Patent Description:
PTL <NUM> discloses a shut-off valve device that determines a stall state or a step-out state of a stepping motor.

This shut-off valve device includes a drive control circuit that controls driving of the stepping motor and a valve abnormality circuit that determines a stall state or step-out state of the stepping motor. As illustrated in <FIG>, the shut-off valve device is capable of determining the stall state or step-out state by comparing a maximum value or a wave height of the maximum value in a drive voltage waveform detected from the stepping motor with a predetermined threshold. <FIG> is a graph illustrating a current level change while the stepping motor is driven.

PTL2 discloses a step-out detection method for stepping motors. In the step-out detection method, a motor current waveform in a stepping motor driver that drives the stepping motor is converted into a rectangular wave signal, and this rectangular wave signal is converted into a voltage signal. Then, a voltage value acquired from the voltage signal is compared with a reference voltage to determine occurrence of the step-out state. <CIT> discloses a motor control circuit for detecting a step-out of a stepping motor. A reference voltage determined based on the ratio between resistors is fed, along with a shaped waveform, to a voltage comparator where they are compared constantly with each other. Then the voltage of the shaped waveform exceeds the reference voltage, the voltage comparator delivers a comparison output. When a stepping motor steps out, the voltage is subjected to chopping immediately after switching the conducting direction of a coil and the shaped waveform exceeds the reference voltage. Consequently, the comparison output of the voltage comparator delivers a signal at the stage of step-out. A control circuit then makes a decision that the stepping motor has stepped out and stops the motor or delivers an alarm to another device. <CIT> discloses a device for detecting disconnection for use in a stepping motor driver having a driver circuit which comprises a pair of windings wound in a bifilar turn arrangement; a pair of MOSFETs connected to the other end of each winding; a common current detecting resistor connected between MOSFETs and ground; a first reference voltage generator for producing a first reference voltage; a second reference voltage generator for producing a second reference voltage lower than first reference voltage; a decision circuit for comparing the detection voltage on current detecting resistor with second reference voltage to produce an alarm signal when detection voltage is higher than second reference voltage; and a disconnection detector for receiving an alarm signal from decision circuit after comparator produces a chopper signal to produce a disconnection signal upon occurrence of line-disconnection in one of the windings. <CIT> discloses a fault detecting and processing method for a continuous variable valve lift mechanism relating to the technical field of engines and used for discovering and processing the problem of motor stalling. The fault detecting method comprises the steps that a motor is started, and a practical valve lift of the continuous variable valve lift mechanism in a preset time period is obtained; and when the practical valve lift is unequal to a target valve lift in the preset time period, and the valve lift difference between the practical valve lift and the target valve lift is greater than a preset difference, or when the practical valve lift is unequal to the target valve lift in the preset time period, and the practical valve lift changing rate of the practical valve lift is smaller than a preset changing rate, motor shaft seizing is confirmed. The fault detecting and processing method is used for judging whether motor shaft seizing occurs, so that motor stalling is eliminated in time.

Both PTL1 and PTL2 disclose techniques focused on a difference in current and voltage waveforms between the normal and step-out states. These techniques are capable of detecting a waveform difference in a stable step-out state. However, in a practical operating environment, the stepping motor often repeats unstable behavior such as slight rotation or return. In such case, the waveform difference becomes unclear and it becomes difficult to distinguish between the normal and step-out states.

The present disclosure provides a stepping motor abnormality detecting device that is capable of correcting a waveform detected in an unstable state to reliably detect an abnormality of the stepping motor.

The invention is set out in appended claim <NUM>.

The present disclosure provides the stepping motor abnormality detecting device capable of detecting the abnormality of the stepping motor even in the unstable operating environment.

Exemplary embodiments will be detailed below with reference to the drawings. However, detailed description more than necessary may be omitted. For example, details of broadly-known facts or duplicate description of substantially the same structure may be omitted. This is to prevent the following description from becoming redundant more than necessary and facilitate understanding of those skilled in the art.

The attached drawings and the following description are provided to enable those skilled in the art to sufficiently understand the present disclosure, and do not intend to limit the subject matters in the scope of claims.

The first exemplary embodiment will be described below with referent to <FIG>.

<FIG> is a block diagram of an example of a configuration of stepping motor abnormality detecting device <NUM> according to the first exemplary embodiment. As illustrated in <FIG>, stepping motor <NUM> is connected to stepping motor driver <NUM>. Stepping motor driver <NUM> is connected to power supply <NUM> via current level detector <NUM>. Current level detector <NUM> is also connected to determiner <NUM>. Determiner <NUM> and stepping motor driver <NUM> are connected to controller <NUM> and controlled by controller <NUM>.

Power supply <NUM> is configured by connecting a plurality of primary lithium batteries (not illustrated) in parallel. Power supply <NUM> has a battery capacity equivalent to a current capacity consumed by an electrical system within a validity period of verification. The validity period is, for example, <NUM> years.

Current level detector <NUM> has instantaneous current level detector <NUM> that detects a current level of instantaneous current flowing in stepping motor driver <NUM>. Current level detector <NUM> further includes integrator <NUM> that integrates the current level detected, and power supply impedance estimator <NUM> that estimates impedance of power supply <NUM> (hereinafter referred to as power supply impedance).

Stepping motor driver <NUM> is controlled by controller <NUM>, and outputs a drive pulse for driving stepping motor <NUM> to drive stepping motor <NUM>.

When stepping motor <NUM> is employed in a gas meter, stepping motor <NUM> is regarded as a valve for controlling a gas flow rate. In this case, stepping motor <NUM> performs two types of operation: a shut-off operation to shut off gas and a return operation to release the gas shut-off operation.

Determiner <NUM> includes corrector <NUM>. Corrector <NUM> uses the power supply impedance acquired by power supply impedance estimator <NUM> to correct the current level detected by instantaneous current level detector <NUM> and integrated by integrator <NUM>. Still more, determiner <NUM> includes first comparator <NUM> and second comparator <NUM>. Each of first comparator <NUM> and second comparator <NUM> compares the current level corrected by corrector <NUM> with a predetermined determination threshold. The determination threshold used in first comparator <NUM> is set by first determination threshold setter <NUM>. The determination threshold used in second comparator <NUM> is set by second determination threshold setter <NUM>.

Controller <NUM> controls stepping motor driver <NUM>. Controller <NUM> performs the shut-off and return operations of the gas meter by operating stepping motor <NUM> via stepping motor driver <NUM>. Still more, controller <NUM> retains timing information that specifies timing to detect the current level by current level detector <NUM>. Furthermore, controller <NUM> stores a determination result acquired by determiner <NUM>.

<FIG> is a block diagram illustrating an example of a configuration of current level detector <NUM> according to the first exemplary embodiment.

Instantaneous current level detector <NUM> has resistance <NUM>.

Integrator <NUM> integrates the current flowing from resistance <NUM> to stepping motor driver <NUM> by resistance <NUM> and capacitor <NUM>. Capacitor <NUM> is connected to ground (GND).

Analog-digital converter <NUM> has a function to convert a current level of input current from an analog value to a digital value. More specifically, using an output voltage of power supply <NUM> as a reference voltage, voltage acquired by integrating current flowing in resistance <NUM> by integrator <NUM> is converted into a digital value. Accordingly, the smaller the digital value is, the larger the current is. In the present exemplary embodiment, this digital value is regarded as the current level. The converted digital value is output to determiner <NUM>, and determiner <NUM> uses this digital value for determination. Analog-digital converter <NUM> also functions as power supply impedance estimator <NUM>.

