JP2015202014A - stepping motor drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the accuracy of constant-current control of a driving current of a stepping motor.SOLUTION: Regenerative control means detects a value of an electric current running through a motor coil and when the current value exceeds a regenerative threshold value set to be higher than a preset value, temporarily turns off all transistors, runs an electric current from the motor coil toward a power supply side through a bypass circuit, and regenerates it to the motor coil through another load circuit connected with the power supply.

Description

  The present invention relates to a stepping motor driving circuit that controls current flowing in a motor coil of a stepping motor by chopping.

  A typical stepping motor drive circuit includes a first circuit connected between a power source and one end of the motor coil and between the other end of the motor coil and the ground so that a current flows in one direction of the motor coil of the motor. A transistor pair and a second transistor pair connected between the power source and the other end of the motor coil and between one end of the motor coil and the ground so that current flows in the other direction of the motor coil. A rotational driving force is applied to the motor by operating the pair in a complementary manner at a predetermined timing (see, for example, Patent Document 1).

Japanese Patent Laid-Open No. 9-154297

  In the above drive circuit, the current value flowing through the motor coil is monitored, and when the current value exceeds a predetermined value, the transistor connected between the power source and the motor coil is turned off to supply power to the motor coil. By performing chopping to stop, the current generated in the motor coil is consumed in the circuit configured in the drive circuit, and the current flowing in the motor coil is controlled to be constant.

  However, when the load on the motor suddenly becomes lighter, the motor coil becomes a generator and a large amount of power is generated in the motor coil. The circuit in the drive circuit at the time of chopping cannot consume that power. As a result, the constant current waveform of the drive current is disturbed, causing noise and the drive efficiency of the stepping motor being deteriorated.

  Accordingly, an object of the present invention is to improve the accuracy of constant current control of the driving current of a stepping motor.

  The stepping motor drive circuit according to the present invention includes a power supply, a motor coil, a first transistor pair, a second transistor pair, a bypass circuit, a direction control circuit, a chopping means, and a regeneration control means. The first transistor pair is composed of two transistors provided with a motor coil sandwiched on a circuit in which a power source, a motor coil, and ground are connected in series and current flows in one direction of the motor coil. The power source, the motor coil, and the ground are connected in series and are composed of two transistors provided on both sides of the motor coil on a circuit that allows current to flow in the other direction of the motor coil. The bypass circuit is provided corresponding to each of the transistors constituting the first transistor pair and the second transistor pair, and connects between the power supply and the motor coil or between the motor coil and the ground without going through each transistor. To do. Of each bypass circuit, the one between the power supply and the motor coil passes only the current flowing from the motor coil to the power supply side, and the one between the motor coil and the ground passes only the current from the ground side to the motor coil side. Shed. The direction control circuit is configured to complementarily switch on / off of the first transistor pair and the second transistor pair at a predetermined timing. The chopping means detects the value of the current flowing through the motor coil, and when the current value exceeds a preset set value, until the current value drops below the set value, Only one of the transistors is turned off. The regenerative control means detects the current value flowing through the motor coil, and temporarily turns off the transistor that is turned on when the current value exceeds a preset regenerative threshold value. A current is supplied from the motor coil to the power source side via the bypass circuit, and a regenerative operation is performed to regenerate the motor coil via another load circuit connected to the power source.

  Here, the bypass circuit in the drive circuit of the present invention includes a circuit constituted by a parasitic diode present in each transistor.

  In a preferred embodiment, the regenerative control means is configured to turn on the transistor that has been turned off by the regenerative operation when the value of the current flowing through the motor coil becomes equal to or less than the regenerative threshold value. As a result, the regenerative operation can be terminated at an appropriate timing, and the accuracy of constant current control of the motor coil can be improved.

