Motor drive control device, motor unit, and motor drive control method

Abstract

To more quickly detect short-circuit of a motor coil.SOLUTION: In a motor-driving controller 3, a control circuit 1 comprises a drive control signal generation part 10 for generating a drive control signal Sd in such a manner that a motor 4 is in a drive state according to a drive command Sc; a current limit value setting part 15 for setting a current limit value Ith; a current limit value 16 for instructing it to the drive control signal generation part 10 to stop excitation of a coil 41, when current flowing through the coil 41 of the motor 4 reaches the current limit value Ith; a timer part 19 for measuring time during which the coil 41 is excited by a drive circuit 2; and a short circuit determination part 17 that performs a short circuit determination processing for determining whether or not the coil 41 is short-circuited, based on the time measured by the timer part 19. According to the short circuit determination processing, the short circuit determination part 17 determines that the coil 41 is short-circuited, when the time measured by the timer part 19 is smaller than a threshold value.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a motor drive control device, a motor unit, and a motor drive control method, and for example, to a motor drive control device for driving a stepping motor.

Background Art

[0002] In a motor, if the coil is short-circuited for some reason, a large current may flow through a drive circuit such as an inverter circuit for driving the motor and the motor, which may cause the drive circuit and the motor to fail. In order to avoid a failure caused by a short circuit of the coil, it is necessary to detect more quickly that the coil is in a short-circuited state and stop driving the motor.

[0003] As a conventional technique for controlling the current of a motor, for example, Patent Document 1 discloses a motor drive control device having a current limiting function for limiting the current flowing through the coil of a stepping motor so as not to exceed a preset value.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] Incidentally, many programmable processing devices such as microcontrollers that perform general motor drive control have a current limiting function disclosed in Patent Document 1. However, the current limiting function disclosed in Patent Document 1 is a function for limiting the coil current when switching the motor drive mode from excitation mode (charge mode) to damping mode, for example. The current is not limited unless the coil current exceeds a preset limit value for a certain period of time or longer, so it cannot prevent large currents that flow instantaneously. Thus, the current limiting function of a microcontroller is not specialized for detecting coil short circuits, and even if this function is simply used, a coil short circuit cannot be detected unless a large current flows for a certain period of time or longer.

[0006] Furthermore, motor drive control devices with an overcurrent detection function that activates when a large current flows are also known. While some of these overcurrent detection functions allow the setting of the detection time and detection current value to be changed by a microcontroller, the degree of flexibility is limited. Therefore, even with a motor drive control device that has an overcurrent detection function, a short circuit in the coil cannot be detected unless a large current flows for a certain period of time or longer.

[0007] This invention has been made in view of the above-mentioned problems, and aims to enable faster detection of short circuits in motor coils. [Means for solving the problem]

[0008] A motor drive control device according to a typical embodiment of the present invention comprises a control circuit that generates a drive control signal for controlling the drive of a motor, and a drive circuit that energizes the coil of the motor based on the drive control signal, wherein the control circuit includes a drive control signal generation unit that generates the drive control signal so that the motor enters a drive state in response to a drive command, a current limit value setting unit that sets a reference current limit value for limiting the current flowing through the coil, a current limit unit that instructs the drive control signal generation unit to stop energizing the coil when the current flowing through the coil reaches the current limit value, a timing unit that measures the time the coil is energized by the drive circuit, and a short-circuit determination unit that performs a short-circuit determination process to determine whether the coil of the motor is short-circuited based on the time measured by the timing unit, wherein the short-circuit determination unit determines that the coil is short-circuited when the time measured by the timing unit is less than a threshold value. [Effects of the Invention]

[0009] According to the motor drive control device of the present invention, a short circuit in the motor coil can be detected more quickly. [Brief explanation of the drawing]

[0010] [Figure 1] This is a block diagram showing the configuration of a motor unit according to an embodiment. [Figure 2A] This diagram shows the connection relationship between the H-bridge circuit and the motor coil. [Figure 2B] This diagram shows the connection relationship between the H-bridge circuit and the motor coil. [Figure 3] This diagram shows the configuration of the control circuit in the motor drive control device according to the embodiment. [Figure 4] This figure shows an example of the current waveforms in each phase coil when a motor is driven using a single-phase excitation method in normal control mode. [Figure 5] This is an enlarged view of the current waveform in the range of reference numeral 410 in Figure 4. [Figure 6] This figure shows an example of the current waveform of the A-phase coil when the motor is driven in hold control mode before normal motor operation starts. [Figure 7] This figure shows an example of the coil current characteristics in hold control mode before the motor starts normal operation. [Figure 8] This flowchart shows the flow of the short-circuit detection process by the control circuit in the motor drive control device according to the embodiment. [Figure 9] This is a flowchart showing the flow of the cumulative time calculation process (step S2). [Figure 10] This is a flowchart showing the process (step S7) for determining whether or not there is a short circuit in the coil. [Modes for carrying out the invention]

[0011] 1. Overview of the Embodiment First, a general overview of a typical embodiment of the invention disclosed in this application will be provided. In the following description, as an example, reference numerals on the drawings corresponding to the components of the invention are indicated in parentheses.

[0012] [1] A motor drive control device (3) according to a typical embodiment of the present invention comprises a control circuit (1) that generates a drive control signal (Sd) for controlling the drive of a motor (4), and a drive circuit (2) that excites the coils (41, 41A, 41B) of the motor based on the drive control signal, wherein the control circuit comprises a drive control signal generation unit (10) that generates the drive control signal so that the motor enters a drive state in accordance with a drive command (Sc), a current limit value setting unit (15) that sets a reference current limit value (Ith) for limiting the current flowing through the coil, and the coil The motor has a current limiting unit (16) that instructs the drive control signal generation unit to stop exciting the coil when the current flowing reaches the current limit value, a timing unit (19) that measures the time the coil is excited by the drive circuit, and a short-circuit determination unit (17) that performs a short-circuit determination process to determine whether the coil of the motor is short-circuited based on the time measured by the timing unit, wherein the short-circuit determination unit determines that the coil is short-circuited when the time measured by the timing unit is less than a threshold value.

[0013] [2] In the motor drive control device described in [1] above, the motor is a stepping motor having two phase coils (41A, 41B), the timing unit measures the time the coils are energized for each phase, and the short-circuit determination unit performs the short-circuit determination process for each phase based on the time for each phase measured by the timing unit.

[0014] [3] In the motor drive control device described in [1] or [2] above, the timing unit may repeatedly measure the time the coil is energized, and the short-circuit determination unit may determine that the coil is short-circuited in the motor when the time (cumulative time, average time, etc.) based on the time measured by the timing unit for a set number of measurements is less than the threshold.

[0015] 〔4〕In the motor drive control device described in 〔3〕 above, the short-circuit determination unit may include a cumulative time calculation unit (170) that calculates a cumulative time (Ta) obtained by accumulating the measurement times measured by the time measurement unit for a preset number of measurement times, and a determination unit (171) that determines that the coil in the motor is short-circuited when the cumulative time is less than the threshold value.

[0016] 〔5〕In the motor drive control device according to any one of 〔1〕 to 〔4〕 above, the control circuit has a hold control mode for moving and maintaining the rotor (40) of the motor to a predetermined standby position before the start of normal drive or before the stop of the normal drive as a control mode for controlling the drive of the motor, and the short-circuit determination unit may perform the short-circuit determination process during the period when the control mode is the hold control mode.

