JPS6134631B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention does not require any special detection element,
This invention relates to a motor that detects an alternating current magnetic field. In a normal motor, when an external magnetic field is applied to the motor, the motor's drive coil acts as a kind of transformer, weakening the current flowing through the coil in order to rotate the rotor in the normal direction. The engine may stop, the rotational torque may be lowered, or the rotational speed may differ from the normal rotational speed. This is a serious drawback in motors and products using motors, so in order to design motors and products that are strong against external magnetic fields, we need to detect the magnitude of the external magnetic field and generate an alarm based on the magnitude. or change the motor drive conditions. In conventional motors and products using motors, special elements are used to detect this external magnetic field.
For example, external AC magnetic fields have been detected by using magnetoresistive elements, Hall elements, reed switches, etc., and equipping motors or products using motors with these elements. That is, another element was required for magnetic field detection. Therefore, for example,
Electronic wristwatches using motors require sprues for inserting these elements, which limits the ability to make electronic wristwatches smaller and thinner.
Moreover, the power consumption by these elements shortens the battery life of electronic wristwatches, and the addition of these elements also increases the cost of the product. The present invention seeks to eliminate these drawbacks and provides a motor that is strong against external alternating magnetic fields and a motor that utilizes external alternating magnetic fields to provide special information. Next, the principle of the alternating current magnetic field detection device of the present invention will be explained, but before that, the configuration of the most suitable motor to which the detection principle of the present invention is applied will be explained. 1 is a coil wound around a magnetic core made of a high magnetic permeability material, 2 is a stator made of a high magnetic permeability material, and 3 is a rotor made of a permanent magnet material magnetized into two poles in the radial direction. As shown in FIG. 2, a pulse is applied to this motor in which the direction of the current applied to the coil 1 is reversed every time, thereby causing the rotor 3 to rotate in a fixed direction. The feature of the present invention is that the motor coil 1 is used as an alternating current magnetic field detection element without using a special magnetic field detection element, and more specifically, the detected voltage is amplified by switching between a high resistance loop and a low resistance loop. It's about doing. The voltage induced in the coil 1 when the motor is exposed to an alternating magnetic field will be described below. FIG. 3 schematically depicts the coils and magnetic core 4 of the motor. Since the coils used in motors usually have an elongated shape, the external magnetic field tends to concentrate on the magnetic core 4 of the coil, and depending on the shape, the magnetic flux density can be about 10 times higher, although it cannot be said that this is true. is normal. The voltage V induced in the coil 1 at this time is given by the number of turns of the coil being n and the magnetic core 4 being
If the magnetic flux of is Φ, it is given by V=-n·dΦ/dt... As the magnetic core, one with the shape shown in Table 1 was used.

[Table] In this case, assuming that the magnetic flux density inside the magnetic core is 10 times that of the external one, the magnetic flux Φ of the magnetic core 4 is given by the following equation. Φ=10×S×B×Sinwt... Here, S is the cross-sectional area of the magnetic core 4, and B (Gauss) is the peak value of the magnetic flux density of the alternating magnetic field. , from the formula V=-10×h×S×B×w× _cps wt=-10×1
×10 ⁴ (turn) × 0.64 × 10 ^-4 (m ² ) × B × 10 ^-4
(wb/m ² )×2π×50(Hz)× _cps wt=−6.4π×
10 ^-2 × B × _cps wt [V] = −0.20 × B _cps wt [V],
Therefore, if the magnetic flux density B of the external magnetic field is 2 Gauss, then V=-0.4 _cps wt [V]. if,
If the motor is used in something like a wristwatch where space for an energy source is limited, then 0.4
Since the control circuit cannot be operated with a detection voltage of about [V], it is necessary to amplify the voltage enough to control the C-MOS inverter. However, the current situation is such that it is difficult to create a C-MOS amplifier that operates stably, and the greatest feature of the present invention is that it can detect an alternating current magnetic field of about 1 oersted without using such an amplifier. It is in. In addition, here we considered the state when the magnetic core 4 exists alone in the magnetic field, but in reality, the magnetic core 4 is arranged as one component of the motor, so it gathers around the magnetic core 4 due to the bypass effect by the stator. The magnetic flux is reduced compared to the case alone. Since the induced voltage in the coil 1 becomes correspondingly smaller, the method according to the present invention becomes more effective in detecting a magnetic field on the order of 1 oersted. A feature of the AC magnetic field detection device of the present invention is that by alternately connecting low impedance elements and high impedance elements, e.g. low resistance and high resistance, to both ends of the motor coil, the voltage induced in the coil by an external magnetic field is converted into a special This allows for amplification without using an amplifier, making it easier to detect the presence of an external magnetic field. Furthermore, the detection can be performed reliably by making the connection time with the low resistance longer than with the high resistance. FIG. 4 shows an external magnetic field detection circuit consisting of a motor drive circuit 200 and an external magnetic field detection circuit consisting of an amplification section 201 and a detection section 202. Generally, all elements except the motor coil 20 are C-MOS.
