JPH0226298A - Stepping motor driver - Google Patents

Abstract

PURPOSE:To rotate a platen easily through a manual operation by limiting the holding current of an apparatus and reducing the stop holding power thereof as occasion demands. CONSTITUTION:When a platen is manually rotated at the time of stopping of a stepping motor 2, a rotation detector 20 detects said speed variation, causes a holding current limiter part 30 to limit a holding current, and facilitates the rotation of said platen. Also, when said platen is rotated at a speed higher than a certain speed, its manual rotation can be conducted in the state of completely no rotation holding power. Further, when the manual rotation of the platen is stopped, an integral voltage e0 disappears and a stop holding power again works on the stepping motor 2.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a stepping motor drive device that controls a stepping motor that drives a driven section.

(Prior Art) Stepping motors are used in various devices because their rotation angle and rotation speed can be easily controlled. For example, in printing devices and the like, it is used to drive driven parts such as platens and ink ribbon drive rollers.

Now, a printing device equipped with a driven part driven by such a stepping motor can perform various types of printing such as binary printing suitable for documents, multi-value printing suitable for images with shading, and color printing. can be done.

When performing these various types of printing, various conditions must be met in order to maintain a high quality finish. For example, when performing color printing, multiple colors (cyan, magenta, yellow, etc.) are superimposed to perform color printing. In the case of printing by wrapping recording paper around a platen, the platen is rotated once for each color printing, making a total of three rotations to complete one sheet of printing. Now, the problem in this case is that the printing start positions for each color must be accurately aligned. If this printing start position is different for each color, the colors will not overlap properly, resulting in unclear printing. Therefore, as described above, a stepping motor is used to drive the platen so that the printing start position can be aligned relatively easily and accurately.

This stepping motor is controlled by a stepping motor drive device, and drives and stops its driven portion, here an example of which is a platen.

FIG. 2 shows a configuration diagram of the main parts of a conventional printing device.

In the figure, a stepping motor drive device 1, a stepping motor 2, and a platen 3 are shown. Further, recording paper 4 is wound around the platen 3.

The stepping motor drive device 1 is a circuit that supplies a driving current and a holding current to the stepping motor 2, and is a circuit that controls driving and stopping of the stepping motor 2. The stepping motor 2 is a motor that receives drive current from the stepping motor drive device 1 and drives the platen 3. Further, when the platen is stopped, a holding current is supplied to maintain a predetermined stopped state. The platen 3 is a roller that conveys the recording paper 4 wound around its circumferential surface.

FIG. 3 shows a circuit diagram around the main parts of the conventional stepping motor drive device 1 shown in FIG. 2.

The figure shows the stepping motor drive device 1 shown in FIG.
A circuit diagram of a motor drive circuit 5 provided therein and a circuit diagram of main parts of the stepping motor 2 are shown.

In the figure, a motor drive circuit 5 includes a PNP transistor Q and a diode D1. PNP
The emitter of transistor Q5 is connected to drive power supply terminal 10. Further, the base is connected to a control terminal 11 connected to a control circuit (not shown). The collector is connected to the cathode of diode DI. The anode of the diode D1 is connected to the holding power supply terminal 1 via the resistor R1.
Connected to 2.

On the other hand, the excitation coil ρ1 of the stepping motor 2. β2.
β3. One end of JZ4 is connected to P of the motor drive circuit 5.
It is connected to the collector of NP transistor Qa. And excitation coil f2If22. f23. The other ends of J24 are NPN transistors Q, Q2, Qa, respectively.
, Q4 is connected to the collector. NPN transistors Q-, Qa.

The bases of Qa and Q4 are connected to control terminals 15, 16, and 17°18, respectively, which are connected to a control circuit (not shown). NPN transistors Ql, Q2. Qa, Q
The emitter of No. 4 is grounded.

When driving the stepping motor 2, the motor drive circuit 5 configured as described above applies a drive voltage Vp to the drive power supply terminal 10.
p is applied. A control signal is applied to the control terminal 11 by a control circuit (not shown), and the PNP transistor Q5 is turned on.

