoder 5 is counted by a CPU 6 in synchronization with pulses from a fixed-period timer 7 the period of which is shorter than that of polar position level signals from a pole detector 2, and is stored on a RAM 9. Simultaneously polar position levels are stored at every period of abnormality detection. When the polar position levels stored are changed and also when a theoritical pulse counted value which is theoritically calculated during the period of change of independently stored polar position level signal is K, the CPU 6 identifies abnormality of the encoder if the pulse counted value is smaller than 2*K/3 or larger than 3*K/2, and then outputs I encoder abnormality.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of detecting an abnormality of an encoder, and more particularly, an abnormality of an encoder for detecting a signal abnormality of a two-phase encoder by using a phase level signal for controlling a servo motor. It relates to a detection method.

[0002]

2. Description of the Related Art Conventionally, the rotary shaft of a servo motor has been
An encoder, a resolver, etc. for detecting the rotation angle and the rotation speed of the motor are attached, and the rotation speed and the like of the motor are controlled based on the detection output.

On the other hand, another encoder is attached to a shaft that requires an accurate rotation angle and rotation speed while receiving the rotation force of the servo motor, and the output of the encoder is fed back to the motor to give a predetermined rotation speed or stop. Speed control and position control are performed so that the position and the like can be obtained. If an abnormality occurs in the encoder itself during such control, there is a risk that the motor may run out of control or the operation of the motor may become unstable. Therefore, conventionally, various methods for detecting an abnormality in the encoder signal have been considered.

FIG. 10 shows an example of a conventional encoder signal abnormality detection circuit. In this circuit, an A-phase encoder level signal is set to a differential signal A and a non-A by a differential driver 11, these are transmitted using separate lines, and then received by a differential receiver 12 again. Abnormality determination is differential signal A and non-A
Is input to the EXOR element 13 and the output from the EXOR element 13 is observed. If it is normal, there should be no output, and if it is output, it is an error signal. However,
This detection method can only detect abnormalities in the transmission line such as disconnection and noise that gets on the transmission line, and cannot detect abnormalities in the encoder itself.

Therefore, as a method of detecting the abnormality of the encoder itself, the abnormality of the encoder having the level signals of the U, V and W phases indicating the absolute position and the level signals of the A and B phases indicating the direction and speed is detected. The method is disclosed in JP-A-63-2.
No. 84415. Here, U,
A logic circuit that determines whether the U, V, and W phase signals are abnormal because the V and W phase level signals have the same level at the same time, and the UP and DN obtained from the rising and falling edges of the A and B phase signals. A hysteresis circuit for detecting that each pulse is continuous for a plurality of pulses, and a logic circuit for synthesizing an A, B-phase signal abnormality by the fact that the output of the hysteresis circuit does not occur during one phase of the U, V, W phases. It is used to detect an encoder error.

[0006]

However, in the conventional method, as described above, two kinds of signals of the A phase and the inverted A phase must be transmitted, so that the number of transmission lines increases. There was a flaw. In addition, there is a problem that it is not possible to deal with the case where pulse noise is mixed in other than the transmission path or the encoder signal itself is lost. In addition, Japanese Laid-Open Patent Publication No. Sho 6-96, which detects an abnormality in the encoder
In the publicly known technique described in JP-A-3-284415,
In addition to the two-phase signal generator for generating the A and B phases inside the encoder, a three-phase generator for generating the U, V and W phases is required. For this reason, an extra rotating plate or the like is required, resulting in an increase in cost. This was the same when a servomotor was used as the motor. Further, in the above-mentioned known technique, since the logic circuit is used, U, V,
In the relationship between the W phase and the A and B phases, it was difficult to perform complicated and delicate abnormality detection.

The present invention has been made to solve the above-mentioned problems, and an object thereof is to provide a simple method for detecting an abnormality of an encoder when a servo motor and an encoder are used in combination. I am trying.