Built into the IC. Here, the principle of amplification will be explained in detail, and the configuration and operation of the circuit will be explained later. In Figure 4, 21 and 22 are P-type MOS FETs.
Gate (hereinafter abbreviated as P gate), 23, 24, 2
Numerals 5 and 26 are N-type MOS FET gates (hereinafter abbreviated as N gates), and detection resistors 28 and 29 and a motor coil 20 constitute a drive circuit and an amplification section. The method of amplifying the detection signal is when the motor is not driven.
The closed loop of the motor coil 20, N gates 23 and 24 and the closed loop of the motor coil 20, detection resistor 29 and N gates 26 and 23 are alternately switched. The voltage induced in the coil by the external magnetic field is first short-circuited in the closed loop of N gates 23 and 24. These N gates 23 and 24 are motor drive transistors, and their ON resistance is generally several
It is about 10Ω, and the voltage generated in the coil is this ON.
Since it is short-circuited with a resistor, a relatively large current flows. Next, the motor coil 20, the N gate 26, 2
3. When the closed loop of the detection resistor 29 is switched, since the motor coil 20 has an inductance component, there is an effect that continues to flow the relatively large current that was flowing before switching, and the detection resistor 29 is momentarily generates a large voltage,
Thereafter, the voltage reaches a steady state determined by the detection resistor 29, the induced voltage due to the external magnetic field, the coil resistance, etc., and becomes stable. In this steady state, the voltage when the detection resistor is increased to infinity is the voltage when the above-mentioned switching is not performed. Next, in this method, a magnification factor for amplifying the induced voltage due to the external magnetic field is determined. A in FIG. 5 is an N gate, and B in FIG. 5 is its equivalent circuit. The switch 40 is turned on and off by a gate signal. 39 is ON when driving
The resistor and diode 41 are PN junction diode between the substrate and the drain, and the capacitor 42 is the PN junction capacitance between the substrate and the drain, the drain gate capacitance, and
It is the sum of butt capacitance, stray capacitance, etc. If this equivalent circuit is replaced with the P gate and N gate of FIG. 4, and the battery is a large capacity capacitor and an ideal power source, the equivalent circuit of this detection method will be as shown in FIG. 6. 43 is the voltage V ₀ generated by the external magnetic field, 44
is the inductance L Henry of the coil that makes up the motor, 45 is the internal resistance of the coil γΩ, 47
is the loop selector switch, 46 is the N gate ON
Resistance γNΩ. However, here, this γNΩ is ignored because it is sufficiently smaller than the value of the coil resistance. 48
is the parasitic capacitance of the N gate and P gate, and is the sum of the parasitic capacitance of the N gate 24 and the P gate 22,
This is C Huarado. 49 is a detection resistor, RsΩ, 50 and 52 are parasitic diodes between the substrate and drain of the N gate and P gate, and 51 is a driving battery, which is a commonly used silver battery for watches. V _D =1.57V. The output voltage of terminal 53 becomes the detection voltage VRS,
It is input to the voltage detection element. The response when the changeover switch 47 is switched can be theoretically determined based on the equivalent circuit shown in FIG. a=1/2(γ/L+1/CRs), b=γ+Rs
/LCRs =Rs/Rs+γV ₀ , w=√｜ ² −｜ 1) When a ² > b, VRs = E[1-{1/w(a-DL/γ) sinhwt+coshwt}e ^-at ] ) When a ² = b, V _Rs = E{1-( 1+at-DL/γbt)e ^-at } ) When a ² < b, V _Rs = E[1-1/w(a-DL/γb) sinwt+coswt
} e ^-at ] However, t ₀ is the connection time of the low resistance loop, and t is the time. The V _Rs waveform of the above equation is as shown in FIG. 7A. Next, when this V _Rs is actually calculated based on an example, L=11 Henry, C=75PF, Rs=
Under the conditions of 150KΩ, γ = 2.8KΩ, V ₀ = 0.1V, t ₀ = ∞, the time to reach the peak voltage of V _Rs is:
