JP2002084791A - Stepping motor driving circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a stepping motor driving circuit capable of reducing the induced voltage generated by a backlash without increasing the cost and more accurately conducting a zero detection. SOLUTION: An angle sift amount θ1 of a rotor 3 when a needle 6 is moved from another step 1 to a detecting step 7 of a zero detection exciting signal for rotating the rotor 3, so that the needle 6 moves in a zero position direction decided by a stopper 7, is set larger than an angle sift amount θ of the rotor 3 due to the backlash after a part of a member to be driven contacts the stopper 7. Thus, the induced voltage generated before the part of the member contacts the stopper 7 can be distinguished from an induced voltage generated due to the backlash, and the contact of the needle 6 with the stopper can be accurately decided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepper motor drive circuit and, more particularly, to a stopper in which a pointer whose position is controlled by a stepper motor (or a part of a driven member driven by the stepper motor) determines its zero position. A zero position detection process (hereinafter referred to as zero detection) for detecting whether or not the stopper has been set to the zero position by detecting an induced voltage generated by rotation of the rotor in order to detect whether or not the contact has occurred. The present invention relates to a stepper motor drive circuit that can be performed at a time.

[0002]

2. Description of the Related Art In-vehicle meters, such as a speedometer for displaying a vehicle speed and a tachometer for displaying an engine speed, include:
In recent years, stepper motors have been frequently used for reasons of pointing accuracy and price. However, due to vibration of a vehicle equipped with a stepper motor, an erroneous drive signal generated by engine noise, or the like, there is a difference between a movement amount of the pointer that should be moved and an actual movement amount of the pointer that is linked to the rotation of the stepper motor. May occur. Assuming such a case, for example, at the timing of turning on the ignition switch,
The pointer is returned to the zero position determined by the stopper, and a zero position setting process for initial setting of the counting mechanism is performed in synchronization with the position of the pointer at this time. In the above process, the zero detection, which detects an induced voltage generated by the rotation of the rotor, is conventionally performed to determine whether the pointer has returned to the zero position, that is, whether the pointer has contacted the stopper. Have been done.

[0003]

However, since the rotor is connected to the pointer via a plurality of gears, there is a so-called backlash caused by loosening and play caused by the rotation. Therefore, in the zero detection, the rotor may further rotate by a certain angle determined by the backlash even after the pointer abuts on the stopper. The excessive rotation due to the backlash generates an induced voltage of a magnitude that cannot be ignored in the step of determining whether the stopper is in contact with the stopper, and hinders accurate zero detection. That is, since the level of the induced voltage generated by the backlash is often near the reference voltage level for determining the stopper contact, whether the detected induced voltage is the induced voltage generated before the stopper contact, or It was difficult to determine whether the voltage was induced by backlash after contact, and it was difficult to perform accurate zero detection. Also, if there is no backlash in the step of judging stopper contact,
In some cases, the rotor reversely rotates (reverse the rotation direction at the time of zero detection), which also makes accurate zero detection difficult.

In order to solve the above-mentioned problem, it is conceivable to adjust the dimensions of the stopper and the like so that the backlash is moderate at the timing of detecting the induced voltage.
When a small multi-pole magnetized rotor is used, very high dimensional accuracy is required, and maintaining this requires a very high cost. Even if the dimensional adjustment is possible, the yield is deteriorated due to the variation of each part, which also causes the cost to increase.

Accordingly, the present invention has been made in view of the above-mentioned circumstances, and has been made to provide a stepper motor drive circuit capable of reducing an induced voltage generated by backlash and enabling more accurate zero detection without increasing cost. It is an issue.

[0006]

According to a first aspect of the present invention, there is provided a stepper motor drive circuit comprising:
As shown in FIG. 1, FIG. 2 and FIG. 4, the rotor 3 in which the N pole and the S pole are alternately and uniformly magnetized, and in response to an excitation signal in which one cycle is constituted by a plurality of excitation steps. A stepper motor for rotating the rotor 3 having first and second coils C1 and C2 arranged at a predetermined angle to each other, and a pointer 6 driven by the rotor 3
Excitation signal supply means for generating the excitation signal for rotating the rotor 3 so as to move in the zero position direction defined by the following, and supplying the excitation signal to the first and second coils C1 and C2; Contact determining means for determining whether or not a part of the driven member has contacted the stopper 7 based on an induced voltage generated along with the driven member, based on the determination by the contact determining means. Is a stepper motor drive circuit provided with a synchronization function for synchronizing a position where the stopper abuts on the stopper 7 with a counting mechanism, wherein the excitation signal is supplied to the first and second coils C1 and C2, respectively. In a specific step of the one cycle, in synchronization with the timing at which a part of the driven member contacts the stopper 7,
The method includes a detection step 7 including a signal waveform for causing at least one of the first and second coils C1 and C2 to function as an induction voltage detection. The amount of angular displacement of the rotor 3 is larger than the amount of angular displacement of the rotor 3 due to backlash after a part of the driven member comes into contact with the stopper 7.

