Micro projector device and control method thereof

The present invention provides a micro projector device including a MEMS mirror, a laser source module, a detection module, and a control unit. The MEMS mirror has a first portion and a second portion, the first portion pivots to the second portion, and the first portion oscillates in relation to the second portion. The laser source module generates a laser light to a reflection plane of the first portion of the MEMS mirror. The detection module detects a capacitance value between the first portion and the second portion. The control unit determines the relative position between the first portion and the second portion according to the capacitance value, and provides image data to the laser source module according to the relative position. The reflection plane of the first portion is configured to reflect the laser light from the laser source module to a projection plane.

CROSS REFERENCE TO RELATED APPLICATIONS

This Application claims priority of China Patent Application No. 201310495379.3, filed on Oct. 21, 2013, the entirety of which is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to micro projector devices, and more particularly to micro projector devices having MEMS mirror.

2. Description of the Related Art

Nowadays, a projector is used as a display device for electronic devices (such as a computer) to output images. A conventional projector provides a light source for outputting an image by using a metal-halide lamp, such as an ultra-high pressure mercury lamp, so it is difficult to reduce the size of a conventional projector. For ease of carrying, some projectors use a laser light source and MEMS (Micro Electro Mechanical Systems) components to make the optical system of the projector smaller. A laser projector has the advantages of being compact, light and thin in comparison with a projector using a metal-halide lamp. However, in the operation of image output, the laser projector requires precise synchronization of image data with the scanning position of the laser light, in order to make the image clear.

BRIEF SUMMARY OF THE INVENTION

An embodiment of a micro projector device comprises a MEMS mirror, a laser source module, a detection module and a control unit. The MEMS mirror has a first portion and a second portion. The first portion pivots to the second portion, and the first portion oscillates in relation to the second portion. The laser source module generates a laser light to a reflection plane of the first portion of the MEMS mirror. The detection module detects an equivalent capacitance value between the first portion and the second portion. The control unit determines the relative position between the first portion and the second portion according to the equivalent capacitance value, and provides image data to the laser source module according to the relative position. The reflection plane of the first portion is configured to reflect the laser light from the laser source module to a projection plane.

In an embodiment, the first portion of the MEMS mirror further comprises a first driving electrode, and the second portion of the MEMS mirror further comprises a second driving electrode. When the control unit provides a scan driving signal to the first driving electrode or the second driving electrode, the first portion oscillates in relation to the second portion according to the scan driving signal. On the other hand, the control unit stops providing the scan driving signal to the first driving electrode or the second driving electrode, and the first driving electrode is adjacent to the second driving electrode.

In an embodiment, the detection module further provides a high-frequency carrier signal to the first driving electrode of the MEMS mirror, detects the amplitude of the high-frequency carrier signal of the first driving electrode, and determines the equivalent capacitance value according to the amplitude of the high-frequency carrier signal.

In an embodiment, the MEMS mirror uses the laser light of the laser source module to scan for a first scan direction of the projection plane by the oscillation of the first portion, and a trace of the laser light on the first scan direction forms one of the scan lines of an image.

The present invention also provides a micro projector control method for a micro projector device, and the micro projector device has a MEMS mirror with a first portion oscillating in relation to a second portion. The micro projector control method comprises: detecting an equivalent capacitance value between the first portion and the second portion; determining the relative position between the first portion and the second portion according to the equivalent capacitance value; determining image data according to the relative position; generating a laser light to a reflection plane of the first portion of the MEMS mirror according to the image data; and reflecting the laser light to a projection plane by the reflection plane of the first portion.

In an embodiment, wherein the first portion of the MEMS mirror further comprises a first driving electrode, the second portion of the MEMS mirror further comprises a second driving electrode, and the micro projector control method further comprises: providing a scan driving signal to the first driving electrode or the second driving electrode, and the first portion oscillates in relation to the second portion according to the scan driving signal when the first driving electrode or the second driving electrode receives the scan driving signal. On the other hand, when the first driving electrode and the second driving electrode do not receive the scan driving signal, the first driving electrode is adjacent to the second driving electrode.

In an embodiment, the micro projector control method further comprises: providing a high-frequency carrier signal to the first driving electrode of the MEMS mirror; detecting amplitude of a high-frequency carrier signal of the first driving electrode; and determining the equivalent capacitance value according to the amplitude of the high-frequency carrier signal.

In an embodiment, the micro projector control method further comprises: using the laser light of the laser source module to scan for a first scan direction of the projection plane by the oscillation of the first portion of the MEMS mirror, and a trace of the laser light on the first scan direction forms one of the scan lines of an image.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments, or examples, illustrated in the drawing are now disclosed using specific language. It will nevertheless be understood that the embodiments and examples are not intended to be limiting. Any alterations and modifications in the disclosed embodiments, and any further applications of the principles disclosed in this document are contemplated as that which would normally occur to one of ordinary skill in the pertinent art.

FIG. 1is a block diagram illustrating an embodiment of the micro projector device according to the invention. The micro projector device100comprises a MEMS (Micro Electro Mechanical Systems) mirror110, a control unit130, a detection module120and a laser source module140. The MEMS mirror110is configured to reflect a laser light from the laser source module140by a reflection plane of the MEMS mirror110, and make the laser light scan on the projection plane P for displaying an image. In more detail, as shown inFIG. 2A, the MEMS mirror110has a first portion112having the reflection plane and a second portion114, and the first portion112can oscillate in relation to the second portion114. Therefore, since the first portion112oscillates, the reflected laser light L scans on the projection plane P with the oscillation direction of the first portion112, and a trace of the laser light L forms one of the scan lines of the image. For example, inFIG. 2B, when the first portion112of the MEMS mirror110moves to a position112A, the laser light L from the laser source module140is reflected to a scan point A on the projection plane P. When the first portion112of the MEMS mirror110moves to a position112B, the laser light L from the laser source module140is reflected to a scan point B on the projection plane P. It should be noted that during the period of the laser light L scanning from the scan point A to the scan point B by oscillation of the first portion112, the laser source module140sequentially emits the laser light L with the color and intensity corresponding to the image data of the scan point A to B in the image. Because the oscillation frequency of the first portion112of the MEMS mirror110is high, human eye may observe that a trace (ex., the scan point A to B) of the laser light L forms one of the scan lines of the image.

In addition, in some embodiments for displaying the whole image on the projection plane P, the first portion112of the MEMS mirror110not only oscillates in a horizontal direction, but also a vertical direction. Therefore, when the MEMS mirror110finishes scanning one horizontal scan line, the first portion112shifts along the vertical direction to scan the next horizontal scan line, so that the scanning of the whole image can be accomplished. Furthermore, due to the invention not focusing on the structure of the MEMS mirror, the related detail is not described, and any MEMS mirror can perform the above scanning operations for a laser light should be included in the embodiments of the invention.

The operations of the first portion112of the MEMS mirror110oscillating in relation to the second portion114are briefly described herein.FIG. 2Cis a schematic diagram illustrating a portion of the MEMS mirror110. As shown inFIG. 2C, the first portion112of the MEMS mirror110has a driving electrode112E with a comb-structure, the second portion114of the MEMS mirror110has a driving electrode114E with a comb-structure, and the first portion112pivots to the second portion114via a rotation shaft R. In some embodiments, the control unit130provides a scan driving signal with a resonant frequency of the MEMS mirror110to the driving electrode112E, and the driving electrode114E is electrically connected to ground. Therefore, the first portion112oscillates in relation to the second portion114by the rotation shaft R, because of the electrostatic force between the driving electrode112E and the driving electrode114E. In the other embodiments, the control unit130may provide the scan driving signal with a resonant frequency of the MEMS mirror110to the driving electrode114E, and the driving electrode112E is electrically connected to ground. Also, when the control unit130does not provide the scan driving signal to the driving electrode112E or the driving electrode114E, the driving electrode112E stops and is adjacent to the driving electrode114E.

The laser light L scans on the projection plane P to display the image based on the above-mentioned operations, but the image may be unclear or incorrect when the image data received by the laser source module140mismatches the scan position of the laser light L.

In order to match the image data received by the laser source module140with the scan position of the laser light L, the control unit130further obtains the oscillation angle of the first portion112of the MEMS mirror110to determine the scan position of the laser light L, and provide the image data of the determined scan position to the laser source module140.

In some embodiments, in order to determine the oscillation angle of the first portion112, the detection module120detects the equivalent capacitance value between the driving electrode112E of the first portion112and the driving electrode114E of the second portion114. It should be noted that the distance between the driving electrode112E and the driving electrode114E changes when the oscillation angle of the first portion112changes, and correspondingly the equivalent capacitance value between two electrodes changes when the distance between two driving electrodes changes. Therefore, the control unit130can analyze the equivalent capacitance value between the driving electrode112E and the driving electrode114E to determine the oscillation angle of the first portion112of the MEMS mirror110, such that the scan position of the laser light L can be determined accordingly.

Note that the equivalent capacitance value may be different when the manufacture, size or structure of the MEMS mirror110is different. Therefore, in some embodiments, the control unit130stores a look-up table or an algorithm with the correlation between equivalent capacitance value and the oscillation angle of the first portion112of the MEMS mirror110. When the control unit130obtains the equivalent capacitance value between the driving electrode112E and the driving electrode114E, the control unit130can determine the scan position of the laser light L according to the look-up table or algorithm.

In some embodiments, the detection module120provides a high-frequency carrier signal to the driving electrode112E via a resistor and the driving electrode114E is connected to ground. The detection module120detects an amplitude of the high-frequency carrier signal of the driving electrode112E. Because a decay of the amplitude of the high-frequency carrier signal at the driving electrode112E changes in response to changes to the equivalent capacitance value of the MEMS mirror110, the detection module120can determine the equivalent capacitance value of the MEMS mirror110according to the amplitude of the high-frequency carrier signal of the driving electrode112E, and provide the equivalent capacitance value to the control unit130.

FIG. 3is a circuit diagram illustrating an embodiment of the detection module according to the invention. In the embodiment, the detection module comprises an adder circuit302, a band-pass filter circuit304, an amplifier circuit306and a low-pass filter circuit308.

The adder circuit302is configured to add a high-frequency carrier signal to the scan driving signal for the MEMS mirror110, and comprises operational amplifiers OP1, OP2, resistors R1, R2, R3, R4, R5, a DC-voltage source VDC1and a capacitor C1. One terminal of the resistor R1is connected to a node N1, the other terminal of the resistor R1is connected to a negative input terminal of the operational amplifiers OP1, and the node N1receives the scan driving signal. One terminal of the resistor R2is connected to a node N2, the other terminal of the resistor R2is connected to the negative input terminal of the operational amplifiers OP1, and the node N2receives the high-frequency carrier signal. One terminal of the resistor R3is connected to the negative input terminal of the operational amplifiers OP1, and the other terminal of the resistor R3is connected to an output terminal of the operational amplifiers OP1. One terminal of the resistor R4is connected to the positive input terminal of the operational amplifiers OP1, and the other terminal of the resistor R4is connected to one terminal of the capacitor C1and a positive voltage terminal of the DC-voltage source VDC1. The other terminals of the capacitor C1and the DC-voltage source VDC1are connected to ground. The output terminal of the operational amplifiers OP1is connected to one terminal of the resistor R5, the other terminal of the resistor R5is connected to a positive input terminal of the operational amplifiers OP2and one of the driving electrodes (ex, driving electrode112E) of the MEMS mirror, and the other driving electrode (ex, driving electrode114E) is connected to ground. Therefore, a scan driving signal carrying a high-frequency carrier signal can be transmitted to the MEMS mirror110, and drive the oscillation of the MEMS mirror110. Also, the operational amplifier OP2is a buffer, and its negative input terminal is connected to its output terminal.

The band-pass filter circuit304comprises capacitors C2, C3, resistors R6, R7and an operational amplifier OP3. One terminal of the capacitors C2is connected to the adder circuit302(the output terminal of the operational amplifier OP2), and the other terminal of the capacitors C2is connected to one terminal of the resistor R6and one terminal of the capacitor C3. The other terminal of the resistor R6is connected to an output terminal and a negative input terminal of the operational amplifier OP3, and the other terminal of the capacitor C3is connected to a positive input terminal of the operational amplifier OP3and one terminal of the resistor R7. The other terminal of the resistor R7is connected to ground.

The amplifier circuit306comprises a capacitor C4, diodes D1, D2, D3, resistors R8, R9, R10, R11, R12, R13and operational amplifiers OP4, OP5. One terminal of the resistor R8is connected to the band-pass filter circuit304(the output terminal of the operational amplifier OP3) and a positive input terminal of the operational amplifier OP4, and the other terminal of the resistor R8is connected to ground. A negative input terminal of the operational amplifier OP4is connected to an anode of the diode D1and one terminal of resistor R9, and an output terminal of the operational amplifier OP4is connected to a cathode of the diode D1and an anode of the diode D2. The other terminal of the resistor R9is connected to a terminal of the resistor R10, a negative input terminal and output terminal of the operational amplifier OP5. The other terminal of the resistor R10is connected to a cathode of the diode D2and an anode of the diode D3. A cathode of the diode D3is connected to a terminal of the resistor R11and a terminal of the resistor R13. The other terminal of the resistor R11is connected to the capacitor C4and the resistor R12, the other terminals of the capacitor C4and the resistor R12are connected to ground. The other terminal of the resistor R13is connected to a positive input terminal of the operational amplifier OP5.

The low-pass filter circuit308comprises resistors R14, R15, R16, capacitors C5, C6, a DC-voltage source VDC2and an operational amplifier OP6. One terminal of the resistor R14is connected to the amplifier circuit306(the output terminal of the operational amplifier OP5), the other terminal of the resistor R14is connected to the capacitor C5and a positive input terminal of the operational amplifier OP6, and the other terminal of the capacitor C5is connected to ground. A negative input terminal of the operational amplifier OP6is connected to a terminal of the resistor R15and a terminal of the resistor R16. The other terminal of the resistor R15is connected to the capacitor C6and a positive voltage terminal of the DC-voltage source VDC2, and the other terminal of the capacitor C6and a negative terminal of the DC-voltage source VDC2are connected to ground. The other terminal of the resistor R16is connected to an output terminal of the operational amplifier OP6. The output terminal of the low-pass filter circuit308(the output terminal of the operational amplifier OP6) is connected to the control unit130.

It should be noted that the equivalent capacitance value of the MEMS mirror110changes when it oscillates, and the high-frequency carrier signal changes accordingly. Therefore, the detection module120uses the adder circuit302, the band-pass filter circuit304, the amplifier circuit306and the low-pass filter circuit308to analyze the decay of the high-frequency carrier signal, and the control unit130can determine the equivalent capacitance value of the MEMS mirror110according to the analyzed signal. For example, after the scan driving signal with the high-frequency carrier signal passes through the band-pass filter circuit304, the amplifier circuit306and the low-pass filter circuit308, the signal at the output terminal of the low-pass filter circuit308(the output terminal of the operational amplifier OP6) has a frequency substantially equal to the frequency of oscillation of the MEMS mirror110(variation of the equivalent capacitance value). The amplitude variation of the signal at the output terminal of the low-pass filter circuit308corresponds to the oscillation of the MEMS mirror110. In other words, the level of the signal at the output terminal of the low-pass filter circuit308can correspond to the oscillated position of the MEMS mirror110. Therefore, there is a one-to-one relationship between the level of the signal at the output terminal of the low-pass filter circuit308and the oscillated position of the MEMS mirror110, and the control unit130can determine the oscillation angle of the first portion112of the MEMS mirror110.

FIG. 4is a flowchart of an embodiment of a control method for the micro projector device100shown inFIG. 1. In step S402, the control unit130provides a scan driving signal with a resonant frequency of the MEMS mirror110to the driving electrode112E of the first portion112or the driving electrode114E of the second portion114of the MEMS mirror110, and the first portion112of the MEMS mirror110having a reflection plane oscillates in relation to the second portion114. In step S404, the detection module120detects the equivalent capacitance value between the driving electrode112E and the driving electrode114E.

Next, in step S406, the detection module120provides the equivalent capacitance value to the control unit130. In step S408, the control unit130determines the oscillation angle of the first portion112of the MEMS mirror110according to the equivalent capacitance value. In step S410, the control unit130obtains image data which corresponds to the oscillation angle of the first portion112of the MEMS mirror110(It means the image data corresponds to the position of the projection plane P where the laser light L reflects to), and provides the image data to the laser source module140. Finally, in step S412, the laser source module140emits a laser light L to the MEMS mirror110, and the laser light L is reflected to the projection plane P by the MEMS mirror110. It should be noted that the steps mentioned above are performed repeatedly, so the laser light L scans the projection plane P to display the image.