[0008]

In order to achieve this object, an encoder abnormality detecting method of the present invention is directed to a servomotor having a pole detector for detecting a pole position and outputting a plurality of pole position level signals. A method of detecting an abnormality of an encoder for detecting an output rotation angle, wherein the encoder generates A and B phase pulses for detecting the output rotation angle of a servo motor in a short cycle, and a predetermined cycle shorter than the cycle of the pole position level signal. The number of pulses is counted for each abnormality detection cycle, the counted number of pulses is stored as a pulse count value, the pole position level is stored for each abnormality detection cycle, and there is a change in the stored pole position level. And the theoretical pulse count value theoretically calculated during the changing period of the pole position level signal is K, whether the pulse count value is smaller than 2 * K / 3,
Alternatively, when the value is larger than 3 * K / 2, it is detected that the encoder is abnormal and an encoder abnormality signal is output.

[0009]

In the encoder abnormality detecting method of the present invention comprising the above means, the pole detector of the servomotor detects the pole position of the motor and outputs a plurality of pole position level signals. The encoder detects the output rotation angle of the servo motor, detects the output rotation angle of the servo motor in a short cycle, and outputs an output pulse. The counting device counts the pulses at every predetermined abnormality detection period that is shorter than the period of the pole position level signal. The control device stores the counted number of pulses as a pulse count value, and also stores the pole position level for each abnormality detection cycle. The control device sets the theoretical pulse count value theoretically calculated during a change cycle of the pole position level signal stored separately when there is a change in the stored pole position level as K. When the pulse count value is less than 2 * K / 3, or
When the value is larger than 3 * K / 2, it is detected that the encoder is abnormal and an encoder abnormality signal is output.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An encoder abnormality detecting method according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing the configuration of equipment used in an encoder abnormality detection method according to an embodiment of the present invention. The two-phase encoder 5 is composed of slits of an A channel that generates an A phase level signal and a B channel that generates a B phase level signal, and a photoelectric element that reads the slits.
The A phase and B phase level signals are pulse signals having a 90-degree phase difference. The rotation direction of the two-phase encoder 3 is detected by using this phase difference. The details will be described later. Two
The counter value signal line for outputting the value obtained by counting the pulses of the A-phase and B-phase level signals from the phase encoder 3 is cpu.
Connected to 6.

The signal lines of the U-phase level signal, the V-phase level signal and the W-phase level signal of the pole detector 2 of the AC servomotor 1 are connected to the status input port 4. Where U,
The V and W phases are outputs that detect the pole positions of the normal three-phase windings of the AC motor, and have waveforms as shown in FIG. The state input port 4 is a port for the cpu 6 to read the U, V and W phase level signals. Encoder 5
And cpu6 are connected. The cpu 6 is connected with a constant cycle timer 7, a ROM 8 and a RAM 9. c
The pu 6 counts the number of pulses generated by the two-phase encoder 5 in synchronization with the pulse generated by the constant period timer 7, and stores the counted number of pulses in the connected RAM 9. The R0M8 stores a program for an encoder abnormality detection method described below and the like.

Next, the operation of the encoder abnormality detecting device having the above configuration will be described. FIG. 2 shows a timing chart of signal generation. Further, FIG. 3 shows a flowchart of control relating to abnormality detection. AC servo motor 1
However, consider the case where the two-phase encoder 3 is rotating in the direction in which the counter value increases.

First, a method of counting the counter value of the two-phase encoder 3 will be described.

[Table 1] As summarized in Table 1, when the A-phase signal is “High” and the B-phase signal is “rising”, or when the A-phase signal is “falling” and the B-phase signal is “High”,
Alternatively, when the A-phase signal is “Low” and the B-phase signal is “falling”, or when the A-phase signal is “rising” and the B-phase signal is “Low”, the counter value is incremented by 1. When the A-phase signal is "Low" and the B-phase signal is "rising", or when the A-phase signal is "rising" and the B-phase signal is "High", or when the A-phase signal is "High" and B When the phase signal is "falling",
Or the A phase signal is "falling" and the B phase signal is "L"
When it is “ow”, the counter value is decremented by 1.

When calculated in this way, the two-phase encoder 3
When rotating so as to output the A and B phase signals shown in FIG. 5, the counter value increases in proportion to the rotation angle. Two
When the phase encoder 3 rotates in the opposite direction, the A and B phase signals become as shown in FIG. 6, and the counter value decreases in proportion to the rotation angle.