The peak voltage at this time is 4.2 V for about 30 μsec, and the magnification is about 42 times, indicating that the detection signal can be easily amplified without using an analog signal amplifier. However, this theoretical value assumes that the voltage generated in the coil is constant, but in reality, in the case of a closed loop with high resistance, the time constant of the closed loop is small and the time to reach a steady voltage is relatively quick. When switching to a closed loop with low resistance, the time constant is large and it takes a long time for the voltage to reach a steady state. To explain based on the above example, in the case of a closed loop with high resistance, V _Rs becomes a nearly steady voltage in about 0.2 msec, but in the case of a low resistance loop, the time constant is determined by τ = L / γ. , τ = 3.9msec, and the low resistance loop is 3.9msec.
Even if it continues, the current will only be 63% of the steady current. However, the frequency of the alternating current magnetic field that is most commonly encountered is the commercial power frequency of 50Hz or 60Hz, and its period is 20msec or 16.7msec. In order to detect the magnetic field of that frequency, a detection period of at least 20 msec is required. When detecting a magnetic field by switching between a low-resistance loop and a high-resistance loop within this time, the longer the time in which the low-resistance loop is in place, the more likely it will be generated when switching to the next high-resistance loop. The voltage will be higher. However, in the case of 50Hz magnetic field detection, if the switching period is set to 1/4 period, or 5 msec,
The voltage will be 1/√2 of the peak voltage, or 7.1%. Furthermore, when the time ratio of the low resistance loop and the high resistance loop is 1:1, the low resistance loop time becomes 2.2 msec, which is shorter than the time constant of 3.9 msec shown in the above example. Therefore, in order to increase the detection sensitivity in the detection method of the present invention, it is necessary to set the time ratio of the low resistance loop and the high resistance loop so that the low resistance loop becomes longer. B in FIG. 7 is a diagram of the detected voltage when the high resistance loop time is 0.5 msec and the low resistance loop time is 1.5 msec based on the above-mentioned conditions for a 50 Hz alternating current magnetic field. In this case, the detection signal amplification factor is approximately 15 times. C in FIG. 7 is a diagram showing this situation, and 5
The straight line 5 is the voltage generated in the coil without switching, and the straight line 56 is the amplification factor of about 5 when the low resistance loop is switched for 0.5 msec and the high resistance loop is switched for 0.5 msec. Further, the straight line 57 shows the case where switching is performed with a high resistance loop of 0.5 msec and a low resistance loop of 1.5 msec. In this way, the high-resistance loop and low-resistance loop switching time cannot be taken very long to detect AC magnetic fields at commercial frequencies. It can be seen that the time for the low resistance loop should be longer than the time for . As explained above, the detection signal can be amplified simply by switching the circuit including the coil, and the voltage can be adjusted between the reference voltage and the reference voltage without using an analog amplifier, etc., which is difficult to fabricate in a C-MOS IC for a watch. By determining this, the alternating current magnetic field can be detected. Furthermore, since the amplification factor can be increased by a factor of 10 or more, it becomes possible to make a judgment based on the threshold voltage of the C-MOS inverter, which is advantageous in terms of power consumption of the entire circuit, circuit configuration, and IC area. Although this embodiment has been described using a resistor as an impedance element for detection, similar detection is possible using a capacitance component or an inductance component. In addition, in this example, all the detection elements are C-
Since it is built into a MOSIC, the low resistance element utilizes the characteristics of the unsaturated part of an active element called a buffer transistor. There is no problem in using active elements in this way. However, when actually configuring the present invention, as in the embodiment used in the present invention, the low resistance loop is the ON resistance of the buffer transistor, and the high resistance loop is the ON resistance of the IC.