According to the first aspect of the present invention, when a transition is made from another step 1 to the detection step 7 in the excitation signal for rotating the rotor 3 so that the pointer 6 moves in the zero position direction defined by the stopper 7. Is larger than the angular displacement θ of the rotor 3 due to backlash after a part of the driven member abuts on the stopper 7. Thereby, the distinction between the induced voltage generated before a part of the driven member contacts the stopper 7 and the induced voltage generated by the backlash becomes clear, and it is accurately determined that the pointer 6 has contacted the stopper. become able to.

According to a second aspect of the present invention, there is provided a stepper motor driving circuit according to the first aspect of the present invention. The amount of angular displacement of the rotor 3 at the time of transition is larger than the amount of angular displacement at the time of another inter-step transition.

According to the second aspect of the present invention, the amount of rotation of the rotor 3 increases when transitioning from the other step 1 to the detecting step 7, so that the induced voltage due to the change in magnetic force increases accordingly. The difference between the two induced voltages generated when the stopper abuts and before the abutment increases. As a result, it is easy to determine whether the stopper is in contact with the stopper, and zero detection can be reliably performed. Further, since the amount of angle shift due to the detection step 7 becomes large, the difference from the amount of angle shift due to backlash becomes clear, and it is possible to more accurately determine that the pointer 6 has come into contact with the stopper.

A stepper motor drive circuit according to a third aspect of the present invention has been made to solve the above problem. As shown in FIGS. 1, 2 and 4, in the stepper motor drive circuit according to the second aspect, Is a pair of three magnetic poles, and the excitation signal is characterized by comprising one detection step 7 and six excitation steps 1 to 6 for uniformly changing the angle of the rotor 3.

According to the third aspect of the present invention, the rotor 3 is formed into three magnetic pole pairs, and the excitation signal is detected one step 7 and the six excitation steps 1 to uniformly shift the angle of the rotor 3.
6, the detection step 7
Causes the angular displacement of the rotor 3 to be 30 degrees. When the amount of angular displacement of the rotor 3 in the detection step 7 becomes 30 degrees,
Compared to the same 18 degrees when the rotor 3 has 5 magnetic pole pairs,
The induced voltage generated by the backlash becomes relatively small.

In order to solve the above-mentioned problem, a stepper motor drive circuit according to a fourth aspect of the present invention is, as shown in FIGS. 2 and 3, a part of the driven member in the stepper motor drive circuit of the third aspect. Is set so that the magnetic pole change point of the rotor 3 coincides with the first or second coil C1, C2 functioning as an induced voltage detection when the rotor 3 comes into contact with the stopper 7. It is characterized by.

According to the fourth aspect of the present invention, when a part of the driven member comes into contact with the stopper 7, the magnetic pole change point of the rotor 3 is changed to the coil C2 functioning as an induced voltage detection.
Is set to match. That is, FIG.
As shown in (B), the magnetic pole change point of the rotor 3 is set to coincide with the coil C2 when the stopper abuts. With this setting, as shown in FIG. 4B, it is easy to set the magnetic force change due to the backlash to be smaller than the peak value near the center point of N1.

According to a fifth aspect of the present invention, there is provided a stepper motor driving circuit according to any one of the first to fourth aspects, wherein the stepper motor driving circuit is mounted on a vehicle. And

According to the fifth aspect of the present invention, the stepper motor drive circuit is mounted on a vehicle. The vehicle is in an environment where the amount of backlash tends to fluctuate due to temperature change or looseness due to vibration, etc., but according to the present invention, these fluctuations are predicted and the angle displacement of the rotor 3 is set as described above. It becomes possible. Further, by using the driving coil and the induced voltage detecting coil together, the size of the stepper motor housing can be reduced.

[0016]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a stepper motor drive circuit of the present invention and an application example thereof.