[0017] 〔6〕In the motor drive control device described in 〔5〕 above, during the period when the control mode is the hold control mode, it includes a first period (710) in which the current limit value setting unit changes the current limit value to a predetermined value as time elapses, and a second period (711) in which the current limit value setting unit fixes the current limit value to the predetermined value. The current limit value setting unit makes the current limit value constant during a partial period (712) within the first period, and the short-circuit determination unit may perform the short-circuit determination process during the partial period.

[0018] 〔7〕In the motor drive control device according to any one of 〔1〕 to 〔6〕 above, the control circuit has a normal control mode for moving the rotor of the motor to the rotation position specified by the drive command as a control mode for controlling the drive of the motor, and the short-circuit determination unit may perform the short-circuit determination process in the normal control mode.

[0019] [8] In the motor drive control device described in any of [1] to [7] above, the drive circuit includes an H-bridge circuit (21, 21A, 21B) consisting of a plurality of switching elements (22 to 25) whose on / off state is controlled by the drive control signal, and the timing unit measures the time during which the plurality of switching elements are turned on so that current flows in one direction through the coil, and the measured time is the time during which the coil is energized.

[0020] [9] A motor unit (5) according to a typical embodiment of the present invention is characterized by comprising a motor drive control device (3) described in any of [1] to [8] above, and the motor (4).

[0021]

[10] A typical embodiment of the present invention is a motor drive control method for rotating a motor rotor (40) by exciting coils (41, 41A, 41B) of a motor (4), comprising: a first step of exciting the coils so that the motor enters a drive state in accordance with a drive command (Sc); a second step of stopping the excitation of the coils when the current flowing through the coils exceeds a current limit value which is a reference for limiting the current flowing through the coils; a third step of measuring the time during which the coils are excited; and a fourth step of performing a short-circuit determination process (S2 to S7) to determine whether or not the coils of the motor are short-circuited based on the time measured in the third step, wherein the short-circuit determination process in the fourth step includes a step (S7, S71, S72) of determining that the coils are short-circuited when the time measured in the third step is less than a threshold.

[0022] 2. Specific Examples of Embodiments Hereinafter, specific examples of embodiments of the present invention will be described with reference to the figures. In the following description, common components in each embodiment will be denoted by the same reference numerals, and repeated descriptions will be omitted.

[0023] <Embodiment 1> Figure 1 is a block diagram showing the configuration of the motor unit 5 according to the embodiment. As shown in Figure 1, the motor unit 5 comprises a motor 4 and a motor drive control device 3 that drives the motor 4. The motor unit 5 is applicable to various devices that use a motor as a power source, such as an actuator usable in HVAC (Heating Ventilation and Air-Conditioning) as an air conditioning unit for automotive applications.

[0024] Motor 4 is, for example, a stepping motor. In this embodiment, as an example, motor 4 will be described as a two-phase stepping motor.

[0025] The motor 4 includes a rotor 40, an A-phase coil 41A, A-phase stator yokes 42A_1, 42A_2, a B-phase coil 41B, and B-phase stator yokes 42B_1, 42B_2.

[0026] The rotor 40 is equipped with a multi-pole magnetized permanent magnet such that the south poles and north poles are alternately arranged along the circumference. Figure 1 shows an example where the rotor 40 has two poles.

[0027] The stator yokes 42A_1, 42A_2, 42B_1, and 42B_2 are positioned to divide the circumferential direction around the rotor 40 into four equal parts. For example, the A-phase stator yoke 42A_1 and the A-phase stator yoke 42A_2 are positioned opposite each other with the rotor 40 in between. The B-phase stator yoke 42B_1 and the B-phase stator yoke 42B_2 are positioned opposite each other with the rotor 40 in between, and perpendicular to the direction in which the A-phase stator yokes 42A_1 and 42A_2 are aligned.

[0028] The stator yokes 42A_1, 42A_2, 42B_1, and 42B_2 have windings (coils) wound in the same direction. For example, the windings wound on stator yoke 42A_1 and stator yoke 42A_2 are connected in series, and the two windings together are referred to as the A-phase "coil 41A". Similarly, the windings wound on stator yoke 42B_1 and stator yoke 42B_2 are connected in series, and the two windings together are referred to as the B-phase "coil 41B".

[0029] When current flows through the A-phase coil 41A, the A-phase stator yokes 42A_1 and 42A_2 are excited, and when current flows through the B-phase coil 41B, the B-phase stator yokes 42B_1 and 42B_2 are excited. The rotor 40 rotates as the phase of the currents flowing through coils 41A and 41B is periodically switched. An output shaft (not shown) is connected to the rotor 40, and the output shaft is driven by the rotational force of the rotor 40, thereby realizing, for example, the actuator function described above.

[0030] In this embodiment, if coils 41A and 41B are not distinguished, they may simply be referred to as "coil 41".

[0031] The motor drive control device 3 is a device for driving the motor 4. The motor drive control device 3 controls the rotation and stopping of the motor 4 by controlling the energization state of the coils 41A and 41B of each phase of the motor 4, for example, based on a drive command Sc from a higher-level device 6.

[0032] As shown in Figure 1, the motor drive control device 3 has a control circuit 1 and a drive circuit 2. The drive circuit 2 is a circuit that drives the motor 4 by energizing the coils 41A and 41B of the motor 4. Based on the drive control signal Sd output from the control circuit 1, the drive circuit 2 energizes the coils 41A and 41B of the motor 4, thereby rotating the rotor 40 of the motor 4.

[0033] The drive circuit 2 includes an inverter circuit 21A for exciting the A-phase coil 41A, an inverter circuit 21B for exciting the B-phase coil 41B, a current detection circuit 20A for detecting the current of the A-phase coil 41A, and a current detection circuit 20B for detecting the current of the B-phase coil 41B.

[0034] Inverter circuits 21A and 21B are, for example, H-bridge circuits. Hereafter, inverter circuit 21A will also be referred to as "H-bridge circuit 21A," and inverter circuit 21B as "H-bridge circuit 21B." Furthermore, when there is no distinction between H-bridge circuits 21A and 21B, they will simply be referred to as "H-bridge circuit 21."

[0035] H-bridge circuits 21A and 21B have, for example, identical circuit configurations. The configuration of the A-phase H-bridge circuit 21A will be described below as a representative example.

[0036] Figures 2A and 2B show the connection relationship between the H-bridge circuit 21A and the coil 41A of the motor 4.

[0037] As shown in Figures 2A and 2B, the H-bridge circuit 21A has a plurality of switching elements 22-25 whose on / off state is controlled by a drive control signal Sd.

[0038] Switching elements 22 and 23 are connected in series between the power supply voltage Vdd and the ground voltage. Similarly, switching elements 24 and 25 are connected in series between the power supply voltage Vdd and the ground voltage. The node where switching elements 22 and 23 are connected to each other is connected to the negative terminal AN of coil 41A, and the node where switching elements 24 and 25 are connected to each other is connected to the positive terminal AP of coil 41A.

[0039] The switching elements 22-25 are, for example, transistors. Note that, as shown in Figures 2A and 2B, diodes 26-29 may be connected in parallel with each of the switching elements 22-25. Diodes 26-29 may be parasitic diodes of the transistors acting as switching elements 22-25, or they may be diode elements as separate electronic components from the switching elements 22-25.

