JP2004229383A - Motor driver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a motor driver which can effectively use a battery without waste. <P>SOLUTION: A digital camera 2 includes a temperature sensing element 80 for sensing the temperature of the battery 75, and a voltage sensing element 82 for sensing the electromotive force of the battery 75. When the battery 75 is judged that the battery 75 is lower than a predetermined temperature by a judging circuit 85 and the electromotive force of the battery 75 is lower than a predetermined voltage by the judging circuit 85, an electric signal is input to a CPU 53. A change signal is sent from the CPU 53 to drivers 58, 67 and 72 in response to the electric signal, and the drivers are switched from a normal mode to a power saving mode. Then, the duties of a voltage pulses to be respectively supplied from the drivers 58, 67 and 72 to motors 56, 65 and 70 are changed. The time that the voltage pulses are on is shortened, and the mean value of the currents supplied to the motors 58, 67 and 72 is reduced. Accordingly, the current consumption of the motor is reduced. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a motor drive device, and more particularly to a motor drive device using a battery as a power source.
[0002]
[Prior art]
With currently available cameras with Auto Focus (hereinafter abbreviated as AF) and cameras with Auto Exposure (hereinafter abbreviated as AE), the zoom lens automatically moves when the camera is pointed at the subject. The zooming, focusing, and exposure are adjusted by moving the focus lens and operating the aperture. The movement of the zoom lens in the optical axis direction and the movement of the focus lens in the optical axis direction are performed by a motor that rotates using a direct current supplied from a battery as a power source. In addition, a shutter opening / closing operation, a diaphragm operation, a lens barrier opening / closing operation, and the like are also executed by the motor.
[0003]
In the motor, a magnetic field is formed by a direct current supplied from a battery, and the rotor is rotated using this magnetic field. Using the rotational force of this rotor as power, the zoom lens, the focus lens, and the like are moved via gears. The capacity of the battery loaded in the camera is limited, and various devices have been made to effectively use the battery (see, for example, Patent Document 1). In Patent Document 1, a drive signal supplied to the motor at the time of startup or braking is intermittently performed so that a large inrush current does not flow at the time of startup or braking of the DC motor. As a result, the occurrence of inrush current is prevented, the consumption of extra power due to the occurrence of inrush current is avoided, and the battery with limited capacity is effectively used to extend the life of the battery.
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 2002-238286
[Problems to be solved by the invention]
However, when the temperature of the battery is low, if an attempt is made to start by supplying power to the motor in the same way as at room temperature, the battery's internal resistance is higher than at room temperature, so the battery's electromotive force is significantly higher. There is a problem that the battery usage time decreases because the voltage drops below the minimum voltage required for the operation of the device.
[0006]
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a motor drive device capable of effectively using a battery without waste.
[0007]
[Means for Solving the Problems]
In order to achieve the above object, in the motor drive device of the present invention, temperature detection means for detecting the temperature of a battery that supplies drive power to the motor, electromotive force detection means for detecting the electromotive force of the battery, and temperature detection A determination circuit for determining that the temperature detected by the means is lower than a predetermined temperature and the electromotive force detected by the electromotive force detection means is lower than a predetermined voltage; and the determination circuit is configured such that the temperature of the battery is lower than the predetermined temperature, In addition, when it is determined that the electromotive force of the battery is lower than a predetermined voltage, the driving power supplied to the motor is lowered.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
A digital camera embodying the present invention is shown in FIG. A motor-driven lens barrel 4 and a strobe light emitting unit 6 are provided on the front surface of the digital camera 2 shown in FIG. On the side surface, a speaker 8, an insertion port 10 for connecting a USB cable, and an insertion port 12 for connecting an AC adapter are provided. A shutter button 14 is provided at the top.
[0009]
The back surface of the digital camera 2 is shown in FIG. On the back side, a finder 15 for confirming a subject, a button 17 for switching various modes, a button 19 for performing a zoom operation, and a liquid crystal screen 20 for displaying a through image and a captured image are provided. By operating the buttons 17 and 19, the setting of the digital camera 2 can be determined from the auto mode, night view mode, daytime sync mode, and manual mode.
