JP7572002B2 - Rotation angle detection method, rotation angle detection program, and rotation angle detection device - Google Patents

Description

The present invention relates to a rotation angle detection method, a rotation angle detection program, and a rotation angle detection device.

There has been a conventional device for acquiring information about the rotation of an electric motor equipped with a commutator, the device including a rotation angle calculation unit that calculates the rotation angle of the electric motor based on the terminal voltage of the electric motor and the current flowing through the electric motor, a first signal generation unit that generates a first signal based on a ripple component contained in the current flowing through the electric motor, a second signal generation unit that generates a pseudo ripple signal as a second signal indicating that the electric motor has rotated a predetermined angle based on the first signal and the rotation angle, and a rotation information calculation unit that calculates information about the rotation of the electric motor based on the output of the second signal generation unit (see, for example, Patent Document 1).

International Publication No. 2018-123453

However, in conventional devices, during the period when the motor rotates by inertia after the power supply to the motor is stopped, the ripple component cannot be detected as the current decays, and the angle error tends to become large.

The objective of the present invention is to provide a rotation angle detection method, a rotation angle detection program, and a rotation angle detection device that can determine the rotation angle of an electric motor with high accuracy when the motor is rotating by inertia.

A rotation angle detection method according to an embodiment of the present invention, comprising a current measurement process for measuring a current flowing through an electric motor, and a rotation angle detection process for determining a rotation angle of the electric motor based on a current value measured by the current measurement process, in which the rotation angle detection process determines a time constant of the attenuation of the electric motor current based on the current value measured by the current measurement process from a predetermined time after the polarity of the current value of the reverse current measured by the current measurement process while the electric motor is rotating by inertia and the absolute value of the current value reaches a peak value until the current value measured by the current measurement process becomes zero, and determines the rotation angle during the inertia rotation based on the determined time constant.

It is possible to provide a rotation angle detection method, a rotation angle detection program, and a rotation angle detection device that can determine the rotation angle of an electric motor with high accuracy when the electric motor is rotating by inertia.

1 is a diagram illustrating a rotation angle detection device 100 according to an embodiment. 2 is a diagram showing a connection state between a DC motor 10 and a drive circuit 20. FIG. 1 is a diagram showing changes over time in current i and angular velocity ω before and after the DC motor 10 is turned off. 2 is a diagram showing the angular velocity ω and current i of the DC motor 10 during the period when the DC motor 10 rotates by inertia. FIG. FIG. 11 is a flowchart showing a process performed by a rotation angle detection unit 133B to detect a rotation angle.

The following describes an embodiment that applies the rotation angle detection method, rotation angle detection program, and rotation angle detection device of the present invention.

<Embodiment>
1 is a diagram showing a rotation angle detection device 100 according to an embodiment. The electric motor whose rotation angle is detected by the rotation angle detection device 100 is not limited to an electric motor that drives a power window of a vehicle, but here, as an example, a form in which the rotation angle detection device 100 according to the embodiment is used as a rotation angle detection device for a power window electric motor will be described.

In addition to the rotation angle detection device 100, FIG. 1 shows a DC (Direct Current) motor 10, a resistor 15, a drive circuit 20, a DC power supply 30, a power window 50, and a drive mechanism 51.

The DC motor 10 has terminals 11 and 12, and is driven by a drive circuit 20 connected to the terminals 11 and 12. The resistor 15 is connected to the terminal 12 of the DC motor 10, and is used to detect the current of the DC motor 10. The drive circuit 20 drives the DC motor 10 with DC power supplied from a DC power source 30. The drive circuit 20 drives the DC motor 10 by being controlled by a drive control unit (not shown), but the drive control unit is omitted here.

The power window 50 is a power window for a vehicle, and is opened and closed by a driving force transmitted from the rotor of the DC motor 10 via a driving mechanism 51. The driving mechanism 51 is provided inside the door panel of the vehicle, and is a mechanical mechanism such as a regulator that converts the rotational force of the rotor of the DC motor 10 into a driving force for the power window 50 in the up and down directions.

The rotation angle detection device 100 includes a filter circuit 110, an IC (Integrated Circuit) chip 120, and a microcomputer 130.

The filter circuit 110 has LPFs (Low Pass Filters) 111 and 112. The voltage between the terminals 11 and 12 of the DC motor 10 is input to the LPF 111, which removes high-frequency noise and other components contained in the voltage before outputting the voltage to the microcomputer 130. The voltage between both ends of the resistor 15 is input to the LPF 112 as a voltage representing the current of the DC motor 10, which removes high-frequency noise and other components contained in the voltage before outputting the voltage to the microcomputer 130.

The IC chip 120 has a BPF (Band Pass Filter) 121 and a ripple detection unit 122. The voltage between both ends of the resistor 15 is input to the BPF 121 as a voltage representing the current of the DC motor 10, and high-frequency noise and low-frequency noise contained in the voltage are removed and the voltage is output to the ripple detection unit 122. The ripple detection unit 122 detects ripples contained in the data representing the current input from the BPF 121, converts them into pulses, and outputs them to the microcomputer 130.

The microcomputer 130 has A/D (Analog to Digital) converters 131 and 132, and a processing unit 133. The microcomputer 130 is realized by a computer including a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), an input/output interface, and an internal bus. The A/D converters 131 and 132 and the processing unit 133 are functional blocks that represent the functions of the program executed by the microcomputer 130.

The A/D converter 131 converts the output of the LPF 111 into a digital signal and outputs it to the processing unit 133. Since the output of the LPF 111 represents the voltage of the DC motor 10, the output of the A/D converter 131 is digital data representing the voltage value of the DC motor 10.

The A/D converter 132 converts the output of the LPF 112 into a digital signal and outputs it to the processing unit 133. Since the output of the LPF 112 is a signal representing the current of the DC motor 10, the output of the A/D converter 132 is digital data representing the current value of the DC motor 10.

The processing unit 133 has a current measuring unit 133A, a rotation angle detecting unit 133B, and a memory 133C. The current measuring unit 133A and the rotation angle detecting unit 133B are functional blocks that represent the functions of the program executed by the microcomputer 130. The memory 133C is a functional block that represents the memory of the microcomputer 130.

The current measurement unit 133A performs a current measurement process to measure the current flowing through the DC motor 10 based on the output of the A/D converter 132. The current measurement unit 133A outputs data representing the measured current value to the rotation angle detection unit 133B.

The rotation angle detection unit 133B performs a rotation angle detection process to determine the rotation angle during the inertial rotation of the DC motor 10 based on the output (voltage value) of the A/D converter 131, the output (current value) of the current measurement unit 133A, and the pulse input from the ripple detection unit 122. The inertial rotation of the DC motor 10 refers to a state in which a voltage is applied from the drive circuit 20 to the DC motor 10 to drive the DC motor 10 (DC motor 10 is on), and then the application of voltage is cut off (DC motor 10 is turned off) and the rotor of the DC motor 10 rotates by inertia. The DC motor 10 rotates by inertia when a drive control unit (not shown) controls the drive circuit 20 and the voltage applied from the drive circuit 20 to the DC motor 10 is cut off.

The rotation angle detection unit 133B determines the rotation angle of the rotor of the DC motor 10 during the inertial rotation period of the DC motor 10. The rotation angle of the rotor of the DC motor 10 is synonymous with the rotation angle of the DC motor 10. A specific method for determining the rotation angle will be described later with reference to Figures 2 to 5.

The memory 133C stores programs and data used by the current measurement unit 133A and the rotation angle detection unit 133B when executing processing, the output (voltage value) of the A/D converter 131, the output (current value) of the current measurement unit 133A, and pulse data input from the ripple detection unit 122, etc.

Next, the connection state between the DC motor 10 and the drive circuit 20 will be described with reference to FIG. 2. FIG. 2 is a diagram showing the connection state between the DC motor 10 and the drive circuit 20. The drive circuit 20 has two switches 21 and 22. FIG. 2(A) shows the connection state of the drive circuit 20 that turns on the DC motor 10.