[0040] Switching elements 22-25 selectively switch on and off based on the drive control signal Sd, thereby switching the energized state of coil 41A. For example, as shown in Figure 2A, in charge mode, when current I flows from terminal AP to terminal AN of the A-phase coil 41A (A-phase + excitation), the drive control signal Sd turns on switching elements 23 and 24 and turns off switching elements 22 and 25. Then, as shown in Figure 2B, in through-protection mode, all switching elements 22-25 are turned off, allowing current to flow from ground potential through diodes 29 and 26 to the power supply voltage Vdd.

[0041] On the other hand, although not shown in the diagram, when current -I is flowed from terminal AN to terminal AP of the A-phase coil 41A as an excitation mode (A-phase excitation), the drive control signal Sd turns on the switching elements 22 and 25 and turns off the switching elements 23 and 24.

[0042] In this way, by selectively turning on and off the switching elements 22-25 of the H-bridge circuit 21A based on the drive control signal Sd, the energized state (direction of energization) of the A-phase coil 41A can be switched. Similarly, for the B-phase, by selectively turning on and off the switching elements 22-25 of the H-bridge circuit 21B, the energized state of the B-phase coil 41B can be switched.

[0043] Current detection circuit 20A is connected to H-bridge circuit 21A, detects the current flowing through coil 41A, and outputs a current detection signal Sia. Current detection circuit 20B is connected to H-bridge circuit 21B, detects the current flowing through coil 41B, and outputs a current detection signal Sib. Current detection circuits 20A and 20B include, for example, a shunt resistor. The shunt resistor is connected in series with H-bridge circuits 21A and 21B between the power supply voltage Vdd and the ground voltage, and outputs the voltage generated across the shunt resistor as current detection signals Sia and Sib. Note that current detection circuits 20A and 20B can employ various known circuit configurations capable of detecting the current flowing through coils 41A and 41B of the motor 4, and are not limited to the circuit configuration including the shunt resistor described above.

[0044] The drive circuit 2 may also have a pre-drive circuit for driving the switching elements 22-25 of each H-bridge circuit 21A, 21B based on the drive control signal Sd.

[0045] Control circuit 1 is a circuit that provides overall control of the motor drive control device 3. The control circuit 1 is a program processing unit (e.g., a microcontroller) having a configuration in which a processor such as a CPU, various storage devices such as RAM and ROM, and peripheral circuits such as timers (counters), A / D conversion circuits, D / A conversion circuits, and input / output I / F circuits are interconnected via a bus. In this embodiment, the control circuit 1 is packaged as an IC (integrated circuit), but is not limited to this. The control circuit 1 and the drive circuit 2 may be packaged together.

[0046] The control circuit 1 has, for example, the function of controlling the drive of the motor 4 by generating a drive control signal Sd and supplying it to the drive circuit 2, and the function of detecting a short circuit in the coil 41 of the motor 4.

[0047] Figure 3 is a diagram showing the configuration of the control circuit 1 in the motor drive control device 3 according to the embodiment.

[0048] As shown in Figure 3, the control circuit 1 has a drive control signal generation unit 10, a current value acquisition unit 14, a current limit value setting unit 15, a current limiting unit 16, a short-circuit detection unit 17, a storage unit 18, and a timing unit 19 as functional units for realizing the above-mentioned functions.

[0049] These functional units are realized, for example, in the program processing unit (microcontroller) as the control circuit 1 described above, by having the processor perform calculations using various parameters stored in the memory according to the program stored in the memory, and by controlling peripheral circuits such as A / D conversion circuits and timers.

[0050] The drive control signal generation unit 10 is a functional unit that generates a drive control signal Sd so that the motor 4 enters a drive state according to the drive command Sc. For example, the drive control signal generation unit 10 includes a drive command acquisition unit 11, a control mode determination unit 12, and a signal output unit 13.

[0051] The drive command acquisition unit 11 acquires a drive command Sc for the motor 4 input from outside the motor drive control device 3 (for example, from a higher-level device 6). The drive command Sc includes, for example, information specifying the rotational position of the motor 4 or information instructing the motor 4 to stop rotating. The drive command Sc is, for example, a PWM signal.

[0052] The drive command acquisition unit 11 acquires information on the target rotational position of the motor 4 (target rotational position) by analyzing the drive command Sc, for example, and provides it to the control mode determination unit 12.

[0053] The control mode determination unit 12 determines the control mode for controlling the drive of the motor 4. The signal output unit 13 generates and outputs a drive control signal Sd according to the control mode determined by the control mode determination unit 12.

[0054] The drive control signal Sd is a signal used to control the on / off state of each switching element 22-25 in the H-bridge circuits 21A and 21B.

[0055] The control circuit 1 has, for example, a normal control mode and a hold control mode as control modes.

[0056] The normal control mode is a control mode for moving (rotating) the rotor 40 of the motor 4 to a rotational position (target rotational position) specified by a drive command Sc given from the higher-level device 6. In the following explanation, driving the motor 4 in the normal control mode will also be referred to as "normal drive".

[0057] The hold control mode is a control mode for moving (rotating) the rotor 40 of the motor 4 to a predetermined standby position (target standby position) before starting or stopping normal operation of the motor 4, and then maintaining (holding) the rotor 40 in the standby position.

[0058] For example, when power is supplied to the motor drive control device 3 and the motor drive control device 3 starts up, the control mode determination unit 12 sets the control mode to hold control mode. In hold control mode before the motor 4 starts normal operation, the signal output unit 13 generates and outputs a drive control signal Sd to move the rotor 40 (output shaft) of the motor 4 to a preset target standby position (initial position). Once the rotor 40 reaches the initial position, the signal output unit 13 generates and outputs a drive control signal Sd to stop (fix) the rotor 40 at the initial position in order to prevent the rotor 40 from moving from the initial position due to a load being applied to the rotor 40.

[0059] Subsequently, when the control circuit 1 receives a drive command Sc from the higher-level device 6, the control mode determination unit 12 switches the control mode from hold control mode to normal control mode. In normal control mode, the signal output unit 13 generates and outputs a drive control signal Sd so that the rotor 40 moves to the target rotation position specified by the drive command Sc, and the motor 4 starts normal driving. Once the rotor 40 reaches the target rotation position, the control mode determination unit 12 switches the control mode from normal control mode to hold control mode, which is the mode before the motor 4 stops normal driving.

[0060] In the hold control mode before the motor 4 is normally stopped, the signal output unit 13 generates and outputs a drive control signal Sd to stop the rotor 40 at the target standby position in order to prevent the rotor 40 from moving from the target standby position due to a load being applied to the rotor 40. As a result, the rotor 40 of the motor 4 moves to the target standby position and is fixed in that position.

[0061] The signal output unit 13 generates and outputs a drive control signal Sd to energize the A-phase coil 41A and the B-phase coil 41B at a predetermined timing based on a predetermined excitation method in order to move the rotor 40 to a target rotation position or a target standby position.

[0062] Here, the predetermined excitation method is, for example, one of the known single-phase excitation method, two-phase excitation method, one-to-two-phase excitation method, and microstep method. Information specifying the excitation method is stored, for example, in the memory unit 18, and the signal output unit 13 generates a drive control signal Sd according to the information specifying the excitation method stored in the memory unit 18.