  The stepping motor drive circuit of the present invention temporarily turns off a transistor that is turned on when a current value flowing through the motor coil exceeds a regenerative threshold value that is set higher than a set value. Since the regenerative control means configured to execute a regenerative operation for causing the current from the motor coil to flow to the power supply side via the power supply and regenerating to the drive circuit via another load circuit connected to the power supply, When a large amount of power is generated in the motor coil due to a sudden lightening of the load on the stepping motor, the power can be efficiently consumed by another load circuit. Thereby, the constant current control of the motor coil can be performed more stably, and the generation of noise of the stepping motor and the decrease in driving efficiency can be suppressed.

It is a circuit diagram which shows roughly one Example of a stepping motor drive circuit. It is a circuit diagram which shows the electric current path | route (state 1) at the normal time in the Example. It is a circuit diagram which shows the electric current path | route (state 2) at the time of the chopping in the Example. It is a circuit diagram which shows the electric current path | route (state (3)) at the time of regeneration in the Example. It is a timing chart which shows the operation | movement of the Example. It is a circuit diagram which shows schematically the other Example of a stepping motor drive circuit. It is a circuit diagram which shows the electric current path | route (state 1) at the normal time in the Example. It is a circuit diagram which shows the electric current path | route (state 2) at the time of the chopping in the Example. It is a circuit diagram which shows the electric current path | route (state (3)) at the time of regeneration in the Example.

[Example 1]
An embodiment of a stepping motor driving circuit will be described with reference to FIG. FIG. 1 shows only one phase constituting a stepping motor driving circuit. For example, in the case of a two-phase motor, another circuit having the same configuration is provided.

  This drive circuit includes two transistor pairs, and on / off of these transistor pairs is complementarily switched at a predetermined timing by the direction control circuit 4, and the direction of the current flowing through the motor coil 2 is switched. Rotational power is applied to the stepping motor. In this embodiment, the flow direction from one end side to the other end side of the motor coil 2 (the direction of the arrow from the left side to the right side in the figure) is the forward direction, and the opposite direction (the direction from the right side to the left side in the figure) is reversed. The direction.

  One transistor pair is a transistor pair for causing a current to flow in the forward direction of the motor coil 2. The transistor Q 11 connected between the power source VM and one end of the motor coil 2 and the other end of the motor coil 2 are grounded. The transistor Q22 is connected between the two transistors. Hereinafter, this transistor pair is referred to as “first transistor pair Q11, Q22”. Between the other end of the motor coil 2 and the transistor Q22, a diode D22 is connected which allows current to flow only from the other end side of the motor coil 2 to the transistor Q22 side. The diode D22 is not necessarily provided. In order to prevent the current from flowing through the parasitic diode of the transistor Q22 when a current flows from the ground side to the motor coil 2 side in the state (2) (see FIG. 3) or the state (3) described later. However, when the parasitic diode of the transistor Q22 is used as a bypass circuit without providing the bypass circuit B2, the diode D22 is not necessary.

  The other transistor pair is a transistor pair for causing a current to flow in the reverse direction of the motor coil 2. The transistor Q12 connected between the power source VM and the other end of the motor coil 2 and one end of the motor coil 2 are grounded. The transistor Q21 is connected between the two transistors. Hereinafter, this transistor pair is referred to as “second transistors Q12, Q21”. Between one end of the motor coil 2 and the transistor Q21, a diode D21 is connected to flow current only from one end side of the motor coil 2 to the transistor Q21 side. Similarly to the diode D22, the diode D21 is not necessarily provided. When the parasitic diode of the transistor Q21 is used as a bypass circuit without providing the bypass circuit B1, the diode D21 is not necessary.

  Transistors Q21 and Q22 are connected to ground through a common resistor R. The resistor R is a current monitoring resistor for monitoring the value of the current flowing through the motor coil 2, and the magnitude of the current flowing through the resistor R is monitored by the current monitoring circuit 6. The current monitoring circuit 6 will be described later. The current monitoring resistor R is not necessarily provided at this position, and may be any position as long as the current value flowing through the motor coil 2 can be monitored. For example, a current monitoring resistor may be connected in series in the immediate vicinity of the motor coil 2.