[0010]
A block diagram of the digital camera 2 is shown in FIG. The lens barrel 4 includes a convex lens 24a, a zoom lens 24b, and a focus lens 24c, and a subject is imaged on the CCD image sensor 27 through an optical system formed by these lens groups. The CCD image sensor 27 has a charge accumulation time determined by a timing generator (hereinafter abbreviated as T / G) 28. The exposure amount is adjusted by the aperture / shutter 29. The electrical signal generated by the CCD image sensor 27 is input to the analog processing circuit 30.
[0011]
The analog processing circuit 30 includes a CDS (correlated double sampling circuit) and an AMP (amplifier). The electric signal input to the analog processing circuit 30 is converted into an RGB image signal for each cell of the CCD image sensor 27. They are combined, amplified, and converted to digital data. The generated digital data is temporarily stored in the buffer memory 32.
[0012]
Next, the digital data in the buffer memory 32 is input to the image processing circuit 35 and subjected to image processing such as white balance, γ processing, contour correction and the like to generate image data. When the image data is stored by pressing the shutter button 14, the image data is input from the image processing circuit to the compression processing circuit 38 and compressed, and the compressed image data is recorded on the recording medium 42 via the media controller 40. . When the digital camera 2 is set to the replay mode, the image data recorded on the recording medium 42 is read out to the VRAM 45 and displayed on the liquid crystal screen 48.
[0013]
When the digital camera 2 is set to the manual mode and the user commands the zoom operation by operating the button 19, a command signal is input from the operation unit 50 to the CPU 53, and the driving amount of the motor 56 is calculated from the command signal. Is done. A command signal for commanding the operation of the motor 56 is input to the motor driver 58, and the motor 56 rotates by this command signal.
[0014]
When the digital camera 2 is in the auto mode, calculation is performed by the AE calculation circuit 60 and the AF calculation circuit 62 based on the measurement value of the distance measuring sensor (not shown). A command signal for driving the motor 65 is input from the CPU 53 to the motor driver 67 from the calculation result in the AE calculation circuit 60, and the motor 65 is driven. Further, a command signal for driving the motor 70 is input from the CPU 53 to the motor driver 72 from the calculation result of the AF calculation circuit, and the motor 70 is driven. In the auto mode, the motor 58 is driven in addition to the motor 65 and the motor 70 to perform imaging. The motor 56, the motor 65, and the motor 70 are DC (direct current) motors. The driving power of the motors 56, 65, and 70 is supplied from the battery 75 to the respective drivers 58, 67, and 72. Is supplied through.
[0015]
The motor 56, the motor 65, and the motor 70 have their rotational speeds controlled by pulse width modulation (hereinafter abbreviated as PWM) control, and the motors 56, 65, and 70 are driven by their respective drivers 58, 67, and 72. It is driven by supplied voltage pulses. At this time, the duty representing the ON / OFF time ratio of the pulses is controlled by the drivers 58, 67 and 72. The drivers 58, 67, and 72 can switch between a normal mode in which the voltage pulse to be supplied is high and a power saving mode in which the pulse voltage is lower than that in the normal mode. Power consumption is controlled.
[0016]
The digital camera 2 includes a thermistor 80 that contacts the battery 75 and detects the temperature of the battery 75, and a voltage detection IC 82 that detects the electromotive force of the battery 75. The current output from the thermistor 80 and the voltage detection IC 82 is input to the determination circuit 85, where the temperature of the battery 75 and the electromotive force of the battery are determined. The current input to the determination circuit 85 by the thermistor 80 varies depending on the detected temperature, and the current input from the voltage detection IC 82 to the determination circuit 85 varies depending on the detected voltage.
[0017]
The voltage detection IC 82 is also used to detect the remaining amount of the battery 75. When the voltage of the battery 75 drops and the electromotive force falls below the lower limit voltage determined by the manufacturer, the user is notified of battery replacement. The lower limit voltage is a minimum voltage required for the digital camera 2 to operate without any trouble, and is determined by the manufacturer.
