JP2009229862A - Blade drive unit and imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a blade drive unit capable of eliminating occurrence of step-out phenomenon without making a stepping motor large in size. <P>SOLUTION: The blade drive unit includes: a blade member 4 that restricts a quantity of light; a stepping motor 1 that drives the blade member; a position detecting means 3 for detecting the position of the blade member; and drive control means 101 and 102 for switching the supply of power to the stepping motor according to an output signal from the position detecting means. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a blade driving device that drives a blade member that forms a shutter blade or a diaphragm blade for regulating the amount of light, and an imaging device that includes the blade driving device.

  Conventionally, a stepping motor has been used as a drive source of a device for driving a shutter blade or a diaphragm blade for regulating the amount of light of a camera or the like. The stepping motor has an advantage that the position and speed can be easily determined by open loop control, and the control system is simplified. On the other hand, the stepping motor has a problem of causing a step-out phenomenon. The step-out phenomenon is a phenomenon in which the load torque is higher than the driving torque, and the rotor of the stepping motor cannot follow the command signal and stops rotating.

  Along with recent demands for miniaturization and higher performance of cameras, motors are also required to be smaller, save power, and speed up. Since these all work in the direction of inducing a step-out phenomenon, in order to realize these, measures against the step-out phenomenon are indispensable. In order to avoid the step-out phenomenon, the motor drive torque must be provided with a margin, and it was difficult to use a small motor.

  As a countermeasure against the step-out phenomenon, Patent Document 1 discloses the following technique. When the aperture blade is moved by driving the stepping motor, a specific aperture value detection unit is provided that outputs a signal when the aperture value of the aperture blade reaches a specific value. When no signal is output from the specific aperture value detection unit, it is determined that a step-out phenomenon has occurred. If the step-out phenomenon is detected, first, the rotor is returned to the initial position by low-speed, high-torque driving. After that, the speed of the aperture blade is made slower than when the step-out phenomenon is detected, so that the torque is improved and the step-out phenomenon does not occur.

  However, the technique disclosed in Patent Document 1 shows a countermeasure when a step-out phenomenon occurs, and does not prevent the step-out phenomenon from occurring. For this reason, if the torque of the motor is small, the step-out phenomenon will not change.

On the other hand, there is a technology that performs so-called brushless driving that attaches a position sensor that detects the rotor position of the stepping motor and prevents the out-of-step phenomenon by switching the energization to the coil as the rotor rotates. It is disclosed in Patent Document 2. By using this type of motor in the shutter device, a shutter device in which a step-out phenomenon does not occur can be obtained. In addition, this driving technique can perform high-speed and high-efficiency driving rather than driving the stepping motor by open loop control. Therefore, the use of this type of motor is useful for increasing the speed and efficiency of the shutter device.
Japanese Patent Laid-Open No. 2-105121 JP-A-10-150798

  However, since the motor having the configuration shown in Patent Document 2 needs to incorporate a position sensor for reading the position of the rotor into the motor, the motor is increased in size, and the shutter device and the diaphragm device, that is, the blades This hinders downsizing of the driving device.

(Object of invention)
An object of the present invention is to provide a blade driving device and an imaging device that can eliminate the occurrence of a step-out phenomenon without increasing the size of a stepping motor.

  To achieve the above object, the present invention provides a blade member that regulates the amount of light, a stepping motor that drives the blade member, a position detection unit that detects the position of the blade member, and an output signal of the position detection unit. Accordingly, the blade drive device has drive control means for switching the energization state of the coil of the stepping motor.

  Similarly, in order to achieve the above object, the present invention is an imaging device including the blade driving device of the present invention.

  According to the present invention, it is possible to provide a blade driving device or an imaging device that can eliminate the occurrence of the step-out phenomenon without increasing the size of the stepping motor.

  The best mode for carrying out the present invention is as shown in Examples 1 to 3 below.

  FIG. 1 is an exploded perspective view showing a configuration of a shutter device which is an example of a blade driving device according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 1 denotes a brushless stepping motor, which includes a stator having first and second coils and a rotor having a magnet. Then, the rotor can be rotated by a predetermined angle by sequentially switching the direction of the current flowing through the first and second coils. The stator of the stepping motor 1 is fixed to the main plate 5 by a method not shown.

