JP2020204480A - Rotational speed detection device - Google Patents

Abstract

To increase noise immunity.SOLUTION: A rotational speed detection device 40 comprises low pass filters 42 and 43 which reduce noise included in first pulse signals AS and BS, a Z-phase low pass filter 44 which reduces noise included in a Z-phase pulse signal ZS, a signal selection unit 46, and a rotational information calculation unit 47. When a first condition is that a variation of a speed command value ω* is equal to or smaller than a preliminarily determined first threshold and a second condition is that variations of the first pulse signals AS and BS are equal to or smaller than a preliminarily determined second threshold, the signal selection unit 46 selects the Z-phase pulse signal ZS if at least one of the first condition and the second condition is satisfied. The rotational information calculation unit 47 calculates a rotational speed ω from a pulse signal selected by the signal selection unit 46.SELECTED DRAWING: Figure 1

Description

The present invention relates to a rotation speed detection device.

The rotation speed detection device that detects the rotation speed of a rotating body such as a motor includes an encoder that outputs a pulse signal as the rotating body rotates, an arithmetic unit that calculates the rotation speed of the rotating body based on the number of pulses of the pulse signal, and a calculation unit. To be equipped. The encoder described in Patent Document 1 has an A-phase pulse signal in which a plurality of pulses are generated during one rotation of the rotating body, a plurality of pulses are generated during one rotation of the rotating body, and a phase difference from the A-phase pulse signal. It outputs a B-phase pulse signal at 90 ° and a Z-phase pulse signal in which one pulse is generated during one rotation of the rotating body. When detecting the rotation speed of a rotating body using an encoder that outputs an A-phase pulse signal, a B-phase pulse signal, and a Z-phase pulse signal, the calculation unit performs the rotating body based on the number of pulses of the A-phase pulse signal and the B-phase pulse signal. Calculate the rotation speed of.

Japanese Unexamined Patent Publication No. 2013-134068

The rotation speed detection device may include a low-pass filter for each phase pulse signal in order to reduce noise contained in each phase pulse signal. The frequency of the pulse signal increases as the number of pulses generated during one rotation of the motor increases. Therefore, the cutoff frequency of the low-pass filter is as high as the low-pass filter in which a pulse signal with a large number of pulses generated during one rotation of the motor is input. Set high. Therefore, the cutoff frequency of the low-pass filter for the A-phase pulse signal and the B-phase pulse signal is set higher than the cutoff frequency of the low-pass filter for the Z-phase pulse signal. The A-phase pulse signal and the B-phase pulse signal include noise due to a frequency lower than the cutoff frequency. Due to this noise, the error of the rotation speed detected by the rotation speed detection device may become large.

An object of the present invention is to provide a rotation speed detection device capable of improving noise resistance.

The rotation speed detection device that solves the above problems outputs a first pulse signal in which a plurality of pulses are generated during one rotation of the rotating body and a second pulse signal in which one pulse is generated during one rotation of the rotating body. A rotation speed detection device that detects the rotation speed of the rotating body from the output of the encoder, which has a higher cutoff frequency than the first low-pass filter that reduces noise contained in the first pulse signal and the first low-pass filter. A second low-pass filter that is low and reduces noise contained in the second pulse signal, and a first condition that the amount of change in the speed command value is equal to or less than a predetermined first threshold value, that is, the first pulse signal. Assuming that the amount of change is equal to or less than a predetermined second threshold value, the second pulse signal is selected when at least one of the first condition and the second condition is satisfied. The signal selection unit that selects the first pulse signal when the second pulse signal is not selected, and the first pulse signal when the first pulse signal is selected by the signal selection unit. A calculation unit that calculates the rotation speed and calculates the rotation speed from the second pulse signal when the second pulse signal is selected by the signal selection unit is provided.

