JPH0433594A - Step motor driving method - Google Patents

Abstract

PURPOSE:To maintain the displacement of load approximately constant even in the case of 1-2 phase excitation by setting the conduction current control level, in an exciting step where the number of motor coil to be conducted is high, lower than that in an exciting step where the number of motor coil to be conducted is low. CONSTITUTION:A driver control section 1 perform constant current control based on two conduction current control values, i.e. control currents, I1, I2 for one-phase excitation and two-phase excitation in 1-2 phase excitation driving. When switching is made such that the conduction current control value (control current I2) in an excitation step (two-phase excitation) where the number of motor coil to be conducted is high is smaller than the conduction current control value (control current I1) in an excitation step (one-phase excitation) where the number of motor coils to be conducted is low, outputtorque of motor in one-phase excitation and two-phase excitation are approximately equalized thus suppressing fluctuation of feeding amount (displacement) of motor with respect to a load in 1-2 phase excitation driving.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for driving a stepping motor used in a scanner section, a thermal recording section, etc. of a facsimile machine, and for causing a constant displacement of a load.

(Prior art) ゛Currently, in the G3 facsimile, the density of transmission pixels in the sub-scanning direction is 3.85 pel/mm and 7.7 pel/mm.
Two modes have been standardized, and 1.5.4pe
The l/mm mode is also about to be standardized.

As described above, facsimile machines are provided with modes with different transmission pixel densities, so the minimum unit for reading a document or feeding a recording paper in the scanner section or thermal recording section differs depending on the mode.

Said 15.4pe1. The feed corresponding to /mm mode is
Due to the limit of miniaturization of the unit step angle in the two-phase stepping motor used, or the limit of the reduction ratio of the power transmission system, 1-2 phase excitation, which alternately excites the two-phase stepping motor to the first phase and the second phase, is called 1-2 phase excitation. Half-step driving is often used.

(Problem to be Solved by the Invention) In the half-step drive described above, the number of motor coils energized differs for each step, and as a result, the torque generated near the stable point of the motor rotor changes, so the load increases. When connected, a problem arises in that the amount of rotation per step varies.

Figure 4 shows the stable point after rotation of the motor rotor (displacement 0-O)
It is an explanatory diagram showing the relationship between displacement δ(O) from It shows. From this approximate straight line, in the vicinity of the stable point, the following equation (1) holds true: ]'=-, r-N, .■.O. However, K7 is a proportionality constant, N is the number of teeth of the motor rotor, and ■ is the control current value.

Here, assuming that the friction load is F, the control load is D, and the inertia at the motor shaft of the system is J, the equation of motion when the loaded system is maintained is as follows.

At this time, the response of the motor rotor for one step is as shown in either FIG. 5(a) or FIG. 5(b). In other words, when the control load is relatively small, Fig. 5 (
If the control load converges to the stable point O8 after rotation in an oscillatory manner as shown in a), and the control load is large, then θ becomes stable in an overdamped manner as shown in FIG. 5(b). Calm down.

In the facsimile scanner section or thermal recording section,
Since there is no margin for the 1 to 1 torque output, the
)) resulting in an overdamped response.

In the case of an overdamped response as shown in Figure 5(b), the frictional load F always acts in the opposite direction to the displacement direction, so
The stopping point of the motor rotor is T(0
)=F, which corresponds to the position of the displacement O1. Basically O
01 throat will stop before the stable point where =O.

If only 2-phase excitation is performed in a 2-phase stepping motor, stopping just before the O point for each step will not affect the feed pitch of the motor rotor, but the above-mentioned 1-2 phase excitation In the case where the above (1)
) The value of the proportionality constant KT in the equation changes every 1-step, so the value of 01 changes, and as shown in Figure 6, the rotational displacement varies in length and short every other step. Put it away.

Figure 6 shows the displacement of the motor rotor when a two-phase stepping motor is excited in 1-2 phases. are shown respectively.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for driving a stepping motor in which the displacement of the load is substantially constant even with -2 phase excitation.

(Means for Solving the Problems) In order to achieve the objective of "1 of 2", the present invention provides a two-phase stepping motor provided for displacing a load, by reducing the number of motor coils energized by an excitation step. In a method for driving a stepping motor in which the number of motor coils to be energized is different, the current control value for energizing the motor coil in an excitation step in which a large number of energized motor coils is energized is set to 5. The current control value is set to a value smaller than the current control value so that the amount of displacement of the load at each excitation step is approximately constant.