Next, the relationship between changes in the U, V and W phase signals and the counter value when the AC servomotor 1 rotates will be described. When the AC servomotor 1 rotates, the U, V, W phase level signals change as shown in FIG. The combinations of the levels of the U, V, and W phase level signals are a, b, c, and
There are six states indicated by d, e, and f. The U, V, W signal levels repeat this combination. Meanwhile, cpu
6 is U, V, W by the signal from the constant period timer 7.
The inspection of the signal level of the phase and the reading of the counter value are periodically executed. The times at which the signal from the constant cycle timer 7 is generated are t1 to t6. Here, t2-t1 is the constant period T2, which is a value sufficiently smaller than T1.

On the other hand, the U-phase signal level represents the pole position of the servo motor and is determined by the structure of the servo motor. The encoder itself reads the A channel and the B channel formed around the disk, and is determined by the structure of the encoder. Therefore, the amount of change in the counter value during the constant period T1 should always be a constant value. Then, the value can be obtained in advance from the number of encoder pulses per rotation of the two-phase encoder 3, the frequency per rotation of the U-phase level signal, and the like. The theoretical value is the value thus obtained.

Next, a method of detecting an abnormality will be described with reference to the flowchart of FIG. At time t5, cpu6 performs the following processing. First, the signal levels of the U, V and W phases are read (S1). Then, the signal level is compared with the signal level read at the previous time t4 (S2). Since the signal level has not changed here, the abnormality detection of the encoder is not performed and the signal levels of the U, V and W phases are stored (S8).

At time t6, cpu6 is first U,
The signal levels of the V and W phases are read (S1). Then, the signal level at the previous time t5 is compared (S2). Since the signal level has changed this time, the cpu 6 recognizes that the motor has rotated. Since the signal level of the V phase has changed at t6, the V phase is stored as the changed phase this time (S3).

Next, the counter value of the two-phase counter 3 is read, and the difference from the counter value at the time t4 read last time is set to T (S4). When the value of T is smaller than 2 * K / 3 or larger than 3 * K / 2,
When the phase changed this time is different from the phase changed last time, an abnormality of the encoder is determined (S6) and an abnormality signal is output (S10). The reason why the phase change is added to the abnormality determination will be described later. At time t6, the value of T is 2 because the V phase different from the W phase changed at time t4 is changing.
If it is smaller than * K / 3 or larger than 3 * K / 2, an encoder abnormality is detected.

Next, the relationship between the theoretical counter value K generated during T1 and the actually counted counter value T will be described. The abnormality detection cycle T2 is the change cycle T1 of the U, V, and W phases.
Must be sufficiently shorter than at least T2 <T
Must be 1/2. First, consider the case of n * T2 <T1 <(n + 1) * T2 (n> 2 or n = 2) Expression 1. Expression 1 can be transformed into Expression 2 as follows: T1 / (n + 1) <T2 <T1 / n (n> 2 or n = 2). FIG. 11 shows the relationship between T1 and T2.
T1 is the change cycle of the U, V, W phases, T2 is the abnormality detection cycle, that is, the cycle of the signal output from the constant cycle timer 7, and T5 is the recognition interval of the signal level change of the U, V, W phases. is there.

M is the number of times of performing the inspection shown in the flowchart of FIG. 3 according to the output of the constant period timer 7 during T1. m = n when T2 <T3 + T4 <2 * T2
−1, and when T3 + T4 <T2, m = n. m
= N−1, T5 = nT2, which is substituted into Equation 2 to obtain n * T1 / (n + 1) <nT2 <n * T1 / n n * T1 / (n + 1) <T5 <T1 Equation 3 m = N, T5 = (n + 1) T2, which is substituted into Equation 2 to obtain (n + 1) * T1 / (n + 1) <(n + 1) * T2 <(n + 1) * T1 / n T1 <T5 <( n + 1) * T1 / n Equation 4 From Equation 3 and Equation 4, the possible values of T5 are: n * T1 / (n + 1) <T5 <(n + 1) * T1 / n where n> 2 or n = 2

The minimum value of n * T1 / (n + 1), (n +
1) The maximum value of * T1 / n is when n is 2,
T5 becomes 2 * T / 3 <T5 <3 * T1 / 2 Equation 5 no matter how many times T5 is interrupted. At a constant speed, the change of the counter value during T5 is 2 * K / 3 <(change amount during T5) <3 * K / 2, where K is the theoretical change amount of the counter value during T1. Become. This is the case when the motor is at maximum speed, and when the speed is low, the number of interrupts during T1 increases, so T
1 = T5 is approached and does not deviate from Equation 5.
Therefore, if the two-phase encoder 3 is normal, 2 * K / 3 <T <3 * K / 2. Considering the absolute value, the rotation of the motor may be either forward or reverse.

Next, the case where the two-phase encoder 3 is abnormal will be described. For example, consider a case where one or both of the A-phase signal and the B-phase signal are fixed at a certain level. In that case, the counter value takes any one of 0, 1 and -1, as shown in FIGS. Therefore, 2 * K / 3> T, and it is determined to be abnormal. Therefore, even if the encoder does not move due to disconnection or the like, the method of the present invention can detect an abnormality.

When the motor reverses, the output is as shown in FIG. In this case, the U, V, and W phases are changed between time t2 and time t3, but the motor is only reversed, so that the change T in the counter value is changed between time t2 and time t3. There is a possibility that 2 * K / 3> T. In order to prevent erroneous determination in this case, when the phase of the level signal changed last time and the phase of the level signal changed this time are the same, even if the change T of the counter value is 2 * K / 3> T. , It is determined to be normal (S6).

Although the AC servomotor has been described in this embodiment, the present invention can be applied to a motor having means for detecting the rotational position of the motor shaft, for example, a variable reactance motor.

[0026]

As is apparent from the above description, according to the abnormality detecting method of the encoder of the present invention, the phase level signal of the pole detector of the servo motor is used and the change of the counter value is compared with the theoretical value. Since the abnormality is determined by detecting the abnormality of the encoder itself, it is possible to prevent the motor from running out of control.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an apparatus used for carrying out an embodiment embodying the present invention.

FIG. 2 is a timing chart showing timings of various signals.

FIG. 3 is a flowchart showing a procedure of an abnormality detection method that is an embodiment of the present invention.

FIG. 4 is a timing chart showing timings of various signals when the servo motor is reversed in the middle.

FIG. 5 is a signal diagram showing a counter when the servomotor is rotating normally.

FIG. 6 is a signal diagram showing a counter when the servo motor is rotating in the reverse direction.

FIG. 7 is a signal diagram showing a state when the A and B phase signals are both disconnected.

FIG. 8 is a signal diagram showing a state when the B-phase signal is disconnected.

FIG. 9 is a signal diagram showing a state when the A-phase signal is disconnected.

FIG. 10 is a block diagram showing a configuration of a conventional abnormality detection device.

FIG. 11 is an explanatory diagram showing a relationship between abnormality detection cycles.

[Explanation of symbols]

 1 Servo motor 2 Poles detector 4 State input port 5 Two-phase encoder 6 cpu 7 Constant period timer 8 ROM 9 RAM

Claims (1)

[Claims] 1. A method for detecting an abnormality of an encoder for detecting an output rotation angle of a servo motor having a pole detector for detecting a pole position and outputting a plurality of pole position level signals, wherein the encoder outputs the servo motor. A- and B-phase pulses for detecting the rotation angle in a short cycle are generated, the pulse is counted in each predetermined abnormality detection cycle shorter than the cycle of the pole position level signal, and the counted number of pulses is stored as a pulse count value. Then, the pole position level is stored for each abnormality detection cycle, and when the stored pole position level is changed, and theoretically calculated during the change cycle of the pole position level signal. When the theoretical pulse count value is K, the pulse count value is smaller than 2 * K / 3 or larger than 3 * K / 2. It detects that it is abnormal, the abnormality detection method of an encoder and outputting an encoder error signal.