JPS6142234B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an electronic timepiece, and more particularly to a method for determining the stop position of a rotor of a step motor, which is an electromechanical conversion mechanism thereof. More specifically, by determining the position of the rotor, the step motor is always driven with an optimal pulse width, thereby achieving low power consumption of the electronic timepiece. Conventionally, the display mechanism of a commonly used analog electronic timepiece is constructed as shown in FIG. The output of the step motor, which is composed of the stator 1, coil 7, and rotor 6, is
The information is transmitted to the center wheel 4, the third wheel 3, and the second wheel 2, and the second hand
It drives the minute hand, hour hand, and calendar mechanism. On the other hand, the circuit configuration for driving this display mechanism is as shown in FIG.
A drive pulse is applied to the excitation coil 14, which changes the direction of the current every second, and the bipolar magnetized rotor 6 rotates 180 degrees every second to drive the wheel train. go. However, this conventional circuit configuration can only supply drive pulses of a fixed width to the motor, so even when a large load is applied, such as when driving a calendar mechanism, there is sufficient power to allow the step motor to rotate normally. The drive pulse width is set with a safety factor of Therefore, a large amount of current is consumed to drive the motor, and especially when the load is low, the current is completely wasted. In addition, at low temperatures, the power supply voltage decreases due to an increase in battery internal resistance, so the motor drive pulse must be set in advance so that an output torque with sufficient margin is generated, taking into account the resulting decrease in motor output torque. It is necessary to keep it. This also results in wasted current consumption under normal temperatures. Furthermore, it is also necessary to consider in advance the increase in frictional load due to changes over time. In any case, more current is consumed than necessary to maintain a high degree of safety in normal rotation of the motor, and this has been a major hindrance to reducing the power consumption of electronic watches incorporating step motors. As a means of solving this problem, the motor is normally driven with a shorter pulse width than conventional motors, and when the motor rotates, it supplies a pulse of the same width as before or an even narrower pulse, so that the motor is always kept in line with the load condition and output torque condition of the motor. A method has been considered in which the step motor is driven with an optimal pulse width depending on the situation. The most important thing in realizing driving with such an optimal pulse width is to "determine whether or not the rotor has rotated." Various methods have been proposed to detect the rotation of the rotor, but the reliability of the detection is insufficient, the number of elements in the detection circuit increases, and the detection circuit processes analog signals. The current situation is that a fully satisfactory detection method has not yet been found. For example, in Figure 3,
FIG. 2 is a diagram showing a conventional method of detecting rotor rotation, in which a shows a current waveform flowing through an excitation coil, b shows a drive pulse, c shows a signal for chopper amplification, and d shows a chopper amplified voltage waveform. It is something. In this method, as shown in a, the currents 15 and 16 induced on the side that appear only when the rotor rotates are
In this method, the voltage is amplified chopperly during the detection interval Ts, and rotation is determined when the level of the amplified voltage is larger than the reference potential Vth, as shown in d. The drawback of this detection method is that when the drive pulse width T _D exceeds a certain value, even though the rotor is rotating normally,
There is a risk that no current will be induced on the side and it will be judged as non-rotating, and there is a restriction on the drive pulse width T _D. Furthermore, non-detection section Tw, detection section
The setting of Ts differs depending on the type of step motor, and there are disadvantages in mass production such as the setting of Tw and Ts being delicate. The present invention aims to eliminate such conventional drawbacks, provide a highly reliable and mass-producible method for determining rotor rotation, and reduce the power consumption of electronic watches. Hereinafter, the present invention will be explained in detail based on the drawings. First, we will explain the principle of rotation of a step motor, and then move on to the principle of determining rotor rotation. Figure 4 is a diagram showing a two-pole step motor.
7 is an excitation coil, 18 is a rotor made of hard magnetic material such as samarium cobalt, and N and S as shown in the figure.
It is magnetized to two poles. It should be specified in advance that determining the direction of the magnetic poles of the rotor means determining the position of the rotor, and therefore determining the rotation of the rotor. On the other hand, 19 is a stator with inner notches 22-a, 22-
b, which determines the static pulling position of the rotor. That is, the direction forming approximately 90 degrees with the inner notches 22-a and 22-b is the static pull position, which is the position where the rotor stops. Moreover, the stator 19 is 20-
2 with outer notches a, 20-b and surrounded by dotted lines
The portions 1-a and 21-b are tapered and are in a state where they are easily magnetically saturated. As shown in Figure 5,
When the coil is not energized, the rotor 18
Most of the magnetic flux from the permanent magnets that make up the magnetic flux forms magnetic paths such as 24, but some of the magnetic flux forms magnetic paths such as 21-a and 21-b, such as 23-a and 23-b.
It passes through a part of b where magnetic saturation is likely to occur. 21
The minimum width δ of the stator in the -a and 21-b sections is normally set to about 0.1 mm for watch step motors, and it may also depend on the thickness of the stator and the amount of gap between the rotor and stator. 21-
Parts a and 21-b are almost saturated. Let us consider the inductance of the excitation coil 17 in this state. First, as shown in FIG. 5, when a current is passed through the exciting coil 17 in the direction in which the rotor is to be rotated, the magnetic flux caused by the coil is initially 25-a, 25-a, 2
A magnetic path as shown in 5-b is formed, and each of the magnetic paths attempts to pass through the magnetically saturated portions 21-a and 21-b. However, as explained above, 21-a and 21-b are almost saturated in this direction and have a magnetic permeability close to that of air, so the magnetic resistance Rm increases, and therefore The inductance L is small, and the current is at the rising portion 2 as shown in Figure 6.
It shows a sharp rise at 6'. Expressing this mathematically,

[Table] Where, L: inductance, N: number of coil turns, Rm: magnetic resistance, τ: time constant, V: power supply voltage, R: coil DC resistance, t: time. In a certain case, when a current is passed in the direction shown in the diagram, Rm increases, so L decreases,
Therefore, τ becomes small and the current shows a sharp rise. On the other hand, consider a case where the rotor rotates 180 degrees as shown in Figure 7, and the N and S magnetic poles are reversed from those shown in Figure 5. The magnetic flux due to the coil 17 is initially
Construct magnetic paths as shown in 25-a and 25-b,
They each try to pass through the magnetically saturated portions 21-a and 21-b. However, in parts 21-a and 21-b, the rotors are opposite to those in FIG.
In the directions 5-a and 25-b, there is no saturation state and the magnetic resistance Rm is small. Therefore, as shown in the equation, since the inductance L becomes large, the time constant becomes large, and the current waveform shows a rising portion 28' with a small slope as shown in FIG. T _R in Fig. 8 is 21-a, 21-
It shows the time until the b part is saturated and the current shows a sharp rise. Note that T _D indicates the excitation time of the coil. Further, FIG. 9 shows an enlarged view of the rising portions 26' and 28' of the current waveforms in FIGS. 6 and 8. To show an experimental example, stator inner diameter
2.1mm, stator thickness 0.5mm, 21-a, 21-b
When minimum width δ = 0.1mm, rotor outer diameter 1.5mm, rotor thickness 0.5mm, number of coil turns N = 10000 turns, coil DC resistance 2.7KΩ, and power supply voltage 1.5V, T _R in Fig. 9 is T _R = When 0.93 msec and Ts = 0.25 msec, the current at point P and point q is ip≒97μ, respectively.
A, iq=50μA. In other words, if a current is instantaneously passed through the coil with a pulse width of Ts = 0.25 msec as a detection pulse, the ip
Since the current value is either ≒97 μA or iq≒50 μA, if this can be determined, the position of the rotor can be determined. In other words, it can be determined whether or not it has rotated. The present invention extracts this minute current as a rebound voltage and determines the position of the rotor. FIG. 10 is a diagram showing the principle of generation of rebound voltage, in which 17 is the excitation coil 30, 3 of the step motor.
Reference numerals 1, 32, and 33 indicate switching elements. In the figure, a shows a state in which the excitation coil is turned off, and b shows a state in which the switching element 32 is turned off and 30
The figure shows that a detection pulse is generated by turning on the switch, and a current flows as shown in 34. c shows a state in which the switching element 33 is turned off from state b and the current flowing through the coil is abruptly interrupted. At this time, the potential at point X, which is one end of the coil
Vx shows a waveform as shown in FIG. In the same figure,
_VDD is the power supply voltage, and Vsp indicates the maximum value of the rebound voltage that occurs when the current flowing through the coil is abruptly interrupted. This Vsp is the coil
It largely depends on the current that was flowing just before it was turned off. In the present invention, by using this Vsp, ip and iq in FIG. 9 are determined to determine the rotor position, but the switching elements 30, 31, 3 in FIG.