The cutoff frequency of the second low-pass filter is lower than the cutoff frequency of the first low-pass filter. Therefore, the noise of the second pulse signal whose noise is reduced by the second low-pass filter is reduced as compared with that of the first pulse signal. When the rotation speed is calculated using the second pulse signal, the error in the rotation speed due to the influence of noise can be reduced as compared with the case where the rotation speed is calculated using the first pulse signal. On the other hand, the number of pulses generated when the rotating body makes one rotation is smaller in the second pulse signal than in the first pulse signal. Therefore, when the rotation speed of the rotating body is calculated using the second pulse signal, the rotation speed is detected when the rotation speed changes, as compared with the case where the rotation speed is calculated using the first pulse signal. Will take longer. Moreover, when the rotation speed changes, the rotation speed cannot be calculated accurately. That is, when the rotation speed is calculated using the second pulse signal, it is difficult to respond to the change in the rotation speed.

When the first condition is satisfied, the amount of change in the speed command value is equal to or less than the first threshold value, and it can be said that the change in the rotation speed due to the change in the speed command value is unlikely to occur. When the first condition is satisfied, the rotation speed is unlikely to change, so that the rotation speed can be calculated using the second pulse signal. When the second condition is satisfied, it can be said that the rotation speed of the rotating body has not changed significantly due to load fluctuation or the like. When the second condition is satisfied, the rotation speed is unlikely to change, so that the rotation speed can be calculated using the second pulse signal.

As described above, it is necessary to calculate the rotation speed using the first pulse signal by calculating the rotation speed from the second pulse signal when at least one of the first condition and the second condition is satisfied. When is low, the rotation speed is calculated from the second pulse signal. Therefore, when it is necessary to cope with the change of the rotation speed while improving the noise resistance, the change of the rotation speed can be dealt with by using the first pulse signal.

Regarding the rotation detection device, the signal selection unit may select the second pulse signal when both the first condition and the second condition are satisfied.
When the second pulse signal is selected when either the first condition or the second condition is satisfied, the first condition is satisfied but the second condition is not satisfied, or the second condition is satisfied. However, the second pulse signal may be selected even when the first condition is not satisfied. In this case, the second pulse signal may be selected even though the rotation speed is likely to change. On the other hand, by selecting the second pulse signal when both the first condition and the second condition are satisfied, the second pulse signal can be selected in a state where the change in the rotation speed is unlikely to occur.

According to the present invention, noise resistance can be improved.

Schematic diagram of the motor and the motor drive device. The schematic diagram of the A-phase pulse signal, the B-phase pulse signal, and the Z-phase pulse signal generated when the motor rotates. The flowchart which shows the process which a signal selection part performs.

Hereinafter, an embodiment of the rotation speed detection device will be described.
As shown in FIG. 1, the motor drive device 10 is a device for driving the motor 11. The motor 11 of the present embodiment is a three-phase AC motor including three coils U, V, and W. The motor 11 may be mounted on any device. For example, the motor 11 may be mounted on an electric compressor and used to drive a compression mechanism, or may be mounted on an industrial vehicle such as a forklift to drive a hydraulic pump of a hydraulic mechanism or rotate an axle. It may be used for. In the present embodiment, as an example, a case where the motor 11 is mounted on the electric compressor will be described. Electric compressors are used in vehicle air conditioners.

The motor drive device 10 includes a battery B, a smoothing capacitor C, an inverter 20, an encoder 22, and a phase current detection unit 23. The inverter 20 includes an inverter circuit 21 and a control device 31. The inverter circuit 21 includes six switching elements Q1 to Q6. As the switching elements Q1 to Q6, for example, IGBT: Insulated Gate Bipolar Transistor or MOSFET is used. The switching element Q1 constituting the u-phase upper arm and the switching element Q2 constituting the u-phase lower arm are connected in series. The switching element Q3 forming the v-phase upper arm and the switching element Q4 forming the v-phase lower arm are connected in series. The switching element Q5 constituting the w-phase upper arm and the switching element Q6 forming the w-phase lower arm are connected in series. A battery B is connected to each of the switching elements Q1 to Q6 via a smoothing capacitor C.

The switching element Q1 and the switching element Q2 are connected to the u-phase terminal of the motor 11. The switching element Q3 and the switching element Q4 are connected to the v-phase terminal of the motor 11. The switching element Q5 and the switching element Q6 are connected to the w-phase terminal of the motor 11. The inverter circuit 21 having the switching elements Q1 to Q6 constituting the upper and lower arms converts the DC voltage, which is the voltage of the battery B, into an AC voltage and supplies it to the motor 11 in accordance with the switching operation of the switching elements Q1 to Q6. The switching elements Q1 to Q6 perform a switching operation by being controlled by the control device 31.

The phase current detection unit 23 detects the phase currents of at least two phases. In the present embodiment, the phase current detection unit 23 includes a current sensor that detects the u-phase current Iu and a current sensor that detects the w-phase current Iw.

The encoder 22 is an incremental encoder. As the encoder 22, an optical type encoder 22 may be used, or a magnetic type encoder 22 may be used. The encoder 22 outputs the A-phase pulse signal AS, the B-phase pulse signal BS, and the Z-phase pulse signal ZS as the motor 11 rotates as a rotating body. The rotation of the motor 11 is the rotation of the rotor of the motor 11 or the rotation of the rotating shaft that rotates integrally with the rotor.

As shown in FIG. 2, the A-phase pulse signal AS is a signal in which a plurality of pulses are generated during one rotation of the motor 11. The B-phase pulse signal BS is a signal in which a plurality of pulses are generated during one rotation of the motor 11. The A-phase pulse signal AS and the B-phase pulse signal BS have the same number of pulses generated during one rotation of the motor 11. The B-phase pulse signal BS is a signal having a phase difference from the A-phase pulse signal AS. The phases of the A-phase pulse signal AS and the B-phase pulse signal BS are 90 ° out of phase with each other. The Z-phase pulse signal ZS is a signal in which one pulse is generated during one rotation of the motor 11. The A-phase pulse signal AS and the B-phase pulse signal BS are first pulse signals in which a plurality of pulses are generated during one rotation of the motor 11. The Z-phase pulse signal ZS is a second pulse signal in which one pulse is generated while the motor 11 makes one rotation. In the following description, the A-phase pulse signal AS and the B-phase pulse signal BS are collectively referred to as the first pulse signal AS and BS as appropriate.

As shown in FIG. 1, the control device 31 is mainly composed of, for example, a microcomputer. The process executed by the control device 31 may be performed by the CPU executing the process stored in the storage unit, or may be performed by the hardware process by the dedicated electronic circuit. The control device 31 includes a filter unit 41, a counter 45, a signal selection unit 46, a rotation information calculation unit 47, a speed command calculation unit 32, a speed control unit 33, a current vector control unit 34, and a current control unit. 35 and.

The filter unit 41 includes low-pass filters 42, 43, 44 provided corresponding to each phase pulse signal of the encoder 22. The low-pass filters 42, 43, 44 receive an A-phase low-pass filter 42 to which an A-phase pulse signal AS is input, a B-phase low-pass filter 43 to which a B-phase pulse signal BS is input, and a Z-phase pulse signal ZS. Includes a Z-phase lowpass filter 44. The low-pass filters 42, 43, 44 reduce noise contained in each phase pulse signal by reducing components higher than the cutoff frequency of each phase pulse signal. The A-phase low-pass filter 42 reduces noise contained in the A-phase pulse signal AS. The B-phase low-pass filter 43 reduces noise contained in the B-phase pulse signal BS. The Z-phase low-pass filter 44 reduces noise contained in the Z-phase pulse signal ZS.

The cutoff frequency of each of the low-pass filters 42, 43, 44 is set as high as that of the low-pass filters 42, 43, 44 to which a pulse signal having a large number of pulses generated during one rotation of the motor 11 is input. The more pulses generated during one rotation of the motor 11, the higher the frequency of the pulse signal. For example, it is assumed that the resolution of the encoder 22 = the number of pulses of the first pulse signals AS and BS generated during one rotation of the motor 11 is 1000, and the motor 11 is rotating at a speed of 10000 [rpm]. In this case, the frequencies of the first pulse signals AS and BS are 166.7 [kHz] in the case of 1 multiplication that counts only the rising edge of the A-phase pulse signal AS. Further, it is 666.7 [kHz] in the case of quadrupling in which the rising edge and falling edge of each of the A-phase pulse signal AS and the B-phase pulse signal BS are counted. On the other hand, the frequency of the Z-phase pulse signal ZS is 0.1667 [kHz] when only the rising edge of the Z-phase pulse signal ZS is counted. That is, the frequency of the Z-phase pulse signal ZS is 1/1000 of the frequency of the first pulse signals AS and BS in the case of 1 multiplication. Therefore, the cutoff frequency of the A-phase low-pass filter 42 and the B-phase low-pass filter 43 needs to be higher than the cut-off frequency of the Z-phase low-pass filter 44. In other words, the cutoff frequency of the Z-phase low-pass filter 44 is lower than the cut-off frequency of the A-phase low-pass filter 42 and the B-phase low-pass filter 43. Each phase pulse signal that has passed through the filter unit 41 is input to the counter 45. The A-phase low-pass filter 42 and the B-phase low-pass filter 43, which are the low-pass filters 42 and 43 for the first pulse signals AS and BS, are the first low-pass filters. The Z-phase low-pass filter 44 is a second low-pass filter.

The counter 45 counts the edge of the pulse for each of the first pulse signal AS, BS and the Z-phase pulse signal ZS. The counter 45 obtains the count number of the first pulse signals AS and BS in any of the two multiplications for counting the rising edge and the falling edge of the A-phase pulse signal AS, and the above-mentioned one multiplication and four multiplications. The counter 45 obtains the count number of the Z-phase pulse signal ZS by counting only the rising edge of the Z-phase pulse signal ZS or the rising edge and the falling edge of the Z-phase pulse signal ZS.

The signal selection unit 46 selects the first pulse signals AS and BS and the pulse signal used for calculating the rotation speed ω [rpm] of the motor 11 among the Z-phase pulse signals ZS. The process of selecting the pulse signal by the signal selection unit 46 will be described later.

The rotation information calculation unit 47 as a calculation unit calculates the rotation speed ω and the rotation position θ of the motor 11. The rotation information calculation unit 47 calculates the rotation speed ω of the motor 11 from the count number of the pulse signals selected by the signal selection unit 46. When the first pulse signals AS and BS are selected by the signal selection unit 46, the rotation information calculation unit 47 rotates the motor 11 from the count number of the first pulse signals AS and BS during a predetermined predetermined time. Calculate the speed ω. When the Z-phase pulse signal ZS is selected by the signal selection unit 46, the rotation information calculation unit 47 calculates the rotation speed ω of the motor 11 from the count number of the Z-phase pulse signal ZS during a predetermined time. To do. Since the cutoff frequency of the Z-phase low-pass filter 44 is lower than the cut-off frequency of the A-phase low-pass filter 42 and the B-phase low-pass filter 43, the Z-phase pulse signal ZS whose noise is reduced by the Z-phase low-pass filter 44 is the first pulse. Noise is reduced compared to the signals AS and BS. Therefore, when the rotation speed ω is calculated using the Z-phase pulse signal ZS, the error of the rotation speed ω due to the influence of noise is reduced as compared with the case where the rotation speed ω is calculated using the first pulse signals AS and BS. can do. On the other hand, the number of pulses generated when the motor 11 makes one rotation is smaller in the Z-phase pulse signal ZS than in the first pulse signals AS and BS. Therefore, when the rotation speed ω of the motor 11 is calculated using the Z-phase pulse signal ZS, the rotation speed ω changes as compared with the case where the rotation speed ω is calculated using the first pulse signals AS and BS. The time required to detect the rotation speed ω becomes longer. Further, when the rotation speed ω changes, the rotation speed ω cannot be calculated accurately. That is, when the rotation speed ω is calculated using the Z-phase pulse signal ZS, it is difficult to correspond to the change in the rotation speed ω.

The rotation information calculation unit 47 calculates the rotation position θ of the motor 11 from the counts of the first pulse signals AS and BS. The rotation position θ of the motor 11 is, for example, a relative angle when the detection position of the Z-phase pulse signal ZS is used as a reference.