[0063] When generating a drive control signal Sd using a single-phase excitation method, the signal output unit 13 generates and outputs a drive control signal Sd such that the energized state of the A and B phase coils 41A and 41B switches in the following order: "A-phase (+) excitation period" where current flows from terminal AP to terminal AN of the A-phase coil 41A, "B-phase (+) excitation period" where current flows from terminal BP to terminal BN of the B-phase coil 41B, "A-phase (-) excitation period" where current flows from terminal AN to terminal AP of the A-phase coil 41A, and "B-phase (-) excitation period" where current flows from terminal BN to terminal BP of the B-phase coil 41B.

[0064] For example, during the "A-phase (+) excitation period," the signal output unit 13 generates a drive control signal Sd to turn on the switching elements 22 and 25 of the H-bridge circuit 21 while keeping the switching elements 23 and 24 of the H-bridge circuit 21 in the off state. During the "A-phase (-) excitation period," the signal output unit 13 generates a drive control signal Sd to turn on the switching elements 23 and 24 of the H-bridge circuit 21A while keeping the switching elements 22 and 25 of the H-bridge circuit 21A in the off state. The signal output unit 13 similarly generates a drive control signal Sd for the "B-phase (+) excitation period" and the "B-phase (-) excitation period," selectively turning on / off the switching elements 22-25 of the B-phase H-bridge circuit 21B.

[0065] The memory unit 18 is a functional unit for storing various data necessary for motor drive control by the control circuit 1. For example, the memory unit 18 stores various data necessary for generating the drive control signal Sd, and various data necessary for the short-circuit determination process that determines whether or not the coil 41 of the motor 4 is short-circuited. For example, the memory unit 18 stores information 180 of the current limit value Ith, information 181 of the number of determination criteria Nth, information 182 of the determination criterion time Tth, and information 183 of the cumulative time Ta, as well as information specifying the excitation method as described above.

[0066] The current value acquisition unit 14 is a functional unit that acquires the value of the current flowing through the coils 41 of each phase of the motor 4. The current value acquisition unit 14 receives current detection signals Sia and Sib output from the current detection circuits 20A and 20B of the drive circuit 2. The current value acquisition unit 14 includes, for example, an A / D conversion circuit, which converts the voltage of the input current detection signal Sia into a digital value and outputs it as the current value of the A-phase coil 41A. Similarly, the current value acquisition unit 14 converts the voltage of the current detection signal Sib into a digital value using, for example, an A / D conversion circuit, and outputs it as the current value of the B-phase coil 41B.

[0067] The current limit setting unit 15 is a functional unit for setting the current limit value Ith. The current limit value Ith is a reference value for limiting the current flowing through the coil 41 of the motor 4; in other words, it is a value that determines the upper limit of the current in the coil 41.

[0068] Information regarding the current limit value Ith is stored in the storage unit 18 in advance as current limit value Ith information 180. The current limit value setting unit 15 provides the current limit value Ith to the current limiting unit 16 based on the current limit value Ith information 180 read from the storage unit 18. As will be described later, the current limit value setting unit 15 may output a constant (fixed) current limit value Ith, or it may change the current limit value Ith over time.

[0069] The current limiting unit 16 is a functional unit that monitors the current flowing through the coil 41 of the motor 4 and controls it so that the current does not exceed the current limit value Ith. Current monitoring by the current limiting unit 16 is performed for each phase of the motor 4. For example, during the "A-phase (+) excitation period" and "A-phase (-) excitation period" when the A-phase coil 41A is excited, the current of the A-phase coil 41A (current detection signal Sia) is monitored, and during the "B-phase (+) excitation period" and "B-phase (-) excitation period" when the B-phase coil 41B is excited, the current of the B-phase coil 41B (current detection signal Sib) is monitored.

[0070] The current limiting unit 16 instructs the drive control signal generation unit 10 to stop exciting the coil 41 when the current flowing through the coil 41 reaches the current limit value Ith. For example, the current limiting unit 16 compares the current value of the coil 41 output from the current value acquisition unit 14 with the current limit value Ith, and outputs a signal instructing the unit to stop exciting the coil 41, that is, to stop (turn off) the switching elements 22 to 25 of the H bridge circuit 21 by the drive control signal Sd, when the current value of the coil 41 becomes equal to or greater than the current limit value Ith.

[0071] The signal output unit 13 generates and outputs a drive control signal Sd to stop the excitation of coil 41 while the current limiting unit 16 outputs a signal instructing it to stop the excitation of coil 41. For example, during the "A-phase (+) excitation period," if the signal output unit 13 receives a signal from the current limiting unit 16 instructing it to stop the excitation of the A-phase coil 41A, the signal output unit 13 generates a drive control signal Sd to stop (turn off) the switching elements 22 and 25 in the A-phase H-bridge circuit 21A, so that all switching elements 22-25 are turned off (see Figure 2B). As a result, the current of the A-phase coil 41A is limited so as not to exceed the current limit value Ith. The current of the B-phase coil 41B is limited in a similar manner.

[0072] The timing unit 19 is a functional unit for measuring the time (excitation period) during which the coil 41 of the motor 4 is excited by the drive circuit 2. The timing unit 19 can be implemented, for example, by using a counter in the microcontroller that constitutes the control circuit 1.

[0073] The timing unit 19 measures the time during which coils 41A and 41B are energized for each phase of the motor 4 (hereinafter also referred to as "energy generation time"). For example, the timing unit 19 monitors the drive control signal Sd to measure the time during which multiple switching elements 22 to 25 are turned on so that current flows in one direction through coil 41, and defines the measured time as the time during which coil 41 is energized.

[0074] For example, during the "+A phase excitation period" in which current flows from terminal AP to terminal AN of the A phase coil 41A, the timing unit 19 monitors the drive control signal Sd and, when it detects that control has started in the H bridge circuit 21A to turn on the switching elements 22 and 25 and turn off the switching elements 23 and 24, it starts measuring time with the counter. Subsequently, when the timing unit 19 detects that the switching elements 22 and 25 have been turned off during the "+A phase excitation period", it stops measuring time with the counter, stores the measured time in, for example, the storage unit 18, and resets the counter.

[0075] In this way, the timing unit 19 repeatedly measures the time the coil 41 is energized in accordance with the on and off states of the switching elements of the H-bridge circuit 21.

[0076] The short-circuit determination unit 17 is a functional unit that performs a short-circuit determination process to determine whether or not the coil 41 of the motor 4 is short-circuited, based on the excitation time (hereinafter also referred to as "measurement time") measured by the timing unit 19.

[0077] The short-circuit detection unit 17 performs a short-circuit detection process for each phase based on the measurement time for each phase by the timing unit 19. For example, the short-circuit detection unit 17 identifies the excited phase by monitoring the drive control signal Sd, and uses the measurement time of the identified phase to perform a short-circuit detection process for the coil 41 of the excited phase. In the short-circuit detection process, the short-circuit detection unit 17 determines that the monitored coil 41 is short-circuited if the measurement time measured by the timing unit 19 is smaller than a threshold.

[0078] Figure 4 shows an example of the current waveforms of the coils 41A and 41B for each phase when the motor 4 is driven by a single-phase excitation method in normal control mode.

[0079] Figure 4 shows the temporal change in the currents of coils 41A and 41B when the excitation of coil 41 is switched in the following order from time t=0: A-phase (+) excitation period, B-phase (+) excitation period, A-phase (-) excitation period, and B-phase (-) excitation period, when the motor 4 is driven by a single-phase excitation method in normal control mode.