  A bypass circuit B1 is provided for connecting one end of the motor coil 2 and the ground without passing through the diode D21, the transistor Q21, and the resistor R. A diode D31 is provided on the bypass circuit B1 to flow current only from the ground side to one end side of the motor coil 2.

  A bypass circuit B2 is provided for connecting the other end of the motor coil 2 and the ground without going through the diode D22, the transistor Q22, and the resistor R. On the bypass circuit B2, a diode D32 is provided for flowing current only from the ground side to the other end side of the motor coil 2.

  When a current flows through the motor coil 2 in the forward direction, as shown in FIG. 2, the direction control circuit 4 turns on the transistor pair Q11, Q22 and turns off the transistor pair Q12, Q21. ). In this state, the current supplied from the power source VM flows to the ground through the transistor Q11, the motor coil 2, the diode D22, the transistor Q22, and the resistor R in order.

  When a current flows through the motor coil 2 in the opposite direction, the direction control circuit 4 turns on the transistor pair Q12, Q21 and turns off the transistor pair Q11, Q22. In this state, the current supplied from the power source VM flows to the ground through the transistor Q12, the motor coil 2, the diode D21, the transistor Q21, and the resistor R in order.

  In this way, a state in which one of the transistor pairs is turned on and the other transistor pair is turned off is referred to as “state (1)”. FIG. 2 shows only the state 1 in the case where a current flows through the motor coil 2 in the forward direction, and the thick line shows a path through which the current flows.

  The current monitoring circuit 6 detects a current value flowing through the resistor R, that is, a current value flowing through the motor coil 2, and when the detected current value is larger than a preset set value, the difference is amplified to a current control signal. Is configured to output as The current control signal output from the current monitoring circuit 6 is taken into the chopping control circuit 8 and the regeneration control circuit 10.

  When a current control signal is output from the current monitoring circuit 6, the chopping control circuit 8 turns off the transistor Q11 or Q12 that is turned on until the value of the current flowing through the resistor R becomes a set value or less. It is configured.

  Specifically, when the current flowing through the motor coil 2 in the forward direction (state (1)) exceeds the set value, as shown in FIG. The chopping control circuit 8 turns off the transistor Q11, and a circuit is configured in which the current from the motor coil 2 returns to the motor coil 2 via the diode D22, the transistor Q22, the resistor R, and the bypass circuit B1. The bypass circuit B1 is not always necessary. When the bypass circuit B1 is not provided, the diode D21 can be excluded from the circuit, and a circuit via a parasitic diode existing in the transistor Q21 can be used in place of the bypass circuit B1.

  When the current flowing through the motor coil 2 in the reverse direction (state (1)) exceeds the set value, the transistor Q12 is turned off by the chopping control circuit 8, and the motor coil 2 is turned off. Is configured to return to the motor coil 2 through the diode D21, the transistor Q21, the resistor R, and the bypass circuit B2. Note that the bypass circuit B2 is not necessarily required as is the case with the bypass circuit B1. When the bypass circuit B2 is not provided, the diode D22 can be excluded from the circuit, and a circuit via a parasitic diode existing in the transistor Q22 can be used in place of the bypass circuit B1.

  In this way, the transistors Q11 and Q12 are turned off, and one of the transistors Q21 and Q22 is turned on and the other is turned off, thereby forming a circuit for circulating the current from the motor coil 2 in the drive circuit. The state is assumed to be “state (2)”. FIG. 3 shows a state (2) when a current is flowing in the motor coil 2 in the forward direction, and a thick line shows a path through which the current flows.

  In state 2, no current is supplied from the power source VM to the motor coil 2, and the electric power of the motor coil 2 is consumed in the configured circuit. Thereby, the electric current which flows through the motor coil 2 falls. When the current flowing through the motor coil 2 decreases to be equal to or lower than the set value, the drive circuit is returned to the state 1 (see FIG. 2) by the chopping control circuit 8, and the current from the power source VM is supplied to the motor coil 2. The current monitoring circuit 6 and the chopping control circuit 8 constitute chopping means.