The speed command calculation unit 32 calculates the speed command value ω * in a predetermined control cycle according to the difference between the target value and the current value. The speed command calculation unit 32 calculates the speed command value ω * in response to a request from the host control device, for example. The upper control device is, for example, a control device for air conditioning that controls the temperature inside the vehicle interior. Assuming that the target value is the target temperature and the current value is the current temperature, if the difference between the target temperature and the current temperature is large, the amount of change in the speed command value ω * calculated by the speed command calculation unit 32 for each control cycle is also large. When the target temperature is changed or when the electric compressor is started, the difference between the target temperature and the current temperature is large. With the passage of time, the difference between the target temperature and the current temperature becomes smaller, and the difference between the target temperature and the current temperature falls within the allowable range. When the difference between the target temperature and the current temperature falls within the permissible range, the amount of change in the speed command value ω * becomes constant or substantially constant. The state in which the amount of change in the speed command value ω * is constant or substantially constant is the state in which the speed command value ω * is steady.

The speed control unit 33 calculates the speed difference between the speed command value ω * calculated by the speed command calculation unit 32 and the rotation speed ω calculated by the rotation information calculation unit 47. The speed control unit 33 calculates the q-axis current command value Iq * from the speed difference.

The current vector control unit 34 calculates the d-axis current command value Id * by using the rotation speed ω calculated by the rotation information calculation unit 47 and the q-axis current command value Iq * calculated by the speed control unit 33. ..

The current control unit 35 obtains a voltage command value for each three phases from the d-axis current command value Id *, the q-axis current command value Iq *, the rotation position θ, the u-phase current Iu, and the w-phase current Iw. The inverter 20 performs pulse width modulation with respect to the voltage command value from the current control unit 35. As a result, the motor 11 rotates.

Next, the process of selecting the pulse signal by the signal selection unit 46 will be described in detail.
As shown in FIG. 3, in step S1, the signal selection unit 46 determines whether or not the first condition is satisfied. The first condition is that the amount of change in the speed command value ω * is equal to or less than a predetermined first threshold value. The amount of change in the speed command value ω * is the difference between the previous speed command value ω * and the current speed command value ω *. If the calculated difference is equal to or less than the first threshold value, the first condition is satisfied. to decide.

The first threshold value is a value appropriately determined by the user or the designer, and when the rotation speed ω is calculated using the Z-phase pulse signal ZS, it becomes difficult to respond to the change in the rotation speed ω, but this is acceptable in terms of product use. It is a possible value.

The signal selection unit 46 performs the process of step S2 when the determination result in step S1 is affirmative, that is, when the amount of change in the speed command value ω * is equal to or less than a predetermined first threshold value. The signal selection unit 46 performs the process of step S3 when the determination result in step S1 is negative, that is, when the amount of change in the speed command value ω * is larger than the first threshold value.

In step S2, the signal selection unit 46 determines whether or not the second condition is satisfied. The second condition is that the amount of change in the first pulse signals AS and BS is equal to or less than a predetermined second threshold value. The second threshold value is a value appropriately determined by the user or the designer, and when the rotation speed ω is calculated using the Z-phase pulse signal ZS, it becomes difficult to respond to the change in the rotation speed ω. This is an acceptable value.

In the present embodiment, when the count numbers of the first pulse signals AS and BS in the previous control cycle are changed by 10% or more, and the count numbers of the first pulse signals AS and BS this time are changed, the first It is determined that the amount of change in the pulse signals AS and BS exceeds a predetermined second threshold value. On the other hand, when the change in the count number of the first pulse signals AS and BS this time is less than 10% with respect to the count number of the first pulse signals AS and BS in the previous control cycle, the signal selection unit 46 Determines that the amount of change in the first pulse signals AS and BS is equal to or less than a predetermined second threshold value.

In the present embodiment, the calculation method of the change amount of the first pulse signals AS and BS is the count number of the first pulse signals AS and BS in the previous control cycle and the first pulse signal AS in the current control cycle. Although it is a difference from the count number of BS, it may be determined from the pulse interval of the first pulse signals AS and BS instead of the count number.

The signal selection unit 46 is, for example, when the pulse intervals of the first pulse signals AS and BS change by 10% or more with respect to the pulse intervals of the first pulse signals AS and BS in the previous control cycle, and the pulse intervals of the first pulse signals AS and BS change. It may be determined that the amount of change in the pulse signals AS and BS exceeds a predetermined second threshold value. On the other hand, when the change in the pulse intervals of the first pulse signals AS and BS is less than 10% with respect to the pulse intervals of the first pulse signals AS and BS in the previous control cycle, the signal selection unit 46 performs. It may be determined that the amount of change in the first pulse signals AS and BS is equal to or less than a predetermined second threshold value.