To turn on the DC motor 10, switches 21 and 22 are switched to connect the DC motor 10 to the DC power supply 30. FIG. 2(B) also shows the connection state of the drive circuit 20 that turns off the DC motor 10. To turn off the DC motor 10, switches 21 and 22 are switched to disconnect the DC motor 10 from the DC power supply 30. As an example, when the DC motor 10 is turned off, both terminals of the DC motor 10 are connected to the negative terminal of the DC power supply 30. This is a state in which the DC motor 10 is shorted.

Next, the circuit equation that holds for the DC motor 10 according to the theory of DC motors will be explained. For the DC motor 10, the following equations (1) and (2) hold for the DC motor 10 according to the theory of DC motors. L is the inductance of the DC motor 10, R is the resistance of the DC motor 10, J is the inertia of the rotor of the DC motor 10, Ke is the back electromotive force constant of the DC motor 10, Kt is the torque constant of the DC motor 10, Kv is the viscous friction coefficient of the DC motor 10, F is the load of the DC motor 10, u is the drive voltage applied to the DC motor 10 from the drive circuit 20, and i is the current flowing through the DC motor 10 measured by the current measurement unit 133A in FIG. 1. The current i is the current value obtained by the current measurement unit 133A by measuring the output of the A/D converter 132, and when arranged in chronological order, it represents the current waveform.

When the DC motor 10 is turned off, the terminals 11 and 12 of the DC motor 10 are shorted as shown in FIG. 2(B), so that the drive voltage u(t) of the DC motor 10 becomes 0, and the DC motor 10 starts to rotate by inertia. In addition, if the change in current i (di/dt) is zero when the energy discharge of the inductance L is completed, then from equation (1), a proportional relationship is established between the current i and the angular velocity ω of the DC motor 10, as expressed by equation (3). The angular velocity ω is the angular velocity of the rotor of the DC motor 10.

By substituting equation (3) into equation (2) and solving the differential equation assuming that the load F is zero when terminals 11 and 12 of DC motor 10 are shorted, the angular velocity can be expressed by the following equation (4). Here, ω0 is the angular velocity when DC motor 10 starts to rotate by inertia, and τ is the time constant of the decay of angular velocity ω of DC motor 10.

The time constant τ of the decay of the angular velocity ω of the DC motor 10 can be expressed by the following equation (5).

As can be seen from equation (5), the time constant τ is affected by fluctuations in many parameters. Meanwhile, as can be seen from equations (3) and (4), the angular velocity ω of the inertial rotation of the DC motor 10 decays exponentially, and the current i also decays exponentially. In other words, the time constant of decay of the current i of the DC motor 10 is equal to the time constant τ of decay of the angular velocity of the DC motor 10.

Figure 3 shows the time changes in current i and angular velocity ω before and after the DC motor 10 is turned off. Figure 3 (A) shows the time changes in current i and angular velocity ω before and after the DC motor 10 is turned off. When the DC motor 10 is turned off, the DC motor 10 rotates by inertia, the angular velocity ω decays exponentially, and after a certain period of time, the current i also decays exponentially. The reason why the current i lags behind the angular velocity ω is because it flows as a current due to back electromotive force. The current due to back electromotive force is a reverse current that flows in the opposite direction to the current that flows when the DC motor 10 is on.

Here, when the waveform of the current i in FIG. 3(A) is multiplied by -K and superimposed on the angular velocity ω, as shown in FIG. 3(B), the current i is superimposed on the angular velocity ω during the coasting rotation period. This is because the time constant of the decay of the current i of the DC motor 10 is equal to the time constant τ of the decay of the angular velocity of the DC motor 10. For this reason, the rotation angle detection device 100 uses the time constant τ of the decay of the current i of the DC motor 10 instead of the time constant τ of the decay of the angular velocity of the DC motor 10 to obtain the angular velocity ω from the current i, and detects the rotation angle during the coasting rotation period of the DC motor 10 based on the obtained angular velocity ω. In other words, the rotation angle detection device 100 detects the rotation angle during the coasting rotation period of the DC motor 10 by estimating and using the time constant τ of the decay of the current i obtained based on the current i during the coasting rotation period of the DC motor 10 as the time constant τ of the decay of the angular velocity during the coasting rotation period of the DC motor 10.

