Optical scanning projection system

An optical scanning projection system includes a scanning light source component, a second reflecting element, a transparent element, a scanning element, a photosensitive element and a control module. The transparent element receives a main light beam emitted by the scanning light source component and reflects a part of the main light beam to be a reflected light. The reflected light is reflected by the second reflecting element, and the scanning element reflects the reflected light from the second reflecting element in a scanning manner. The photosensitive element receives the reflected light from the scanning element and outputs a sensing signal, and the control module actuates or stops actuating the scanning light source component according to the sensing signal. Therefore, when the scanning element is damaged, the control module may instantly stop actuating the scanning light source component, thereby enhancing the using safety of the optical scanning projection system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 099144614 filed in Taiwan, R.O.C. on Dec. 17, 2010 and Patent Application No. 100121898 filed in Taiwan, R.O.C. on Jun. 22, 2011, the entire contents of which are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to an optical scanning projection system, and more particularly, to an optical scanning projection system for improving safety in use and compensating image distortions.

2. Related Art

Currently, the micro-projection system technique may be classified into two categories. The first category is laser scanning projection technique using laser light as a light source, and the second category is Digital Light Process (DLP) technique or Liquid Crystal on Silicon (LCoS) technique using a Light Emitting Diode (LED) as a light source. As the light source is a LED, there are some problems with the micro-projection system. First, the operating temperature of the micro-projection system may adversely affect the service life and the luminescence efficiency of the LED. Second, the unsatisfactory photoelectric conversion efficiency of the LED leads to that raising the brightness of the micro-projection system is difficult. Moreover, when being turned on for a considerable period, the LED usually causes high power consumption of the system. Accordingly, when LED is used as a light source of the light engine with delicate focus lens set, the structure of the light engine becomes complicated.

With respect to the micro-projection system employing a laser as the light source, because the laser has a wider color gamut and better color saturation, the projected frame is brighter and more colorful. Besides, the laser scanning projection technique merely uses a single micro-mirror to perform the scanning projection to form the projection frame. However, the DLP technique needs many micro-mirrors, which causes difficulties in the yield and cost control. Therefore, comparing with the DLP technique, the laser scanning projection technique has the advantages of better yield and low cost. Furthermore, as the laser light has high brightness, good directivity, and may be projected on any plane, the complicated focus lens set is not required when the laser is used as the light source. Accordingly, the structure of the light engine using LED as the light source is simple, and, therefore, the micro-projection system employing the laser scanning projection technique is small in size and is easy to be built into an electronic device.

Since the laser is a high-power light source, the micro-projection system employing the laser scanning projection technique (hereinafter, referred to as the laser scanning projection system) needs to strictly conform to the laser safety specification. Generally, the laser scanning projection system meets the specification in normal operation. However, when the scanning element (i.e. the micro-mirror) is faulty and, therefore, cannot transform the laser light into the projection frame, a high brightness single light spot which is hazardous to the viewer's eyes will be formed. Moreover, during the laser scanning projection system carrying out the dynamic projection, the content of the projection frames changes quickly. Such quick changes then change the power of the laser light, so that the temperature of the scanning element changes quickly. However, such quick temperature changes influence the amplitude of the scanning element and, therefore, cause the misalignment of the scanning frames played sequentially. As a result, the image distortion and the frame blur are generated. Therefore, it is the trend in research and development for the practitioners in the field on how to solve the safety problem and the frame blur generated in dynamic projection of the laser scanning projection system.

SUMMARY

Accordingly, the present disclosure provides an optical scanning projection system, thereby solving the problems of safety and a frame blur generated in dynamic projection of the laser scanning projection system.

According to the optical scanning projection system in an embodiment of the present disclosure, the optical scanning projection system includes a scanning light source component, a second reflecting element, a transparent element, a scanning element, a photosensitive element and a control module. The scanning light source component may emit a main light beam. The transparent element receives the main light beam and reflects a part of the main light beam to be a reflected light while allowing a part of the main light beam to transmit to become a transmitting light. The second reflecting element reflects the reflected light. The scanning element reflects the transmitting light incident on the scanning element and the reflected light reflected by the second reflecting element in a scanning manner. Then, the photosensitive element receives the reflected light from the scanning element and outputs a sensing signal, and the control module selectively actuates or stops actuating the scanning light source component according to the sensing signal.