  The regeneration control circuit 10 outputs a regeneration signal when the current control signal from the current monitoring circuit 6 exceeds a preset threshold value (regeneration threshold value), or the transistor Q21 that is turned on. Q22 is temporarily turned off.

  When the load on the stepping motor is lightened suddenly, a large amount of power is generated in the motor coil 2 and a large current may flow from the motor coil 2. This can occur both in state 1 (see FIG. 2) and in state 2 (see FIG. 3). When a current flows from the motor coil 2 and the current monitor value of the current monitoring circuit 6 exceeds the set value, the chopping control circuit 8 sets the state 2 and the current control signal from the current monitoring circuit 6 is set to a preset threshold. When the value is exceeded, as shown in FIG. 4, the transistor Q21 or Q22 turned on by the regenerative control circuit 10 is turned off. As a result, all the transistors Q11, Q12, Q21 and Q22 in this drive circuit are turned off. A state in which all the transistors Q11, Q12, Q21, and Q22 are turned off is referred to as “state (3)”.

  Parasitic diodes D111 and D112 exist in the transistors Q11 and Q12, respectively, and current flows from the motor coil 2 side to the power source VM side when the potential on the motor coil 2 side becomes higher than the potential on the power source VM side.

  When the state (3) is reached when the current is flowing through the motor coil 2 in the forward direction, the current from the motor coil 2 is converted into the parasitic diode D112, the power source VM as shown by the thick line in FIG. The motor coil 2 is regenerated through the other load circuit 12 connected to the power source VM, the ground and bypass circuit B1. When the bypass circuit B1 and the diode D21 are not provided, the current from the motor coil 2 is the parasitic diode D112, the power supply VM, the other load circuit 12 connected to the power supply VM, the ground, and the parasitic diode present in the transistor Q21. Then, the motor coil 2 is regenerated.

  When the state (3) is reached when a current flows through the motor coil 2 in the opposite direction, the current from the motor coil 2 is connected to the parasitic diode D111, the power source VM, and the other load circuit connected to the power source VM. 12, Regenerate to the motor coil 2 through the ground and bypass circuit B2. When the bypass circuit B2 and the diode D22 are not provided, the current from the motor coil 2 is the parasitic diode D111, the power supply VM, the other load circuit 12 connected to the power supply VM, the ground, and the parasitic diode present in the transistor Q22. Then, the motor coil 2 is regenerated.

  In this embodiment, the parasitic diodes Q111 and Q112 present in each of the transistors Q11 and Q12 are used as a bypass circuit connecting the transistors Q11 and Q12, but this is a bypass circuit corresponding to the transistors Q21 and Q22. Similarly to B1 and B2, an external bypass circuit that is not a parasitic diode may be provided between the motor coil 2 and the power supply VM. These bypass circuits flow only current from the motor coil 2 to the power source VM side.

  By regenerating the current flowing from the motor coil 2 through the other load circuit 12 in this way, the power of the motor coil 2 can be consumed efficiently and the current flowing through the motor coil 2 can be quickly reduced. The current monitoring circuit 6 and the regeneration control circuit 10 constitute regeneration control means.

  As disclosed in Patent Document 1, when the direction of the current flowing through the motor coil 2 is switched, all the transistors Q11, Q12, Q21, and Q22 are turned off and the current from the motor coil 2 is changed to other values. It has been conventionally performed to regenerate through the load circuit 12 and release the electric power of the motor coil 2. However, the motor coil 2 is not configured to regenerate the current from the motor coil 2 via another load circuit while the motor coil 2 is driven at a constant current, and a large current flows from the motor coil 2. When this occurs, the electric power of the motor coil 2 cannot be consumed, which may cause noise and noise.

[Example 2]
Next, another embodiment of the stepping motor driving circuit will be described with reference to FIG.

