JP2006197749A - Stepping motor driving device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a stepping motor driving device wherein a motor current can be more accurately set even when the resistance value of a current sensing resistor fluctuates. <P>SOLUTION: During initial operation in which a motor is not actuated yet after power is turned on or other like occasions, the stepping motor driving device performs the operation to compute the resistance value of the current sensing resistor. The setting of a selector 4 is changed so that input of ADC 3 becomes equal to the voltage of the current sensing resistor, and the setting of a selector 5 is changed to pass a specific current through the current sensing resistor (S10). Thus, a current from a constant current circuit is supplied (S11). After the setting of the two selectors 4 and 5 is changed, the specific current from the constant current circuit is supplied, and the value of voltage drop in the current sensing resistor is sensed and converted into digital data at the ADC 3 (S12). The accurate resistance value of the current sensing resistor is computed from this digital data and an already known current value (S13). <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a motor control device using a stepping motor.

Conventionally, various techniques have been proposed for motor control of a constant current stepping motor.
JP 2002-78386 A JP-A-7-107787 JP-A-7-303396 JP 7-337093 A JP-A-9-295722

In the invention described in Patent Document 1, the low-speed reference voltage is kept low so that the rotational torque of the stepping motor is controlled to be small, rattling of the mechanism part due to excessive torque is prevented, and noise and vibration are reduced. Yes.
Patent Document 2 discloses a driving device for a stepping motor that prevents an increase in the load on a microcomputer during high-speed rotation.
Patent Document 3 discloses a technique for reducing torque at a low speed by flowing a current having a different magnitude according to the motor speed in a motor control device of a stepping motor driven based on a motor drive pulse.
Patent Document 4 discloses a technology for preventing stepping motor out-of-step due to insufficient torque and noise due to excessive torque due to component errors and changes over time in a motor driving device that rotationally drives a stepping motor with a constant driving current. Is disclosed.
Patent Document 5 discloses a medium control device that can selectively set a driving current or an applied voltage of a stepping motor, and drives a conveying unit with a driving current or an applied voltage optimum for each state.

  By the way, for the current control of the driver, the voltage generated in the current detection resistor and the reference voltage for the preset current are input to the chopping operation comparator, and the voltage is compared by this comparator. A device for controlling ON / OFF of the MOSFET has been used.

The setting of the reference voltage with respect to the preset current is performed in consideration of variations in component constants such as resistance in the circuit design stage. However, if this variation is large, the variation in the set current also becomes large, and it may not be possible to control with the intended current, which may lead to problems such as motor step-out.
Further, there remains a problem that the comparison voltage of the comparator for chopping operation varies due to variations in the current detection resistance.
Furthermore, there is a problem that two circuits are required for the ADC for monitoring the reference voltage and for monitoring the voltage of the current detection resistor.
Accordingly, a first object of the present invention is to provide a stepping motor driving apparatus that can generate an accurate voltage even with respect to variations in components constituting a reference voltage, and can increase the accuracy of motor current setting. Is to provide.
A second object of the present invention is to provide a stepping motor driving device that can set the motor current more accurately even if the resistance value of the current detection resistor varies.
A third object of the present invention is to provide a stepping motor driving apparatus capable of monitoring both a reference voltage and a current detection resistance voltage with a single ADC.

  According to the first aspect of the present invention, the stepping motor driving apparatus monitors the reference voltage value using the ADC, the reference voltage generating means for generating the reference voltage using the PWM control, and the monitoring means. The first object is achieved by providing correction means for correcting the PWM control by feeding back the reference voltage value to the PWM control by the reference voltage generating means.

According to a second aspect of the present invention, in the first aspect of the present invention, a constant current circuit that supplies a constant current, a current detection resistor that detects a current, and a voltage applied to the current detection resistor are compared with the constant current circuit. Switch means for switching between paths of the motor current path, second monitor means for monitoring the voltage drop of the current detection resistor by ADC, and the current detection resistance from the value monitored by the second monitor means The second object is achieved by the resistance value calculating means for calculating the resistance value and the correction means performing correction based on the value calculated by the resistance value calculating means.
According to a third aspect of the invention, there is provided the second switch means according to the second aspect of the invention, further comprising second switch means for switching a path from the ADC to a reference voltage generation means and a path to the current detection resistor. By switching the means, the third object is achieved by operating with a single ADC.

According to the first aspect of the present invention, it is possible to generate an accurate voltage even with respect to variations in components constituting the reference voltage, and it is possible to increase the accuracy of motor current setting.
According to the second aspect of the present invention, the motor current can be set more accurately even if the resistance value of the current detection resistor varies.
According to the third aspect of the present invention, it is possible to monitor both the reference voltage and the current detection resistance voltage with a single ADC without providing a plurality of ADCs.

Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS.
FIG. 1 is a block diagram (only one phase) showing the configuration of the stepping motor driving apparatus according to the present embodiment.
As shown in this figure, this stepping motor driving device includes a CPU (Central Processing Unit) 1, a reference voltage generator (PWM) 2, an ADC 3, selectors 4, 5, a constant current circuit 6, a chopping operation comparator 7, An output MOSFET 8 and a current detection resistor 9 are included.

The CPU 1 calculates the parameters of the reference voltage generation unit PWM2 based on the digital data converted by the ADC 3, controls the reference voltage generation unit 2, and controls the selector 4. The reference voltage generation unit 2 generates a reference voltage by PWM, and the ADC 3 converts the reference voltage and the voltage of the current detection resistor into digital data.
The selector 4 selects either the reference voltage or the voltage of the current detection resistor as the analog input of the ADC 3, and the selector 5 selects whether the current flowing through the current detection resistor is from a normal motor or a constant current circuit. The constant current circuit 6 is for causing a specific current to flow through the current detection resistor, and the chopping operation comparator 7 controls the output MOSFET 8 with the set current as an upper limit so as to operate the motor at the set current.
The current detection resistor 9 detects the output MOSFET 8 that controls the phase current of the motor and the current of the motor.

Next, the processing procedure of this embodiment will be described in detail with reference to the flowcharts of FIGS.
This apparatus carries out the calculation operation of the current detection resistor at the initial operation that does not operate the motor yet, such as after the power is turned on. First, the selector 4 is switched by the CPU 1 so that the input of the ADC 3 becomes the voltage of the current detection resistor, and the selector 5 is switched by the CPU 1 in order to flow a specific current to the current detection resistor (step 10). Is supplied (step 11).
Then, after the two selectors 4 and 5 are switched, a specific current is supplied from the constant current circuit, and the ADC 3 senses the voltage drop value of the current detection resistor and converts it into digital data (step 12). The resistance value of the current detection resistor is calculated by the CPU 1 from the digital data and the already known current value (step 13). Thus, the CPU 1 recognizes an accurate resistance value.

Next, a processing procedure during the operation of the motor will be described with reference to the flowchart of FIG.
Contrary to FIG. 2, the selector 4 is switched by the CPU 1 so that the input of the ADC 3 becomes the reference voltage, and the selector 5 is switched so that the motor current flows through the current detection resistor as in the normal motor operation (step 20).
Then, the motor operation is started (step 21; Y), and during the operation, the value of the reference voltage is sensed by the ADC 3 and converted into digital data (step 22). The digital data is compared with a reference voltage for setting the current value (step 23). If they are the same, the reference voltage is held as it is and the motor operation is continued (step 24; Y).
On the other hand, if they are different as a result of the comparison (step 24; N), the PWM value is corrected so that the reference voltage becomes the same as the reference voltage that becomes the set current value (step 25). While monitoring data from the ADC 3, the PWM value is corrected to bring the reference voltage close to the intended value.

It is the block diagram which showed the structure of the stepping motor drive device which concerns on a present Example. It is the flowchart which showed the control processing procedure in a present Example. It is the flowchart which showed the process sequence at the time of operation | movement of a motor.

Explanation of symbols

1 CPU
2 Reference voltage generator (PWM)
3 ADC
4 Selector 5 Selector 6 Constant Current Circuit 7 Chopping Comparator 8 Output MOSFET
9 Current detection resistor

Claims (3)

Monitoring means for monitoring a reference voltage value using an ADC;
Reference voltage generating means for generating a reference voltage using PWM control;
Correction means for correcting the PWM control by feeding back the reference voltage value monitored by the monitoring means to the PWM control by the reference voltage generating means;
A stepping motor driving device comprising: A constant current circuit for supplying a constant current;
A current detection resistor for detecting current;
Switch means for switching the voltage applied to the current detection resistor between the constant current circuit and a path of a normal motor current path;
Second monitoring means for monitoring the voltage drop of the current detection resistor by ADC;
Resistance value calculating means for calculating the resistance value of the current detection resistor from the value monitored by the second monitoring means;
2. The stepping motor driving apparatus according to claim 1, wherein the correction unit performs correction based on a value calculated by the resistance value calculation unit. Second switch means for switching a path from the ADC to a reference voltage generation means and a path to the current detection resistor;
3. The stepping motor driving apparatus according to claim 2, wherein the stepping motor driving apparatus operates by a single ADC by switching the second switch means.

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