First, an outline of the operation will be described. In the figure, a stepper motor drive circuit 1 receives, for example, count data generated by a counter 2 based on a sensor output PS of a vehicle speed sensor via a count data input terminal RXD. The stepper motor drive circuit 1 includes a rotor 3 of the stepper motor.
An excitation signal output terminal Tx
Output from 1a, Tx1b, Tx2a and Tx2b, and supply them to the first coil C1 and the second coil C2. The first coil C1 and the second coil C2 have N or S poles at their respective ends a and b in response to the excitation signal, and have N and S poles alternately and uniformly magnetized on the rotor 3. The rotor 3 is driven to rotate by suction or repulsion. The rotor 3 is mechanically connected to an output gear 5 via an intermediate gear 4 and drives the output gear 5 to rotate. The rotationally driven output gear 5 has a pointer 6 for indicating a predetermined value of a speed scale allocated on a meter 8 of a speedometer in conjunction with the rotational drive. For example, at the time of speed increase, the rotor 3, the gears 4, 5 and the hands 6 rotate clockwise as indicated by arrows in the figure,
At the time of deceleration or zero detection, it rotates and moves in the opposite direction.

Normally, the pointer 6 indicates a predetermined speed scale on the meter 8 corresponding to the sensor output PS. The pointer 6 is determined by the stopper 7 and the pointer 6
, A position at which movement in the direction opposite to the arrow in the drawing is impossible is defined as a zero position. The display origin on the scale, that is, the speed 0
The km / h point is provided at a point slightly shifted from the zero position in the normal rotation direction.

In contrast to the above-described normal operation, the amount of movement of the pointer 6 and the actual amount of movement of the pointer 6 due to an erroneous drive signal generated by vibration of the vehicle on which the drive circuit 1 is mounted, engine noise, etc. There is a case where a difference occurs between the movement amount and the movement amount. Assuming such a case, for example,
When the ignition switch is turned on, the pointer 6
Is returned to the pointer zero position, and in synchronization with this, a zero position setting process for initial setting the counting mechanism by the counting device 2 is performed. In order to determine whether or not the pointer 6 has returned to the zero position, that is, whether or not the pointer 6 has come into contact with the stopper 7, an induced voltage generated by rotation of the rotor 3 is detected and the above-described zero is determined. An inspection is performed.

In this embodiment, the position where the pointer 6 contacts the stopper 7 is set to the zero position. In addition to the pointer 6, a piece is protruded from the gear 5 so that the piece contacts the stopper 7. The position may be the zero position. In short, any means can be used as long as it is driven by the rotor 3 and can contact the stopper 7 to specify the zero position as described above, and is not limited to the pointers and pieces. This is described as a part of the driven member in the claims. However, in the present embodiment, for simplicity of description, a series of zero detection processing is described as being performed based on the fact that the pointer 6 abuts on the stopper 7 as a representative.

Next, the configuration of the stepper motor and the stepper motor drive circuit 1 will be described. The stepper motor is
Basically, the rotor 3, the first coil C1, and the second coil C2
Consists of The terminals a and b of the first coil C1 are connected to the output terminal TX1 of the stepper motor drive circuit 1, respectively.
The excitation signal for driving the rotor 3 is supplied from a and TX1b. Output terminals TX2 of the stepper motor drive circuit 1 are connected to terminals a and b of the second coil C2, respectively.
a and the TX 2 b supply an excitation signal for driving the rotor 3.

Both the first coil C1 and the second coil C2 drive the rotor 3, and one of them is generated based on the rotation of the rotor 3 at the timing of a predetermined excitation step (detection step) described later. It also functions as an induced voltage detecting element for detecting an induced voltage.

The first coil C1 and the second coil C2
Is connected to an RC circuit as a filter composed of resistors R1 and R2 and a capacitor C1, through which an induced voltage corresponding to the rotation is supplied to an induced voltage input terminal RXI. This induced voltage is used for the zero detection.

The stepper motor drive circuit 1 includes a serial / parallel conversion unit 11, a waveform pattern generation unit 12, an induced voltage comparison unit 14, a zero detection control unit 15, and an output buffer unit 16.
Having.

The serial / parallel converter 11 receives the count data sent from the counter 2 via the count data input terminal RXD, converts the count data into parallel data corresponding to the excitation signals supplied to the coils C1 and C2. The waveform is supplied to the waveform pattern generator 12.