In another embodiment, the optical scanning projection system further comprises a scan driving unit. The control module outputs a synchronization signal to the scanning light source component and outputs a reference signal to the scan driving unit. The scan driving unit drives the scanning element by the reference signal. The control module adjusts an output time of the synchronization signal according to a time difference between the sensing signal, the synchronization signal and the reference signal.

In still another embodiment, the optical scanning projection system includes a scanning light source component, a transparent element, a second reflecting element, a scanning element, a photosensitive element and a control module. The scanning light source component emits a main light beam. The transparent element receives the main light beam and reflects a part of the main light beam to be a reflected light. The second reflecting element reflects the reflected light. The scanning element reflects the reflected light reflected by the second reflecting element in a scanning manner to obtain a detection frame, which includes a detection line, and a light intensity of the detection line does not change with time. The photosensitive element is used to sense the detection line and output a sensing signal. The control module selectively actuates or stops actuating the scanning light source component according to the sensing signal.

According to the optical scanning projection system of another embodiment of the present disclosure, the optical scanning projection system includes a scanning light source component, a detection light source, a laser driving unit, a first reflecting element, a second reflecting element, a scanning element, a photosensitive element and a control module. The scanning light source component and the detection light source respectively emit a main light beam and a detection light beam. The first reflecting element receives and reflects the main light beam to the scanning element. The second reflecting element receives and reflects the detection light beam to the scanning element. The scanning element reflects the main light beam from the first reflecting element and the detection light beam from the second reflecting element in a scanning manner. The photosensitive element receives the detection light beam from scanning element and outputs a sensing signal to the control module. The control module selectively actuates or stops actuating the scanning light source component according to the sensing signal. The laser driving unit is used to continuously drive the detection light source to emit the detection light beam.

The optical scanning projection system of the present disclosure adopts the configuration of the transparent element and scanning element or the arrangement of the detection light source, so that when the scanning element is faulty and cannot operate, the control module may instantly stop actuating the scanning light source component to avoid the single bright spot on the image projected by the optical scanning projection system generated by the failure of the scanning element and avoid causing harm to viewers' eyes. Moreover, the control module adjusts the synchronization signal according to a relation of the synchronization signal, the reference signal and the sensing signal, which may compensate the blur image generated by the scanning element due to the change of the amplitude. Furthermore, in order to avoid that the photosensitive element cannot output the corresponding sensing signal clearly due to the insufficient light intensity of the detection frame and the control module cannot determine if the scanning element operates normally, the configuration of the position of the photosensitive element or the arrangement of the detection light source, the photosensitive element sensing the detection line or the detection frame may be guaranteed to accurately output the corresponding sensing signal based on the characteristic that the light intensity of the detection line does not change with time.

DETAILED DESCRIPTION

FIG. 1Ais a schematic architectural view of an optical scanning projection system according to a first embodiment of the present disclosure andFIG. 1Bis a schematic block diagram of the circuit of the control module ofFIG. 1A. Referring toFIG. 1AandFIG. 1B, the optical scanning projection system100is applicable to a mobile projection device, for example but not limited to, a mobile phone or a personal digital assistant (PDA). The optical scanning projection system100may include, but not limited to, a scanning light source component102, a second reflecting element106, a transparent element108, a scanning element110, a photosensitive element112and a control module114. The second reflecting element106includes a second reflecting surface82, which may be, but is not limited to, a metal layer or a coated reflective layer. The scanning element110may be, but is not limited to, a scanning mirror, and the photosensitive element112may be, but is not limited to, a photodetector (PD). The transparent element108may be, but is not limited to, glass and may be used for packaging of the scanning element110. The transparent element108is disposed on the scanning element110and is in contact with the scanning element110. An angle formed between a surface40of the transparent element108and a surface42of the scanning element110may be, but is not limited to, 8°. That is to say, the angle formed between the surface40of the transparent element108and the surface42of the scanning element110may be any degree. However, the angle must enable the second reflecting element106to receive the reflected light118reflected by the transparent element108without shielding the projection frame84.

In this embodiment, the scanning light source component102may include, but not limited to, a light source50, a light source60, a light source70, a photometer51, a photometer61, a photometer71, a light splitter43and a light splitter44. The light source50may emit a red light beam52, the light source60may emit a green light beam62, and the light source70may emit a blue light beam72. The light source50, the light source60and the light source70may be, but are not limited to, semiconductor lasers. In other words, the light source50, the light source60and the light source70may also be solid-state lasers. A part of the red light beam52may be incident on the photometer51built in the light source50, and the rest part of the red light beam52may be transmitted through the light splitter43and the light splitter44. When the green light beam62is incident on the light splitter43, five percent of the green light beam62may be, but is not limited to, transmitted through the light splitter43and incident on the photometer61. Ninety-five percent of the green light beam62may be, but is not limited to, reflected by the light splitter43and transmitted through the light splitter44. When the blue light beam72is incident on the light splitter44, five percent of the blue light beam72may be, but is not limited to, transmitted through the light splitter44and incident on the photometer71. Ninety-five percent of the blue light beam72may be, but is not limited to, reflected by the light splitter44. Therefore, the photometer51, the photometer61and the photometer71are used to respectively detect if the light source50, the light source60and the light source70respectively emit the red light beam52, the green light beam62and the blue light beam52, but this embodiment is not intended to limit the scope of the present disclosure.

The control module114may include, but not limited to, a video interface30, a video decoder32, a power supply34, a Field-Programmable Gate Array (FPGA)36, a Central Processing Unit (CPU)38and a light source driver39. The light source driver39includes, but not limited to, a switch54, a switch64and a switch74. The switch54is used for actuating the light source50, the switch64is used for actuating the light source60, and the switch74is used for actuating the light source70. The FPGA36is used to control the switch54, the switch64and the switch74, and to determine if the light source50, the light source60and the light source70are damaged according to the result that the photometer51, the photometer61and the photometer71detect the light source50, the light source60and the light source70. The FPGA36is also used to monitor the output power through the detect results, thereby compensating image white balances, but this embodiment is not intended to limit the scope of the present disclosure.

When the power supply34is turned on, the CPU38accesses all parameters of the control module114. Then, the video interface30receives a data signal (not marked) and transfers the data signal to the video decoder32. The video decoder32decodes the data signal into the decoded signal33and then transfers the decoded signal33to the FPGA36, which converts the decoded signal33to grayscale and transfers the converted signal to the light source driver39. The light source driver39drives at least one of the switch54, the switch64and the switch74according to the decoded signal33converted to grayscale and, therefore, correspondingly actuates the light source50, the light source60and the light source70, but this embodiment is not intended to limit the scope of the present disclosure.

The scanning light source component102may emit a main light beam116. In this embodiment, the main light beam116may include a red light beam52, a green light beam62and a blue light beam72, but this embodiment is not intended to limit the scope of the present disclosure. Then, the transparent element108(i.e. the glass) receives the main light beam116and reflects a part of the main light beam116, while allowing a part of the main light beam116to transmit. The part of the main light beam116reflected is hereinafter referred to as reflected light118, and the part of the main light beam116transmitting the transparent element108is referred to as transmitting light120. In this embodiment, the reflected light118equals to five percent of the main light beam116, and the transmitting light120equals to ninety-five percent of the main light beam116, but this embodiment is not intended to limit the percentages of the reflected light118and the transmitting light118.

The second reflecting element106reflects the reflected light118, and the scanning element110(i.e. the scanning mirror) reflects both the transmitting light120incident on the scanning element110and the reflected light116reflected by the second reflecting element106in a scanning manner to respectively obtain a projection frame84and a detection frame86. In other words, the transmitting light120generated after the main light beam116passes through the transparent element108is reflected by the scanning element110in a scanning manner to obtain the projection frame84. The reflected light118generated after the main light beam116passes through the transparent element108firstly is reflected by the second reflecting element106and then is reflected by the scanning element110in a scanning manner to obtain the detection frame86.

In the above scanning manner, by controlling the direction and the amplitude of the scanning element110, the incident light source (i.e. the transmitting light120incident on the scanning element110and the reflected light116reflected by the second reflecting element106) is reflected to form the projection frame84and the detection frame86. The amplitude of the scanning element110relates to the energy of the incident light source. However, when the scanning element110operates normally, the amplitude of the scanning element110is controlled in a predetermined range. In this embodiment, the predetermined range may be, but is not limited to, ±90°.

Referring toFIG. 2AandFIG. 2B,FIG. 2Ais a schematic structural view of the scanning element inFIG. 1AandFIG. 2Bis a schematic view of a scanning path of the scanning element inFIG. 1A. The scanning element110may include a fast shaft90, a slow shaft92, a mirror94and an outer ring96. The fast shaft90is responsible for a horizontal direction X of the scanning path and the slow shaft92is responsible for a vertical direction Y of the scanning path. The mirror94is a reflecting surface of the scanning element110. The outer ring96is an outer frame of the mirror94. When the scanning element110is scanning, the mirror94reflects an incident light source99incident on the scanning element110, and the fast shaft90and the slow shaft92control the scanning path of the reflected light. In this embodiment, according toFIG. 2B, the scanning path starts from a scan point A to a scan point B, and then from the scan point B to a scan point C. Then, it is deduced in this manner to finish the first scanning (not marked), and the second scanning (not marked) moves in a reverse direction the scanning path of the first scanning, that is, starts from the scan point C to the scan point B and then from the scan point B to the scan point A. The following scanning paths may be deduced in this manner and will not be described in details. The scanning element110may produce thirty to sixty sheets of images (i.e. thirty to sixty times of scanning) every second, but this embodiment is not intended to limit the scope of the present disclosure.

Referring toFIG. 1AandFIG. 1B, the photosensitive element112(i.e. the PD) receives the reflected light118from the scanning element110and outputs a sensing signal122. The control module114actuates or stops actuating the scanning light source component102according to the sensing signal122. In other words, the photosensitive element112(i.e. the PD) is configured in the detection frame86to receive the reflected light118from the scanning element110and outputs the sensing signal122. When the photosensitive element112cannot receive the reflected light118from the scanning element110, the control module114stops actuating the scanning light source component102according to the sensing signal122(that is, the FPGA36turns off the switch54, the switch64and the switch74according to the sensing signal122, in which the switch54, the switch64and the switch74respectively are responsible for actuating the light source50capable of emitting the red light beam52, the light source60capable of emitting the green light beam62and the light source70capable of emitting the blue light beam72).

FIG. 3AandFIG. 3Brespectively are schematic views of a time sequence of a synchronization signal, a reference signal and a sensing signal received and transferred by the control module inFIG. 1Awhen the scanning element operates normally and abnormally. In this embodiment, the optical scanning projection system100may further include a scan driving unit125. The control module114controls the scan driving unit125by a reference signal128, and the scan driving unit125drives the scanning element110by the reference signal128. The control module114controls the scanning light source component102by the synchronization signal126(referring toFIG. 3AandFIG. 3B) and may adjust an output time of the synchronization signal126according to the time differences between the sensing signal122, the synchronization signal126and the reference signal128.

In more details, before the shipment of the optical scanning projection system100, a fixed time difference TL1(i.e. the time difference between a rising edge of the synchronization signal126and a rising edge of the reference signal128) normally exists between the synchronization signal126and the reference signal128so that the time of the transmitting light120incident on the scanning element110is synchronized with an operation time of the scanning element110to make the image clearer. Therefore, before the shipment, parameters of the synchronization signal126are set in the control module114(or in the memory and then read by the control module) to make the optical scanning projection system100obtain the clear image when operating normally.

Furthermore, after the optical scanning projection system100is shipped, when the optical scanning projection system100operates normally, the control module114takes the rising edge of the reference signal128as a reference point; the time difference between the rising edge of the sensing signal122and the reference point (i.e. the rising edge of the reference signal128) is TP1microseconds (μs), and the time difference between the rising edge of the synchronization signal126and the reference point (i.e. the rising edge of the reference signal128) is TL1μs. TP1−TL1is a fixed value. When the optical scanning projection system100operates abnormally, for example but not limited to, the variation of the energy of the transmitting light120applied on the mirror94(as shown inFIG. 3A) is too large, the amplitude of the scanning element110is affected to be deviated from the predetermined range, causing the misalignment of the scanning path of the scanning element110(for example but not limited to the changes of the first scanning path and the second scanning path) and further causing the blur of the projection frame84. Here, the time difference between the distorted signal123(i.e. the sensing signal received by the control module114when the projection frame84is blur) and the sensing signal122originally received by the control module114when the optical scanning projection system100operates normally is T μs (i.e. TP2−TP1, where TP2is the time difference between the rising edge of the distorted signal123and the rising edge of the reference signal128).

To make the projection frame84clear, the control module114delays the time of the rising edge of the synchronization signal126of T μs (i.e. TL2−TL1, where TL2is the time difference between the rising edge of the compensation signal127and the rising edge of the reference signal128) so that the time difference between the compensation signal127and the distorted signal123is identical to the original time difference between the synchronization signal126and the sensing signal122obtained when the optical scanning projection system100operates normally. Thus, the projection frame84becomes clear, but this embodiment is not intended to limit the scope of the present disclosure. The rising edge refers to a portion of a signal raised from a low level to a high level.

Furthermore,FIG. 4is a schematic architectural view of an optical scanning projection system according to a second embodiment of the present disclosure. The optical scanning projection system100may further include a first reflecting element104, which is configured between the scanning light source component102and the transparent element108and is used to change the path of the main light beam116incident on the transparent element108. The first reflecting element104may include a first reflecting surface80, which may be, but is not limited to, a metal layer or a coated reflective layer. The details of the operation of the optical scanning projection system100of this embodiment will not be repeated herein again.

FIG. 5is a schematic architectural view of an optical scanning projection system according to a third embodiment of the present disclosure.FIG. 6Ais a schematic view of a detection frame ofFIG. 5, andFIG. 6Bis a schematic view of a projection frame, a light exit aperture and a test area ofFIG. 5. The optical scanning projection system300may include, but not limited to, a scanning light source component302, a transparent element304, a first reflecting element306, a second reflecting element308, a scanning element310, a photosensitive element312and a control module314. The first reflecting element306may include a first reflecting surface46, which may be, but is not limited to, a metal layer or a coated reflective layer. The second reflecting element308includes a second reflecting surface47, which may be, but is not limited to, a metal layer or a coated reflective layer. The transparent element304may be, but is not limited to, glass and may be a protection cover of the scanning element310, and the transparent element304is configured on the scanning element310. The scanning element310may be, but is not limited to, a scanning mirror, and the photosensitive element312may be, but is not limited to, a PD.

The scanning light source component302emits a main light beam316. The first reflecting element306receives and reflects the main light beam316, and the transparent element304receives the main light beam316from the first reflecting element306and reflects a part of the main light beam316. Such reflected part of the main light beam316is called a reflected light318which is, but not limited to, five percent of the main light beam316, but this embodiment is not intended to limit the scope of the present disclosure. The second reflecting element308reflects the reflected light318, and the scanning element310reflects the reflected light318reflected by the second reflecting element308in a scanning manner to obtain a detection frame320. The detection frame320includes a detection line322. The light intensity of the detection line322does not change with time. In other words, the light intensity of the detection line322remains constant when the detection frame320changes. The photosensitive element312is used to sense the detection line322and outputs a sensing signal324. The control module314actuates or stops actuating the scanning light source component302according to the sensing signal324.

In this embodiment, the optical scanning projection system300may further include a housing325, which includes a light exit aperture326and a test area328. The test area328may be configured, but not limited to, on the light exit aperture326. The transparent element304allows a part of the main light beam316to transmit. Such transmitting part of the main light beam316is referred to as a transmitting light330hereinafter which is incident on the scanning element310. The scanning element310reflects the transmitting light330in a scanning manner. The transmitting light330equals, but is not limited to, ninety-five percent of the main light beam316. However, this embodiment is not intended to limit the scope of the present disclosure. A part of the transmitting light330reflected by the scanning element310passes through the light exit aperture326to form a projection frame332. A part of the transmitting light330reflected by the scanning element310is blocked by the test area328and cannot form the projection frame332. The test area328includes a test line334, which corresponds to the detection line322.

In this embodiment, the optical scanning projection system300may further include a scan driving unit323. The control module314controls the scan driving unit323by the reference signal340, and the scan driving unit323drives the scanning element310by the reference signal340. The control module314outputs a synchronization signal to control the scanning light source component302. Besides the control module314adjusts the output time of the synchronization signal according to the time difference between the sensing signal324, the synchronization signal and the reference signal340. Here, the details of the control module314adjusting the synchronization signal will not be described herein again.

FIG. 7is a schematic architectural view of an optical scanning projection system according to a fourth embodiment of the present disclosure. The optical scanning projection system500includes a scanning light source component502, a detection light source504, a laser driving unit505, a first reflecting element506, a second reflecting element550, a scanning element508, a photosensitive element510and a control module512. The detection light source504may be, but is not limited to, a semiconductor laser or a solid-state laser. The first reflecting element506may include a first reflecting surface507, which may be, but is not limited to, a metal layer. The second reflecting element550may include a second reflecting surface551, which may be, but is not limited to, a coated reflective layer. The scanning element508may be, but is not limited to, a scanning mirror, and the photosensitive element510may be, but is not limited to, a PD.

In this embodiment, the scanning light source component502may include, but not limited to, a light source600, a light source610, a light source620, a photometer602, a photometer612and a photometer622. The light source600may emit a red light beam604; the light source610may emit a green light beam614, and the light source620may emit a blue light beam624. The light source600, the light source610and the light source620may be, but are not limited to, semiconductor lasers. The photometer602, the photometer612and the photometer622are used to respectively detect if the light source600, the light source610and the light source620respectively emit the red light beam604, the green light beam614and the blue light beam624. The photometer602may be built in the light source600, and the control module612may determine if the light source600, the light source610and the light source620are damaged according to the detection results of the light source600, the light source610and the light source620made by the photometer602, the photometer612and the photometer622, but this embodiment is not intended to limit the scope of the present disclosure.

The scanning light source component502may emit a main light beam514, and the detection light source504may emit a detection light beam516. In this embodiment, the main light beam514may include the red light beam604, the green light beam614and the blue light beam624. The detection light beam516may be, but is not limited to, red light, but this embodiment is not intended to limit the scope of the present disclosure. It should be noted that the laser driving unit505continuously drives the detection light source504to emit the detection light beam516.

The first reflecting element506receives and reflects the main light beam514; the second reflecting element550receives and reflects the detection light beam516, and the scanning element508reflects both the main light beam514from the first reflecting element506and the detection light beam516from the second reflecting element550in a scanning manner to respectively generate a projection frame540and a detection frame542. In other words, the main light beam514is reflected by the first reflecting element506to the scanning element508, and then is reflected by the scanning element508in a scanning manner to form the projection frame540. The detection light beam516is reflected by the second reflecting element550to the scanning element508and then is reflected by the scanning element508in a scanning manner to form the detection frame542.

With respect to the scanning manner, the direction and amplitude of the scanning element508are controlled to reflect the incident light source (i.e. the main light beam514incident on the scanning element508and the detection light beam516) to form the projection frame540and the detection frame542. The amplitude of the scanning element508relates to the energy of the incident light source, but when the scanning element508operates normally, the amplitude of the scanning element508is controlled in a predetermined range. In this embodiment, the predetermined range may be, but is not limited to, ±90°. The details of the scanning manner will not be described herein again.

The photosensitive element510receives the detection light beam516from the scanning element508and outputs a sensing signal520. The control module512actuates or stops actuating the scanning light source component502according to the sensing signal520. When the photosensitive element510cannot receive the detection light beam516from the scanning element508, the control module512stops actuating the scanning light source component502according to the sensing signal520.

In this embodiment, the optical scanning projection system500may further include a scan driving unit523. The control module512controls the scan driving unit523by the reference signal528, and the scan driving unit523may drive the scanning element508by the reference signal528. The control module512outputs the synchronization signal to control the scanning light source component502. The control module512may adjust the output time of the synchronization signal according to the time difference between the sensing signal520, the synchronization signal and the reference signal528. Here, the details of the control module512adjusting the synchronization signal will not be described herein again.

According to the optical scanning projection system of the present disclosure, the transparent element is configured between the first reflecting element and the scanning element, so that the light that originally is not used to form the projection frame (i.e. the reflected light reflected by the transparent element) may be incident on the scanning element. The scanning element may generate the detection frame in the optical scanning projection system by the reflected light. The photosensitive element is configured in the detection frame, so that as soon as the scanning element is faulty and cannot operate, the control module may instantly stop actuating the scanning light source component. Such timely stop can avoid the single bright spot on the image projected by the optical scanning projection system due to the failure of the scanning element and, therefore, avoid viewers' eyes being harmed by such bright spot. On the other hand, in order to avoid the photosensitive element unable to output the corresponding distinguishable sensing signal due to the insufficient light intensity of the detection frame, either the photosensitive element is provided and the light intensity of the detection line does not change with time or the detection light source is provided. Therefore, the photosensitive element is guaranteed to correctly output the corresponding sensing signal. Therefore, the safety of the optical scanning projection system of the present disclosure may be improved. Moreover, with respect to compensation of the blur projection frame caused by the changes of the amplitude of the scanning element, the output time of the synchronization signal is adjusted through the time differences between the synchronization signal, the reference signal and the sensing signal which are received and transferred by the control module.