Next, a method for detecting angular velocity ω based on current i of DC motor 10 will be described with reference to Figure 4. Figure 4 is a diagram showing angular velocity ω and current i of DC motor 10 during the period when DC motor 10 rotates by inertia. Figure 4 shows an enlarged view of the period of inertia rotation in Figure 3(B). In other words, current i shown in Figure 4 is represented by a waveform that is -K times the waveform of current i in Figure 3(A).

Below, we will explain a method for calculating the current integral value, etc., using the waveform of current i multiplied by -K in order to overlap with the waveform of angular velocity ω as shown in Figure 4, but in actual calculations, it is not necessary to multiply current i by -K. For this reason, when explaining the calculation method, we will use current i as it is.

In FIG. 4, time t0 is the time when the DC motor 10 is turned off (power is turned off), and is the time when the DC motor 10 starts to rotate by inertia. The angular velocity ω0 at time t0 is the angular velocity of the DC motor 10 immediately before the power is turned off. The angular velocity ω0 can be calculated based on the pulse input from the ripple detection unit 122. When the power of the DC motor 10 is turned off, the drive circuit 20 is in the connection state shown in FIG. 2 (B).

Here, we will explain the period from time t0 when the DC motor 10 starts to rotate by inertia to time tend when the current i of the DC motor 10 becomes zero. When the current i becomes zero, it is considered that the rotation of the DC motor 10 stops, so the angular velocity ωend of the DC motor 10 at time tend is considered to be zero.

Time t1 is the time when the polarity of current i reverses. Time t1 is the time when the value of current -Ki multiplied by -K shown in Figure 4 reverses from negative to positive (reverses polarity), and is the time when the value of actual current i reverses from positive to negative (reverses polarity). Therefore, the current value i1 at time t1 is zero.

When the DC motor 10 is turned off, the back electromotive force causes a current to flow in the opposite direction to when the DC motor 10 is on. Time t1 is the time when the polarity of the current i is reversed due to the reverse current caused by the back electromotive force. In addition, the angular velocity ω1 at time t1 is treated as being equal to the angular velocity ω0. This is because, from when the DC motor 10 is turned off until time t1 when the polarity of the current i is reversed due to the back electromotive force, the rotor of the DC motor 10 is hardly braked due to the reverse current i generated by the back electromotive force.

Time t2 is the time when current -Ki reaches its maximum value (current i reaches its peak value). In other words, time t2 is the time when the absolute value of the actual current i reaches its peak value. In other words, time t2 is the time when the actual current i reaches its minimum value. The current value i2 at time t2 is the minimum value of the actual current i and the peak absolute value. Since the current i fluctuates, when the current i measured by the current measurement unit 133A falls within a predetermined range, the rotation angle detection unit 133B determines that the absolute value of the current i has reached its peak value. The angular velocity ω2 at time t2 is attenuated more than the angular velocity ω1 at time t1. This is because braking is applied due to the current i in the opposite direction.

Time t3 is a time point after a predetermined time ΔT has elapsed from time t2 (after the predetermined time has elapsed). The predetermined time ΔT is the time (period) that is considered to be required from when the current -Ki reaches its maximum value until the fluctuation range of the value of the current -Ki settles to a certain degree. In terms of the actual current i, the predetermined time ΔT is the time (period) that is considered to be required from when the absolute value of the current i reaches its peak value until the fluctuation range of the value of the current i settles to a certain degree. As an example, the predetermined time ΔT is approximately 1/10 of the time required from time t2 to the time tend at which the current i becomes zero. Data representing the predetermined time ΔT may be stored in advance in memory 133C.

As mentioned above, after a certain period of time has passed since the start of coasting, the current i decays in the same exponential curve as the angular velocity ω. Therefore, from equation (4), the current i from time t3 onwards can be expressed by the following equation (6) using the current value i3 at time t3.

