JPS61167397A - Abnormal current detector of stepping motor - Google Patents

Abstract

PURPOSE:To simplify a circuit configuration by detecting that a voltage drop becomes the prescribed voltage or higher at a common resistor, and discriminating an abnormal current when the detecting time becomes the prescribed time or higher, thereby allowing a detecting system to be only one. CONSTITUTION:A voltage detector 10 is composed of a transistor Tr5 grounded through resistors R2, R3 at a collector and a Zener diode Dz for deciding the prescribed voltage value to detect that the voltage drop of a common resistor Ra is the prescribed value or higher. A malfunction discriminator 20 outputs a malfunction discrimination signal when the detecting time of the detector 10 becomes the prescribed time or larger. The prescribed time in the discriminator 20 is determined by an input voltage and time constant to an integrator and a reference voltage of a comparator 5.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides normal energization control for stator coils corresponding to each phase of a stepping motor used in terminal devices such as printers or various industrial equipment. The present invention relates to an abnormal current detection device for a stepping motor that detects an abnormality when an undesired current continues to flow.

[Prior Art] Conventionally, as an abnormal current detection device of this kind, for example, assuming a four-phase stepping motor, a device as shown in FIG. 3 has been considered. In the same figure, Ll, L2, L
3, L4 is a stator coil corresponding to each phase of the stepping motor, and one end of each stator coil L1 to L4 is connected to the power supply Vl via a common resistor Ra to reduce heat generation when the motor is driven, and each stator coil L1 to L
The other ends of 4 are transistors Tr1 whose emitters are grounded, respectively.
゜Tr2. Tr3. Connected to the collector of Tr4.

By controlling the application timing of control signals to the bases of the transistors 7r1 to Tr4, energization from the power source 2 to each of the stator coils L1 to L4 is controlled, thereby driving the stepping motor.

On the other hand, each of the stator coils L1 to L4 is connected to each of the transistors 7r1 to Tr4 at its connection end with a current detection circuit 1.2.3 for detecting the current flowing through the stator coil.
4 is connected. To explain the specific configuration of the current detection circuits 1 to 4, a transistor Try (PNP) whose emitter is connected to the voltage ll1vI11 and whose collector is grounded via resistors R2 and R3, and the resistor R
2. It has an integrating circuit composed of a resistor R4 and a capacitor C that integrates the divided voltage by R3, and the base of the transistor Tr5 is connected to the stator coil via the resistor R1. Further, 5 is the circuit power supply voltage Vcc
The voltage divided by resistors FcR5 and R6 is used as the reference voltage (inverting input terminal), and for inputs higher than this reference voltage (
This is a comparator circuit that outputs an H level signal (non-inverting input terminal), and the output of each of the current detection circuits 1 to 4, that is, the output of each integrating circuit, is connected to the comparator circuit 5 through diodes 01, D2, Q3, and Q4. (non-inverting input terminal).

In the above-mentioned device, each time a current flows through the stator coil, the transistor Tr5 of the corresponding current detection circuit becomes conductive, and the capacitor C forming the integrating circuit is charged. Since the time for energizing each stator coil 1 to L4 due to the on/off operation of The comparator circuit 5 maintains an L level output.

On the other hand, a transistor (T
If a current that is not caused by normal conduction 1IIJ- continues to flow through the stator coil due to a short-circuit failure in rl to T"4), the transistor Tr5 of the corresponding current detection circuit continues to conduct during that time, and the output of the integrating circuit When the voltage becomes equal to or higher than the reference voltage of the comparator circuit 5, the output of the comparator circuit 5 becomes H level.

The H level output of the comparator circuit 5 is used as an abnormality detection signal to operate an alarm circuit (not shown).

[Problems to be Solved by the Invention] However, in the conventional abnormal current detection device for a stepping motor as shown in FIG. Since current is detected, a circuit is required to detect the presence or absence of current for each stator coil and coil corresponding to each phase.

Therefore, there are problems in that the circuit configuration becomes complicated and the cost increases. For stator coils that are energized simultaneously, it is possible to put together a circuit that detects the presence or absence of current as described above, but even in that case, multiple detection circuits are required for the stepping motor. becomes.

[Means for Solving the Problems] The present invention has been made by focusing on the above problems, and connects the stator coils corresponding to each phase to the power supply via a common resistor, and also connects the stator coils corresponding to each phase to each stator coil through a common resistor. This is an abnormal current detection device for a stepping motor driven by controlling energization, which has a simplified circuit configuration. The configuration includes a voltage detection means for detecting that the voltage drop across the common resistor exceeds a predetermined voltage value, and an abnormality for determining an abnormality when the detection time by the voltage detection means exceeds a predetermined time. The apparatus further includes a discriminating means.

[Embodiments of the invention] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a circuit diagram showing an example of an abnormal current detection circuit for a stepping motor according to the present invention. This example also concerns a four-phase stepping motor, but in FIG. 1, each of the stator coils 1 to L4 corresponding to each phase has one end connected to the common resistance Ra, as in the case of FIG. Connected to the power supply Vm through, and the other end is energized! l1III
It is connected to transistors Trl to Tr4 for III.

