Background
Conventionally, there is known a linear vibration motor including a stator formed of an electromagnet or a permanent magnet, a vibrator having a permanent magnet or an electromagnet, which vibrates reciprocally with respect to the stator, and a control unit for controlling a driving current supplied to a winding of the electromagnet. In the linear vibration motor, it is necessary to detect the amplitude displacement, velocity, and acceleration of the vibrator in order to keep the amplitude constant. From this viewpoint, the conventional linear vibration motor has a non-energization period during which the amplitude displacement, speed and acceleration of the vibrator are detected (see, for example, japanese patent laid-open No. 2001-16892).
In the case of attempting to efficiently feed current to the electromagnet windings, it is necessary to shorten this non-energization period. Conversely, if an attempt is made to sufficiently extend the non-energization period, the timing of feeding the current to the electromagnet windings will be too late to efficiently supply the current. In order to detect the amplitude displacement, velocity and acceleration of the vibrator in a short period of time, it is necessary to perform operation control using a microcomputer that utilizes highly accurate external oscillation. It is difficult to save cost and reduce the size of the circuit.
Disclosure of Invention
In view of the above, the present invention provides an operation control method of a linear vibration motor capable of performing operation control, with which current can be fed to a winding in a cost-effective and efficient manner.
According to an aspect of the present invention, there is provided a method for controlling an operation of a linear vibration motor including a stator formed of an electromagnet having a winding or a permanent magnet, a vibrator provided with a permanent magnet or an electromagnet having a winding, and a control unit for controlling a driving current supplied to the winding of the electromagnet, the linear vibration motor being configured to reciprocate the vibrator with respect to the stator, the method comprising: setting a non-energization period during which no driving current flows through the winding of the electromagnet, the non-energization period being equal to or greater than 1/4 cycles; detecting an electromotive voltage (electromotive voltage) induced in the winding when the vibrator performs a vibrating motion during the non-energized period; detecting a displacement, a speed, or an acceleration of the vibrator based on the detected electromotive voltage; and optimally, the driving current supplied to the winding is controlled based on the detected displacement, velocity or acceleration of the vibrator and a current supply timing.
With the operation control method of a linear vibration motor of the present invention, it is possible to perform operation control with which current can be fed to the winding in a cost-effective manner.
Drawings
The objects and features of the present invention will become apparent from the following description of embodiments thereof, given in conjunction with the accompanying drawings, wherein:
fig. 1 is a block diagram illustrating a linear vibration motor according to an embodiment of the present invention;
fig. 2 is a circuit diagram showing an amplitude detecting unit and a power supply circuit of the linear vibration motor shown in fig. 1, in which a reference voltage is adjusted according to a battery voltage;
fig. 3 is a waveform diagram for explaining timings of measuring electromotive voltages of windings;
fig. 4 is a circuit diagram showing a modification of the power supply circuit shown in fig. 2;
fig. 5 is a waveform diagram for explaining a timing of measuring an electromotive voltage of a winding in a conventional linear vibration motor; and
fig. 6 is a circuit diagram showing an amplitude detecting unit and a power supply circuit of the linear vibration motor shown in fig. 1, in which a control output unit adjusts a reference voltage according to a battery voltage.
Detailed Description
Hereinafter, a linear vibration motor and a method of controlling the operation of the linear vibration motor according to an embodiment of the present invention will be described with reference to the accompanying drawings, which form a part of the present invention.
Referring to fig. 1, a linear vibration motor according to an embodiment of the present invention includes: a stator 2 having a winding 1; a vibrator 4 having a permanent magnet 3; a frame 5 for holding the vibrator 4; springs 6a and 6b, said springs 6a and 6b being held between the vibrator 4 and the frame 5; an amplitude detection unit 7, the amplitude detection unit 7 detecting the vibration amplitude of the vibrator 4 based on the electromotive voltage induced in the winding 1; and a control output unit 8, the control output unit 8 performing PWM (pulse width modulation) control of the drive current fed to the winding 1 based on the detection result of the amplitude detection unit 7. As shown in fig. 2, the amplitude detection unit 7 includes an amplifier circuit 11 for amplifying the voltage between both ends of the winding 1 and a comparator circuit 12 for comparing the amplified voltage with a reference voltage V0 (i.e., a zero voltage). The time T0 when the amplified voltage is equal to the reference voltage V0 is regarded as a turning point (turning point) of the vibration amplitude. The control output unit 8 sets a non-energization period in which the drive current does not flow through the winding 1 for 1/4 cycles or more from the turning point. The amplitude detection unit 7 further includes an amplitude conversion circuit 14 for periodically sampling the electromotive voltage of the winding 1 during the non-energization period and calculating the vibration amplitude using the maximum value of the sampled electromotive voltages.
In the conventional linear vibration motor, as shown in fig. 5, the vibration amplitude is detected based on the time difference between time T0 at the turning point and time T1 when the electromotive voltage is equal to a specified constant voltage V1. Since the time period for detection is short, the conventional detection method is liable to generate measurement errors and to be affected by noise, which reduces detection accuracy. With the linear vibration motor according to the present embodiment, the amplitude conversion circuit 14 periodically samples the electromotive voltage of the winding 1 during the non-energization period, and calculates the vibration amplitude using the maximum value of the sampled electromotive voltages. Therefore, even if the sampling timing is deviated to some extent, the vibration amplitude can be reliably detected. And, sufficient time remains before the winding 1 is energized again. Therefore, with the linear vibration motor of the present embodiment, the winding 1 can be energized in time, thereby efficiently operating the motor and saving electric power.
For efficient energization, it is preferable to energize the winding 1 in 1/20 cycles from the maximum displacement point or 1/4 cycles from the maximum speed point. The winding 1 can also be energized at a more precise moment if the microcomputer detects a point of maximum amplitude or a point of maximum speed. When a microcomputer is used for control purposes, the vibration amplitude can be detected accurately even when the sampling timing is deviated to some extent. Due to this feature, even when an oscillation circuit with reduced accuracy or an oscillation clock built in a microcomputer is employed, the linear vibration motor can be controlled with more accurate accuracy than in the conventional case.
The use of the microcomputer and the extension of the non-energization period can set the period for detecting the maximum displacement point longer than that in the conventional case. For example, the period for detecting the maximum displacement point may be set equal to 300 milliseconds, which is 100 milliseconds or more longer than the conventional detection period. This makes it possible to control the linear vibration motor without missing the maximum displacement point even when a sudden load change delays the maximum displacement point.
Typically, the drive current supplied to the winding 1 is PWM (pulse width modulation) controlled by using switching devices Q1 and Q2 (see fig. 2) located above and below the inverter circuit for energizing the winding 1. In the control in which the non-energization period is one-half cycle, WPWM (weighted pulse width modulation) control may also be performed on the switching device Q1 located above. With this control, the switching timing of the motor can be made the same, and the current can be supplied at an effective timing even when the amount of current is adjusted according to the load variation.
The battery voltage conversion circuit 15 shown in fig. 6 detects the voltage Vcc of the battery in real time. The control output unit 8 performs amplitude adjustment control according to the detected voltage. If the switching devices Q1 and Q2 are controlled in a uniform pattern regardless of voltage, the current and vibration amplitude will increase when the battery voltage is high. However, with the structure of performing voltage feedback control described above, the vibration amplitude can be controlled to be constant regardless of the voltage difference due to the change in the battery capacity.
Alternatively, as shown in fig. 2, the reference voltage of the comparator circuit 12 may be adjusted by the battery voltage conversion circuit 15, thereby suppressing the amplitude variation caused by the battery voltage Vcc. If the control output unit 8 controls in a uniform mode regardless of the voltage, the current and the vibration amplitude increase when the battery voltage is high. Conversely, when the battery voltage is low, the current and vibration amplitude will decrease. However, if the reference voltage is adjusted as described above, the detected speed of the vibrator is high when the battery voltage remains high. This makes it possible to perform speed reduction control. On the other hand, when the battery voltage is kept low, the detected speed of the vibrator is also low. This makes it possible to perform the speed increase control. Due to this feature, if the reference voltage is appropriately adjusted, the influence of the battery voltage on the vibration amplitude can be eliminated, and the vibration amplitude can be controlled to be constant regardless of the difference in the battery voltage.
If the linear vibration motor is maintained in a high load state for a certain period of time, the maximum value of the electromotive voltage detected during the non-energization period will be equal to or less than a predetermined reference voltage. The state is determined as abnormal, in which case the operation of the linear vibration motor is stopped. Alternatively, the abnormality may be determined by detecting whether a current larger than a certain reference value continuously flows through the winding 1.
If the linear vibration motor is suddenly stopped when the battery voltage decreases to a value less than the reference voltage, there is a possibility that the motor is suddenly stopped, thereby causing mustache or beard hair bundles to be caught in, for example, a hair removal implement. To avoid such a risk, it is preferable to stop the motor slowly by gradually lowering the duty ratio of the upper switching device Q1.
In the case where current is supplied to the linear vibration motor in one direction, a half-bridge circuit having switching devices Q1 and Q2 located above and below may be used as an inverter circuit for energizing the winding 1 shown in fig. 2. This can reduce the number of switching devices, thereby saving cost and reducing size. Fig. 4 shows a half-bridge circuit. Diode D2 is disposed between the ground terminal of the half-bridge circuit and the positive terminal of the winding, while diode D2 is disposed between the negative terminal of winding 1 and the power supply Vcc. Thereby, current can be allowed to flow through the winding 1 again, so that the linear vibration motor can be operated in an efficient manner.
At this time, if the lower switching device Q2 is turned on for longer than one-half cycle, it is possible to effectively use the current flowing through the winding 1 and reduce the current flowing through the diode D1. This allows the use of low cost components with low ratings.
While the invention has been shown and described with reference to a preferred embodiment, it will be understood by those skilled in the art that: various changes and modifications may be made without departing from the scope of the invention as defined in the following claims. For example, the invention may also be applied to actuators comprising a movable stator that is not completely fixed.