In addition, a point between time t3 in FIG. 4 and time tend at which current i becomes zero is designated as t4. The current integral of current i from time t3 to time t4 is designated as Si3, and the current integral of current i from time t4 to time tend is designated as Si4.

The rotation angle detection unit 133B calculates a current integral value Si3+Si4 of the current i from time t3 through time t4 to time tend, and a current integral value Si4 of the current i from time t4 to time tend. The current integral value Si3+Si4 is an example of a first current integral value, and the current integral value Si4 is an example of a second current integral value.

The current integral value Si3+Si4 and the current integral value Si4 can be calculated using the following equations (7) and (8), respectively.

The integration process of current i realized by equations (7) and (8) has a filter effect equivalent to a filter process, and therefore has the effect of removing the ripple component contained in current i.

Time t4 can be expressed by the following equation (9). Kr in equation (9) is an adjustment coefficient that is less than 1 (Kr<1).

Time t4 may be any time between time t3 and time tend, but for the convenience of calculations using current integrals Si3 and Si4 described below, it is preferable that there is a certain period of time until time tend to prevent current integral value Si4 from becoming too small, and that current integral value Si3 and current integral value Si4 are set so that they are not equal.

The time constant τ of the decay of the current i of the DC motor 10 can be calculated from equations (7) and (8) as shown in the following equation (10). The time constant τ of the decay of the current i of the DC motor 10 is equal to the time constant of the decay of the angular velocity of the DC motor 10, so it can be calculated instead of the time constant of the decay of the angular velocity of the DC motor 10.

The natural logarithm in equation (10) includes the division process (Si3+Si4)/Si4, which has the effect of reducing measurement errors of the current of the A/D converter 132, etc., that originate from components included in the circuits such as resistor 15, LPF 112, and A/D converter 132.

In addition, the time constant τ of the decay of the current i of the DC motor 10 may be calculated directly from equation (7) as shown in the following equation (11) instead of equation (10).

Calculating the time constant τ using equation (11) requires fewer calculations and is simpler than calculating the time constant τ using equation (10). However, because it uses current i3, it is more susceptible to the effects of ripple components and measurement errors than the time constant τ calculated using equation (10). Therefore, whether to use equation (10) or equation (11) can be determined based on the application of the rotation angle detection device 100, etc.

After the power supply to the DC motor 10 is turned off at time t0, the time until the contact switching of the switches 21 and 22 of the drive circuit 20 is completed is short, but if we assume that the DC motor 10 rotates at the same speed as when it was on, as described above, until the current i reverses at time t1, the rotation angle of the DC motor 10 can be calculated as follows:

Here, the period from time t0, when the power is turned off, to time tend, is divided into periods (1) and (2) for calculation. Period (1) is the period from time t0 to time t1. Period (2) is the period from time t1 to time tend.

During period (1), the rotor of the DC motor 10 is hardly braked due to the current i generated by the back electromotive force. Therefore, the average angular velocity ω of the DC motor 10 during period (1) is equal to the angular velocity ω0 immediately before the power is turned off, and the DC motor 10 can be considered to be rotating at a constant speed. The angular velocity ω0 can be calculated based on the pulse input from the ripple detection unit 122 immediately before the power is turned off. The rotation angle θ1 at which the DC motor 10 rotates during period (1) can be calculated using the following equation (12).

In addition, during period (2), the angular velocity of DC motor 10 decays, but the angular velocity ω1 at time t1, which is the start point of period (2), can be considered to be equal to the angular velocity ω0 immediately before time t1. Therefore, the rotation angle θ2 at which DC motor 10 rotates during period (2) can be calculated from equation (4) using the following equation (13).

From the above, the rotation angle θ of the DC motor 10 during the period from the time t0 when the power supply to the DC motor 10 is turned off to the time tend when the current i becomes zero can be calculated by the following equation (14) as the sum of the rotation angle θ1 during period (1) and the rotation angle θ2 during period (2).