  A rotary plate 2 is rotatably supported with respect to the base plate 5 and includes a drive pin 21 that rotates the light shielding blade 4 that is a shutter blade. The rotary plate 2 includes a gear portion 22 that meshes with the pinion of the stepping motor 1. Reference numeral 3 denotes a position sensor fixed to the base plate 5 by a method not shown, and can read the position of the light shielding blade 4. In the first embodiment, an optical position sensor is used as the position sensor 3, and the position (opening / closing state) of the light shielding blade 4 is specified by reading the position of the slit 41 provided in the light shielding blade 4. Specifically, the presence / absence of the slit 41 provided in the light shielding blade 4 is detected, and if it is a gap, an L (low level) signal is output, and if it is a slit, an H (high level) signal is output. The position of the light shielding blade 4 (light shielding state) is specified by the number of H and L.

  The light shielding blade 4 is composed of two blade members, and rotates around the hole 42 to open and close the opening 52 provided in the base plate 5 to regulate the amount of light. The light shielding blade 4 is provided with a plurality of slits 41 (four in FIG. 1) as signal generating parts used for position detection. Further, a hole 42 fitted into the drive pin 21 and a projection 43 guided by the cam groove 51 are provided, and the opening amount of the opening 52 opened in the base plate 5 by the rotation of the rotary plate 2 is regulated. As described above, the base plate 5 includes the cam groove 51 for guiding the light shielding blade 4 and the opening 52 for allowing the light beam to pass therethrough. Further, the shaft portion of the rotary plate 2, the stator portion of the stepping motor 1, and the position sensor 3 are fixed to the base plate 5.

  A back cover 6 is fixed to the main plate 5 to prevent the rotary plate 2 from falling off. Reference numeral 7 denotes a cap that prevents the light shielding blade 4 from falling off by being fixed to the base plate 5.

  Next, the interval between the plurality of slits 41 provided in the light shielding blade 4 will be described.

  FIG. 2 shows the relationship between the rotation angle of the rotor and the voltage applied to the first and second coils when the stepping motor 1 is driven by open loop control, and the relationship between the sensor signal of the position sensor 3 at that time. Is shown. Each time the rotor rotates one step, the output signal output from the position sensor 3, that is, the sensor signal is switched from L to H or from H to L.

  Here, the angle at which the light shielding surface of the light shielding blade 4 rotates when the rotor advances one step varies depending on the cam shape of the cam groove 51. Therefore, the interval between the slits 41 provided on the light shielding surface is generally unequal. Therefore, by adjusting the interval between the slits 41, the position sensor 3 outputs a sensor signal as shown in FIG. 2 in accordance with one step of the rotor.

  In the first embodiment, a two-phase driving method is shown in which both the first and second coils are energized. However, the present invention is not limited to this, and only two coils and one coil are energized. Other driving methods such as 1-2 phase driving may be used in which energization is alternately repeated. In this case, the angle of one step of the rotor is changed, but the sensor signal of one pulse is output from the position sensor 3 in accordance with one step of the rotor in the driving method.

  FIG. 3 is a diagram illustrating an electrical configuration of the shutter device according to the first embodiment. In FIG. 3, reference numeral 101 denotes a decoder to which a drive pulse and a rotation direction signal are input. A coil driving unit 102 drives the first coil 1a and the second coil 1b in the stepping motor 1 in accordance with a signal from the decoder 101. Reference numeral 103 denotes a transmission mechanism that transmits the power of the stepping motor 1 to the light shielding blade, and the rotary plate 2 in FIG. 1 corresponds to this.

  In the shutter device configured as described above, it is assumed that a drive start signal (a drive pulse and a rotation direction signal) is input from the outside, such as a shutter release button of a camera being pressed. Then, energization to the first and second coils 1a and 1b is started via the decoder 101 and the coil driving unit 102, and the stepping motor 1 starts rotating. The stepping motor 1 rotates by one step, and its movement is transmitted to the light shielding blade 4 via the transmission mechanism 103. When the light shielding blade 4 rotates by one step, the sensor signal from the position sensor 3 is switched from H to L. Change. In response to the switching of the sensor signal, the decoder 101 switches the direction of energization to the second coil 1b. By switching the energization, the rotor rotates for the next one step. In this way, the direction of energization to the first coil 1a is switched when the sensor signal is switched from L to H, and the direction of energization to the second coil 1b is switched when the sensor signal is switched from H to L. Switch. By doing so, the light shielding blade 4 continues to rotate.

  When the predetermined rotation is completed and the light-shielding blade 4 is closed by a predetermined amount, it stops at that position for an exposure time corresponding to a predetermined shutter speed. Then, the shutter is opened by rotating in the direction opposite to that when closing. In this process, when the operating speed of the light-shielding blade 4 decreases due to a heavy load or a decrease in driving torque due to battery exhaustion, the energization switching timing is delayed accordingly. Therefore, the light shielding blade 4 cannot follow the energization switching timing, and the step-out phenomenon does not occur.