The operation of stepping motor abnormality detecting device <NUM> as configured above will be described below. In stepping motor abnormality detecting device <NUM>, instantaneous current level detector <NUM> acquires a current level while stepping motor <NUM> is driven. Then, corrector <NUM> corrects the current level using the power supply impedance estimated by power supply impedance estimator <NUM>. Then, first comparator <NUM> and second comparator <NUM> compare the current level after correction with the predetermined determination thresholds, and determiner <NUM> determines abnormality of the stepping motor. The operation will be detailed below.

Current level detector <NUM> retains the timing information that specifies timing to detect the current level. Current level detector <NUM> acquires the current level at a predetermined timing, based on the timing information, while stepping motor <NUM> is driven. More specifically, controller <NUM> controls stepping motor driver <NUM> to drive stepping motor <NUM>. While stepping motor <NUM> is driven, analog-digital converter <NUM> converts the current level acquired by instantaneous current level detector <NUM> into a digital value. A timing that analog-digital converter <NUM> acquires the digital value can be arbitrary set. However, the timing is limited to while stepping motor <NUM> is driven. The number of times that analog-digital converter <NUM> acquires the digital value is not limited to once. For example, analog-digital converter <NUM> can calculate an average by acquiring the digital value more than once to prevent faulty determination typically due to noise.

In <FIG>, a current level change is illustrated according to a difference in power supply impedance while stepping motor <NUM> is driven when stepping motor <NUM> is employed for driving a shut-off valve. <FIG> illustrates the current level change in a period when stepping motor driver <NUM> is turned ON at timing A to change the shut-off vale from a full open state to a full close state by closing the shut-off valve until stepping motor driver <NUM> is turned OFF at timing B after the rotation of stepping motor <NUM> is stopped. In <FIG>, the current level is the digital value as described above.

In <FIG>, the current level change immediately before timing B indicates that a load has increased due to stopping of the rotation of stepping motor <NUM>. Still more, <FIG> indicates that the current level is higher, compared with the current level in the normal state, when the impedance is high. Accordingly, it can be confirmed that the current flow is increased by increased internal impedance of the lithium batteries configuring power supply <NUM> due to temperature change and decreased battery capacity.

The current level is acquired by converting instantaneous current flowing in stepping motor driver <NUM> into voltage, using resistance <NUM>. The current level detected is divided by a voltage value of power supply <NUM> and then the result is multiplied by <NUM>. In other words, when stepping motor <NUM> is not operating, the detected current level and the voltage value of power supply <NUM> are equivalent, and thus the calculated current level becomes <NUM>. In <FIG>, the current level change from timing B to timing C indicates a state that the current level gradually reaches <NUM> by the action of integrator <NUM> after current consumption of stepping motor <NUM> becomes <NUM> at timing B.

Stepping motor abnormality detecting device <NUM> acquires the power supply impedance by power supply impedance estimator <NUM> at a moment between operation ON and OFF. More specifically, the power supply impedance is calculated by acquiring a difference between the upper limit of current level, i.e., <NUM>, and the current level detected at each timing of operation ON (timing A) and operation OFF (timing B). As illustrated in <FIG>, when the power supply impedance is high, the aforementioned difference becomes small at operation ON and large at operation OFF. Corrector <NUM> corrects the current level according to the power supply impedance acquired by power supply impedance estimator <NUM>.

As described above, in current level detector <NUM>, analog-digital converter <NUM> converts the current flowing at the predetermined timing while stepping motor is driven into the current level indicated by the digital value. Corrector <NUM> uses the power supply impedance acquired by power supply impedance estimator <NUM> to correct the current level acquired by integrator <NUM> to the current level used for abnormality determination.

<FIG> is a graph illustrating the current level after correcting the current level illustrated in <FIG> by corrector <NUM>. In <FIG>, it can be confirmed that an absolute value of the current level is large at operation ON and during the operation of the stepping motor, and an absolute value of the current level is small at operation OFF. By performing correction described above, the current level change due to power supply impedance can be converted in to a constant current level change. This can significantly reduce faulty determination by determiner <NUM> described later due to variation in power supply impedance. As a result, high precision abnormality detection can be achieved.

<FIG> is a flow chart illustrating an abnormality determining method in determiner <NUM> according to the first exemplary embodiment.

<FIG> is a graph illustrating the current level of stepping motor <NUM> during the normal operation, the current level of stepping motor during abnormal operation (disconnection), the current level of stepping motor <NUM> in a step-out or stuck state, a first threshold (first determination threshold), and a second threshold (second determination threshold).

As illustrated in <FIG>, stepping motor abnormality detecting device <NUM> first detects current level Z1 corrected at the predetermined timing while the stepping motor is driven (Step S1). In the present exemplary embodiment, the predetermined timing is set in a period between point D and point E in <FIG> where the current level is stable. Next, first comparator <NUM> compares current level Z1 with the first threshold (Step S2). In Step S2, when current level Z1 is determined to be greater than the first threshold (Yes in Step S2), determiner <NUM> determines that stepping motor <NUM> is disconnected (R1). On the other hand, when current level Z1 is determined to be equal to or lower than the first threshold in Step S2 (No in Step S2), second comparator <NUM> compares current level Z1 with the second threshold (Step S3). In Step S3, when current level Z1 is determined to be less than the second threshold (Yes in Step S3), determiner <NUM> determines that stepping motor <NUM> is in the step-out or stuck state (R2). When no abnormality is determined through comparison of current level Z1 with the first threshold and the second threshold (No in Step S3), determiner <NUM> determines that stepping motor <NUM> is normally operated (R3). Note that processes in Step S2 and Step S3 may be performed in a reverse order in the flow chart illustrated in <FIG>.

As described above, stepping motor abnormality detecting device <NUM> in the first exemplary embodiment includes power supply <NUM>, current level detector <NUM>, stepping motor driver <NUM>, and determiner <NUM>. Current level detector <NUM> detects the current level of the instantaneous current flowing from power supply <NUM> to stepping motor driver <NUM>, and integrates the instantaneous current level detected to estimate the power supply impedance. Determiner <NUM> corrects the integrated value, using the power supply impedance, and compares the corrected value with the predetermined thresholds.

Accordingly, even during the unstable operation, stepping motor abnormality detecting device <NUM> is capable of detecting the abnormal operation, such as disconnection and sticking, of the stepping motor at high precision without being affected by the unstable operation of the stepping motor because the current level is corrected according to the power supply impedance.

The exemplary embodiment refers to the example of operation in which the current level is detected in a period at the stable current level. However, a current level detection timing is not limited to the period at the stable current level. Even in a period that the current level changes, stepping motor abnormality detecting device <NUM> is capable of detecting the abnormality of the stepping motor by setting the first threshold and the second threshold to values that can determine abnormality.

In the exemplary embodiment, stepping motor abnormality detecting device <NUM> may input only the current level of the current flowing in stepping motor driver <NUM> to analog-digital converter <NUM> without using instantaneous current level detector <NUM> and integrator <NUM>.

Claim 1:
A stepping motor abnormality detecting device (<NUM>) comprising:
a stepping motor driver (<NUM>) configured to output a drive pulse for driving a stepping motor (<NUM>);
a power supply (<NUM>) configured to supply power to the stepping motor driver (<NUM>);
a current level detector (<NUM>) configured to detect a current level of current flowing in the stepping motor driver (<NUM>); and
a determiner (<NUM>) configured to determine whether or not the stepping motor (<NUM>) is in a normal operation state by comparing the current level detected by the current level detector (<NUM>) with a determination threshold predetermined based on a current level when the stepping motor (<NUM>) operates normally,
characterized in that
the current level detector (<NUM>) includes a power supply impedance estimator (<NUM>) that estimates power supply impedance of the power supply (<NUM>), and the determination threshold or the current level is corrected based on the power supply impedance estimated.