In this way, the rotation angle detection device 100 can obtain the rotation angle θ during the period when the DC motor 10 rotates by inertia. Here, the process of detecting the rotation angle by the rotation angle detection unit 133B will be described with reference to FIG. 5. FIG. 5 is a diagram showing a flowchart showing the process of detecting the rotation angle by the rotation angle detection unit 133B. The process shown in FIG. 5 is realized by the processing unit 133 executing the rotation angle detection program of the embodiment, and is realized by the rotation angle detection method of the embodiment. More specifically, as a premise, the current measurement unit 133A executes a current measurement process to measure the current i of the DC motor 10, and the rotation angle detection unit 133B executes the rotation angle detection process shown below.

When the process starts, the rotation angle detection unit 133B determines whether the power supply to the DC motor 10 has been turned off (step S1). As a specific example, the circuit angle detection unit 133B detects the power supply to the DC motor 10 being turned off by detecting a power-off control command output by a drive control unit (not shown) to the drive circuit 20, and sets this point in time as t0. Note that, as an example, the rotation angle detection unit 133B may determine that the power supply to the DC motor 10 has been turned off when the voltage value of the DC motor 10 input from the A/D converter 131 becomes zero (or is equal to or less than a predetermined value close to zero).

The rotation angle detection unit 133B calculates the angular velocity ω0 immediately before the power supply to the DC motor 10 is turned off based on the pulse converted by the ripple detection unit 122 immediately before the power supply to the DC motor 10 is turned off (step S2).

The rotation angle detection unit 133B records the current i measured by the current measurement unit 133A and the time (time) in the memory 133C from time t0 until the current i becomes zero (time tend) (step S3). As a specific example, the rotation angle detection unit 133B sequentially records the elapsed time from time t0 and the current value at that time in the memory 133C as a pair for each operation of a periodic task (a task that is started at a fixed interval using a timer or the like of the microcomputer 130). In step S3, the time t1 at which the polarity of the current i is reversed and the time t2 at which the current i reaches its peak are also recorded. As a specific example, the rotation angle detection unit 133B sequentially checks the paired data of the elapsed time and the current value recorded in the memory 133C from time t0, and records the elapsed time at which the current value becomes zero or the polarity of the current value is reversed as t1 in the memory 133C. In addition, the rotation angle detection unit 133B records the elapsed time corresponding to the smallest current value among all the current values of the data as t2 in the memory 133C.

The rotation angle detection unit 133B calculates time t4 using equation (9), and obtains the current integral value Si3+Si4 and the current integral value Si4 based on the following equations (7) and (8), respectively (step S4). Note that time t3 is obtained by adding a predetermined time ΔT to time t2. The rotation angle detection unit 133B stores time t3, time t4, the current integral value Si3+Si4, and the current integral value Si4 in the memory 133C.

The rotation angle detection unit 133B determines the time constant τ of the decay of the current i of the DC motor 10 based on the formula (10) (step S5). The rotation angle detection unit 133B may also determine the number of time points τ using the formula (11). The rotation angle detection unit 133B may retrieve the current value at the time point t3 as the current i3 used in the formula (11) from the memory 133C.

The rotation angle detection unit 133B calculates the rotation angle θ of the DC motor 10 in the period from the time t0 when the power supply to the DC motor 10 is turned off to the time tend when the current i becomes zero based on the formula (14) (step S6). This completes the series of processes (END).

As described above, the rotation angle θ during the period when the DC motor 10 rotates by inertia can be calculated very easily. Furthermore, since the time constant τ can be calculated in real time during the period of inertia rotation using equation (10), the problems of parameter error and angle accumulation error in conventional methods can be eliminated, and the rotation angle can be detected with extremely high accuracy. Furthermore, for example, the accuracy of the rotation angle in a system including a power window 50 can be greatly improved, and the ability to deal with individual differences, environmental changes, and aging can be greatly improved.

Therefore, it is possible to provide a rotation angle detection method, a rotation angle detection program, and a rotation angle detection device 100 that can determine the rotation angle of the DC motor 10 with high accuracy when the DC motor 10 is rotating by inertia.

The rotation angle detection device 100 determines the time constant τ of the decay of the current i based on the current during the inertial rotation period of the DC motor 10, estimates the determined time constant τ as the time constant τ of the decay of the angular velocity during the inertial rotation period of the DC motor 10, and determines the rotation angle of the DC motor 10, so that the rotation angle of the DC motor 10 can be easily detected based on the current i.

The amount of opening/closing of the power window 50 can also be calculated based on the rotation angle θ detected by the rotation angle detection device 100. For example, when the power window 50 is stopped at a position between fully open and fully closed, the amount of opening/closing of the power window 50 can be determined with high accuracy. The power window 50 is required to be equipped with a pinch prevention mechanism, and when the power window 50 is opened or closed again after being stopped at a position between fully open and fully closed, the position where the power window 50 was stopped must be accurately detected.

In addition, the rotation angle detection device 100 can detect the rotation angle of the DC motor 10 with extremely high accuracy without using expensive devices such as Hall ICs to detect the opening and closing amount of the power window 50, which allows for a significant reduction in manufacturing costs.

The decay time constant τ of the current i is calculated based on time t3, time t4, time tend, the current integral value Si3+Si4, and the current integral value Si4. Therefore, the decay time constant τ of the current i, which can be used instead of the decay time constant τ of the angular velocity ω, can be easily calculated based on the change in the current i over time. In addition, the integration process for calculating the current integral value corresponds to a filter process, which has the effect of removing the ripple component contained in the current i, and the rotation angle of the DC motor 10 can be detected with extremely high accuracy.

In addition, since the time constant τ of the decay of the current i can be obtained based on the formula (10), by incorporating the formula (10) into the program executed by the processing unit 133, the time constant τ of the decay of the current i that can be used instead of the time constant τ of the decay of the angular velocity ω can be easily obtained. In addition, by utilizing the filter effect of the integration process, the ripple component contained in the current i can be removed according to the program executed by the processing unit 133, and the rotation angle of the DC motor 10 can be detected with high accuracy. In addition, since the natural logarithm in the formula (10) includes a division process of the current integral value, the measurement error of the current of the A/D converter 132, etc., which originates from the components contained in the circuits such as the resistor 15, the LPF 112, and the A/D converter 132, can be reduced, and the rotation angle of the DC motor 10 can be detected with high accuracy.

In addition, since the decay time constant τ of the current i is calculated based on time t3 and the current integral value Si3+Si4 of the current value measured by the current measurement unit 133A from time t3 to time tend, the decay time constant τ of the current i that can be used instead of the decay time constant τ of the angular velocity ω can be calculated more easily with fewer calculations. In addition, since the integration process for calculating the current integral value corresponds to a filter process, it has the effect of removing the ripple component contained in the current i, and the rotation angle of the DC motor 10 can be detected with high accuracy.

In addition, since the decay time constant τ of the current i can be calculated based on equation (11), by incorporating equation (11) into the program executed by the processing unit 133, the decay time constant τ of the current i that can be used instead of the decay time constant τ of the angular velocity ω can be easily calculated.

In addition, the rotation angle of the DC motor 10 during coasting rotation is calculated based on the angular velocity ω0 immediately before the time t0 at which the drive of the DC motor 10 is turned off, the time t1, and the decay time constant τ of the current i of the DC motor 10. Therefore, the rotation angle of the DC motor 10 during coasting rotation can be calculated using the decay time constant τ of the current i that can be used instead of the decay time constant τ of the angular velocity ω.

In addition, the rotation angle of the DC motor 10 during inertial rotation is calculated based on equation (14). By incorporating equation (14) into the program executed by the processing unit 133, the rotation angle of the DC motor 10 during inertial rotation can be calculated using the decay time constant τ of the available current i instead of the decay time constant τ of the angular velocity ω.

The above describes the rotation angle detection method, rotation angle detection program, and rotation angle detection device of exemplary embodiments of the present invention, but the present invention is not limited to the specifically disclosed embodiments, and various modifications and variations are possible without departing from the scope of the claims.