[0018]
When the temperature detected by the thermistor 80 is lower than a predetermined temperature by the current input from the thermistor 80 and the voltage detection IC 82, and the voltage detected by the voltage detection IC 85 is lower than the predetermined voltage. Then, an electric signal is input to the CPU 53. The predetermined temperature and the predetermined voltage are values determined in advance by the manufacturer, and are set in the determination circuit 85 before shipment.
[0019]
In response to the electrical signal input from the determination circuit 85, the CPU 53 inputs a change signal that changes the power supplied to the motor to the driver 58, the driver 67, and the driver 72. When this change signal is input to the drivers 58, 67, 72, the mode is switched from the normal mode to the power saving mode, the time during which the voltage pulses supplied to the motors 56, 65, 70 are ON is shortened, and the supplied current Becomes smaller. For this reason, the power consumption of a motor becomes small.
[0020]
FIG. 3 shows voltage pulses that the motor driver 72 supplies to the motor 70 when the digital camera 2 is activated. Note that the control by the motor driver 58 of the motor 56 and the control by the motor driver 67 of the motor 65 are the same as the control by the motor driver 72 of the motor 70. FIG. 3A shows normal mode voltage pulses input to the motor 70 when the temperature of the battery 75 is normal and the battery 75 has sufficient capacity. The motor driver 72 applies the voltage pulse of the voltage Vfa for the time Tfa. The average value of the current is kept constant by repeating this voltage pulse. With this pulse series, the average value of the current supplied to the motor 72 is Ifa. As described above, the voltage pulse shown in FIG. 3A is normally input to the motor 72 and driven.
[0021]
When the determination circuit 85 determines that the temperature detected by the thermistor 80 is lower than the predetermined temperature, and the determination circuit 85 determines that the voltage detected by the voltage detection IC 82 is lower than the predetermined voltage, the determination circuit 85 An electric signal is input to the CPU 53.
In response to this signal, a change signal is input from the CPU 53 to the motor driver 72. As a result, the driver switches from the normal mode to the power saving mode.
[0022]
A voltage pulse sequence input to the motor 72 in the power saving mode is shown in FIG. Although the voltage of the voltage pulse does not change, the time during which the voltage pulse is applied is shortened from Tfa to Tfb. For this reason, the average value of the current input to the motor 72 decreases from Ifa to Ifb. As a result, the rotational speed of the motor 70 driven by the current value Ifb is lower than when it is driven by the current value Ifa. Also, the power consumed at this time is lower than the power consumed in the normal mode. In this way, the power supplied by the battery 75 is reduced, and the electromotive force of the battery 75 is prevented from falling below the lower limit voltage.
[0023]
Next, the operation of the above configuration will be described with reference to FIG. When the digital camera 2 is turned on and started up, the thermistor 80 and the voltage detection IC 82 first detect the temperature and voltage of the battery 75. When the temperature of the battery 75 is higher than a predetermined value, or when the voltage of the battery 75 is higher than a predetermined value, the motor drivers 58, 67, 72 send voltage pulses in the normal mode to the motors 56, 65, 70. To supply. Further, when the temperature detected by the thermistor 80 is lower than the predetermined temperature and the voltage detected by the voltage detection IC 82 is lower than the predetermined voltage, an electric signal is input from the determination circuit 85 to the CPU 53, whereby the CPU 53 A change signal for changing the voltage pulse supplied to the motor to the power saving mode is input to the drivers 58, 67 and 72.
[0024]
When the change signal is input to the motor drivers 58, 67, 72, the driving voltage pulse series supplied to the motors 56, 65, 70 is changed from the normal mode to the power saving mode. In the power saving mode, the time during which the voltage pulse is ON is shorter than in the normal mode, and therefore the drive currents of the motors 56, 65, and 70 are smaller than in the normal mode. As a result, the power supplied by the battery 75 is reduced, and a voltage drop that causes the electromotive force of the battery 75 to fall below the lower limit voltage can be avoided.