[0080] Specifically, the solid line indicated by reference numeral 400 represents the characteristics of the current flowing through the A-phase coil 41A when the A-phase coil 41A is functioning normally, and the dashed line indicated by reference numeral 401 represents the characteristics of the current flowing through the B-phase coil 41B when the B-phase coil 41B is functioning normally. In addition, the solid line indicated by reference numeral 403 represents the characteristics of the B-phase current when the B-phase coil 41B is short-circuited. In Figure 4, the current limit value Ith is set to "I5".

[0081] As shown in reference numerals 400 and 401, when the coil 41 is in a normal state and not short-circuited, when the excitation state of the coil 41 is switched, the current flowing through the coil 41 increases, and the current limiting unit 16 controls the current flowing through the coil 41 so as not to exceed the current limit value Ith = I5.

[0082] Figure 5 is an enlarged view of the current waveform in the range of reference numeral 410 in Figure 4. As shown in Figure 5, during the A-phase (+) excitation period, at time t50 when the current flowing through coil 41 reaches the current limit value Ith = I5, the current limiting unit 16 outputs a signal instructing it to stop exciting coil 41 (turn off switching elements 22 and 25). In response to the signal from the current limiting unit 16, the signal output unit 13 stops outputting the drive control signal Sd to turn off switching elements 22 and 25. As a result, the current in coil 41 gradually decreases from "I5".

[0083] After a certain period of time (Toff) has elapsed, the signal output unit 13 outputs a drive control signal Sd to turn on the switching elements 22 and 25 again.

[0084] Thus, in the normal control mode, when coil 41 is in a normal state, the current in coil 41 is controlled so as not to exceed the current limit value Ith (=I5).

[0085] On the other hand, for example, in the normal control mode, if the B-phase coil 41B is short-circuited, as shown in reference numeral 403, the current detected on the B-phase side increases sharply immediately after the coil 41 to be excited switches from the A-phase to the B-phase.

[0086] As shown in Figure 4, if the coil 41 of the monitored phase is short-circuited, the current will exceed the current limit value Ith between the time the current limiting unit 16 detects that the current of the monitored phase has reached the current limit value Ith and the time the excitation of the monitored phase is stopped. Subsequently, when the switching elements 22 and 25 are turned off, the current in coil 41 drops sharply, but after a certain period Toff has elapsed, when the switching elements 22 and 25 are turned on, the current in coil 41 will again exceed the current limit value Ith. Therefore, if the coil 41 of the motor 4 is short-circuited, as shown in Figure 4, the current in coil 41 will repeatedly increase and decrease sharply in sync with the start and stop of the switching elements 22 and 25 turning on.

[0087] As shown in Figure 4, in motor 4, the rate of change of current over time when coil 41 is short-circuited is much larger than the rate of change of current over time when coil 41 is not short-circuited.

[0088] Therefore, in the motor drive control device 3 according to this embodiment, the short-circuit determination unit 17 determines that the coil 41 is short-circuited when the time from when the excitation of the coil 41 is started until when the excitation is stopped, that is, the time measured by the timing unit 19, is less than a threshold.

[0089] For example, the short-circuit determination unit 17 compares the measurement time for one measurement with a threshold value, and determines that the coil 41 of the monitored phase is short-circuited if the measurement time for one measurement is less than the threshold value. More preferably, the short-circuit determination unit 17 may determine that the coil 41 is short-circuited if the time based on the measurement time by the timing unit 19 for a preset number of measurements is less than the threshold value.

[0090] Examples of the time based on the measurement time by the timing unit 19 for a predetermined number of measurements include the cumulative time Ta, which is the sum of the measurement times by the timing unit 19 for a predetermined number of measurements, and the average value (average time) of the measurement times by the timing unit 19 for a predetermined number of measurements. Here, as an example, the case in which a short-circuit detection process is performed based on the cumulative time Ta will be explained in detail.

[0091] As shown in Figure 3, the short-circuit determination unit 17 may have, for example, an accumulated time calculation unit 170 and a determination unit 171.

[0092] The cumulative time calculation unit 170 is a functional unit that accumulates multiple measurement times measured by the timing unit 19. The cumulative time calculation unit 170 accumulates a predetermined number of measurement times measured by the timing unit 19 and calculates the cumulative time Ta.

[0093] For example, the number of measurements that serve as the criterion for the short-circuit detection process, known as the criterion count Nth, is pre-stored in the storage unit 18 as information 181 about the criterion count Nth. The cumulative time calculation unit 170, for example, accumulates the measurement time for the number of measurements specified by the criterion count Nth stored in the storage unit 18 and stores it in the storage unit 18 as the cumulative time Ta.

[0094] The determination unit 171 is a functional unit that determines whether or not there is a short circuit in the coil 41 based on the cumulative time Ta. The determination unit 171 determines that the coil 41 is short-circuited if the cumulative time Ta stored in the storage unit 18 is smaller than the determination criterion time Tth.

[0095] The judgment criterion time Tth is a reference time (threshold) for determining whether or not there is a short circuit in the coil 41, and is pre-stored in the storage unit 18 as, for example, judgment criterion time Tth information 182. It is preferable that the judgment criterion time Tth be set to a time that is sufficiently shorter than, for example, the time from when the excitation of the coil 41 is started when the coil 41 is normal until the current of the coil 41 reaches the current limit value Ith.

[0096] For example, if the judgment criterion count Nth = 2 (times) and the coil 41 subject to short-circuit judgment is the B-phase coil 41B, the cumulative time calculation unit 170 counts up the value of the counter (+1) each time the measurement by the timing unit 19 starts during the excitation period of the B-phase, thereby measuring the number of measurements by the timing unit 19. Each time the cumulative time calculation unit 170 counts up the number of measurements, it accumulates the measurement time by the timing unit 19 and stores it in the storage unit 18 as cumulative time Ta. Then, when the number of measurements reaches 2, the cumulative time calculation unit 170 adds the measurement time of the second measurement to the accumulated value of the measurement times up to that point, and ends the accumulation of measurement times.

[0097] When the number of measurements reaches the judgment criterion count Nth, the determination unit 171 compares the cumulative time Ta stored in the storage unit 18 with the judgment criterion time Tth. If the cumulative time Ta is equal to or greater than the judgment criterion time Tth, the determination unit 171 determines that the B-phase coil 41B is not short-circuited and continues the excitation control of the coil 41 in normal control mode.

[0098] On the other hand, if the cumulative time Ta is less than the judgment criterion time Tth, the judgment unit 171 outputs an abnormality detection signal So that includes information indicating that the B-phase coil 41B is short-circuited. The abnormality detection signal So is input to, for example, the host device 6.

[0099] The abnormality detection signal So may be input to the signal output unit 13. In this case, the signal output unit 13 may stop the excitation of the B-phase coil 41B (switching of the H-bridge circuit 21B) from the point in time when it is determined that the B-phase coil 41B is short-circuited during the excitation period of the B-phase coil 41B.

[0100] In the example described above, we explained the case where the short-circuit detection unit 17 performs a short-circuit detection process when the control mode is the normal control mode. However, the short-circuit detection unit 17 may also perform a short-circuit detection process when the control mode is the hold control mode.

[0101] Figure 6 shows an example of the current waveform of the A-phase coil 41A when the motor 4 is driven in hold control mode before normal driving starts.