2 and 33 are usually constituted by MOSFETs, and since the substrate of the MOSFET is connected to the source in both the p-channel and the n-channel cases, Vsp in FIG. 11 does not occur. Therefore, in the present invention, the rebound voltage can be detected by the switching procedure explained in FIG. 12. 12th
In the figure, 17 is the excitation coil 30, 31, 3
2, 33, 35, 36 are switching elements, 37
3 shows a resistive element for setting the level of the rebound voltage. A shows a state in which the coil is turned off. b is the switching element 30 from the state of a.
The diagram shows a detection current 38 flowing for determining the position of the rotor by turning on the detection current 38 and turning off the detection current 32. c is switching element 3 from state b
0 and 33 are turned off and 32 and 36 are turned on, the current that has been flowing so far is made to flow in a loop like 39. At this time, a resistance element 37 is provided in the loop indicated by 39, and is configured so that a potential proportional to the amount of current flowing appears at the y point. Figure 13 shows the change in the potential Vy at point y at this time, and in the figure, Vsp indicates the maximum value of the rebound voltage that occurs at the moment the coil is turned off. It goes without saying that Vsp shows a value proportional to the current value just before the current flowing through the coil is cut off, and determining Vsp means determining the current value just before the current flowing through the coil is cut off. It means that. Therefore, in Fig. 9, if the pulse width of the detection pulse is set as Ts, then
Since ip and iq are the current values just before the coil is turned off, Vsp proportional to ip or iq can be obtained, and by comparing and judging this with a comparator etc., the rotor position can be determined. can. 1st
In Figure 4, a shows the detection pulse with a width of Ts, b shows the current waveform flowing through the coil, 40 shows the current waveform when the detection pulse is issued in the direction of rotating the rotor, and 41 shows the current waveform flowing through the rotor. The current waveform is shown when a detection pulse is issued in the direction of attraction. c indicates the rebound voltages 42 and 43 caused by ip and iq, and Vsp·p and Vsp·q indicate the maximum values of the respective rebound voltages. At this time
The threshold potential Vth of the comparator for comparing and determining Vsp·p and Vsp·q may be set to an appropriate value such that Vsp·q<Vth<Vsp·p. Next, a method of setting the resistance element 37 in FIG. 12 will be explained. The current just before the coil is turned off is ip, the DC resistance value of resistor element 37 is Rs, and the coil DC resistance is R.
Then, the rebound voltage is when not rotating: Vsp・p=ip・Rs When rotating: Vsp・q=iq・Rs. In order to maximize the voltage difference between rotation and non-rotation (that is, maximize the detection margin), set Rs so that the rebound voltage Vsp・p during non-rotation is approximately equal to the power supply voltage V. good. In the above experimental example, ip=97μA, V=1.5V Rs=1.5V/97μA=15.5KΩ. Therefore, by setting Rs to around 15KΩ, the voltage difference between rotating and non-rotating can be maximized.
In the above experimental example, when Rs = 15KΩ, Vsp・p=
1.45v, Vsp・q=0.7v, which provides a sufficient potential difference for determination. Next, a circuit configuration for embodying the present invention will be described. FIG. 15 is a block diagram showing an example of a circuit configuration for realizing the present invention, which includes 44 oscillation circuits, 45 frequency division circuits, 46 pulse width synthesis circuits, 47 motor drive circuits, 48 step motors, 49 detection circuits, and 100 correction circuits. , is. 44 oscillation circuit, 4
Although the 5-frequency divider circuit and the 46-pulse width synthesizer circuit are essential elements for realizing the present invention, they are not within the scope of the present invention and will not be described in detail here. Also, they can be easily configured logically. FIG. 16 shows an embodiment of the present invention, in which a motor drive circuit 47, a step motor 48, a rotor position detection circuit 49, and a correction circuit 100 are arranged in a 15th embodiment, respectively.
It corresponds to the figure. In the same figure, 50 and 51 are p-channel MOSFETs, and 52 and 53 are N-channel MOSFETs.