  In the drive circuit of the first embodiment, as shown by the thick line in FIG. 4, when the current flowing from the motor coil 2 is regenerated in another load circuit, the regenerative current to the motor coil 2 is a resistance Since R does not flow, the regenerative current cannot be detected by the current monitoring circuit 6. In the driving circuit of the second embodiment, the current monitoring circuit 6 can detect the regenerative current to the motor coil 2.

  In the second embodiment, a diode D31 and a resistor R ′ are provided on a bypass circuit B1 that connects one end of the motor coil 2 and the ground without a diode D21, a transistor Q21, and a resistor R. The difference is that a diode D32 and a resistor R ′ are provided on a bypass circuit B2 that connects the other end to the ground without going through the diode D22, the transistor Q22, and the resistor R. The resistors R ′ on the bypass circuits B1 and B2 are common, and the bypass circuits B1 and B2 share a path where the resistor R ′ is provided as a part. The current monitoring circuit 6 detects a current value flowing through the resistor R and a current value flowing through the resistor R ′, and when these current values exceed a preset set value, the difference is amplified and used as a current control signal. It is configured to output. The current control circuit 6 calculates a difference between one of the current value flowing through the resistor R or the current value flowing through the resistor R ′ and the set value, and which of the current values is used for calculating the difference from the set value is driven. Depends on circuit conditions.

  In the second embodiment, as in the first embodiment, there are states (1) to (3) as states of the drive circuit, and the states of the transistors Q11, Q12, Q21, and Q22 in the states (1) to (3) are as follows. Same as Example 1. The paths through which current flows in each state are indicated by thick lines in FIG. 6 (state (1)), FIG. 7 (state (2)), and FIG. 8 (state (3)). The paths shown in FIGS. 6 to 8 are when the current flows through the motor coil 2 in the forward direction.

  As indicated by the thick line in FIG. 6, when the drive circuit is in the state (1), the current flowing through the motor coil 2 flows through the resistor R, and no current flows through the resistor R ′. Therefore, in the state 1, the current monitoring circuit 6 outputs a current control signal based on the current value flowing through the resistor R.

  As shown by the thick line in FIG. 7, when the drive circuit is in the state 2, the current flowing through the motor coil 2 flows through both resistances R and R ′, and the current value is the same. Therefore, in the state 2, the current monitoring circuit 6 outputs a current control signal based on the current value flowing through either one of the resistors R and R ′ (which may be either).

  As shown by the thick line in FIG. 8, when the drive circuit is in the state (3), the regenerative current to the motor coil 2 flows through the resistor R ′ and does not flow through the resistor R. Therefore, in the state (3), the current monitoring circuit 6 outputs a current control signal based on the current value flowing through the resistor R ′.

  Since the magnitude of the regenerative current to the motor coil 2 can be detected by the current monitoring circuit 6 detecting the value of the current flowing through the resistor R ′ in the state (3), the current value is the regenerative threshold. The end timing of the regenerative operation can be defined, for example, the regenerative operation is ended when the value becomes lower than the value.

  The constant current control of this embodiment will be described with reference to the timing chart of FIG. In the following description, the current is monitored on the low potential side and chopping is performed on the high potential side.

  When a current flows through the motor coil 2 in the forward direction, the direction control circuit 4 turns on the first transistor pair Q11, Q22 and turns off the second transistor pair Q12, Q21 (state (1)). ). In this state, when the current monitor value detected by the current monitoring circuit 6 exceeds the set value, the current control circuit 6 outputs a current control signal obtained by amplifying the difference between the current monitor value and the set value.

  When the current control signal is output, the chopping control circuit 8 turns off the chopping control signal L that turns on the transistor Q11, turns off the transistor Q11, and the drive circuit enters the state (2). When the drive circuit enters the state (2), the power supply to the motor coil 2 is stopped, and the current monitor value decreases. When the current monitor value becomes equal to or lower than the set value, the chopping control circuit 8 returns the transistor Q11 to the ON state again. In normal times, the current value flowing through the motor coil 2 is controlled to be constant by switching the drive circuit between the state (1) and the state (2) in accordance with the current monitor value.