[0102] The dotted line indicated by reference numeral 600 represents the current limit value Ith. The dashed line indicated by reference numeral 601 represents the characteristics of the current flowing through the A-phase coil 41A when the A-phase coil 41A is functioning normally. On the other hand, the solid line indicated by reference numeral 602 represents the characteristics of the current on the A-phase side when the A-phase coil 41A is short-circuited.

[0103] As shown in reference numeral 601, when coil 41 is in a normal state without a short circuit, in hold control mode, the A-phase coil 41A is energized, and the current flowing through the A-phase coil 41A increases linearly and is controlled so as not to exceed the current limit value Ith=I1. When the current in the A-phase coil 41A reaches the current limit value Ith=I1, the excitation of the A-phase coil 41A is stopped, and after a predetermined time has elapsed, the A-phase coil 41A is energized again. During the hold control period, one or two phases are energized to attract the rotor 40 to the hold position (target rotation position or target standby position), and the rotor 40 is kept attracted to that position, so no switching of the excitation phase occurs.

[0104] On the other hand, in hold control mode, if the A-phase coil 41A is short-circuited, as shown in reference numeral 602, the A-phase current increases sharply immediately after the excitation of the A-phase coil 41A is started, and after the current reaches the current limit value Ith, the current drops sharply when the excitation of the A-phase coil 41A is stopped.

[0105] Thus, when coil 41 is short-circuited in hold control mode, the current of motor 4 repeatedly increases and decreases sharply, just as in normal control mode.

[0106] For example, if the judgment criterion count Nth = 10 (times), and the coil 41 subject to short-circuit judgment is the A-phase coil 41A, the cumulative time calculation unit 170 measures the number of measurements by the timing unit 19 by, for example, counting up (+1) the value of the counter each time measurement by the timing unit 19 is started during the excitation period of the A-phase. Each time the cumulative time calculation unit 170 counts up the number of measurements, it accumulates the measurement time by the timing unit 19, and stores the accumulated time Ta as cumulative time Ta information 183 in the storage unit 18. Then, when the number of measurements reaches 10, the cumulative time calculation unit 170 adds the measurement time of the 10th measurement to the accumulated value of the measurement times up to that point, and ends the accumulation of measurement times.

[0107] For example, if the A-phase coil 41A is short-circuited, the cumulative time calculation unit 170 adds the measurement times ts0 to ts9 from the 1st to the 10th measurement based on the current change indicated by reference numeral 602 in Figure 6 to obtain the cumulative time Ta1 (=ts0+ts1+…+ts9). Also, for example, if the A-phase coil 41A is not short-circuited, the cumulative time calculation unit 170 adds the measurement times tn0 to tn9 from the 1st to the 10th measurement based on the current change indicated by reference numeral 601 in Figure 6 to obtain the cumulative time Ta2 (=tn0+tn1+…+tn9).

[0108] When the number of measurements taken by the timing unit 19 reaches the criterion number Nth (=10 times), the determination unit 171 compares the cumulative time Ta calculated by the cumulative time calculation unit 170 with the criterion time Tth. For example, as shown by reference numeral 601 in Figure 6, if the cumulative time Ta2 for 10 measurements is greater than the criterion time Tth (Ta2 > Tth), the determination unit 171 determines that the A-phase coil 41A is not short-circuited and continues the excitation control of the A-phase coil 41A in hold control mode.

[0109] On the other hand, when the cumulative time Ta1 for 10 times is less than the determination reference time Tth (Ta1 < Tth), as shown by reference numeral 602 in FIG. 6, the determination unit 171 determines that the coil 41A of the A phase is short-circuited, and outputs an abnormality detection signal So including information indicating that the coil 41A of the A phase is short-circuited. Then, the signal output unit 13 generates a drive control signal Sd so as to stop exciting the coil 41A of the A phase after, for example, the time point when the abnormality detection signal So is output (the timing after the 10th measurement time ts9 is calculated).

[0110] Note that in the hold control mode, the control circuit 1 may change the current of the coil 41 to the target value over time.

[0111] FIG. 7 is a diagram showing an example of the current characteristics of the coil 41 in the hold control mode before the normal drive of the motor 4 is started. In FIG. 7, the solid line indicated by reference numeral 701 represents the current characteristics of the coil 41 when the current limit value Ith is gradually increased from zero to the target value (= I3) in the hold control mode at the start of the motor unit 5.

[0112] As shown in FIG. 7, the period during which the control mode is the hold control mode includes, for example, a first period 710 in which the current limit value setting unit 15 changes the current limit value Ith to a predetermined value (target value = I3) over time, and a second period 711 in which the current limit value setting unit 15 fixes the current limit value Ith to a predetermined value (target value = I3). The first period 710 corresponds to the period (the period of being attracted) in which the rotor 40 of the motor 4 is moved to the target standby position at the start of driving, and the second period 711 is the period in which the rotor 40 is held at the standby position at the start of driving after being moved until the start of driving. In this case, the short-circuit determination unit 17 may perform the short-circuit determination process at any timing in the first period 710. For example, the short-circuit determination unit 17 may perform the short-circuit determination process at the time t3 when the current (current limit value Ith) of the coil 41 becomes I2.

[0113] On the other hand, during the period when the current limit value Ith is changing, the magnitude of the current flowing through the coil 41 is unstable. Therefore, when performing control to change the current of the coil 41 to a target current in hold control mode, the current limit value Ith may be kept constant for a portion of the first period 710 in which the current increases, and a short-circuit detection process may be performed for that portion of the period.

[0114] For example, as shown in Figure 7, during a period 712 from time t0 to time t2 in the first period 710 in which the current limit value setting unit 15 changes the current limit value Ith to a predetermined value (e.g., I3) over time, the current limit value setting unit 15 sets the current limit value Ith to a constant value (Ith=I1). As a result, during period 712, the current of the coil 41 is limited to the current limit value Ith=I1 and remains approximately constant. At some point during this period 712 (e.g., time t1), the short-circuit determination unit 17 performs a short-circuit determination process. With this, since the current of the coil 41 is approximately constant during the period in which the short-circuit determination process is performed, it becomes possible to determine the presence or absence of a short circuit in the coil 41 with higher accuracy.

[0115] Note that the period 712 during which the current limit value Ith remains constant does not necessarily have to be the first period of the first period 710. For example, the current limit value Ith may be kept constant for a portion of the period from time t3 to time t4 in Figure 7.

[0116] Next, we will explain the flow of the short-circuit detection process by control circuit 1.

[0117] Figure 8 is a flowchart showing the flow of the short-circuit detection process by the control circuit 1 in the motor drive control device 3 according to the embodiment. Here, as an example, we will explain the processing flow when short-circuit detection is performed based on the cumulative time Ta described above.

[0118] For example, when the control mode is set to normal control mode or hold control mode, and the motor drive control device 3 is driving the motor 4 in the set control mode, the short-circuit determination unit 17 sets a flag indicating the measurement state based on the measurement state of the timing unit 19.

[0119] For example, the flag indicating the measurement status is initially set to “measurement stopped (e.g., 0)”. When the excitation of the monitored phase of motor 4 is started, the timing unit 19 starts measuring the excitation time. At this time, the short-circuit detection unit 17 sets the flag indicating the measurement status to “measurement started (e.g., 1)” in response to the start of measurement by the timing unit 19 (step S1).

[0120] Next, the short-circuit detection unit 17 performs a calculation process for the cumulative time Ta (step S2).

[0121] Figure 9 is a flowchart showing the flow of the calculation process for cumulative time Ta (step S2). In the process of calculating the cumulative time Ta, the short-circuit determination unit 17 first determines whether the flag indicating the measurement status is "measurement started" (step S21). If the flag indicating the measurement status is not "measurement started", that is, if the flag indicating the measurement status is "measurement stopped" (step S21: NO), the short-circuit determination unit 17 terminates the process of calculating the cumulative time Ta (step S2).

[0122] On the other hand, if the flag indicating the measurement status is "measurement started" (step S21: YES), the short-circuit determination unit 17 determines whether the current in the coil 41 of the monitored phase has reached the current limit value Ith (step S22). For example, the short-circuit determination unit 17 determines whether the current in the coil 41 of the monitored phase has reached the current limit value Ith by monitoring whether the timing unit 19 is measuring the excitation time.

[0123] If the timing unit 19 is measuring the excitation time, the short-circuit determination unit 17 determines that the current in the coil 41 of the monitored phase has not reached the current limit value Ith (step S22: NO), and terminates the calculation process of the cumulative time Ta (step S2).

[0124] If the timing unit 19 is not measuring the excitation time (is stopped), the short-circuit determination unit 17 determines that the current in the coil 41 of the monitored phase has reached the current limit value Ith (step S22: YES), and calculates the cumulative time Ta by accumulating the measurement times measured by the timing unit 19 (step S23). The short-circuit determination unit 17 also switches the flag indicating the measurement status from "measurement started" to "measurement stopped" (step S24). After that, the short-circuit determination unit 17 terminates the calculation process of the cumulative time Ta (step S2).

[0125] Returning to Figure 8, after the calculation of the cumulative time Ta (step S2) is completed, the short-circuit determination unit 17 determines whether the flag indicating the measurement status is "measurement stopped" or not (step S3). If the flag indicating the measurement status is not "measurement stopped" (step S3: NO), the short-circuit determination unit 17 returns to step S2.

[0126] If the flag indicating the measurement status is "measurement stopped" (step S3: YES), the short-circuit detection unit 17 increments the measurement count (+1) (step S4). Next, the short-circuit detection unit 17 determines whether the measurement count has reached the criterion count Nth (step S5). If the measurement count has not reached the criterion count Nth (step S5: NO), the short-circuit detection unit 17 waits until the next measurement starts (step S6). After that, the short-circuit detection unit 17 returns to step S1.

[0127] On the other hand, if the number of measurements reaches the judgment criterion count Nth (step S5: YES), the short-circuit determination unit 17 determines whether or not there is a short circuit in the coil 41 of the phase to be monitored (step S7).

[0128] Figure 10 is a flowchart showing the flow of the process (step S7) for determining whether or not there is a short circuit in coil 41.

[0129] In step S7, first, the short-circuit detection unit 17 determines whether the cumulative time Ta is less than the judgment criterion time Tth (step S71). If the cumulative time Ta is less than the judgment criterion time Tth (step S71: YES), the short-circuit detection unit 17 determines that the coil 41 of the monitored phase is short-circuited (step S72). In this case, the short-circuit detection unit 17 outputs an abnormality detection signal So and terminates the process of step S7.

[0130] On the other hand, if the cumulative time Ta is equal to or greater than the judgment criterion time Tth (step S71: NO), the short-circuit determination unit 17 determines that the coil 41 of the monitored phase is not short-circuited (step S73), terminates the process in step S7, and resets the cumulative time Ta. The short-circuit determination process is repeated at regular intervals.

[0131] In the motor drive control device 3 according to this embodiment, the control circuit 1 measures the time during which the coil 41 is excited (excitation time), and stops the excitation and stops measuring the excitation time when the current of the coil 41 reaches the current limit value Ith.

[0132] As described above, when the coil 41 of the motor 4 is short-circuited, the time from when the excitation of the coil 41 starts until the current in the coil 41 reaches the current limit value Ith and the excitation stops is shorter compared to when the coil 41 is not short-circuited. Therefore, the control circuit 1 determines that the coil 41 is short-circuited when the measurement time is less than the threshold. This allows for more rapid detection of a short circuit in the coil 41 of the motor 4.

[0133] Furthermore, many conventional microcontrollers for motor drive control that do not have a coil short-circuit detection function have a function to measure the period during which the motor coil is excited, that is, the period during which each switching element of the H-bridge circuit, which is the motor drive circuit, is turned on.

[0134] Therefore, by applying a conventional microcontroller for motor drive control as the control circuit 1 according to this embodiment, and incorporating the program (software) related to the short-circuit detection process described above into the microcontroller, it becomes possible to realize the short-circuit detection function of the motor 4 at low cost using an existing microcontroller without developing new hardware as the control circuit 1.

[0135] Furthermore, in the motor drive control device 3, the control circuit 1 measures the time that coils 41A and 41B of the motor 4 are energized for each phase, and performs a short-circuit determination process for each phase based on the measured time for each phase. This makes it possible to reliably detect a short circuit in the coils 41 even when the motor 4 has multiple phase coils 41.

[0136] Furthermore, in the motor drive control device 3, the control circuit 1 may calculate the excitation time (cumulative time or average time) based on the measurement time for a predetermined number of measurements, and if that excitation time is less than a threshold, it may determine that the coil 41 in the motor is short-circuited. According to this, for example, even if the current in the coil 41 increases rapidly due to load fluctuations of the motor 4 while the motor 4 is in a normal state, it is possible to prevent false detection of a short circuit in the coil 41 and to achieve a more accurate short-circuit detection function.

[0137] Furthermore, in the motor drive control device 3, the control circuit 1 has a hold control mode as a control mode for controlling the drive of the motor 4, which moves and maintains the rotor 40 of the motor 4 to a predetermined standby position, and the control circuit 1 may perform a short-circuit detection process during the period when the control mode is the hold control mode. According to this, for example, if the motor 4 is operated in hold control mode before normal operation is started, it is possible to detect a short circuit in coil 41 before normal operation of the motor 4 is started and stop the operation of the motor 4. This makes it possible to improve the safety of the operation of the motor 4.

[0138] Furthermore, as shown in Figure 7, the control mode includes a first period 710 in which the control circuit 1 changes the current limit value Ith to a predetermined value (I3) over time, and a second period 711 in which the control circuit 1 fixes the current limit value Ith to the predetermined value (I3). The control circuit 1 may also set the current limit value Ith to a constant value (for example, I1) during a portion of the first period 710 (period 712), and perform a short-circuit detection process during that period 712. According to this, even in hold control mode, which increases the current to a target value, a period is provided during which the current does not change, and short-circuit detection processing is performed during that period, thus preventing a decrease in the accuracy of short-circuit detection.

[0139] Furthermore, in the motor drive control device 3, the control circuit 1 has a normal control mode for moving the rotor 40 of the motor 4 to a rotational position specified by the drive command Sc, as a control mode for controlling the drive of the motor 4, and a short-circuit detection process may be performed in the normal control mode. According to this, even if a short circuit occurs in coil 41 during normal operation of motor 4, it becomes possible to quickly detect the short circuit in coil 41.

[0140] Furthermore, in the motor drive control device 3, the drive circuit 2 includes H-bridge circuits 21A and 21B consisting of a plurality of switching elements 22 to 25 whose on / off state is controlled by a drive control signal Sd, and the control circuit 1 measures the time during which the plurality of switching elements 22 to 25 are turned on so that current flows in one direction through the coil 41, and defines the measured time as the time during which the coil 41 is excited (excitation time). According to this, by monitoring the drive control signal Sd, it is easy to determine whether or not the coil 41 is energized, making it easy to measure the time during which the coil 41 is energized.