It is thought that the diffused resistor and voltage detection element inside are generally C-MOS inverters or comparators. Further, in the description of the present invention, a high resistance is connected in the case of a high resistance loop, but this high resistance may have an infinitely large value, that is, an open loop. Even in this case, there is parasitic capacitance in the buffer transistor,
Because of this capacity component, the amplification is not infinitely large, and detection similar to this explanation is possible. In this case, the advantage is that the timing structure of the circuit becomes simple. Next, a method will be described in which the magnetic field detection device of the present invention is applied to an electronic timepiece to make the timepiece difficult to stop when the timepiece is placed in an alternating current magnetic field. FIG. 8 is a graph showing the relationship between the drive pulse width of the motor and AC magnetic resistance. Normally, the motor is driven in the region indicated by 58 in order to increase its efficiency. However, as the pulse width increases, the rotational position of the rotor and the timing at which the drive pulse ends interfere with each other, causing malfunctions, and the AC magnetic resistance deteriorates. If the drive pulse width is further increased, it enters the region 59 in FIG. In the region No. 59, the drive pulse is cut after the rotor is sufficiently attracted by the magnetic flux of the coil, so it is the strongest against the influence of external magnetic fields. In other words, if an alternating current magnetic field is detected by the method described above and it is detected that the watch is exposed to the alternating magnetic field, the motor drive pulse should be the pulse with the best alternating current magnetic resistance in the region of 58, regardless of efficiency. By forcibly setting the driving pulse in the region 59 or the region 59 with a sufficiently long pulse width, it can be used as a motor that is strong against external magnetic fields. Conventionally, in order to aim for maximum efficiency, motors without magnetic field detection circuits sacrifice some magnetic resistance when setting drive pulses, and increase magnetic resistance by adding input parts such as magnetic shield plates and magnetic shield inner frames. However, the method of the present invention is characterized in that it can be used with the pulse width that gives the motor its highest efficiency, and with its anti-magnetic properties at its highest performance. Next, one embodiment of the present invention will be described in detail with reference to the drawings. FIG. 4 shows a step motor drive circuit and an external magnetic field detection circuit according to the present invention. Note that external magnetic field detection in the embodiments of the present invention will be described below as alternating current magnetic field detection. P gates 21, 22 and N gates 23, 24 are 2
A set of CMOS inverters is constructed, and the output terminals a and b of each are connected to both ends of the coil 20 of the step motor, and at the same time, are connected to one end of the detection resistors 28 and 29. The other ends of the detection resistors 28 and 29 are connected to the source inputs of the N gates 25 and 26. The positive input terminals of the voltage comparators 30 and 31 are connected to one ends of the detection resistors 28 and 29, the negative input terminals are connected to the voltage division point of the reference voltage resistor 34, and the output terminals are both connected to the OR gate 32. One end of the reference voltage resistor 34 is grounded via the N gate 27. The two input terminals of the AND gate 33 are connected to the output of the OR gate 32 and the gate terminal of the N gate 27. P and N gates 21, 22, 23, 24, 25, 2
6, 27 gate terminals 101, 102, 103,
104, 105, 106, 107 and the output terminal 110 of the AND gate 33 are connected to the control circuit 65. As shown in the circuit block diagram of FIG. 9, a control circuit 65 appropriately synthesizes frequency-divided signals obtained from a reference signal generating means 66 that generates a reference signal using a crystal oscillator or the like as an original oscillator, and outputs the signal to the drive circuit and the detector. Outputs signals necessary for circuit operation. Various configurations of the control circuit are possible, examples of which are shown in A and B of FIG. In FIG. 10, A is a circuit diagram, and B is a timing chart of input signals. These signals are 1
Since the period is seconds and can be easily synthesized from the output of the oscillation frequency divider circuit, the circuit diagram of that part is omitted. The reset input R of the SR flip-flop (hereinafter abbreviated as RSFF) 70 is connected to the input terminal 110.
The set input S is connected to the signal 121, the output Q is connected to the input terminals of the AND gates 71 and 72, and the output Q is connected to the input terminals of the AND gates 71 and 72.
The other input terminals of 2 are connected to the signals 123 and 122, and the output terminals are both connected to the input terminal of the OR gate 73. The clock input CL of the D-type flip-flop (hereinafter abbreviated as DFF) 74 is connected to the output terminal of the OR gate 73, and the positive output Q is connected to the AND gates 75 and 76.
The negative output is an AND gate 77,
78 and its own data input terminal D. The other input terminals of the AND gates 75 and 77 are connected to the output of the gate 73, and the AND gates 76 and
The other input terminal of 78 is connected to signal 124.
The output of the AND gate 75 is sent to the output terminal 101 via the inverter 79, and the output of the AND gate 76 is sent to the output terminal 10.
5, the output of 77 is connected to the output terminal 102 via the inverter 80, and the output of 78 is connected to the output terminal 106. In addition, the input terminals of the OR gates 81 and 82 are connected to the outputs of the AND gates 75 and 76, 77 and 78, respectively, and the outputs are connected to the outputs of the inverters 83 and 78, respectively.
It is connected to output terminals 103 and 104 via 84. Now, the operation of this embodiment will be explained in detail using timing charts A and B in FIG. 11 and A and B in FIGS. 4 and 10. At A in FIG. 10, SRFF70 is connected to signal 12
1 every second, the output Q remains in the state of "H" and "L" unless a detection signal is used as the signal 110, as will be explained later. Therefore, the output of the OR gate 73 contains the signal 123.
appears. The DFF74 inverts its output state every time one pulse is input to the clock input CL, and as a result, the signal terminals 101 and 102, 103 and 104,
Waveforms 05 and 106 are outputted alternately every second. This waveform is 10 of A in Figure 11.
1, 102, 103, 104, 105, and 106. The signal 123 is a drive pulse for the step motor during normal operation, and its pulse width is determined from the load of the step motor, the volume given, etc. In this embodiment, it is 5.8 msec. The signal 122 is a forced drive pulse that is generated in place of the normal drive pulse when it is detected that the step motor has entered the magnetic field by the action of the AC magnetic field detection circuit according to the present invention. The pulse width should be the one that provides the best AC magnetic resistance depending on the characteristics of the step motor. Generally, the pulse width of the forced drive pulse is longer than the normal pulse width, but in this example, it is 7.8 msec.
It is. Signal 124 is a detection pulse for performing alternating current magnetic field detection according to the present invention. The entire detection interval is
Among the commercial frequencies 50 Hz and 60 Hz, which are considered to be most frequently encountered in daily life, it is sufficient if one wavelength of 50 Hz, which has the longest wavelength, is 20 msec or more. Also intermittent
Duty ratio and frequency can be selected flexibly,
In this example, the frequency was 512 Hz and the duty ratio was 1:3. (However, it is exaggerated in the figure.) In addition, the signal 107 of A in FIG. This is a signal for masking so that no signal is output, and the frequency is the same as that of the detection pulse 124, and the duty ratio is preferably smaller than that of the detection pulse 124, and in this embodiment, it is 1:7. In the period before the timing of the detection shown in FIG. 11, the P gates 21 and 22 are OFF in FIG.
N gates 25, 26, 27 are OFF, N gate 2
3 and 24 are ON, both ends of the coil 20 are grounded, and the AND gate 33 is masked and the detection signal 11 is
0 is "L". Next, at the timing when the detection pulse rises, the N gates 24, 25, and 27 are turned on, and the closed loop including the coil 20 can be switched intermittently as described in the explanation of the principle. If the step motor is not within the alternating current magnetic field at this time, both ends a and b of the coil are always OV and do not reach the detection threshold level VTH, and the detection signal 110 remains at "L". Therefore, a 5.8 msec drive pulse 68 is applied at the next drive timing. At this timing, only P-gate 22 and N-gate 23 are ON, and motor coil 20 is
Current flows in the direction from a. In the next step about 1 second later, the phase is changed and exactly the same operation is performed. Next, the case where the step motor enters an alternating current magnetic field is shown in FIG. 11B. At this time, at the timing of detection, a signal as shown in B in FIG. 11 appears at both ends a and b of the coil, as explained in the principle. This signal is input to voltage comparators 30 and 31 and compared with a reference voltage V _TH , and if it exceeds V _TH a detection signal 69 is generated. This detection signal 69 is the 10th
It is input to the reset terminal of SRFF 70 in A in the figure to invert its output state. The timing at which the drive pulse immediately after that is output is forced drive pulse 7.
0 is applied to the step motor, and it can be driven stably even in an alternating current magnetic field. This concludes the explanation of the operation of the embodiment. In this way, by utilizing the output of the AC magnetic field detection device of the present invention, it is possible to control the motor drive pulse width, control the motor drive voltage, or use the output to generate an alarm buzzer to notify the presence of an AC magnetic field. It has also become easier to control the drive circuit. The external magnetic field detection device of the present invention is optimal when used in an electronic wristwatch, and can provide a highly sensitive external magnetic field detection device without requiring any new elements in addition to conventional wristwatch components. Not only that, no detection power is required to detect the voltage induced in the motor coil, and the detection circuit also consumes almost no power. Therefore, it is possible to provide an electronic wristwatch equipped with an external magnetic field detection device that is comparable in power consumption and space cost to conventional wristwatches, and its industrial effects are enormous. Further, in the embodiment of the present invention, a motor having the structure shown in Fig. 1 is used, but the present invention also applies to a motor having a structure in which the motor has a coil and the coil induces a voltage by an external magnetic field. Needless to say, it can be applied.

[Brief explanation of the drawing]

Figure 1 is a diagram showing a watch motor, Figure 2 is a waveform diagram showing inverted pulses, Figure 3 is a diagram showing the state of the coil and magnetic flux in a magnetic field, and Figure 4 is a circuit diagram of the drive circuit and detection circuit. , Figure 5 A is the N channel.
Diagram showing FET gate, Figure 5B is N channel
Fig. 6 is an equivalent circuit diagram of the FET gate, Fig. 6 is an equivalent circuit diagram of the detection circuit, Fig. 7A is a waveform diagram showing the detected voltage waveform, Fig. 7B is a waveform diagram showing the detected voltage waveform in an alternating magnetic field, Fig. 7 Figure C is a diagram showing the relationship between magnetic field strength and detection voltage, Figure 8 is a diagram showing the relationship between drive pulse width and AC magnetic resistance, Figure 9 is a block diagram of the control circuit of the present invention, and Figure 10 A is the control circuit. A circuit diagram showing an example of a circuit configuration, FIG. 10B is a waveform diagram showing an input signal, and FIG.
Figures A and 11B are timing charts. 1...Coil, 2...Stator, 3...Rotor, 20
...Motor, 21, 22...D gate, 23, 24,
25, 26... N gate, 28, 29... Impedance element, 30, 31... Comparator, 65... Control circuit, 68... Normal drive pulse, 70... Forced drive pulse, 124... Detection pulse, 200... Drive circuit, 201... Amplification Section, 202...Detection section.

Claims (1)

[Claims] 1. A step motor comprising a reference signal generating means for generating a reference signal, a control circuit for outputting a plurality of signals including a step motor drive signal using an output signal from the reference signal generating means, and at least a stator, a rotor, and a coil. and a drive circuit that inputs a step motor drive signal from the control circuit to drive the step motor, an amplification that alternately connects a low impedance element and a high impedance element to the coil of the step motor. and a detection section that determines the presence or absence of an external magnetic field based on the voltage value generated in the impedance element of the amplification section based on the voltage induced in the coil by the external magnetic field, and each of the impedance elements 2. A magnetic field detection device for an electronic watch, characterized in that when the low impedance elements are alternately connected to the coil, the connection time of the low impedance elements is longer than the connection time of the high impedance elements.