MOSFETs 57 and 58 are NAND elements, and are connected to the gate terminals of p-channel MOSFETS 50 and 51, respectively. The motor drive circuit is configured as described above. 54 and 55 are N channels
The drains of each MOSFET are connected to sandwich the excitation coil 17, while the sources are grounded via a resistive element 56. One end Z of the resistance element 56 is connected to the (+) input terminal 60 of the comparator 59, while the reference potential Vth divided by the resistance elements 63 and 64 is connected to the (-) input terminal 61. If the potential at the point is higher than the reference potential Vth, the output terminal 66 of the comparator outputs “H”.
However, when it is low, "L" is output. (An example of a specific circuit configuration of the comparator 59 is shown in FIG. 18.) The N-channel MOSFET 65 is an element that selects the operation of the comparator 59 and the resistive elements 63 and 64, and "H" is output from the terminal h. Turns ON when input is received. The comparator output 66 is 6
The waveform is shaped by 7,68 inverter elements, 7
1,73 inverter elements, 72,74 NAND
It is connected to a set terminal 70 of a flip-flop circuit 75 made up of elements. FIG. 17 shows an example of signals input to input terminals a, b, c, d, e, f, g, and h in FIG. 16. The input signals a, b, c, d, e, f, g, and h in FIG. 17 are respectively input to the input terminals a, b, and h in FIG.
It shows signals input to c, d, e, f, g, and h. In FIG. 17, T _D1 , T _D2 , and T _D3 are drive pulse widths for driving the step motor, and the most suitable pulse width is selected from among many available pulse widths such as 2.44, 2.93, 3.17, 3.42, and 3.66 msec, for example. The pulse width that is considered to be is output. Tw indicates the waiting time until the rotor, which was driven by To, finishes its transient vibration and comes to a complete stop. For example 62msec
It is set to a certain degree. Ts is the detection pulse width,
The width of the pulses issued to determine the rotor position is deepened. For example, T _F of Ts = 0.25 msec is an interval in which the rebound voltage generated by interrupting the current flowing due to the detection pulse is detected,
For example, it is sufficient to set Ts to approximately 1 msec. T _M
determines a correction drive pulse with a wide pulse width that is issued when it is determined that the rotor does not rotate, and is set to, for example, T _M =6.8 msec. Further, in the figure, V _Z indicates the potential at point z in FIG. 16, and Q ₇₆ indicates the signal at the output terminal 76 of the flip-flop circuit 75 in FIG. 16. As described above, the detection circuit 49 includes the switch means 1.
01 and a determination circuit 102 that determines the terminal voltage of the resistor 56. The switch means 101 is
It is composed of MOSFETs 52, 53, 54, and 55. Further, the correction circuit 100 includes an OR gate 69,
Flip-flop circuit 75, AND gate 57,
58. The drive circuit 47 includes P-channel MOSFETs 50 and 51 and N-channel MOSFETs 50 and 51.
It is composed of MOSFETs 52 and 53. Next, follow the time chart in Figure 17 to the 16th
The operation of the figure will be explained. First, in the section with a width of T _D1 , P channel MOSFET 50, N
The channel MOSFET 53 is turned ON and the excitation coil 17 is excited with a pulse width of T _D. Now suppose that the rotor rotates due to this excitation. After the time Tw has elapsed, the rotor has completely finished its transient vibration and is at rest. In this state, if a current is caused to flow in the same direction as the previous excitation direction using a detection pulse with a width of Ts, the inductance is large and the current has a slope because the excitation direction by this detection pulse is the direction that attracts the rotor. Shows a small rise. When the current reaches the T _F section during its rise, 50 and 53 become
OFF and replaced by 52 and 55 N channels
Since the MOSFET is turned on, the current flowing through the coil is abruptly interrupted and a rebound voltage is generated by the resistor element 56. However, since the rise of the current is small, the maximum value of the rebound voltage Vsp ₁ is the standard of the comparator 59. The potential does not exceed Vth, and the comparator outputs "L". Since the reset signal 75 has been reset in advance by the reset signal g, the output Q ₇₆ remains at "L". Therefore, the correction pulse T _M is generated by the NAND element 57.
will be cut and not output. In the next section with a width of T _D2 , p-channel MOSFET 5
1. The N-channel MOSFET 52 is turned on, and the excitation coil 17 is excited with a pulse width of T _D2 . Now suppose that for some reason it does not rotate. Furthermore, after the time Tw has elapsed, the rotor is completely stationary, and in this state, the detection pulse with a width of Ts causes a current to flow in the same direction as the excitation direction of the drive pulse, so the rotor is moved by the drive pulse. Since the rotor was not rotating, the magnet was excited in the direction that caused the rotor to rotate. Therefore, the inductance becomes small and the current shows a sharp rise. When the period T _F is reached, MOSFETs 51 and 52 are turned off and N-channel MOSFETs 53 and 54 are turned on instead, producing a rebound voltage Vsp ₂ as shown by Vz in FIG. Since Vsp ₂ exceeds the reference potential Vth of the comparator, the comparator outputs "H", which is waveform-shaped by inverter elements 67 and 68, and passed through OR element 69 to flip-flop 7.
Set terminal 70 of No. 5 is set to "H". When the flip-flop circuit 75 is set, 76 goes “H”
Therefore, a correction pulse having a width of T _M is output through the NAND element 58. Since this T _M is a sufficiently long pulse considering the safety factor, the rotor
Rotates 180° to ensure normal hand movement. In the operation after T _D3 , either of the two operations is repeated and the step motor is driven with the optimum drive pulse width.
In this way, flip-flop 75, gate 58, and gate 58 control whether or not to output a correction drive pulse. Figure 18 shows an example of a specific circuit configuration of the comparator in Figure 16, showing p-channel MOSFETs 77 and 78 and
It consists of 79, 80, and 81. 60 is the (+) terminal of the comparator, 61 is the (-) terminal, 66
is the output terminal. 62 which is the gate terminal of 81
is connected to the drain terminal of the N-channel MOSFET 65 in FIG. In the embodiment shown in FIG. 16, the spike voltage is determined by a comparator, but it is also possible to determine the spike voltage by using the threshold potential of an inverter element or a Schmitt trigger circuit. The next major concern is how much current is consumed by the detection pulse. No matter how reliable a detection method can be provided, since the ultimate purpose of rotor position determination is low power consumption, it will be meaningless if the detection pulse causes large power loss. This is because it will be put away. To determine how much power is consumed by the detection pulse, it is sufficient to compare the power consumption by the normal drive pulse and the power consumption by the detection pulse. Figures 19 and 20 show current waveforms due to drive pulses. Figure 19 shows the drive pulse in the drive direction, that is, the direction in which the rotor is to be rotated; Figure 20 shows the current waveform in the attraction direction, that is, the direction in which the rotor This shows a case where a driving pulse is issued in the direction of attracting . However, in both figures, the horizontal axis represents time and the vertical axis represents current, and the pulse width is 3.15 msec. Normally, it is driven with the waveform shown in Figure 19, and the detection pulse is the second one.
Since it is output as a waveform up to Ts = 0.25 msec in Fig. 0, in order to compare the power consumption of the detection pulse and the power consumption of the normal drive pulse, use the area Ps of the shaded area in Fig. 20 and the shaded area of Fig. 19. All you have to do is compare the area Po. According to experiments, the normal drive pulse width is 3.15m.
sec, when the detection pulse width is 0.25 msec, Ps/Po≒1.1×10 ^-2 = 1.1%, and the power consumption due to the detection pulse is hardly a problem. Further, as another example of a circuit configuration for realizing the present invention, a configuration example as shown in FIG. 21 can be cited. In the figure, 17 is an excitation coil, 82 and 83 are P-channel MOSFETs, 84, 85, and 86 are N-channel MOSFETs, and 87 and 88 are resistance elements, and there are two detection positions for the rebound voltage: 89 and 90. . This circuit configuration example uses basically the same method as the circuit configuration example shown in Figure 16 to determine the rotor position, but in Figure 21 it is possible to detect the rebound voltage at both ends of miles 89 and 90. This is different from the circuit configuration example described above. However, the basic movement is the 16th
Since it is similar to the case shown in the figure, a detailed explanation of this operation will be avoided here. As described above, according to the present invention, the detection pulse width is small, and therefore the position of the rotor can be determined with power consumption that is hardly a problem. In addition, detection reliability is high because detection is performed in the stopping section where the rotor is most stable.
It is extremely reliable because the rotor position can be determined without being affected by mechanical factors such as the moment of inertia of mechanical parts such as the wheel train and needles, and the roughness torque of the wheel train. Therefore, there is little variation during mass production, and there is no need for any particular adjustment, resulting in excellent mass productivity. Furthermore, all circuit configurations are
It can be built into CMOSIC. In addition, by detecting the rotor position with high reliability, it is possible to drive conventional motors with low power consumption, which is extremely effective for electronic watches that aim to be thinner, smaller, and lower in cost. big. According to the configuration of the present invention, a switch means is provided which applies a detection pulse having a pulse width that does not drive the rotor to the drive circuit, and short-circuits both ends of the coil via a high resistance element at the same time as the detection pulse is cut off. Since it is equipped with a correction circuit that detects the voltage generated in the element by a determination circuit, detects the rotor position, and outputs a correction pulse when a non-rotation position is detected, it has the following effects. (a) That is, the present invention can increase the sensitivity of the detection voltage by combining a detection pulse that does not drive the rotor with a switch means that loops both ends of the coil through a high resistance element at the same time as the detection pulse is cut off. At the same time, the combination of the detection pulse width and the high resistance element makes it easy to set an appropriate detection voltage value, resulting in reliable rotor position detection. (b) The detection pulse width should be as small as possible because we want to increase detection reliability by reducing the probability of overlapping with mechanical or magnetic disturbances, but in this application, the width of the detection pulse is Since the voltage is detected in a loop through a high resistance element, reliable detection can be performed even if the detection pulse width is small, which is advantageous in terms of reliability.

[Brief explanation of the drawing]

FIG. 1 shows a commonly used analog type display mechanism. FIG. 2 is a block diagram showing a conventional circuit configuration. FIGS. 3a to 3d are diagrams showing a conventional rotor rotation detection method. FIG. 4 is a diagram showing a two-pole step motor. FIG. 5 is a diagram showing a magnetic path when the coil is excited in the driving direction. Figure 6 shows the current waveform when the rotor rotates normally. FIG. 7 is a diagram showing a magnetic path when the coil is excited in a direction that attracts the rotor. FIG. 8 is a diagram showing a current waveform when the coil is excited in a direction that attracts the rotor. FIG. 9 is an enlarged view of the rising portion of the current waveform in FIGS. 6 and 8. 1st
Figures a, b, and c are diagrams showing the principle of generation of rebound voltage. FIG. 11 is a diagram showing changes in the potential at point x in FIG. 10. FIGS. 12a, b, and c show examples of circuit configurations according to the present invention. FIG. 13 is a diagram showing changes in potential at point y in FIG. 12. FIGS. 14a, 14b, and 14c are diagrams showing detection pulses, detection current waveforms, and rebound voltages according to the present invention. FIG. 15 is a block diagram showing an example of a circuit configuration according to the present invention. FIG. 16 is a diagram showing an example of a specific circuit configuration of a motor drive circuit and a detection circuit according to the present invention. FIG. 17 is a diagram showing a time chart for driving the circuit configuration example of FIG. 16. FIG. 18 is a diagram showing an example of a specific circuit configuration of the comparator in FIG. 16. FIG. 19 is a diagram showing current waveforms during normal driving. FIG. 20 is a diagram showing a current waveform when the rotor is excited in a direction that attracts it. FIG. 21 is a diagram showing still another embodiment according to the present invention.

Claims (1)

[Claims] 1. An oscillation circuit, a frequency divider that divides the output signal of the oscillation circuit, a drive circuit that operates based on the output signal of the frequency divider, and a step comprising a rotor, a stator, and a coil and driven by the drive circuit. In an electronic timepiece having a motor, a rotor position detection circuit 49 connected to the coil is connected to the rotor position detection circuit, and when the position detection circuit determines a non-rotation position of the rotor position, a correction drive pulse is sent to the drive circuit. The rotor position detection circuit short-circuits both ends of the coil via a high-resistance element at the same time as the detection pulse of a small pulse width applied to the coil and which cannot drive the rotor ends. and a determination circuit 1 that detects the terminal voltage generated at the terminal of the high resistance element and determines the rotor position.
02. An electronic watch characterized by having: