JPS6235360B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention primarily relates to an improvement in the operation detection circuit of a step motor of an electronic wristwatch.

In particular, for step motors that require low power consumption, such as ultra-compact step motors for electronic wristwatches, methods of reducing power consumption include improving the electric-mechanical conversion efficiency of the step motor itself. The most important part of the corrective drive system is the so-called corrective drive system, in which the rotor is driven, and if for some reason the rotor does not rotate normally, the rotor is quickly re-driven with higher power than normal. ,
How to detect rotation or non-rotation of the rotor. As a method for this purpose, a method of determining whether the rotor rotates or not rotates based on the voltage or current induced in the excitation coil due to the rotation and vibration motion of the rotor after application of a normal drive pulse has been considered.

FIGS. 1 and 2 show an example of a conventional step motor and a drive circuit. Drive inverter 4
When the output becomes "H", a current flows in the direction of the arrow in the excitation coil 3 (hereinafter abbreviated as "coil"), forming magnetic poles in the stator 1, and moving the rotor 2 one step (in this example, a two-pole rotor). So 180
゜) Rotate. Next, in order to rotate the coil 3 by one more step, the output of the inverter 5 should be set to H and the output of the inverter 4 should be set to "L" in order to cause current to flow through the coil 3 in the opposite direction. An example of the current waveform of the coil 3 at this time is shown in FIG. Section A is the current caused by the drive pulse applied by the drive inverter 4 or 5, and section B is the current induced in the coil 3 and generated in the loop 7 by the rotation and vibration movement of the rotor. Since the current waveform in this section B changes depending on the load condition of the step motor, the load condition of the step motor can be detected by detecting the change in the current waveform.

The conventionally considered detection circuit is the fourth one.
The circuit is as shown in FIG. The operating principle of this circuit is common to the circuit of the present invention and will be described in detail later. Now, the circuits shown in FIGS. 4 and 5 each include an impedance element (resistance) 16 and a binary logic element (comparator or logic gate) 17.
Since only one input terminal is prepared and the input terminal is switched by a switching element, when configuring it on an IC,
Although it has the advantage that the increase in area due to impedance elements and binary logic elements is small, the substrate of the gate (Fig. 4, 15, 16, Fig. 5, 28, 29) through which analog signals pass is connected to the impedance element from the power supply and ground. Therefore, it occurs due to potential floating. Due to the so-called substrate effect, a phenomenon occurred in which the analog signal detection characteristics of the binary logic element 17 deteriorated as a result. This substrate effect will be explained in detail later.

The present invention has been made in order to eliminate the drawbacks of the conventional example as described above, and has been made for the purpose of providing a detection circuit having high performance detection characteristics.

Hereinafter, the present invention will be explained in detail with reference to the drawings.
FIG. 6 is an example of a detection circuit according to the present invention.

P-type MOSFET gates (hereinafter abbreviated as gates) 10 and 12 and N-type MOSFET gates (hereinafter abbreviated as gates) 11 and 13 are the conventional example shown in FIG. 2, and constitute drive inverters 4 and 5. It is a gate. Output terminals 18 and 19 of the drive inverter
is connected to both ends of the coil 3, and at the same time the detection resistor 4 is connected to both ends of the coil 3.
0 and 41 are directly connected to the positive inputs of voltage comparators 44 and 45, respectively. The waveform detection circuit of this embodiment includes the detection resistors 40, 41 and the voltage comparator 4.
4 and 45, the voltage comparator 4
By connecting both the negative inputs of 4 and 45 to the intermediate terminal of the power supply voltage dividing resistor 47 for obtaining the reference voltage, it is possible to detect whether the induced voltage waveform generated in the coil reaches a certain voltage value or higher. are doing.

Next, the principle of operation detection by this circuit will be explained. FIG. 7 shows the input signals of each gate. Section _T1 is the timing at which a drive pulse is applied to the coil. That is, since only gates 10 and 13 are in the ON state, current flows from the power supply along the path indicated by arrow 22. Next, assume that only the gates 13 and 42 are turned on.
At this time, a closed loop 23 including the coil 3 and the detection resistor 40 is formed. At this time, the induced voltage in the coil 3 due to the movement of the rotor 2 is e, and the voltage between the coil 3 and the gate 4 is
2 and 13, and the resistance value of the detection resistor 40 is R, the potential V ₁₈ at the connection point 18 is V ₁₈ =
It is expressed as eR/(R+r). Here, if R≫r, then V ₁₈ =e. Therefore, as long as the condition R≫r is satisfied, V ₁₈ can be regarded as the induced voltage in the coil. FIG. 8 shows an example of the waveform of _V18 . In this example, the detection resistance value is 50KΩ, the coil resistance is 28KΩ, and the number of turns is
At 9800 turns, the step motor is almost under no load. From this induced voltage waveform _V18 , the rotation angle θ of the rotor can be estimated approximately as shown in FIG. As the load on the step motor increases, the peak value of the induced voltage waveform gradually decreases while maintaining a similar shape, and the period of vibration becomes longer.

Next, in FIG. 9, the induced voltage waveforms and rotor rotation angles at maximum load and overload are shown as a and b.

At the maximum load Q, the rotor rotates slowly and does not vibrate after rotating one step, so there are few fluctuations in the induced voltage. Furthermore, in the case of overload b, a large peak voltage is induced in the load direction when the rotor returns to its initial position. Various methods can be considered for determining whether the rotor is rotating or non-rotating from the induced voltage waveform, but determining based on the presence or absence of the peak q shown in FIG. 8 is simple and reliable in terms of circuitry. In other words, in order to avoid false detection due to the peak p after the drive pulse is applied, detection starts several milliseconds later, and if the induced voltage reaches a predetermined voltage level or higher within a predetermined time, it is determined to be rotating, and if it does not, it is determined to be non-rotating. do. However, with this method, as shown in Figure 9a, the motor is considered to be non-rotating even though it is rotating at maximum load, but when this detection circuit is used in a correction drive method, etc. The rotor will not rotate too much, only an excessive amount of correction pulses in the same direction will be generated.

The above is the basic principle of motion detection used in the circuit of the present invention.

Next, after applying the driving pulse, the high resistance circuit and the low resistance a
We will discuss the effect of switching the circuit intermittently. Conventional drive circuits are driven by two inverters as shown in Figure 2, so when not driving, both ends of the motor coil are short-circuited due to the low resistance in the driver formed with the inverter, and at this time, as shown in Figure 3. Current flows through this short circuit, and this current is consumed as heat by the low resistance transistor for the driver, thereby applying braking to the rotor. Also, the 6th
In the system shown in the figure, high-resistance detection resistors 40 and 41 are connected in series in addition to the driver circuit, and the current in the braking circuit is smaller than that in the former. Therefore, when braking the rotor, switching between these two circuits is performed. A timing chart at this time is shown in FIG. This causes a sudden change in current in the braking circuit. However, since the motor coil has a large inductance, it cannot follow this change in current, and the time constant τ= due to the resistance R of the braking circuit and the inductance L of the coil
It shows the first-order lag response L/R. At this time, the voltage generated across the detection resistor 40 or 41 is zero volts in the braking circuit shown in FIG. 3 tries to keep the current flowing during braking as shown in Fig. 3, so a high voltage is momentarily generated across the detection resistor 40 or 41, which has a relatively high resistance, and then this voltage is increased by the above-mentioned time constant τ. The high voltage is attenuated and becomes a voltage having the voltage waveform shown in FIG. The voltage waveform at this time is shown in FIG. The feature of this method is that it is possible to amplify the voltage induced by the motor during braking by simply switching the resistance value of the circuit that performs rotor braking, and the peak voltage q of the waveform shown in Figure 8 is approximately 0.6 volts. On the other hand, the peak voltage shown in FIG. 10 is 1 volt or more. Therefore, in order to detect the peak voltage q shown in FIG. 8, a comparator with a threshold voltage of about 0.2 volts was required. However, when considering a comparator for a watch, its driving voltage is around 1.5 volts, so its operating range is narrow, and a comparator with a threshold of about 0.2 volts has low sensitivity.
In order to increase this amplification, it was necessary to take measures such as increasing the area of the comparator on the IC.

In contrast, with this method, since a peak voltage of 1 volt or more can be obtained, the comparator's highest sensitivity range of about 6.5 to 1.0 volts can be used, making comparator design easier and reducing the area of the comparator within the IC. It looks like it's going to be a bit of a bit of a bit of a bit of a bit of a bit of a bit of a bit of a bit of a bit of a bit of a bit of.

Furthermore, the voltage comparators 44 and 45 shown in FIG.
It is possible to replace it with an inverter, which is the simplest component within a CMOSIC, or it is also possible to input it directly to the input of a flip-flop.

Next, the aforementioned substrate effect will be described.

The portions of the gates 15 and 16 shown in FIG. 4 are shown in FIG. 11a. Also, transmission gate 2 in Fig. 5
8 and 29 are shown in FIG. 12a. The function of the N-channel transistor 55 in FIG. 12a is equivalent to that in FIG. 11a, so it will be explained with reference to FIG. 11a.

N-channel transistor 52 in FIG. 11a
The back gate is made up of P-well and is grounded to Vss. Here, when the source side is set as Vin and the drain side is set as Vout, and the voltage applied to Vin is varied, a characteristic of curve 53 shown in FIG. 11b is obtained. The characteristics of an ideal analog switch are:
This is the characteristic of 54 in Figure 1b. Therefore, it can be seen that the usage shown in FIG. 11a has a limit as an analog signal switching element.

In particular, as used in electronic watches, V _DD =
If the threshold voltage of a 1.57V, N-channel transistor is about 0.5V, the range that matches the ideal transfer characteristic of 54 will be 0.5V or less, and a detection signal of 0.5V or more will be generated. Even in this case, the result is that it can only be transmitted as a 0.5V signal.

This is the substrate effect that occurs because the source potential is not connected to the substrate.

Figure 12a shows a P channel transistor and an N channel transistor.
The transmission gate is a combination of channel transistors and is generally used as an analog switch.The N-channel transistor 55 exhibits the same operation as the N-channel transistor shown in FIG. 11a, and the P-channel transistor 56 is an N-channel transistor. 55 is passed through an inverter 57 to become a gate signal. In FIG. 12b, the characteristic 58 is the signal transmission characteristic of the N-channel transistor, 59 is the signal transmission characteristic of the P-channel transistor, and the transmission characteristic of the transmission gate as shown in FIG. 12a is shown in 60. Also, since there is no distinction between drain and source, it is also shown as 62 characteristics. What is important here is that with respect to the ideal analog switch characteristic 61, there will be a portion where the error becomes large.

Generally speaking, when the drive voltage (gate voltage here) is sufficiently high compared to the threshold voltage of the transistor, this substrate effect decreases and becomes close to a straight line. When the driving voltage and the driving voltage are relatively close to each other, the range of this error becomes large.

Therefore, when determining whether the rotor is non-rotating or rotating based on the magnitude of the analog signal depending on whether the rotor is non-rotating or rotating, analog signals such as those shown in FIGS. 11a and 12a are used in the transmission path of this detection signal. Turning on the switch had the disadvantage of making the operation unstable.

As explained above, according to the present invention, a high-performance step motor operation detection circuit can be realized, and the step motor can be used with low power consumption and high efficiency, and its industrial value is immeasurable. .

It goes without saying that the present invention can be applied not only to the step motor and detection circuit shown in the embodiments, but also to any detection circuit using similar means.

[Brief explanation of the drawing]

Fig. 1 is an example of a step motor to which the present invention is applied, Fig. 2 is an example of a step motor drive circuit, Fig. 3 is an example of a coil current waveform when driving a step motor, and Figs. 4 and 5 are examples of a step motor drive circuit. An example of a conventional motion detection circuit, FIGS. 6 and 7 show an embodiment of the motion detection circuit according to the present invention, and its timing chart, and FIGS. 8 and 9 show an example of a coil induced voltage waveform and a rotor waveform. A graph showing the rotation angle, FIG. 10, is an example of a detected voltage waveform according to an embodiment of the present invention, and FIGS. 11a, b, and 12a, b are explanatory diagrams of the substrate effect. 1...Stator, 2...Rotor, 3...Coil, 4,
5... Drive inverter, 10, 11, 12, 1
3, 15, 16, 25, 26, 42, 43...
MOSFET gate, 28, 29... Transmission gate, 21, 30, 31, 40, 41... Detection resistor (impedance element), 17, 27, 4
4, 45... Voltage comparator (waveform detection circuit), 20,
47...Reference voltage setting resistor.

Claims (1)

[Claims] 1. After applying a drive pulse from a drive circuit to a step motor whose main components include a magnetized rotor, a stator, and a coil for temporarily magnetizing the stator, a drive pulse is generated in the coil. In an operation detection circuit that detects the induced voltage based on the free vibration of the rotor and determines rotation or non-rotation of the step motor, a gate element forming a closed loop including a coil and an impedance element in series after applying a driving pulse, and a gate element forming a closed loop including a coil and an impedance element in series after applying a driving pulse are used. a voltage comparator that determines whether the rotor is rotating or non-rotating by comparing a reference voltage value with a voltage value generated as a result of the induced current flowing in the closed loop based on the free vibration of the rotor; There is a pair of impedance elements and a voltage comparator each, and the pair of impedance elements and voltage comparators are directly connected to both ends of the coil, and each impedance element is selected by the gate element according to the polarity of the drive pulse. 1. An operation detection circuit for a step motor, characterized in that the circuit is selectively selected to form the closed loop. 2. The step motor operation detection circuit according to claim 1, wherein the impedance element is a resistance element, and the resistance value thereof is greater than or equal to the DC resistance value of the coil. 3. The step motor operation detection circuit according to claim 2, wherein the voltage comparator is a comparator, and the reference voltage is obtained by dividing a power supply voltage by a certain impedance element.