Further, in the figure, 10 is a voltage detection circuit that detects that the voltage drop across the common resistor Ra exceeds a predetermined voltage value. The transistor Tr5 has a transistor Tr5 that is grounded through resistors R2 and R3, and a Zener diode Dl that determines the predetermined voltage value.
5 is connected to a common resistor Ra and a common connection point of each of the stator coils L1 to L4 via a resistor R1 and a Zener diode Dz. Reference numeral 20 denotes an abnormality determination circuit that outputs an abnormality determination signal when the detection time in the voltage detection circuit 10 exceeds a predetermined time. It has a comparison circuit 5 which uses a voltage obtained by dividing the power supply Vcc by resistors R5 and R6 as a reference voltage, and outputs an H level signal as an abnormality determination signal when the output from the integrating circuit exceeds the reference voltage, The above integration circuit is the voltage detection circuit 1
The divided voltage across resistors R2 and R3 at 0 is integrated. The predetermined time in the abnormality determination circuit 20 is determined by the input voltage to the integration circuit and its time constant, and the reference voltage of the comparison circuit 5.

Next, the operation will be explained according to the timing chart shown in FIG.

The transistors Tr1 to 7r4 for controlling the energization of the stator coils L1 to 4 are operated, for example, for the transistor 7r4 until time t2, from time t4 to t6, after time t8, and for the transistor tr2 from time tl to t3,
Time t5 to t7, transistor tr3, time t2 to t4, time t6 to t8, transistor tr4
For up to time t1, from time t3 to t5, time t1
Thereafter, when each stator coil L1 is turned on at the same time and drive control of the stepping motor is performed, each stator coil L1
The currents 11 to 14 flowing through L4 appear as a sawtooth waveform when each corresponding transistor T' is in the on state. Therefore, the voltage at the common resistor Ra due to this superposition of currents in each stator coil The descent Va is at time t
A sawtooth waveform occurs between i and ti+1 (i = 1.2..., 8). And this voltage drop V
a is a Zener diode Qz in the voltage detection circuit 10
When the Zener voltage voz or higher becomes higher than the voltage detection circuit 10, the transistor Tr5 of the voltage detection circuit 10 becomes conductive, and the abnormality determination circuit 20
The capacitor C of the integrating circuit is charged with a predetermined time constant. Here, in the normal case, the time during which the voltage drop Va resulting in the sawtooth waveform exceeds the Zener voltage is relatively short.1. The voltage charged to the capacitor C in the integrating circuit does not reach the reference voltage of the comparator circuit 5, and the output of the comparator circuit 5 remains at the L level.

On the other hand, assuming that, for example, the transistor Tr2 for controlling the energization of the stator coil L2 causes a short-circuit failure or the like after time t5, and the transistor Tr2 becomes conductive after time t5, the current I2 that originally flows through the stator coil L2 should be cut off at time t7, time t7
Since the current continues to flow through the stator coil 2 thereafter, the voltage drop va across the common resistor Ra does not drop at time T7. As a result, the voltage drop is 1. between time t6 and tl. The state in which /a is equal to or higher than the Zener voltage VDZ is maintained even after time t7, during which time the transistor 7r5 of the voltage detection circuit 10 becomes conductive, and the abnormality determination circuit 20
The capacitor C of is charged.

When the charging voltage of the capacitor C reaches the reference voltage of the comparator circuit 5, the output of the comparator circuit 5 rises to H level. That is, an abnormality determination signal is output from the abnormality determination circuit 20.

In this embodiment, a four-phase stepping motor has been described, but the present invention can of course be applied to other stepping motors. Moreover, other methods may be used for controlling the energization of the stator coils corresponding to each phase.

[Effects of the Invention] As described above, according to the present invention, it is detected that the voltage drop across the common resistor connected between each stator coil and the power supply is equal to or higher than a predetermined voltage, and this detection time is set to a predetermined time. Since the abnormal current is determined when the current exceeds the specified time, only one detection system is required even for multi-phase stepping motors, which simplifies the circuit configuration and reduces costs. becomes.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing an example of an abnormal current detection device for a stepping motor according to the present invention, FIG. 2 is a timing chart showing an example of the operation of the abnormal current detection device for a stepping motor shown in FIG. 1, and FIG. 1 is a circuit diagram showing an example of a conventional abnormal current detection device for a stepping motor. 10... Voltage detection circuit 20... Abnormality determination circuit Ra
...Common resistance 11, L2. L3, 14... stator coil Trl,
Tr2. Tr3. Tr4--Transistor Tr
5...Transistor (PNP) Dz...Zener diode R4...Resistor C...Capacitor patent applicant Fujitsu Ltd. m1 diagram

Claims (1)

[Claims] An abnormal current detection device for a stepping motor driven by connecting a stator coil corresponding to each phase to a power source via a common resistor and controlling energization from the power source to each stator coil. The voltage detecting means detects that the voltage drop of the voltage exceeds a predetermined voltage value, and the abnormality determining means determines an abnormality when the detection time of the voltage detecting means exceeds a predetermined time. Abnormal current detection device for stepping motors.