  When the current monitor value further increases even in state (2), or the current control signal exceeds a preset regeneration threshold value due to a rapid increase in current monitor value in state (2) The regeneration signal is output from the regeneration control circuit 10, the transistor Q22 is turned off (OFF), and the drive circuit is in the state (3). When the drive circuit is in the state (3), the current flown from the motor coil 2 flows into another load circuit via the parasitic diode D112 and the power source VM, and is regenerated to the motor coil 2 via the ground.

  The current monitoring circuit 6 outputs a current control signal based on the value of the current flowing through the resistor R ′, and when the current control signal falls below the regeneration threshold, the regeneration control circuit 10 turns off the regeneration signal output. By turning on the transistor Q22, the drive circuit is returned to the state (2).

  The above operation is executed until a predetermined timing at which the current flow direction is switched, and when the predetermined timing is reached, all the transistors Q11, Q12, Q21 and Q22 are turned off and the motor coil 2 is discharged for a certain period of time. Wait. During this standby time, the electric power of the motor coil 2 is released by regeneration. After the standby time has elapsed, constant current control is performed in which a current flows in the reverse direction.

  The current value flowing through the motor coil 2 can be monitored in any of the states (1) to (3), such as when a current monitoring resistor is connected in series with the motor coil in the immediate vicinity of the motor coil 2. When a resistor is provided at a position, it is not necessary to provide two resistors R and R ′ for current monitoring as in the second embodiment.

  In the first and second embodiments described above, the current is detected on the low potential side and the chopping is performed by the high potential transistors (Q11 and Q12). However, the current is detected on the high potential side. The present invention can also be applied to the case where chopping is performed by the low potential side transistors (Q21 and Q22).

2 Motor coil 4 Direction control circuit 6 Current monitoring circuit 8 Chopping control circuit 10 Regenerative control circuit 12 Other load circuit VM Power supply Q11, Q12, Q21, Q22 Transistors D21, D22, D31, D32 Diode D111, D112 Parasitic diode

Claims (2)

Power supply,
Both ends are connected between the power source and the ground, and a motor coil for driving the motor,
A first transistor pair consisting of two transistors provided across the motor coil on a circuit that connects the power source, the motor coil, and the ground in series to flow current in one direction of the motor coil;
A second transistor pair composed of two transistors provided across the motor coil on a circuit that connects the power source, the motor coil, and the ground in series to flow current in the other direction of the motor coil;
Provided corresponding to each of the transistors constituting the first transistor pair and the second transistor pair, between the power supply and the motor coil or between the motor coil and the ground without passing through each transistor. A bypass circuit to be connected, wherein only a current flowing from the motor coil to the power source side flows between the power source and the motor coil, and the motor from the ground side flows between the motor coil and the ground. A bypass circuit for passing only current to the coil side;
A direction control circuit configured to complementarily switch on / off of the first transistor pair and the second transistor pair at a predetermined timing;
The current value flowing through the motor coil is detected, and when the current value exceeds a preset setting value, any of the transistor pairs that are on until the current value becomes equal to or less than the set value. Chopping means configured to turn off only one transistor;
The current value flowing through the motor coil is detected, and when the current value exceeds a regeneration threshold set higher than the set value, the transistor that is turned on is temporarily turned off, Regenerative control means configured to execute a regenerative operation in which a current from the motor coil is caused to flow to the power supply side via a bypass circuit and is regenerated to the motor coil via another load circuit connected to the power supply. And a stepping motor drive circuit comprising:   The said regeneration control means is comprised so that the transistor turned off by the said regeneration operation may be returned to ON, when the electric current which flows through the said motor coil becomes below the threshold value for regeneration. Stepping motor drive circuit.

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