  In the first embodiment, the operating speed of the light shielding blade 4 varies depending on the load. For example, when it is desired to accurately determine the shutter speed, the speed may be controlled by a known method such as adjusting the currents flowing to the first and second coils through the feedback control.

  According to the first embodiment, the position sensor 3 for reading the position of the light shielding blade 4 is provided outside the stepping motor, that is, the light shielding blade 4, and the stepping motor 1 is provided in accordance with the movement of the light shielding blade 4. 1. The energization of the second coils 1a and 1b is switched. Therefore, the occurrence of the step-out phenomenon can be eliminated. That is, the step-out phenomenon is a phenomenon in which the movement of the rotor of the stepping motor 1 cannot follow the command signal. If a method of switching the energization to the first and second coils 1a and 1b in accordance with the movement of the rotor, the occurrence of the step-out phenomenon can be eliminated. As a result, it is not necessary to provide a margin for the drive torque so as not to cause the step-out phenomenon, and a smaller motor can be used.

  Furthermore, since it is not necessary to provide a plate member having a slit in the stepping motor, the axial dimension of the stepping motor 1 can be reduced, and the overall size of the apparatus can be reduced.

  The signal generated by the slit 41, which is the signal generating unit in the first embodiment, is a signal for one pulse when the stepping motor 1 is moved by one step.

  In the first embodiment, the position sensor 3 is used to determine the timing of the energization switching signal of the stepping motor 1. However, other applications of the position sensor 3 may be used for detecting a rebound phenomenon after the light-shielding blade 4 is completely closed, or for confirming an F value (aperture value) setting when used as a diaphragm blade. . At this time, since the movement of the light-shielding blade 4 which is the final driving member, not the stepping motor 1 or the rotary plate 2, is detected, there is no influence of play or the like possessed by each component and accurate detection is possible. Is possible.

  Next, a blade driving device according to Embodiment 2 of the present invention will be described. In the first embodiment, the plurality of slits 41 are provided on the light shielding blade 4 as a signal generating unit used for detecting the position of the light shielding blade 4, but in the second embodiment, the signal generation provided on the light shielding blade is provided. The method of providing the portions is different from that of the first embodiment. The description of the same parts as those in the first embodiment is omitted.

  In Example 1, after the rotation angle of the stepping motor reaches the position of the step corresponding to the voltage applied to the first and second coils, the voltage applied to the first and second coils is The value is changed according to the step position. On the other hand, in the second embodiment of the present invention, the position of the slit 41 provided in the light shielding blade 4 is shifted from the case of the first embodiment. That is, in the second embodiment, a voltage having a value corresponding to a certain step is applied to the first and second coils, and before the stepping motor 1 reaches the rotation angle corresponding to the value, the first and second voltages are applied. The voltage applied to the coil is changed to the value of the next step. In other words, the timing of switching the current flowing through the coils (first and second coils 1a and 1b) is adjusted by shifting the position of the slit so that the sensor signal is switched earlier than in the first embodiment. Yes. As a result, the efficiency of the stepping motor 1 can be increased.

  The reason will be described. Since the exciting current of the stepping motor 1 is affected by the inductance of the coil, it rises with a delay from the exciting voltage. Therefore, as the rotation of the rotor increases, the phases are switched before the exciting current reaches a constant value, and the torque is reduced. As a countermeasure, by increasing the current switching timing as the rotor speed increases, the delay in the rise of the current can be covered, and the excitation current can reach a constant value even at high speeds, thus stabilizing the torque. Can be made. Here, the amount by which the current switching timing is advanced is represented by a phase with respect to the current switching period is called an advance angle.

  FIG. 4 shows a conceptual diagram of the torque and advance angle of the stepping motor 1. FIG. 5 is a diagram showing the relationship between the rotation angle (horizontal axis) of the rotor, the rotor speed, the advance angle, and the sensor signal of the position sensor. As shown in FIG. 5, the rotor speed required at that time is determined according to the rotation angle of the rotor. Accordingly, by shifting the slit position according to the position of the rotor, it becomes possible to give an arbitrary advance angle according to the rotational speed. As shown in FIG. 5, the delay of the rise of the current can be covered by shifting the position of the slit so that the sensor signal is switched earlier than in the case of the first embodiment.

  However, as can be seen from FIG. 5, the torque at low speed decreases as the advance angle increases. Therefore, in the second embodiment, the advance angle is set to 0 when the stepping motor 1 is started. As can be seen from FIG. 4, when the speed is low, the torque is highest when the advance angle is zero. Then, as the rotor speed increases, the advance angle is added (medium advance → large advance). By doing this, the maximum torque at each speed is obtained. The drive torque is reduced by reducing the advance angle during deceleration and by setting the advance angle to a negative advance angle before stopping. Thereby, the speed of the rotor is reduced to suppress the occurrence of rebound.

  Here, how the advance angle is changed will be described. In the present invention, the current switching timing is determined by the position of the slit. In the first embodiment, the slit interval is always set so that the advance angle is 0 ° (first embodiment of the sensor signal in FIG. 5). The advance angle can be changed by shifting the slit position in the direction in which the current switching timing is advanced with respect to the slit of the first embodiment (second embodiment of the sensor signal in FIG. 5).

  Further, the rotor position and the rotor speed have a correlation as shown by the rotor speed in FIG. Once the rotor position is determined, the required rotor speed is determined. Further, by determining the advance angle based on the slit position as described above, the advance angle can be determined according to the position of the rotor. Therefore, an arbitrary advance angle can be given according to the change in speed.

  The effect in Example 2 of this invention is demonstrated.

  By giving an advance angle to the switching timing to the coil as described above, it is possible to improve the torque at high speed and increase the efficiency of the stepping motor. As a result, even with a smaller stepping motor, the light-shielding blade can be driven, and downsizing of the entire apparatus can be achieved. Alternatively, when stepping motors of the same size are used, the light shielding blade can be driven with a smaller current, and power saving of the apparatus can be achieved.

  Further, in the second embodiment, a signal generation unit is provided in a light shielding blade that is developed in a planar shape instead of a rotary encoder for detecting the position of the rotor. For this reason, a different advance angle can be given for each step by changing the interval between the slits of the light shielding blade. For example, as the opening amount adjusted by the plurality of light shielding blades 4 is smaller, the overlapping amount of the light shielding blades 4 is increased, the frictional force is increased, and the driving of the stepping motor 1 necessary for changing the light amount by one step is performed. Since the amount is small, it is desirable to keep the advance angle small. On the contrary, the larger the opening amount, the smaller the overlapping amount of the light shielding blades 4 decreases, the frictional force decreases, and the stepping motor driving amount necessary to change the light amount by one step increases. It is desirable to enlarge it. Further, since the advance angle is given by changing the interval between the slits of the light shielding blade, the advance angle can be given without using an electric circuit, and the load on the circuit can be reduced.

  The signal generated by the slit 41, which is a signal generation unit in the second embodiment, becomes a signal for one pulse when the stepping motor 1 is moved by one step, and has a phase difference different for each pulse with respect to the sensor signal. It is like that.

  In the first embodiment, the position of the slit is read using an optical sensor. However, the position sensor used in the shutter driving device according to the third embodiment is not limited to this. Hereinafter, Example 3 of the present invention will be described with reference to the drawings. Description of the same parts as those in the first embodiment will be omitted.

  In Embodiment 3 of the present invention, a magnetic sensor such as a Hall element or MR sensor is used for position detection instead of an optical sensor, and the N pole and S pole are alternately magnetized at a fine pitch as a signal generation unit. Use thin permanent magnets. Then, the magnetic signal generated by the permanent magnet is magnetically read using a magnetic sensor, and the driving state of the light shielding blade 4 is detected. In addition, the signal generator is attached to the rotary plate instead of the light shielding blade. The number of position sensors is two.

  When an optical sensor is used as the position sensor as in the first and second embodiments, the position cannot be detected if another member overlaps the signal generator (slit). However, when a magnetic sensor is used as in the third embodiment, even if another member overlaps the signal generation unit (permanent magnet), the position can be detected if the member is a non-magnetic material. is there. For this reason, the freedom degree of arrangement | positioning of components can be increased.

  In the third embodiment, the signal generator is provided on the rotary plate. The amount of rotation of the light shielding blade when the motor rotates one step varies depending on the shape of the cam groove. For this reason, when the signal generation unit is attached to the light shielding blade, the interval between the slits and the magnetization pitch of the signal generation unit is not always constant. However, when the rotary plate is connected to the stepping motor by a gear, the amount of rotation of the rotary plate when the motor rotates one step is constant. In this case, by providing the rotary plate with the signal generating unit, the slits and the magnetization pitch as the signal generating unit can be set at a constant interval, and the signal generating unit can be easily manufactured.

  Further, by using two position sensors, the rotation direction of the light shielding blade can be detected. When there is only one position sensor as in the first and second embodiments, it is premised that the light-shielding blade does not reverse during driving, and if it reverses, it does not operate normally. Since there is only one position sensor, an abnormal operation is detected because an L signal is output after the H signal even when the light-shielding blades are rotating normally or rotated in the reverse direction by an external force. Can not do it.

  On the other hand, when two position sensors are provided as in the third embodiment, the reverse rotation of the light-shielding blade can be detected by checking which position sensor signal is switched. As shown in FIG. 6, the energization to the first coil is switched according to the first sensor signal, and the energization to the second coil is switched according to the second sensor signal. Thereby, even when the light-shielding blade rotates in the reverse direction, the position of the rotor can always correspond to the energization direction of the coil, and abnormal operation can be avoided.

(Correspondence between the present invention and the embodiment)
The light-shielding blade 4 corresponds to a blade member that regulates the amount of light of the present invention, and the stepping motor 1 corresponds to a stepping motor that drives the blade member of the present invention. Further, the slit 41, the position sensor 3, the permanent magnet (not shown), and the magnetic sensor (not shown) correspond to the position detecting means for detecting the position of the blade member of the present invention. The decoder 101 and the coil drive unit 102 correspond to drive control means for switching the energization state of the stepping motor according to the output signal of the position detection means of the present invention. Further, the slit 41 and a permanent magnet (not shown) correspond to a signal generation unit of the present invention, and the position sensor 3 and a magnetic sensor (not illustrated) correspond to a sensor unit of the present invention. The transmission mechanism 103 corresponds to a transmission mechanism that transmits the power of the stepping motor to the blade member and rotates the blade member of the present invention.

It is a disassembled perspective view which shows the shutter apparatus which concerns on Example 1 of this invention. It is a figure which shows the relationship between the applied voltage to the 1st, 2nd coil with which the stepping motor which concerns on Example 1 of this invention is equipped, and the sensor signal of the position sensor which detects the position of the light-shielding blade. It is a figure which shows the outline of the electrical constitution of the shutter apparatus which concerns on Example 1 of this invention. It is a figure which shows the relationship between the torque of a stepping motor with which the shutter apparatus which concerns on Example 2 of this invention is equipped, and rotation speed. It is a figure which shows the state of the sensor signal of the rotor speed of the stepping motor with which the shutter apparatus which concerns on Example 2 of this invention is equipped, the advance angle, and the position sensor. It is a figure which shows the relationship between the applied voltage to the 1st, 2nd coil with which the stepping motor which concerns on Example 3 of this invention is equipped, and the sensor signal of the 1st, 2nd position sensor which detects the position of a light-shielding blade. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Stepping motor 1a 1st coil 1b 2nd coil 2 Rotary plate 3 Position sensor 4 Light shielding blade 5 Ground plate 101 Decoder 102 Coil drive part 103 Transmission mechanism

Claims (7)

A blade member that regulates the amount of light;
A stepping motor for driving the blade member;
Position detecting means for detecting the position of the blade member;
And a blade drive device comprising drive control means for switching a state of energization to the coil of the stepping motor in accordance with an output signal of the position detection means. The position detection means includes a signal generation unit and a sensor unit that reads a signal generated in the signal generation unit,
2. The blade drive according to claim 1, wherein the signal generation unit is a slit provided in the blade member, and the presence or absence of the slit is optically read by the sensor unit to detect the position of the blade member. apparatus. A transmission mechanism for transmitting the power of the stepping motor to the blade member and rotating the blade member;
The position detection means includes a signal generation unit and a sensor unit that reads a signal generated in the signal generation unit,
The said signal generation part is a permanent magnet provided in the said transmission mechanism, The magnetic signal of this permanent magnet is magnetically read by the said sensor part, and the position of the said blade member is detected. Blade drive device.   4. The blade driving device according to claim 2, wherein the signal generated by the signal generating unit is a signal for one pulse when the stepping motor is moved by one step.   The signal generated by the signal generating unit is a signal for one pulse when the stepping motor is moved by one step, and has a phase difference different for each pulse with respect to an output signal of the position detecting means. Item 4. The blade driving device according to Item 2 or 3.   The blade member is composed of a plurality of light shielding blades, and the amount of light is regulated as the overlapping amount of the light shielding blades increases, and the phase difference is set to be smaller as the amount of light restriction is larger. The blade driving device according to claim 5.   An imaging apparatus comprising the blade driving device according to claim 1.

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