[0025]
In the above embodiment, the power consumption of the motor is suppressed by changing the duty of the voltage pulse. However, the power consumption of the motor may be suppressed by changing the voltage of the voltage pulse. As a result, the power supplied to the motor can be lowered.
[0026]
Moreover, in the above, the power consumption of the motor is reduced by changing the voltage pulse supplied to the motor, and the load on the battery is reduced. However, the power consumption is reduced by operating the motors so that the driving time does not overlap. You may do it. As shown in FIG. 5A, the drive times of the motors at the normal time overlap each other. For this reason, the power consumption at the peak time is large. On the other hand, when the battery temperature is low and the electromotive force of the battery is low, as shown in FIG. 5B, the zoom motor drive time, the focus motor drive time, the aperture / shutter motor drive time, The driver is controlled so that it does not overlap with the lens barrier drive time, and the power consumption during peak hours is suppressed. As a result, it is possible to avoid a temporary voltage drop of the battery accompanying a large power consumption and a temporary capacity reduction of the battery, and the battery can be used for a longer time.
[0027]
In this embodiment, the power supplied to the motor is suppressed by changing the duty of the voltage pulse in the power saving mode. However, the circuit for the power saving mode configured by transistors and resistors and the circuit normally used And switching to a power saving circuit in the power saving mode to lower the voltage applied to the motor. As shown in FIG. 6, when the temperature of the battery is low and the voltage is low, the circuit is switched to a circuit holding a larger resistance by a change signal input from the CPU, and the voltage is lowered by this resistance and supplied to the motor. Reduce the supply current. Thereby, it is possible to prevent the electromotive force of the battery from falling below the lower limit voltage when the motor is started, and to use the battery for a longer time.
[0028]
In the above embodiment, a DC motor is used as the motor. However, other motors such as a brushless motor or a stepping motor may be used. The brushless motor and the stepping motor can also be driven by voltage pulses, and the power consumption of the motor can be reduced by controlling the voltage pulses as in the case of the DC motor.
[0029]
【The invention's effect】
As described above, the motor driving device of the present invention includes a temperature detection unit that detects the temperature of the battery, an electromotive force detection unit that detects the electromotive force of the battery, and a determination unit that determines the detected temperature and voltage. And control means for controlling the power supplied to the motor, and the power supplied to the motor is lowered when the battery temperature is low and the battery voltage is low. As a result, it is possible to avoid a sudden increase in the internal resistance of the battery by forcibly drawing a current from the battery at a low temperature. For this reason, it becomes possible to prevent that the electromotive force of a battery falls below a minimum voltage at the time of starting of a motor, and drive power can be supplied to a motor for a long time.
[Brief description of the drawings]
FIG. 1 is a perspective view of a digital camera embodying the present invention.
FIG. 2 is a block diagram of the digital camera shown in FIG.
FIG. 3 is an explanatory diagram of voltage pulses supplied to a motor.
FIG. 4 is a flowchart showing the operation of the digital camera.
FIG. 5 is an explanatory diagram showing drive times of a zoom motor, a focus motor, an aperture / shutter motor, and a barrier motor.
FIG. 6 is an explanatory diagram showing a relationship among a motor, a supply current, and an electromotive force of a battery.
[Explanation of symbols]
2 Digital camera 53 CPU
56 Motor 58 Motor Driver 65 Motor 67 Motor Driver 70 Motor 72 Motor Driver 75 Battery 80 Thermistor 82 Voltage Detection IC
85 judgment circuit

Claims (1)

A temperature detecting means for detecting a temperature of a battery for supplying driving power to the motor; an electromotive force detecting means for detecting an electromotive force of the battery; and a temperature detected by the temperature detecting means is lower than a predetermined temperature and the electromotive force detection. A determination circuit for determining that the electromotive force detected by the means is lower than a predetermined voltage, and when the determination circuit determines that the battery temperature is lower than the predetermined temperature and the battery electromotive force is lower than the predetermined voltage. And a motor drive device provided with power control means for reducing the drive power supplied to the motor.

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