The waveform pattern generation unit 12 includes a filter unit (not shown), a SIN / COS conversion unit, and a pulse width modulation (PW
M) It basically consists of an output unit. The filter unit performs a filtering process on the received parallel data based on a predetermined arithmetic expression. The SIN / COS conversion unit updates the SIN / COS quadrant data and the SIN / COS data at predetermined time intervals based on the operation result of the filter unit, and outputs the updated data to the PWM output unit. The PWM output unit is SIN
The data updated every predetermined time from the / COS converter is converted into a PWM signal to generate an excitation signal to be supplied to the coils C1 and C2, and the excitation signal output terminals TX1a, TX1
1b, TX2a, and TX2b. The waveform pattern generation unit 12 also responds to a command signal from the zero detection control unit 15 to output excitation signals (C1a, C1b, C2a) described later.
And a C2b signal), which are output to the output buffer 1
6, the excitation signal output terminals TX1a, TX1b, T
X2a and TX2b. The waveform pattern generation unit 12 also generates a dedicated drive waveform for controlling the rotor 3 in microsteps for showing a smooth movement of the hands. It is also possible to control to output this dedicated drive waveform.

The induced voltage comparing section 14 is basically composed of a comparator, and receives the induced voltage supplied from the terminal RXI to determine whether the indicator 6 has come into contact with the stopper 7 or not. The reference voltage value is compared with a predetermined reference voltage value, and the comparison result is supplied to the zero detection control unit 15. This reference voltage can be changed by the reference voltage setting terminal RXR according to the temperature, aging and the like. The reference voltage setting terminal RXR is configured by, for example, a combination of a set of pin switches. The above-mentioned reference voltage can be changed in consideration of a use environment, a change with time, and the like.

The zero detection control unit 15 includes an induced voltage comparison unit 14
In response to the comparison result from the control unit and the zero detection command signal from the zero detection command signal input terminal RXZ, the waveform pattern generation unit 12
The excitation signals (C1a, C1b, C2) shown in FIG.
a and C2b signal), and outputs the generated excitation signal via the output buffer unit 16 and outputs a zero detection monitor signal indicating that zero detection processing is being performed. Further, the zero detection control unit 15 issues a command to the serial / parallel conversion unit 11 to stop storing the count data in response to the zero detection command signal from the counting device 2.

Further, the zero detection control section 15 generates a detection timing signal at a predetermined timing in synchronization with the excitation signal, and disconnects the corresponding output buffer section 16 from the waveform pattern generation section 12 at that timing. This timing signal is also supplied to the induced voltage comparison unit 14.

The counting device 2 receives a sensor output PS which is converted from a speed signal (not shown) and converted into a predetermined signal level by an interface (I / F) 22. Based on the sensor output PS input when the zero detection monitor signal from the terminal TXM of the stepper motor drive circuit 1 is H (active), the counting device 2
The sensor output PS and the corresponding target rotation angle of the stepper motor are calculated by a software program of the apparatus, and angle data (or count data) for controlling the rotation of the stepper motor is generated at the target rotation angle. Output from the count data output terminal TXD. Further, the counting device 2 generates a zero detection command signal by using a power ON signal of an ignition switch or the like as a trigger and outputs the signal from a zero detection command signal output terminal TXZ.

The counting device 2 further includes a zero detection monitor signal receiving terminal RXM, and receives the zero detection monitor signal from the stepper motor drive circuit 1. Zero detection monitor signal from L to H
, That is, in response to the end of the zero detection, the counting device 2 sets the counting mechanism of the counting data to an initial value. The counting device 2 does not respond to the sensor output PS during the period when the zero detection monitor signal is L, and therefore does not generate the count data and does not send data to the output terminal TXD. Further, in the present embodiment, the zero detection command signal is input from the terminal TXZ. However, this signal can be added to the serial data and determined and generated in the step motor drive circuit 1.

Next, signal waveforms used in the present embodiment and a reference example described later will be described with reference to FIG. FIG.
FIG. 4 is a diagram showing a signal waveform and a detection timing signal in each excitation step of an excitation signal used in the present embodiment and a reference example. In FIG. 2, the numbers in the rectangles indicate the step numbers. It is assumed that the rotor supplied with the excitation signal is a multi-pole pair. In this rotor, an excitation signal as shown in FIG. 1 is applied to a pair of coils C1 and C2 shown in FIG. Is done. Coil C
Reference numeral 2 also functions as a detection and induction voltage output element at a predetermined timing. At the time of zero detection, the rotor rotates counterclockwise in the direction opposite to the direction shown by the arrow shown in FIG.

As shown in FIG. 2, the excitation signal for rotating the rotor is composed of a C1a signal, a C1b signal, a C2a signal and a C2b signal, which are a combination of H (high level) and L (low level). It consists of. H is, for example, 5 volts, and L is 0 volts. A C1a signal and a C1b signal as shown in FIG. 6 are supplied to both terminals a and b of the coil C1, respectively.
Similarly, C2a is connected to both terminals a and b of the coil C2.
And a C2b signal. In each of the coils C1 and C2 supplied with these signals, a current flows according to the potential difference of the signals supplied to their terminals a and b, and the coil end facing the rotor becomes an N pole or an S pole. The rotor is driven to rotate by being repelled or attracted by the N or S poles uniformly magnetized on the rotor. These excitation signals are generated by the waveform pattern generator 12 in response to a command from the zero detection controller 15 shown in FIG. 1 and output via the output buffer 16.

One cycle of the excitation signal for rotating the rotor so that the pointer linked to the rotor moves in the direction of the zero position determined by the stopper includes a plurality of excitation steps 1, 7a, 7b, 6, 5 , 4, 3 and 2. As the excitation step changes in the order of 1, 7a, 7b, 6, 5, 4, 3, and 2, the rotor rotates counterclockwise by a predetermined angle. It is assumed that the steps 1, 7a, 7b, 6, 5, 4, 3, and 2 are allocated at equal time intervals.

For example, when the excitation signal is supplied to a rotor having five magnetic pole pairs, the angle of the rotor is shifted by 18 degrees when transitioning from the excitation step 1 to 7a. Excitation step 7a
When transitioning from step 7b to step 7b, the angle does not change because the waveform of the excitation signal does not change. When transitioning from the excitation step 7b to the excitation step 6, the angle shift is 9 degrees. Similarly, when transitioning from the excitation steps 6 to 5, the excitation steps 5 to 4, the excitation steps 4 to 3, and the excitation steps 3 to 2, the angle shift is 9 degrees. It should be noted that the angle shift amount at the time of transition from the excitation step 2 to the excitation step 1 of the next cycle is also 9 degrees.

Further, for example, when the excitation signal is supplied to a rotor having three magnetic pole pairs, the angle of the rotor is shifted by 30 degrees when transitioning from the excitation step 1 to 7a. When transitioning from the excitation step 7a to 7b, the angle of the excitation signal does not change because the waveform of the excitation signal does not change. At the time of transition from the excitation step 7b to the excitation step 6, the angle shift amount is 15 degrees. Similarly, excitation steps 6 to 5, excitation steps 5 to 4, excitation steps 4 to 3, and excitation steps 3 to 2
, The angle shift is 15 degrees. It should be noted that the angle shift amount at the time of transition from the excitation step 2 to the excitation step 1 of the next cycle is also 15 degrees.

The detection timing signal is supplied to the excitation step 7
This is a control signal for detecting the induced voltage generated in the coil C2 at the timings a and 7b. The detection timing signal is set to be H at the excitation step 7 in which both the signal C2a and the signal C2b supplied to both ends a and b of the coil C2 become L (zero volt). In response to the detection timing signal, the induced voltage generated in the coil C2 is supplied to the induced voltage comparison unit 1 via the RC circuit shown in FIG.
4 is supplied. When the pointer touches the stopper, the rotor can no longer rotate counterclockwise, so the induced voltage should theoretically be zero. Therefore, the induced voltage is lower than the reference voltage for judging the contact of the pointer with the stopper. At this point, the supply of the excitation signal for zero detection is stopped, and the zero detection can be terminated with this.

The excitation signal of the cycle consisting of a plurality of excitation steps as described above is used until the pointer comes into contact with the stopper and the rotor cannot rotate, that is, the induced voltage detected by the coil C2 is detected by the detection steps 7a and 7b. Is repeated in principle until the voltage falls below a predetermined reference voltage.

Here, the reason why the excitation steps 7a and 7b having the same signal waveform are continuously assigned is that the angular displacement from the previous excitation step 1 is smaller than the displacement in the transition between other steps. By making it larger,
This is to increase the value of the induced voltage to be generated and to easily determine whether or not the pointer has contacted the stopper. That is, since the induced voltage should be close to zero when the pointer comes into contact with the stopper, by increasing the induced voltage value generated by the excitation steps 7a and 7b, the induced voltage between before and after the stopper comes into contact is increased. The difference is larger. As a result, it is easy to determine whether or not the pointer has contacted the stopper 7, and as a result, zero detection can be performed more reliably. In addition, since the amount of angular displacement due to the detection steps 7a and 7b increases, the difference between the amount of angular displacement due to backlash and the amount of angular displacement corresponding to the magnetic peak point increases, and it is more accurate that the pointer 6 comes into contact with the stopper. Can be determined. In this specification, steps 7a and 7b may be collectively described as step 7 for convenience.