(Function) By adopting the above means, it is possible to switch the energizing current control value so that the motor output torque during phase excitation and the motor output torque during two-phase excitation are approximately the same, and each excitation step The amount of displacement of the load at is approximately constant.

(Example) Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a block diagram schematically showing a motor drive circuit to which an embodiment of the stepping motor drive method according to the present invention is applied. In this motor drive circuit, the circuit configuration is related to a bipolar-driven two-phase stepping motor. , both ends of two motor coils A and B are connected to the emitter-collector connections of two transistors Tr (total of 4), and each transistor Tr
The base of the driver is connected to the driver control section 1. Further, R is a resistor 6 connected in series with the motor coils A and B.

In the figure, a transistor Tr is turned on and off by a driver control unit 1-, and a voltage VAI VAI is applied to each motor coil A, I3, and the voltage is reversed depending on the step.
Vo+Vn is applied. Also, each motor coil A, +
3 flows to ground via a resistor R, and the voltage V ref across this resistor R is fed back to the driver control unit 1 as a current monitor value (vref/R). The driver control unit 1 performs constant current control by chopping when the value of the voltage Vref at both ends (r+if) reaches a set value (energizing current control value).

In this embodiment, constant current control is performed using two energizing current control values: a control current 11 during 1-phase excitation in 1-2 phase excitation drive, and a control current 2 during 2-phase excitation.

FIG. 2 shows the setting state of the current control value in this embodiment. The control current I1r■, (1
, >L), and the energizing current control value of each motor coil A, 13 is determined by the state of the energizing current (excitation state) to each motor coil A, B shown in FIG. When the current applied to one motor coil is zero, that is, during the phase excitation state, the control current is set to ■, and when the current is applied to both motor coils, that is, during the two-phase excitation state, the control current is The control current is set to I7. Here, the control current I,,I, is determined by the equation (1) above, KT
l・工□=nia.・■2...It is determined through experiments that the following relationship (3) holds true. however,
KA is a proportional constant during one-phase excitation, and KT2 is a proportional constant during two-phase excitation.

As mentioned above, the current control value (control current I2) to be applied to the motor coil in the excitation step where a large number of energized motor coils (during two-phase excitation) is changed to the energization current control value (control current I2) in an excitation step where a large number of energized motor coils are energized (during one-phase excitation). By switching the current control value (control current I□) to the motor coil to a smaller value (x2<■, The motor outputs 1 to 1 torque during phase excitation are approximately the same, and variations in the motor feed amount (displacement amount) with respect to the load in 1-2 phase excitation drive can be suppressed.

(Effects of the Invention) According to the present invention, even if driving is performed to change the number of motor coils to be energized by the excitation step, the motor output 1 to rk can be reduced by changing the control value of the current to be energized to the motor coils. It is possible to provide a method for driving a stepping motor in which the change in load at each excitation step is substantially constant.

[Brief explanation of drawings]

Fig. 1 is a block diagram schematically showing a motor drive circuit to which an embodiment of the stepping motor driving method according to the present invention is applied, and Fig. 2 shows the setting state of the current control value of the present embodiment to the motor coil. 3 is an explanatory diagram showing the magnitude of the control current, FIG. 3 is an explanatory diagram illustrating the state of the current flowing through each motor coil, and FIG. 4 is a diagram showing the displacement of the motor rotor from the stable point,
An explanatory diagram showing the relationship between this displacement and one herk of motor output, Figures 5 (a) and (b) are explanatory diagrams showing the response state of the motor rotor for one step, and Figure 6 is a conventional two-phase stepping It is an explanatory view showing displacement of a motor rotor when a motor is excited in 1-2 phases. 1... Driver control unit, A, B - Motor coil of stepping motor, 1"r-1-transistor,
R...Resistance. Patent applicant Rico Co., Ltd. - =10-

Claims (1)

[Claims] In a stepping motor driving method in which a two-phase stepping motor provided for displacing a load is driven so that the number of motor coils energized differs depending on the excitation step, the motor in the excitation step in which a large number of motor coils energize is driven. The control value of the current applied to the coil is set to a smaller value than the control value of the current applied to the motor coil in excitation steps where a small number of motor coils are energized, so that the amount of displacement of the load at each excitation step is approximately constant. A method for driving a stepping motor, characterized in that: