JP2009229517A - Actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an actuator in which the resonance frequency of oscillators is measured and adjusted with a simple circuit configuration. <P>SOLUTION: The actuator includes: a movable plate (13); a supporting part (11); a torsion bar (14) which oscillatably supports the movable plate on the supporting part; an angular degree detection sensor (20) which is formed on the torsion bar; a driving means (30) which oscillates the movable plate; and a resonance frequency adjustment means (30) which adjusts the resonance frequency of the oscillators (13 and 14) composed of the movable plate and the torsion bar, wherein the angular degree detection sensor (20) includes a piezo resistor (21) which receives the supply of a bias current (I<SB>B</SB>) and generates a voltage corresponding to the torsion of the torsion bar, and the resonance frequency adjustment means includes a variable current source (34) which adjusts the bias current level supplied to the piezo resistor corresponding to the resonance frequency to be set on the oscillator. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an improvement in an actuator that drives a reflection mirror used in, for example, an optical scanner or an image forming apparatus.

  Optical deflectors applied to displays, printers, and the like that use laser light are currently required to perform high-speed scanning operations when drawing images. In order to realize this high-speed scanning operation, a polygon mirror or a galvanometer mirror is used, but there is a limit in improving the high-speed performance. Therefore, it has been proposed to use a MEMS mirror manufactured by microfabricating a silicon (Si) substrate by MEMS (Micro Electro Mechanical System) technology. Since the MEMS mirror vibrates at a high resonance frequency, there is an advantage that drawing with higher resolution is possible.

However, the resonance frequency of the MEMS mirror may vary due to an error in processing the vibrator during manufacturing, or a desired resonance frequency may not be obtained due to the temperature of the vibrator during use. For the former, it is conceivable to perform trimming of the vibrator, and for the latter, it is possible to keep the vibrator portion at a constant temperature. Therefore, the invention described in Patent Document 1 proposes to control the resonance frequency of the vibrator by providing a heater on the vibrator chip and changing the Young's modulus of the material constituting the vibrator depending on the temperature. Yes. In the invention described in Patent Document 2, an angle sensor is provided in the vibrator so as to detect the vibration frequency of the vibrator.
JP-A-9-197334 JP 9-512904 gazette

  However, since the heater that changes the spring constant (such as Young's modulus) of the vibrator is provided in the spring portion of the vibrator realized with a fine structure, there is little space in space for arranging the heater resistance and wiring. If the vibrator can be provided with both a heater that changes the spring constant and an angle sensor that detects vibration, it is possible to adjust the resonance frequency only on the actuator side including the vibrator. Forming an angle sensor in addition to the heater also has difficult problems such as insufficient space and complexity of functional parts and wiring layout.

  Accordingly, an object of the present invention is to provide an actuator capable of measuring the resonance frequency of a vibrator that tends to vary from product to product with a simple circuit configuration and adjusting the resonance frequency on the vibrator side. .

  In order to achieve the above object, an actuator of the present invention includes a movable plate, a support portion, a torsion bar that supports the movable plate so as to vibrate on the support portion, an angle detection sensor formed on the torsion bar, A driving means for vibrating the movable plate; and a resonance frequency adjusting means for adjusting a resonance frequency of a vibrator composed of the movable plate and the torsion bar. The angle detection sensor is supplied with a bias current. The resonance frequency adjusting means adjusts the level of the bias current supplied to the piezoresistor corresponding to the resonance frequency to be set for the vibrator. Includes a variable current source to regulate.

  By adopting such a configuration, the angle detection sensor provided on the torsion bar can be used for adjusting the resonance frequency of the vibrator. This eliminates the need to individually correct the variation in the resonance frequency of individual vibrators that occurs during actuator fabrication by trimming. Further, it is not necessary to separately provide an adjustment heater for adjusting the resonance frequency in the actuator, which is convenient in terms of productivity. Moreover, it is possible to avoid wiring such as a heater and layout out to a fine part, and the condition is good.

  The torsion bar is constituted by a semiconductor substrate, the piezoresistor is formed by an impurity doped region formed in the semiconductor substrate, and the bias current flows through the impurity doped region, and in a direction orthogonal to the current direction of the bias current. A voltage corresponding to the twist is obtained. Accordingly, the piezoresistor is formed integrally with the reaction substrate, and a sensor having high sensitivity only for torsion of the torsion bar can be obtained.

  It is desirable to set the resonance frequency by causing the piezoresistor to generate heat by the bias current and changing the spring characteristics of the torsion bar. The resonance frequency can be set by changing the spring characteristics (such as Young's modulus and stress) by heat.

  A reflection mirror is formed on the movable plate. Thereby, an optical actuator is configured.

  The angle detection sensor is preferably composed of, for example, a four-terminal strain gauge. Thereby, the heat generation of the piezoresistor is adjusted by the bias current supplied to the current terminal, and an output corresponding to the twist angle can be obtained at the voltage terminal.

  The image forming apparatus of the present invention includes an actuator having the above-described configuration and advantages.

  Embodiments of the present invention will be described below with reference to the drawings.

  First, an example of an image forming apparatus using an optical scanner that forms scanning light using the actuator of the present application will be described.

(Image forming device)
FIG. 7 shows a projector which is an example of an image forming apparatus. The projector includes light source devices 911 to 913 that output R, G, and B light beams modulated by R, G, and B image signals, a light beam combining device 92, optical scanners 93 and 94, and a fixed mirror 95. It has.

  The light beam combining unit 92 combines the three color light beams emitted from the light source devices 911 to 913 into one light beam, and sends the combined light beam to the optical scanner 93. The combined light beam becomes a light beam scanned in the left-right direction by the optical scanner 93 (main scanning), and further becomes a light beam of two-dimensional scanning scanned in the vertical direction by the optical scanner 94 (sub-scanning). This scanning light beam is further reflected by a fixed mirror 95 to form a color image on the screen S.

  The rotation speed of the optical scanner 94 that performs sub-scanning is lower than the rotation speed of the optical scanner 93 that performs main scanning. For example, the oscillation (vibration) frequency of the optical scanner 94 that performs sub-scanning is about 60 Hz, and the oscillation (vibration) frequency of the optical scanner 93 that performs main scanning is about 10 to 256 kHz.

  In addition to the laser projector described above, there are various types of image forming apparatuses such as a laser printer. Optical scanners are also used in bar code readers and the like.

(Example)
Next, an actuator used for an optical scanner or the like will be described. FIG. 1 is a plan view of an actuator used in the present invention, and FIG. 2 is a diagram for explaining a four-terminal strain gauge used in this actuator.

As shown in FIG. 1, the actuator 10 includes a support frame 11 constituting a frame body, a movable plate 13 having a mirror 12 that reflects light on the surface, and the movable plate 13 swinging with respect to the support frame 11. It has a pair of torsion bars 14 and 14 supported so as to be capable of (vibration). For example, the actuator 10, the support frame 11, the movable plate 13, and the torsion bar 14 are integrally formed by patterning a silicon substrate (semiconductor substrate).
The silicon substrate is a P-type substrate, and as shown in the drawing, the lateral crystal orientation is <110>, the vertical crystal orientation is <110>, and the crystal orientation in the direction perpendicular to the paper surface is <100>. .

  A driving electrode 16 is fixed to the bottom of the concave portion of the support frame 11 so as to face the movable plate 13. When a drive voltage is applied to the drive electrode 16 from an external circuit, the movable plate 13 is attracted to the drive electrode 16 side by electrostatic force, and the movable plate 13 rotates about the torsion bar 14 as a rotation axis. When the application of the drive voltage is released, the movable plate 13 returns to the original state by the torsion spring force of the torsion bar 14. By applying a drive voltage to the drive electrode 16 periodically, the movable plate swings (vibrates), and a vibrating mirror that scans the light beam is obtained.

An angle detection sensor 20 is integrally formed on a part of the torsion bar 14. As shown in FIG. 2, the angle detection sensor 20 includes a piezoresistor 21 in a vertically long rectangular region formed on a silicon semiconductor substrate, and a bias current that applies a bias current I _B to the rectangular region of the piezoresistor 21 from the left end toward the right end. Pads (terminals) 22 and 24, voltage measuring pads (terminals) 23 and 25 for deriving the voltages at the upper and lower ends of the rectangular region of the piezoresistor 21 to the outside, and electric wiring for connecting them are configured. The vertically long region of the piezoresistor 21 extends in the axial direction of the torsion bar 14, and the rotation angle (the terminals 23 and 25) are at the left and right ends of the rectangular region of the piezoresistor 21 that is perpendicular to the axial direction. An output voltage corresponding to the rotational stress is obtained. This piezoresistor 21 functions as a four-terminal strain gauge. The piezoresistor 21 is arranged in consideration of the crystal orientation of a P-type <100> silicon substrate. For example, an appropriate amount of phosphorus (P) is doped into a region of 200 μm length × 40 μm width of the silicon substrate. It is formed as a region.

As described above, the piezoresistor 21 has a resistance value corresponding to the torsional stress, and a voltage corresponding to the stress is generated at both ends of the piezoresistor due to the bias current flowing through the resistor. The piezoresistor 21 is used as a heater for changing the spring constant of the torsion bar (spring) 14. When heat is generated in the piezoresistor 21, heat is transmitted to the pair of torsion bars 14, 14 formed integrally with the piezoresistor 21, and the spring constant (Young's modulus, stress, etc.) of the torsion bar 14 changes. Since the resonance frequency of the vibrator made of movable plate 13 and the sea Deployment bar 14 is dependent on the spring constant, the current transducer by setting the appropriate value by changing the bias current I _B supplied to the piezo resistor 21 Can be set to a desired resonance frequency.

  FIG. 3 is an explanatory diagram illustrating a resonance frequency adjustment unit that adjusts the resonance frequency. As shown in the figure, the resonance frequency adjusting unit is realized by a plurality of components in the control unit 30 of the image forming apparatus configured by a microcomputer system. The control unit 30 includes a CPU 31, a memory unit 32, a temperature detection unit 33, a bias current supply unit 34, a frequency detection unit 35, a drive circuit unit 36, a database unit 37, and the like. In addition, the control part 30 has shown only the part relevant to control of an actuator.

  The CPU 31 executes a control program stored in the memory unit 32 to control each unit and perform data processing. The memory unit 32 stores control programs and data. The temperature detector 33 detects the temperature of the actuator (vibrator). For example, a table (graph) of temperature vs. resistance value characteristics of the piezoresistor 21 is stored in the memory in advance, and the temperature of the vibrator is estimated from the detected resistance value of the piezoresistor 21.

  The bias current supply unit 34 is a variable current supply source that outputs a current of a level according to an instruction from the CPU 31, and supplies a bias current to the piezoresistor 21 via the terminals 22 and 24 of the angle detection sensor 20. Further, the bias current supply unit 34 can transmit the voltage value and the current value applied to both terminals to the CPU 31 so that the resistance value of the piezoresistor 21 can be calculated. The frequency detection unit 35 is connected to the voltage measurement terminals 23 and 25 of the angle detection sensor 20, and performs filtering processing, waveform processing, and the like on a sinusoidal voltage signal generated in the piezoresistor 21 due to oscillation (vibration) of the transducer. The vibration frequency is detected by performing a counting process or the like.

  The drive circuit 36 supplies a drive voltage signal to the drive electrode 16 of the actuator in accordance with a command from the CPU 32. In this embodiment, the movable plate 13 is driven by an electrostatic force. However, when driven by electromagnetic force, a drive current is supplied to a movable coil (not shown).

  The database unit 37 holds various data used for control. For example, as shown in FIGS. 5 and 6 to be described later, a table (graph) of the bias current versus resonance frequency characteristic of the vibrator, the rotation angle of the movable plate (or torsion bar) versus the output of the piezoresistor (angle detection sensor). Various data such as a voltage characteristic table (graph) are stored in advance.

  Next, an example of adjusting the resonance frequency will be described with reference to the flowchart shown in FIG. The CPU 31 of the control unit 30 controls the frequency adjustment when the image forming apparatus is started for the first time of the day or when the room temperature (or vibrator temperature) is lower than the predetermined temperature. Run the routine. As described above, the CPU 31 can estimate the temperature from the resistance value of the piezoresistor 21 (step S12).

  First, the CPU 31 causes the angle detection sensor 20 to output a bias current of a predetermined level for detection to the bias current supply unit 34. As a result, an initial (reference) bias current flows through the piezoresistor 21. Further, the CPU 31 operates the frequency detection unit 35 to observe the output voltages of the voltage output terminals 23 and 25 (step S14).

Next, the CPU 31 causes the drive circuit 36 to output a drive signal having a predetermined period (1 / f ₀ ) (step S16). After a certain period of time during which the vibrator is activated and the vibration is stabilized, the CPU 31 reads the measurement frequency f _S detected by the frequency detector 35 (step S18).

The CPU 31 obtains a frequency difference Δf between the target frequency f ₀ to be set for the vibrator and the measurement frequency f _S (step S20). When the frequency f _S detected by the frequency detector 35 is equal to the target frequency fo (Yes at Step S22), the CPU 31 ends the process with the bias current fixed (Step S28).

If the detected frequency f _S is deviated from the target frequency fo (Step S22, No), CPU 31 calculates the bias current ΔI corresponding to Delta] f, the command to increase the current ΔI from the bias current I _B (frequency A command to decrease (when increasing) or a command to decrease (when increasing frequency) is commanded to the bias current supply unit 34. As a result, the supply current of the bias current supply unit 34 changes, the amount of heat generated by the piezoresistor 21 is adjusted, and the spring constant of the vibrator changes (step S24).

  FIG. 5 shows an example of a change in characteristics of bias current versus resonance frequency when the oscillation (vibration) angle of the vibrator is 13.54 degrees. From the figure, it can be seen that when the bias current is increased, the resonance frequency of the vibrator decreases substantially linearly.

After a predetermined time during which the temperature of the vibrator stabilizes, the CPU 31 measures the resonance frequency of the vibrator (step S26), and again determines whether the detected frequency f _S deviates from the target frequency fo (step S20). . When the detected frequency f _S deviates from the target frequency fo (No at Step S22), Steps S24, S26, and S20 are repeated to adjust the bias current to adjust the resonance frequency of the vibrator to the target resonance frequency fo. . If the frequency f _S is equal to the target frequency fo (step S22, Yes), the bias current is fixed and the process is ended (step S28).

FIG. 6 shows the rotation angle versus output voltage characteristics of the angle detection sensor 20. Each characteristic curve indicated by a square point, a triangular point, and a round point in the figure shows an example in which the bias current is 3 mA, 5 mA, and 7 mA, respectively. In order to use the piezoresistor 21 as a heater, the output voltage level of the angle detection sensor 20 changes by changing the bias current. However, it is possible to make the piezoresistor 21 compatible as a heater and an angle detection sensor by previously holding the rotation angle versus output voltage characteristics at each bias current in the database 37 and selecting the characteristics corresponding to the set bias current. Also, as shown in FIG. 6, the output voltage (V _PZR ) of the angle detection sensor is a linear characteristic with respect to the rotation angle (A), so an approximate expression, A = F (V _PZR , I _B ) Alternatively, the rotation angle may be calculated and obtained.

  The resonance frequency component in the output voltage of the angle detection sensor 20 has information in the time axis direction of the output voltage, so that it is not affected by the level change of the bias current.

  As described above, the method of shifting the resonance frequency of the vibrator according to the present embodiment uses the piezoresistive region of the angle detection sensor as a heater. By applying a bias current applied to the piezoresistive region, heat is generated in the piezoresistive region, so that heat is transmitted to the torsion bar formed integrally with this region, and the Young's modulus and torsional stress of the torsion bar also change. Since the resonance frequency depends on this temperature, the current resonance frequency can be shifted to a desired resonance frequency by changing the supplied bias current.

  In this embodiment, in order to adjust the resonance frequency of the vibrator, when a bias current is supplied to the piezoresistor, the piezoresistor serves as a heater to change the temperature of the torsion bar. As a result, the gauge rate of the strain gauge also changes. However, since the relationship between the temperature and the change rate of the gauge rate is stored as data in advance and stored in a database, it can be corrected appropriately.

  Further, although the gauge factor changes with respect to the environmental temperature where the vibrator is placed, as described above, it can be easily compensated by measuring the resistance value between the bias current terminals.

  The actuator of the present application can be used for various types of image forming apparatuses such as projectors and printers, optical scanners, and the like, and is not limited to the embodiments.

  As described above, in the present invention, the four-terminal strain gauge formed on the torsion bar is used not only to detect the rotation angle of the movable plate but also to adjust the resonance frequency of the vibrator. It is not necessary to correct the frequency variation at the time of manufacturing the child by a trimming device or to add a heater, so that the productivity of the vibrator (actuator) is improved.

FIG. 1 is an explanatory diagram illustrating the configuration of the actuator. It is an enlarged view of the angle detection sensor (distortion sensor) provided in the torsion bar. It is explanatory drawing explaining the control system of the resonance frequency of an actuator. It is a flowchart explaining adjustment of a resonant frequency. It is a graph explaining the bias current versus resonance frequency characteristic of an angle detection sensor. It is a graph explaining the rotation angle versus output voltage characteristic of an angle detection sensor. It is explanatory drawing explaining the example of an image forming apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Actuator, 11 Support part, 12 Mirror, 13 Movable plate, 14 Torsion bar (torsion spring), 16 Drive electrode, 20 Angle detection sensor, 21 Piezoresistor, 22-25 Electrode pad (terminal), 30 Control part, 31 CPU 32 memory, 33 temperature detection unit, 34 bias current supply unit (variable current source), 35 frequency detection unit, 36 drive circuit, 37 database unit

Claims (6)

A movable plate,
A support part;
A torsion bar that supports the movable plate on the support portion so as to vibrate;
An angle detection sensor formed on the torsion bar;
Driving means for vibrating the movable plate;
Resonance frequency adjusting means for adjusting the resonance frequency of the vibrator composed of the movable plate and the torsion bar,
The angle detection sensor includes a piezoresistor that receives a bias current and generates a voltage corresponding to the twist of the torsion bar.
The resonance frequency adjusting means includes an adjustable current source that adjusts a level of a bias current supplied to the piezoresistor corresponding to a resonance frequency to be set for the vibrator.   The torsion bar is constituted by a semiconductor substrate, the piezoresistor is formed by an impurity doped region formed in the semiconductor substrate, and the bias current flows through the impurity doped region in a direction orthogonal to the current direction of the bias current. The actuator according to claim 1, wherein a voltage corresponding to the twist is obtained.   3. The actuator according to claim 1, wherein the resonance frequency is set by causing the piezoresistor to generate heat by the bias current and changing a spring characteristic of the torsion bar.   The actuator according to claim 1, wherein a reflection mirror is formed on the movable plate.   The actuator according to any one of claims 1 to 4, wherein the angle detection sensor is a four-terminal strain gauge.   An image forming apparatus using the actuator according to claim 1.