Further, referring to the reference example shown in FIG.
The embodiment shown in FIG. 4 will be described. FIG. 3 relates to a reference example for understanding the embodiment shown in FIG. 4, and FIG. 3A is a schematic view of a rotor used in the reference example. FIG. 3B is a graph showing a change in magnetic force accompanying rotation of the rotor of FIG. FIG. 4A is a schematic diagram of a rotor used in the present embodiment. FIG. 4B is a graph showing a change in magnetic force accompanying rotation of the rotor of FIG. 4A.

As shown in FIG. 3A, the rotor assumed in the reference example has five magnetic pole pairs. N1 to N5 and S1 to S5
Indicates that five N poles and five S poles are alternately and uniformly magnetized, and the numbers assigned to them are for convenience of explanation, and there is no physical difference. A pair of N
The angle between the pole and the south pole is 72 degrees, and the angle shift at the detection step 7 of the excitation signal shown in FIG. 2 is 18 degrees (detection step shift angle θ2). The excitation signal shown in FIG. 2 is applied to the rotor, and the rotor rotates in the direction of the arrow in FIG. 2 to perform zero detection.

The graph of FIG. 3B shows the change in magnetic force that occurs when each of the magnetic poles N1, S1, N2,... Passes over the detection coil with the rotation of the rotor. The magnetic force change peaks at the midpoint between the magnetic poles N1, S1, N2,.
It turns out that it becomes zero at the magnetic pole change point.

Here, it is assumed that the magnetic pole change point (change point from S5 to N1) of the rotor is set to match the coil C2 when the pointer comes into contact with the stopper. Then, the rotation angle due to the backlash is set to θ as shown in the figure, for example, 20 degrees. If θ is larger than the detection step transition angle θ2 (= 18 degrees) as shown in the drawing, the peaks of the magnetic force change due to θ and θ2 become equal. That is, since the induced voltage values by θ and θ2 are also equal, it is difficult to determine whether the detected induced voltage is generated before the stopper abuts or is generated by backlash after the abutment. As described in the conventional example, accurate zero detection is difficult.

On the other hand, as shown in FIG.
In the present embodiment, the rotor has three magnetic pole pairs. N1 to N3 and S1 to S3 indicate that three N poles and S poles are alternately and uniformly magnetized, respectively, and the numbers assigned to them are for convenience of explanation as in FIG. There is no physical difference. The angle between the pair of north pole and south pole is 120 degrees, and the angle transition in the detection step 7 of the excitation signal shown in FIG. 2 is 30 degrees (detection step transition angle θ1).
The excitation signal shown in FIG. 2 is applied to the rotor, and the rotor rotates in the direction of the arrow in FIG. 2 to perform zero detection.

The graph of FIG. 4B shows the change in magnetic force that occurs when each of the magnetic poles N1, S1, N2,... Passes over the detection coil as the rotor rotates. It can be seen that the magnetic force change peaks at the midpoint between the magnetic poles N1, S1, N2,... And becomes zero at the magnetic pole change point, as in the example of FIG.

Here, it is assumed that the magnetic pole change point (change point from S3 to N1) of the rotor is set to match the coil C2 when the pointer comes into contact with the stopper. This makes it easier to set the magnetic force change due to the backlash to be smaller than the peak value near the center point of N1. Then, the rotation angle due to the backlash is represented by θ as shown in the figure. Since the components constituting the stepper motor are the same as in the example of FIG.
Θ in (B) is equivalent to that shown in FIG.
For example, it is 20 degrees.

In the present embodiment, since the rotor has three magnetic pole pairs, the detection step transition angle θ1 in the detection step 7 is 30 degrees, which is 30 degrees from the change point of S3 and N1.
In terms of degree, the magnetic force change, that is, the induced voltage value becomes maximum. The rotation angle θ due to backlash is 20 as described above.
Therefore, as shown in this figure, the distance until reaching the peak point of the change in magnetic force increases, and the rotation angle θ due to backlash does not reach the peak point, as shown in FIG. That is, the induced voltage generated by the backlash is smaller than the induced voltage generated before the stopper abuts. As a result, the induced voltage generated before the stopper abuts and the induced voltage generated by the backlash can be clearly distinguished, and accurate zero detection can be performed.

According to the present embodiment, the excitation signal is
Is used as it is, and the rotor is changed from five magnetic pole pairs to three magnetic pole pairs, so that the amount of angular displacement of the rotor before the stopper abuts in the detection step 7 is calculated by the angle expected to occur due to backlash. It is set to be larger than the displacement. This facilitates the distinction between the induced voltages before and after the stopper abuts, and enables accurate zero detection.
It may be considered that the induced voltage generated by the backlash is made smaller than the induced voltage generated before the stopper abuts.

In addition, according to the present embodiment, the adjustment accuracy of the output gear and the stopper 7 on the case side of the motor is reduced. That is, since it is not necessary to adjust the amount of backlash by highly adjusting the stopper 7 on the case side, the manufacturing cost can be reduced and a low-cost stepper motor can be provided.

Further, as shown in FIG. 1, it is very effective to mount the stepper motor drive circuit of this embodiment on a vehicle. In other words, the vehicle is in an environment where the amount of backlash tends to fluctuate due to temperature changes or looseness due to vibration, etc.
According to the present embodiment, it is possible to set the angle shift amount of the rotor 3 by predicting these changes as described above, so that zero detection can be accurately performed even if the backlash amount slightly changes. become able to. Therefore, it is very effective to mount the stepper motor drive circuit of this embodiment on a vehicle. In addition, since the coil C2 serves as both a driving coil and an induced voltage detecting coil, the size of the stepper motor housing can be reduced, which is very effective for a vehicle where living space is limited.

In the above-described embodiment, three magnetic pole pairs have been described as an example. However, by optimizing the arrangement of the excitation signal and the drive coil and further reducing the number of magnetized poles, the induced voltage due to backlash is further reduced. It is also possible.

In the above-described embodiment, the stepper motor drive circuit drives only one stepper motor. However, by performing time-division control, it is possible to correspond to a tachometer, a fuel gauge, a thermometer, a turbo meter, and the like. A plurality of stepper motors can also be driven. In this case, the method described in the above embodiment may be applied in a time-division manner to the zero detection corresponding to each stepper motor.

In this embodiment, the coil C2 pulls the N pole in the excitation step 1, but may pull the S pole. In this case, the rotation pattern of the rotor 3 when it comes into contact with the stopper 7 and the signal waveform at each excitation step are different from those of the present embodiment.

Further, in the present invention, the rotation direction of the rotor at the time of zero detection is not limited to the direction shown in this embodiment.
It is also possible to change the polarity of the coils C1 and C2, change the position of the stopper, and the like. For example, a position determined by a stopper that appears only when the zero position is detected may be the zero position.

[0055]

As described above, according to the first aspect of the present invention, when the transition from the other step 1 to the detection step 7 is made, the amount of angular displacement of the rotor 3 is determined by a part of the driven member. Since it is larger than the amount of angular displacement of the rotor 3 due to backlash after contact with the stopper 7, the induced voltage generated before the stopper abuts in the detection step 7 is larger than the induced voltage generated due to backlash. Conversely, the induced voltage generated by the backlash is smaller than the induced voltage generated before the stopper abuts. Therefore, the two induced voltages can be clearly distinguished from each other, and it can be accurately determined that the pointer 6 has contacted the stopper. As a result, accurate zero detection becomes possible. In addition, by setting the angle shift amount of the rotor 3 as described above, the adjustment accuracy of the output gear and the stopper 7 on the case side of the motor is reduced. That is, since it is not necessary to adjust the amount of backlash by highly adjusting the stopper 7 on the case side, the manufacturing cost can be reduced and a low-cost stepper motor can be provided.

According to the second aspect of the present invention, the amount of rotation of the rotor 3 increases when transitioning from the other step 1 to the detecting step 7, so that the induced voltage due to the change in magnetic force increases accordingly. As a result, it is possible to reliably detect the induced voltage when the rotor 3 is rotating, that is, before the part of the driven member comes into contact with the stopper. of course,
Since the induced voltage should be close to zero when a part of the driven member comes into contact with the stopper, the difference between the induced voltages when the driven member is in contact with the stopper and when it is not in contact is large. As a result, it is easy to determine whether or not a part of the driven member has contacted the stopper 7, that is, zero detection can be reliably performed. Further, since the amount of angle shift due to the detection step 7 becomes large, the difference from the amount of angle shift due to backlash becomes clear, and it is possible to more accurately determine that the pointer 6 has come into contact with the stopper.

According to the third aspect of the present invention, the rotor 3 is formed into three magnetic pole pairs, and the excitation signal is converted into one detection step 7 and the six excitation steps 1 to 1 for uniformly changing the angle of the rotor 3.
6, the detection step 7
Causes the angular displacement of the rotor 3 to be 30 degrees. When the amount of angular displacement of the rotor 3 in the detection step 7 becomes 30 degrees,
Compared to the same 18 degrees when the rotor 3 has 5 magnetic pole pairs,
The induced voltage generated by the backlash becomes relatively small, the stopper contact determination becomes easy, and accurate zero detection becomes possible.

According to the fourth aspect of the present invention, when a part of the driven member comes into contact with the stopper 7, the magnetic pole change point of the rotor 3 coincides with the coil C2 functioning for detecting the induced voltage. Is set to That is, FIG.
As shown in (2), when the stopper abuts, the magnetic pole change point (change point from S3 to N1) of the rotor 3 is set to match the coil C2. With this setting,
As shown in FIG. 4B, it is easy to set the magnetic force change due to the backlash to be smaller than the peak value near the center point of N1. As a result, it is easy to determine whether the stopper is in contact with the stopper, and accurate zero detection can be performed.

According to the fifth aspect of the present invention, the stepper motor drive circuit is mounted on a vehicle. That is, the vehicle is in an environment where the amount of backlash is likely to fluctuate due to temperature change or looseness due to vibration, etc., but according to the present invention, these fluctuations are predicted and the amount of angular displacement of the rotor 3 is calculated as described above. Since it can be set, even if the amount of backlash fluctuates slightly, zero detection can be accurately performed. Therefore, it is very effective to mount the stepper motor drive circuit of the present invention on a vehicle. In addition, the dual use of the drive coil and the induction voltage detection coil makes it possible to reduce the size of the stepper motor housing. Therefore, it is very effective to apply the present invention to a vehicle having a limited living space.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a stepper motor drive circuit of the present invention and an application example thereof.

FIG. 2 is a diagram illustrating a signal waveform and a detection timing signal in each excitation step of an excitation signal used in the present embodiment and a reference example.

FIG. 3A is a schematic diagram of a rotor used in a reference example. FIG. 3B is a graph showing a change in magnetic force accompanying rotation of the rotor of FIG.

FIG. 4A is a schematic view of a rotor used in the present embodiment. FIG. 4B is a graph showing a change in magnetic force accompanying rotation of the rotor of FIG. 4A.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stepper motor drive circuit 2 Counter 3 Rotor 4 Intermediate gear 5 Output gear 6 Pointer 7 Stopper 8 Scale

Claims (5)

[Claims] 1. A rotor in which N and S poles are alternately and uniformly magnetized, and wherein said rotor is rotated in response to an excitation signal comprising one cycle of a plurality of excitation steps. And a stepper motor having first and second coils disposed at an angle of 1 mm, and generating the excitation signal for rotating the rotor so that a pointer driven by the rotor moves in a zero position direction defined by a stopper. Determining whether or not a part of the driven member has contacted the stopper based on an excitation signal supply unit that supplies the first and second coils; and an induced voltage generated by rotation of the rotor. A stepper motor driving circuit having a synchronization function for synchronizing a position where a part of the driven member abuts on the stopper with a counting mechanism based on the determination by the contact determination means. A path, wherein the excitation signal is composed of excitation signals supplied to the first and second coils, respectively, and synchronized with a timing at which a part of the driven member contacts the stopper, At certain steps in a cycle,
A detection step including a signal waveform for causing at least one of the first and second coils to function as an induced voltage detection; and an amount of angular displacement of the rotor when transitioning to the detection step from another step. A stepper motor drive circuit, wherein the amount of angular displacement of the rotor due to backlash after a part of the driven member abuts on the stopper is larger. 2. The stepper motor drive circuit according to claim 1, wherein the amount of angular displacement of the rotor when transitioning to the detecting step from another step is larger than the amount of angular displacement during another inter-step transition. A stepper motor drive circuit. 3. The stepper motor drive circuit according to claim 2, wherein the rotor is a three-pole pair, and the excitation signal includes one detection step and six excitations for uniformly changing the angle of the rotor. A stepper motor drive circuit comprising steps. 4. The stepper motor drive circuit according to claim 3, wherein when a part of the driven member comes into contact with the stopper,
A stepper motor drive circuit, wherein a magnetic pole change point of the rotor is set to coincide with the first or second coil functioning as an induced voltage detection. 5. The stepper motor drive circuit according to claim 1, wherein the stepper motor drive circuit is mounted on a vehicle.