HK1002613B - Method for feeding a monophase stepping motor - Google Patents

Description

The present invention relates to a stepper motor power process, particularly for watch parts, as described in the preamble to claim 1.

Several types of stepper motor powering for quartz watches are known. In the Swiss patent CH-B-634194, a powering process in which the motor is powered by a pulse of constant duration and amplitude was described. This process has the disadvantage of high energy consumption because the power pulse is not adapted to the actual load of the motor. Other solutions were made, allowing the power supply of the motor to be adapted to the load.In patent application EP-A-0 345 224 a new stepper motor feeding process has been proposed which allows the motor to be supplied with voltage pulses of varying duration according to load with relatively simple means. Recent tests on this feeding mode have shown that improvements to this process can be made to reduce the energy consumption of the motor. The purpose of the present invention is to propose a stepper motor feeding process which will achieve a greater saving in consumption.The objective is achieved by means of the measures set out in the characteristic part of claim 1.

The invention will be better understood by reading the following description, referring to the attached drawings, in which: Figure 1 shows the basic design of a stepper motor of the bipolar single-phase type;Figure 2 shows the static torque diagram of a stepper motor of the above type;Figure 3 shows a type of supply pulse of this motor;Figure 4a shows the current and voltage applied to the motor according to the method of supply described in the invention, the motor not being charged by mechanical torque;Figure 4b shows the power supply and the motor applied according to the same supply process of Figure 4a, but the motor being charged by mechanical torque;Figure 5 shows the voltage variation of the motor during the interval of T5i of two partial current displacements;Figure 6 shows the schematic diagram of a power supply element separation of the engine according to the method of supply in Figure 6;Figure 7 shows the schematic diagram of the engine according to the process of partial current displacements;Figure 6 shows the schematic diagram of the power supply unit separation of the engine according to the time variation of the current in Figure 6.

Figure 1 shows a schematic representation of a single-phase, bipolar stepper motor, consisting of a rotor with a cylindrical permanent magnet 1 with a diameter magnetization, a stator with a coil 2, a coil core 3 and the polar parts 4a and 4b made of soft ferromagnetic material.

The positioning torque Ta is due to the interaction between the magnet and the geometry of the static polar parts. The mutual torque Tab is due to the interaction between the field created by the coil when it is powered. The torque Tm is the sum of all the mechanical torques acting on the rotor. This figure shows that the Ta and Tab torques are offset by an angle of about 45 degrees. At rest, the rotor is initially positioned at the point S1 by the Ta torque. When a voltage pulse is sent under the coil, the rotor moves in the direction of S2 by the Tab torque action.

The engine coil is normally fed by a pulse at constant voltage and duration, as shown in Figure 3. The pulse duration is chosen to be long enough to allow the engine to step in adverse conditions such as a drop in battery voltage or an increase in mechanical torque Tm. However, most of the time the engine is not loaded and runs at its rated voltage; the constant and long enough duration of the pulse makes unnecessary energy loss in normal operating conditions.

Figure 4a shows the current and voltage applied to the motor coil according to the method of supply described in the present invention, the motor being only subjected to mechanical torque.

The total-duration T7 pulse of the split voltage is formed by a partial pulse of duration T4 and 11 partial pulses of variable duration T6i, separated by time intervals T51, T52 --- T5i of variable duration. $\text{U = R.i + L . di/dt + K.Ω}$ - What? in which: U = applied voltageL = inductancei = currentt = timeK = coupling factor expressing the change in the mutual flux between the magnet and the coilΩ = angular velocity

After this first partial voltage pulse, i.e. from t = T4, the motor coil is short-circuited. $\text{0 = R.i + L . di/dt + K.Ω}$ - What? When this current decreases to a reference value Iréf, i.e. at the instant t = T4 + T51, the coil is again fed by a second partial pulse of constant voltage, of duration T61 equal to the previous T51 short-circuit duration. The current in the coil during the duration T61 increases from the Iréf value to the i2 value and the motor coil is again short-circuited at the instant t = T4 + T51 + T61 = T4 + 2 T51 and so on. For this operating case, i.e. when the motor is not loaded, the total T7 duration of the pulse is 4.8 ms and the motor consumption is 0.65 μAs.

Figure 4b shows the current and voltage applied to the motor by the same power supply process as in Figure 4a, but the motor is charged with a mechanical torque of 0,2 μNm. The total duration of the T7 pulse is increased from 4.8 ms in the previous case to 10.8 ms in the present case and the motor consumption in the present case is 1.7 μA. There is therefore an automatic adaptation of the total pulse duration to the load of the motor, and it is thanks to this adaptation that the power supply process of the invention allows the energy supplied by the battery to be saved.

Figure 5 shows the change in current during the time interval T5i separating two partial voltage pulses. $\text{T5i ≈}\frac{\text{L.Δi}}{\text{R.im + K.Ω}}$

Equation (3) shows that the length of the time interval T5i depends on the engine's rotational speed. An increase in the engine's mechanical torque causes a decrease in the rotational speed Ω, which will result in an increase in the interval T5i.

The total duration T7 of the pulse is given by - What? In this equation, n is the total number of partial pulses of duration T6i (n = 11 in the example shown in Figures 4a and 4b).

Equations (3) and (4) explain the adjustment of the pulse length to the load by the feeding process of the present invention.

Figure 6 shows the block diagram of an example of the implementation of the power process according to the invention. The time base signal from the Q oscillator is sent to the split and form circuit 10, at the output of which the To power period of the engine and the TB base period of the oscillator are obtained.

A measuring resistor r is connected in series with the motor M at the output of the Driver 14 and the measuring block 13 transforms the voltage at the terminals of the measuring resistor r into a signal giving the current i image before sending it to the comparator 12.

Err1:Expecting ',' delimiter: line 1 column 396 (char 395)

Figure 8 shows the detail of element 14 (Driver) of the block diagram in Figure 6. The output transistors 31, 32, 33, 34 are H-mounted and controlled by the D1, D2, D3, D4 signals from circuit 25.

Claims (7)

1. Method for feeding a monophase stepping motor for a timepiece, adapted to supply the motor with chopped-voltage pulses of variable duration T₇ as a function of the load conditions and as a function of the feed voltage of the motor, characterized in that it acts so that each pulse of chopped voltage is composed of a first partial voltage pulse of duration T₄ and of a train of partial voltage pulses of the same polarity as that of the first partial pulse and of variable duration T_6i, and so that the intervals of time T_5i separating the said partial voltage pulses are variable as a function of the load conditions and as a function of the feed voltage of the motor, and so that each variable duration T_6i is proportional to the interval of time T_5i which precedes it.
2. The method according to claim 1, characterized in that the coil of the motor is short-circuited during said intervals of time T_5i.
3. The method according to claims 1 and 2, characterized in that each said interval of time T_5i is delimited by the end of a said partial pulse of duration T₄ or of duration T_6i and by the moment following this end when the current of the coil of the motor is equal to or less than a reference value I_ref.
4. The method according to claims 1, 2 and 3, characterized in that said chopped pulse is composed of a constant number of partial pulses.
5. The method according to claim 1, 2 and 3, characterized in that said chopped pulse is interrupted when said interval of time T_5i exceeds a reference value T_ref.
6. The method according to claims 1, 2, and 3 or according to claims 1, 2 and 4, characterized in that the coil of the motor is short-circuited between two said chopped pulses.
7. The method according to claim 6, characterized in that two successive chopped pulses of duration T₇ are of the same polarity or of opposite polarities.