The signal selection unit 46 performs the process of step S4 when the determination result in step S2 is affirmative, that is, when the amount of change in the first pulse signals AS and BS is equal to or less than the second threshold value. The signal selection unit 46 performs the process of step S3 when the determination result in step S2 is negative, that is, when the amount of change in the first pulse signals AS and BS exceeds the second threshold value.

As described above, in the present embodiment, when both the first condition and the second condition are satisfied, the process of step S4 is performed, and when at least one of the first condition and the second condition is not satisfied. Is the process of step S3.

In step S3, the signal selection unit 46 selects the first pulse signals AS and BS. When the first condition is not satisfied, the amount of change in the speed command value ω * is larger than the predetermined first threshold value, and the speed difference becomes large. In this case, it is preferable to quickly make the rotation speed ω follow the speed command value ω * to reduce the speed difference. That is, it is preferable to increase the control response of the inverter 20. If the rotation speed ω is calculated using the Z-phase pulse signal ZS, the inverter 20 cannot be controlled in response to a change in the rotation speed ω quickly. On the other hand, when the rotation speed ω is calculated using the first pulse signals AS and BS, the inverter 20 can be controlled in response to a change in the rotation speed ω quickly. Therefore, when the first condition is not satisfied, the first pulse signals AS and BS are selected in order to improve the control responsiveness of the inverter 20.

When the second condition is not satisfied, it can be said that the rotational speed ω has changed significantly due to the occurrence of load fluctuations, etc., even though the amount of change in the speed command value ω * is equal to or less than the predetermined first threshold value. .. In this case, the first pulse signals AS and BS are selected in order to improve the control response of the inverter 20.

In step S4, the signal selection unit 46 selects the Z-phase pulse signal ZS. When both the first condition and the second condition are satisfied, the inverter 20 is not required to have high control response, so the Z-phase pulse signal ZS is selected.

In step S5, the signal selection unit 46 outputs the pulse signal selected in step S3 or step S4 to the rotation information calculation unit 47. As a result, the rotation information calculation unit 47 calculates the rotation speed ω using the pulse signal selected by the signal selection unit 46. The processes of steps S1 to S5 are repeated in a predetermined control cycle.

In the present embodiment, the filter unit 41, the counter 45, the signal selection unit 46, and the rotation information calculation unit 47 function as the rotation speed detection device 40 that detects the rotation speed ω from the output of the encoder 22.

The operation of this embodiment will be described.
When the first condition is satisfied, the amount of change in the speed command value ω * is equal to or less than the first threshold value, and it can be said that the change in the rotation speed ω of the motor 11 due to the change in the speed command value ω * is unlikely to occur. When the first condition is satisfied, the rotation speed ω of the motor 11 is unlikely to change, so that the rotation speed ω can be calculated using the Z-phase pulse signal ZS. When the second condition is satisfied, it can be said that the amount of change in the first pulse signals AS and BS is small, and the rotation speed ω of the motor 11 does not change significantly due to external factors such as load fluctuation. When the second condition is satisfied, the rotation speed ω of the motor 11 is unlikely to change, so that the rotation speed ω can be calculated using the Z-phase pulse signal ZS.

The effect of this embodiment will be described.
(1) The signal selection unit 46 selects the Z-phase pulse signal ZS when both the first condition and the second condition are satisfied, and the first pulse signals AS and BS when the Z-phase pulse signal ZS is not selected. Select. The rotation information calculation unit 47 calculates the rotation speed ω from the pulse signal selected by the signal selection unit 46. When it is less necessary to calculate the rotation speed ω using the first pulse signals AS and BS, the rotation speed ω is calculated from the Z-phase pulse signal ZS. Therefore, when it is necessary to cope with the change of the rotation speed ω while improving the noise resistance of the rotation speed detection device 40 in the situation where the first condition and the second condition are satisfied, the first pulse signals AS and BS Can be used to respond to changes in the rotational speed ω.

(2) The signal selection unit 46 selects the Z-phase pulse signal ZS when both the first condition and the second condition are satisfied. When the Z-phase pulse signal ZS is selected when either the first condition or the second condition is satisfied, the first condition is satisfied but the second condition is not satisfied, or the second condition is The Z-phase pulse signal ZS may be selected even when the first condition is not satisfied although it is satisfied. In this case, the Z-phase pulse signal ZS may be selected even though the rotation speed ω is likely to change. On the other hand, by selecting the Z-phase pulse signal ZS when both the first condition and the second condition are satisfied, the Z-phase pulse signal ZS can be selected in a state where the rotation speed ω is unlikely to change. ..

The embodiment can be modified and implemented as follows. The embodiments and the following modifications can be implemented in combination with each other to the extent that they are technically consistent.
○ The signal selection unit 46 may select the Z-phase pulse signal ZS when either the first condition or the second condition is satisfied. In this case, the signal selection unit 46 determines whether both the first condition and the second condition are satisfied, and selects the Z-phase pulse signal ZS when either the first condition or the second condition is satisfied. It may be a thing. Further, the signal selection unit 46 may determine only whether the first condition is satisfied, or may determine only whether the second condition is satisfied.

By selecting the Z-phase pulse signal ZS when the first condition is satisfied, the noise resistance of the rotation speed detection device 40 can be improved in the situation where the first condition is satisfied. If the amount of change in the speed command value ω * is not less than or equal to the predetermined first threshold value, the rotation speed ω is calculated by using the first pulse signals AS and BS to change the rotation speed ω. Corresponding to, the rotation speed ω can be calculated accurately and quickly. By selecting the Z-phase pulse signal ZS when the second condition is satisfied, the noise resistance of the rotation speed detection device 40 can be improved in the situation where the second condition is satisfied. Further, when the rotation speed ω changes due to load fluctuation or the like, the rotation speed ω is calculated by using the first pulse signals AS and BS, so that the rotation speed ω is accurately adjusted in response to the change in the rotation speed ω. It is good and can be calculated quickly.

○ The rotation speed detection device 40 may be used in addition to the inverter 20. For example, it may be used in a drive control device that controls a DC motor. The drive control device includes, for example, two switching elements connected in series with each other and a control unit for controlling the switching elements. The speed of the DC motor is controlled according to the duty ratio of the two switching elements. The control unit switches the switching element on and off according to the rotation speed ω detected by the rotation speed detection device 40.

○ The rotation information calculation unit 47 may calculate the rotation speed ω from the pulse interval of the pulse signal.
○ The rotation speed detection device 40 may detect the rotation speed of a rotating body other than a motor such as a tire, a wheel, or a gear.

11 ... Motor as a rotating body, 22 ... Encoder, 40 ... Rotation speed detector, 42 ... A-phase low-pass filter as the first low-pass filter, 43 ... B-phase low-pass filter as the first low-pass filter, 44 ... Second low-pass filter Z-phase low-pass filter as a filter, 46 ... signal selection unit, 47 ... rotation information calculation unit as a calculation unit.

Claims (2)

Rotational speed of the rotating body from the output of an encoder that outputs a first pulse signal in which a plurality of pulses are generated during one rotation of the rotating body and a second pulse signal in which one pulse is generated during one rotation of the rotating body. It is a rotation speed detection device that detects
A first low-pass filter that reduces noise contained in the first pulse signal,
A second low-pass filter having a lower cutoff frequency than the first low-pass filter and reducing noise contained in the second pulse signal.
The first condition is that the amount of change in the speed command value is equal to or less than the predetermined first threshold value, and the second condition is that the amount of change in the first pulse signal is equal to or less than the predetermined second threshold value. Then, the second pulse signal is selected when at least one of the first condition and the second condition is satisfied, and the first pulse signal is selected when the second pulse signal is not selected. Signal selection section and
When the first pulse signal is selected by the signal selection unit, the rotation speed is calculated from the first pulse signal, and when the second pulse signal is selected by the signal selection unit, the rotation speed is calculated. A rotation speed detection device including a calculation unit that calculates the rotation speed from a second pulse signal. The rotation speed detection device according to claim 1, wherein the signal selection unit selects the second pulse signal when both the first condition and the second condition are satisfied.