As a result, the drive voltage VPII is applied from the drive power supply terminal 10 to the excitation coils 21 to 4 of the stepping motor 2 via the PNP transistor Q. Here, a control circuit (not shown) sequentially applies phase-shifted pulse-like control signals to the control terminals 15 to 18. As a result, the NPN transistors Ql-Q4 are repeatedly turned on and off in a predetermined order, and the rotor of the stepping motor 2 (not shown) rotates.

(Problem to be Solved by the Invention) For example, in color printing, when printing the first color and printing the second color, it is necessary to print the same color as the first color in order to prevent color shift and uneven printing. It is essential that printing of the second color is started from the starting position. Therefore, −
The stop position of the stepping motor 2 is maintained so that the stop position does not move unnecessarily due to external force during the stop. That is, when the stepping motor 2 is stopped, a control signal is applied by a control circuit (not shown) to turn off the PNP transistor Q5, and at the same time the holding voltage Vp is applied to the stepping motor 2 from the holding power supply terminal 12 through the resistor R1 and the diode D1. Supply current. For example, if the last drive current is supplied to the excitation coil f24, the holding current will be supplied to this excitation coil °C4.

Due to this holding current, a rotational force that causes the rotor (not shown) of the stepping motor 2 to rotate in the forward and reverse directions is not generated, but a stopping holding force that maintains the stopped position is generated.

Now, suppose that for some reason it becomes necessary to move the platen manually when the platen is stopped, that is, when a holding current is supplied to the stepping motor 2 and a stopping holding force is generated. In this case, if a reduction gear or the like is provided between the stepping motor 2 and the platen, even if the stopping force of the stepping motor 2 is small, it will be a fairly large force against the platen. For this reason, there is a problem in that manual rotation of the platen always requires a force that exceeds this stopping and holding force, which poses a problem in operability.

The present invention has been made with attention to the above points, and even if the platen is in a stopped state and the stop holding force of the stepping motor is acting, the stop holding force can be reduced as necessary, and it can be easily operated manually. The object of the present invention is to provide a printing device that can rotate the printing device.

(Means for Solving the Problems) A stepping motor drive device of the present invention includes a stepping motor that drives a driven section, and a predetermined drive current that is supplied to the stepping motor when the stepping motor is driven, and when the stepping motor is stopped. and a motor drive circuit that supplies a holding current to maintain the stop position of the driven part at a predetermined position, the motor drive circuit is configured to control the driven part when the driven part is manually rotated. A rotation detecting section that detects a change in the speed of the driven section, and a holding current limiting section that limits the holding current when the rotation detecting section detects a change in the speed of the driven section.

(Function) In the above device, when the stepping motor is to be manually rotated, the rotation detecting section detects a change in the speed of the platen. When the rotation detection section detects a speed change, the holding current limiting section limits the holding current applied to the stepping motor. Thereby, the stopping force of the stepping motor can be weakened.

(Example) FIG. 1 shows a circuit diagram around the main parts of a stepping motor drive device according to the present invention.

Comparing the circuit shown in FIG. 1 with the conventional circuit shown in FIG. 3, there is no difference in the circuit configuration of the stepping motor 2.

On the other hand, the motor drive circuit 5 includes a PNP transistor Q
, diode D+, and resistor R1, a rotation detecting section 20 and a holding current limiting section 30 are newly added.

Note that the same parts as in FIG. 3 are given the same reference numerals, and redundant explanations will be omitted as appropriate.

Now, the rotation detection section 20 includes a diode D2 and a resistor R2.
, R3, and a capacitor CI. The anode of diode D2 is connected to the collector of PNP transistor Q.

One ends of resistors Rz and Rs are connected to the cathode of the diode D2. The other end of resistor R2 is grounded. The other end of resistor R3 is connected to one end of capacitor CI. The other end of capacitor C1 is grounded. An integrating circuit is formed by this resistor R1 and capacitor C1. The resistor R2 is a resistor for discharging the capacitor CI.

Next, the holding current limiting section 30 includes a Zener diode ZD,
, a resistor R4, and an NPN transistor Q6. The cathode of the Zener diode ZD is connected to one end of the capacitor CI of the rotation detection section 20. The anode of the Zener diode ZD is connected to one end of the resistor R4 and the base of the NPN transistor QB. The other end of resistor R4 is grounded. The collector of NPN transistor Q6 is connected to the anode of diode Dl. The emitter is grounded.

In the above configuration, the operations when driving the platen and when stopping the platen and holding the stopped position are the same as those already explained in FIG. 3.

Next, a case will be described in which the platen is manually rotated when the platen is stopped.

Here, it is assumed that the holding current i4 is supplied to the excitation coil 424 and the platen is stopped.

That is, the holding voltage Vp is applied to the holding power supply terminal 12,
A holding current i4 flows through the excitation coil β4 via the resistor R1 and the diode D. At this time, the NPN transistor Q4 receives a control signal from the control terminal 18 and is in an on state.

In this state, when the platen is manually rotated, the rotor (not shown) of the stepping motor 2 rotates accordingly. and the excitation coil 9 of the stepping motor 2.
4, an induced voltage eI4 proportional to the angular velocity ω of the rotor is generated. This induced voltage e14 is, in principle, generated based on a change in the magnetic flux φ4 of a permanent magnet of a rotor (not shown) interlinked with the exciting coil f24, and a change in the holding current i4 flowing through the exciting coil ℃4. Then, it becomes the sum of the back electromotive force e1 generated by the self-inductance L4.

Therefore, the following formula holds.

6.4=e, +e, ------- [1] Note that L4 is the inductance of the exciting coil β4.

Further, when the number of turns of the exciting coil β4 is set to n, the magnetic flux linkage Φ4 in which the magnetic flux φ4 of the permanent magnet interlinks with the exciting coil β4 can be expressed by the following equation.

Φ4=n・φ4--- [3] Furthermore, when the rotor of the stepping motor is rotated by an angle θ, the magnetic flux linkage Φ4(θ
) is expressed as the following equation, and it is clear that it is almost a sine wave.

Φ4(θ)=nΦM CO3Pθ---[4][Φ
M: Maximum value of interlinkage magnetic flux Φ9, P: number of pole teeth The speed at which the platen is manually rotated, that is, the angular velocity ω accompanying the rotation of the stepping motor 2. When formula [4] is transformed, Φe(t) =nΦMcos pθ---[5].

Then, Faraday's law of electromagnetic induction and [5] above formula [
1. According to formulas [2] and [6], e +4”-n P
(JJΦM SIN P ωt--(i4-L4)--
−[7]t.

Here, the holding current i4 flowing through the excitation coil °C4 is almost constant, and the change in the self-inductance L4 can be ignored, so the second term in equation [7] can be deleted.

Next, detailed operation of the motor drive circuit according to the present invention will be explained using FIGS. 4 and 5.

FIGS. 4 and 5 are graphs showing voltages at various parts within the motor drive circuit.

First, FIG. 4(a) shows the waveform of the induced voltage e14 generated in the exciting coil I24 when the rotor of the stepping motor 2 rotates at an angular velocity ω. As shown in the figure, when the rotor is rotated at an angular velocity ω, the induced voltage 814 becomes a sine wave with a maximum value of nPωΦ2 and a period of 2π/Pω.

This induced voltage et< is rectified by a diode D2 to obtain a rectified voltage e' as shown in FIG. 4(b). This rectified voltage e' is input to an integrating circuit composed of a resistor R3 and a capacitor C1, and is integrated by a predetermined time constant determined by the resistor R3 and the capacitor C1. As a result,
The cathode of the Zener diode ZD is shown in Figure 4 (C
) is applied as an integrated voltage e0.

Further, when the rotor of the stepping motor 2 is rotated at an angular velocity ω2 that is twice the angular velocity ω, an induced voltage IBI4 having a period of 2π/Pω2 is generated as shown in FIG. 5(a). This is rectified by the diode D1 in the same manner as described above to produce a rectified voltage e' as shown in FIG. 5(b). Then, this rectified voltage e' is input to an integrating circuit composed of a resistor R5 and a capacitor C1, and as shown in FIG.
The integrated voltage e as shown in . get. This integrated voltage 60
is applied to the cathode of the Zener diode Z D +.

Now, when the integrated voltage e0 reaches the Zener voltage of the Zener diode ZD, a reverse current flows through the Zener diode ZD. Therefore, the NPN transistor Q
Base current flows to the base of NPN transistor Q
B turns on, lowering the collector-emitter resistance of NPN transistor Q6.

As a result, the holding current i flowing through the excitation coil I24
4 flows into the collector of NPN transistor Q6.

That is, the holding current i4 is bypassed to the collector of the NPN transistor Q6.

As a result, the stopping force acting on the rotor of the stepping motor 2 is reduced, and the platen can be easily rotated.

Now, this decrease in rotation holding force is caused by the NPN transistor Q
6 depends on the amount of holding current bypassed to the collector.

As can be seen from FIGS. 4(C) and 5(C), the faster the platen is rotated, the faster the stepping motor 2
The integral voltage e0 increases as the angular velocity of the rotor increases. Therefore, the reverse voltage applied to the Zener diode Z D + also increases, making it possible to supply more base current.

Thereby, the collector current of NPN transistor Q6 can be increased.

As described above, when the platen is manually rotated when the stepping motor 2 is stopped, the rotation detection unit 20 detects this speed change, causes the holding current limiting unit 30 to limit the holding current, and controls the platen. Make rotation easier. Also,
By rotating the platen at a speed higher than a certain speed, manual rotation can be performed without any rotation holding force. Furthermore, when manual rotation of the platen is stopped, the integrated voltage e. disappears, and the stepping motor 2
A stopping force is applied to the

The present invention is not limited to the above embodiments.

Although the description has been given using a stepping motor that drives a platen as an example, it is not limited to platen driving, and can also be implemented with, for example, a stepping motor that drives an ink ribbon driving roller, so-called driving by a stepping motor. The present invention can be applied to any structure as long as it is desired to easily remove the stopped and held state of the driven part.

(Effects of the Invention) The stepping motor drive device of the present invention configured as described above has the following features:
In a stepping motor, which is maintained in a stopped state by the stopping force generated by the holding current, the holding current can be restricted as necessary to reduce the stopping force and the platen can be easily rotated manually. .

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram around the main parts of a stepping motor drive device according to the present invention, FIG. 2 is a configuration diagram of the main parts of a conventional printing device, and FIG. 3 is a circuit diagram around the main parts of a conventional stepping motor drive device. The circuit diagram and FIGS. 4 and 5 are graphs showing voltages at various parts in the motor drive circuit according to the present invention. DESCRIPTION OF SYMBOLS 1... Stepping motor drive device, 5... Motor drive circuit, 20... Rotation detection part, 30... Holding current limiting part, Q,... PNP transistor, C6... NPN transistor, DI D2...Diode, ZD,...Zener diode, R,, R,, R3, R,...Resistor, C1...Capacitor. Patent applicant Oki Electric Industry Co., Ltd. Figure 2 Figure 4

Claims (1)

[Scope of Claims] A stepping motor that drives a driven part; A predetermined driving current is supplied to the stepping motor when the stepping motor is driven; and when the stepping motor is stopped, the stopped position of the driven part is maintained at a predetermined position. and a motor drive circuit that supplies a holding current for the drive, the motor drive circuit comprising: a rotation detection section that detects a change in speed of the driven section when the driven section is manually rotated; A stepping motor drive device comprising: a holding current limiting section that limits the holding current when the rotation detecting section detects a speed change of the driven section.