[0141] <<Extension of the Embodiment>> Although the present invention has been specifically described above based on embodiments, it goes without saying that the present invention is not limited thereto and can be modified in various ways without departing from its essence.

[0142] For example, the number of phases of the motor 4 in the above embodiment is not limited to two phases.

[0143] Furthermore, the motor 4 in the above embodiment is not limited to a stepping motor. For example, the motor may be a brushless DC motor.

[0144] Furthermore, while Figure 7 illustrates a case where the current (current limit value Ith) increases linearly during the first period 710 of the hold control mode, the case is not limited to this. For example, the current (current limit value Ith) may increase in a stepped manner or in a curved manner during the first period 710. Furthermore, the short-circuit detection process for coil 41 in hold control mode is not limited to the hold control mode period before the normal operation of motor 4 starts as shown in Figure 6 or Figure 7, but can also be applied to the hold control mode period before the normal operation of motor 4 stops.

[0145] Furthermore, in the above embodiment, an example was given in which the measurement time by the timing unit 19 is accumulated for a predetermined number of times, but the number of measurements to be accumulated is not particularly limited. For example, as described above, the measurement time may not be accumulated, and a short circuit determination may be made by comparing the measurement time of one measurement with a threshold value.

[0146] Furthermore, in the above embodiment, when the coil is excited, the switching element does not turn off between the time it is turned on and the time the coil current reaches the current limit. On the other hand, in the case of PWM control, where the PWM duty cycle is determined for each carrier frequency, the switching element repeatedly turns on and off according to the carrier frequency even before the coil current reaches the current limit. The present invention can also be used in such control cases. In the above embodiment, the time from when the switching element turns on until the coil current reaches the current limit and the switching element turns off was measured, but in the case of PWM control, the same effect as in the above embodiment can be obtained by measuring the time from when the coil excitation starts until the coil current reaches the current limit.

[0147] Furthermore, while the example given illustrates a case where each functional part of the control circuit 1 is primarily implemented by program processing such as a microcontroller, the example is not limited to this, and some or all of the functional parts of the control circuit 1 may be implemented by dedicated circuits (hardware).

[0148] Furthermore, the flowchart described above is merely an example illustrating the operation and is not limited to it. In other words, the steps shown in each diagram of the flowchart are specific examples and are not limited to this flow. For example, the order of some processes may be changed, other processes may be inserted between each process, or some processes may be performed in parallel. [Explanation of Symbols]

[0149] 1...Control circuit, 2...Drive circuit, 3...Motor drive control device, 4...Motor, 5...Motor unit, 6...Host device, 10...Drive control signal generation unit, 11...Drive command acquisition unit, 12...Control mode determination unit, 13...Signal output unit, 14...Current value acquisition unit, 15...Current limit value setting unit, 16...Current limit unit, 17...Short circuit detection unit, 18...Storage unit, 19...Timer unit, 20A, 20B...Current detection circuit, 21, 21A, 21B...H-bridge circuit (inverter circuit), 22~25...Switching element, 26~29...Diode, 40...Rotor, 41, 41A ,41B...coil, 42A_1,42A_2,42B_1,42B_2...stator yoke, 170...cumulative time calculation unit, 171...determination unit, 180...current limit value Ith information, 181...judgment criterion count Nth information, 182...judgment criterion time Tth information, 183...cumulative time Ta information, AP,AN,BP,BN...terminals, Ith...current limit value, Nth...judgment criterion count, Sc...drive command, Sd...drive control signal, Sia,Sib...current detection signal, So...abnormality detection signal, Ta,Ta1,Ta2...cumulative time, Tth...judgment criterion time.

Claims

1. A control circuit that generates a drive control signal to control the drive of a motor, The system includes a drive circuit that energizes the motor coils based on the drive control signal, The aforementioned control circuit is A drive control signal generation unit generates the drive control signal so that the motor enters a drive state in accordance with the drive command, A current limit value setting unit sets a reference current limit value for limiting the current flowing through the coil, A current limiting unit instructs the drive control signal generation unit to stop exciting the coil when the current flowing through the coil reaches the current limit value, A timing unit that measures the time the coil is energized by the drive circuit, The system includes a short-circuit determination unit that performs a short-circuit determination process to determine whether or not the coil of the motor is short-circuited based on the time measured by the time measurement unit, The short-circuit determination unit determines that the coil is short-circuited if the time measured by the timing unit is less than a threshold value during the short-circuit determination process. The drive circuit includes an H-bridge circuit consisting of a plurality of switching elements whose on / off state is controlled by the drive control signal. The timing unit monitors the drive control signal and repeatedly measures the time during which the plurality of switching elements are turned on so that current flows in one direction through the coil, and takes the measured time as the time the coil is energized. The short-circuit determination unit is, A cumulative time calculation unit calculates the cumulative time obtained by accumulating the measurement time by the timing unit for a predetermined number of measurement times, The system includes a determination unit that determines that the coil in the motor is short-circuited when the cumulative time is less than the threshold. Motor drive control device.

2. In the motor drive control device according to claim 1, The motor is a stepping motor having two phase coils, The timing unit measures the time the coil is energized for each phase. The short-circuit determination unit performs the short-circuit determination process for each phase based on the time for each phase measured by the timing unit. Motor drive control device.

3. In the motor drive control device according to claim 1 or 2, The control circuit has a control mode for controlling the drive of the motor, which is a hold control mode for moving and maintaining the rotor of the motor to a predetermined standby position before the start of normal drive of the motor or before the stop of normal drive. The short-circuit determination unit performs the short-circuit determination process during the period when the control mode is the hold control mode. Motor drive control device.

4. In the motor drive control device according to claim 3, During the period in which the control mode is the hold control mode, the current limit value setting unit includes a first period in which it changes the current limit value up to a predetermined value over time, and a second period in which it fixes the current limit value at the predetermined value. The current limit value setting unit keeps the current limit value constant for a portion of the first period. The short-circuit determination unit performs the short-circuit determination process during the aforementioned period. Motor drive control device.

5. In the motor drive control device according to any one of claims 1 to 4, The control circuit has a control mode for controlling the drive of the motor, which is a normal control mode for moving the rotor of the motor to a rotational position specified by the drive command. The short-circuit determination unit performs the short-circuit determination process in the normal control mode. Motor drive control device.

6. A motor drive control device according to any one of claims 1 to 5, The motor comprises Motor unit.

7. A motor drive control method for rotating the rotor of a motor by exciting the coil of the motor with a drive circuit including an H-bridge circuit consisting of a plurality of switching elements whose on / off state is controlled by a drive control signal, The first step is to energize the coil so that the motor enters a drive state in accordance with the drive command, A second step is to stop the excitation of the coil when the current flowing through the coil exceeds a current limit value that serves as a reference for limiting the current flowing through the coil. A third step involves monitoring the drive control signal to repeatedly measure the time during which the multiple switching elements are turned on so that current flows in one direction through the coil, and taking the measured time as the time the coil is energized. A fourth step is to calculate the cumulative time obtained by accumulating the time measured in the third step for a predetermined number of measurement times, The fifth step includes determining that the coil in the motor is short-circuited if the cumulative time is less than a threshold. Motor drive control method.

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