REFERENCE SIGNS LIST 10 DC motor 11, 12 Terminal 15 Resistor 20 Drive circuit 30 DC power supply 50 Power window 51 Drive mechanism 100 Rotation angle detection device 110 Filter circuit 111, 112 LPF
120 IC chip 121 BPF
122 Ripple detection unit 130 Microcomputer 131, 132 A/D converter 133 Processing unit 133A Current measurement unit 133B Rotation angle detection unit 133C Memory

Claims (10)

A current measurement process for measuring a current flowing through the electric motor;
a rotation angle detection process for determining a rotation angle of the electric motor based on a current value measured by the current measurement process,
The rotation angle detection process calculates a time constant of decay of the current of the motor based on the current value measured by the current measurement process from a predetermined time after the polarity of the current value of the reverse current measured by the current measurement process while the motor is rotating by inertia and the current value measured by the current measurement process reaches a peak value until the current value measured by the current measurement process reaches zero, and calculates the rotation angle during the inertia rotation based on the calculated time constant. The rotation angle detection method according to claim 1, wherein the rotation angle detection process calculates the time constant τ of the current decay based on time t3 after the predetermined time has elapsed, time tend when the current value measured by the current measurement process becomes zero, time t4 between time t3 and time tend, a first current integral value of the current value measured by the current measurement process from time t3 to time tend, and a second current integral value of the current value measured by the current measurement process from time t4 to time tend. 3. The rotation angle detection method according to claim 2, wherein, in the rotation angle detection process, when the first current integral value is Si3+Si4 and the second current integral value is Si4, a time constant τ of the current decay is calculated based on the following equation (1):

The rotation angle detection method according to claim 1, wherein the rotation angle detection process calculates the time constant τ of the current decay based on a current value i3 measured by the current measurement process at time t3 after the predetermined time has elapsed and a first current integral value of the current value measured by the current measurement process from time t3 to time tend when the current value measured by the current measurement process becomes zero. 5. The rotation angle detection method according to claim 4, wherein, in the rotation angle detection process, when the first current integral value is Si3+Si4, a time constant τ of the current attenuation is calculated based on the following equation (2).

The method for detecting a rotation angle according to any one of claims 1 to 5, wherein the rotation angle detection process determines the rotation angle in the inertial rotation based on the angular velocity ω0 immediately before the time t0 at which the drive of the electric motor is turned off, the time t1 at which the polarity of the current value measured by the current measurement process is reversed after the drive of the electric motor is turned off at the time t0, and the time constant τ of the attenuation of the current. 7. The rotation angle detection method according to claim 6, wherein the rotation angle detection process determines the rotation angle during the inertial rotation of the electric motor based on the following equation (3).

A current measurement process for measuring a current flowing through the electric motor;
a rotation angle detection process for determining a rotation angle of the electric motor based on a current value measured by the current measurement process,
The rotation angle detection process calculates a time constant of decay of the current of the motor based on the current value measured by the current measurement process from a predetermined time after the polarity of the current value of the reverse current measured by the current measurement process while the motor is rotating by inertia and the current value measured by the current measurement process reaches a peak value until the current value measured by the current measurement process reaches zero, and calculates the rotation angle during the inertia rotation based on the calculated time constant. a current measuring unit for measuring a current flowing through the motor;
a rotation angle detection unit that determines a rotation angle of the electric motor based on the current value measured by the current measurement unit,
The rotation angle detection unit calculates a time constant of decay of the current of the motor based on the current value measured by the current measurement unit from a predetermined time after the polarity of the current value of the reverse current measured by the current measurement unit while the motor is rotating by inertia and the absolute value of the current value measured by the current measurement unit reverses and reaches a peak value, until the current value measured by the current measurement unit becomes zero, and calculates the rotation angle during the inertia rotation based on the calculated time constant. The rotation angle detection device according to claim 9, wherein the electric motor is an electric motor that drives a power window drive mechanism.

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