Abstract:
A method for controlling a power of a laser emitting unit includes: receiving a reflected light from an object, where the object reflects light emitted from the laser emitting unit; determining a power of the reflected light; and determining a control signal by referring to a level of the power of the reflected light to control the power of the laser emitting unit.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the priority of US Provisional Application No. 61/949,248, filed on Mar. 7, 2014, which is included herein by reference in its entirety. 
     
    
     BACKGROUND 
       [0002]    Ina conventional optical pick-up head unit (OPU) of a selective laser sintering (SLS) machine or an optical disc drive, a front monitor photodiode sensor (FMD) is used for measuring a power of a laser diode to compensate/adjust the power of the laser diode. However, the FMD increases the manufacturing cost of the OPU. 
         [0003]    In addition, the characteristics of the power of the laser diode will be varied under an environment of varied temperatures, therefore, the conventional OPU may include a temperature sensor to obtain the current temperature, and the OPU needs to find the relationship between the laser power and laser driving current under many different temperatures to build many models, and the OPU may select one model to compensate/adjust the power of the laser diode. However, the temperature sensor also increases the manufacturing cost of the OPU, and it may be difficult to find the appropriate model due to the varied characteristics of the laser diode and/or laser diode aging issue. 
       SUMMARY 
       [0004]    It is therefore an objective of the present invention to provide a method for controlling a power of a laser emitting unit and associated apparatus, which may compensate/adjust the power of the laser diode by using a determined power of a reflected light sensed by a photo detector integrated circuit (PDIC), that is the FMD and the temperature sensor are not used to save the manufacturing cost, and the method and apparatus of the present invention does not need to build models and the power of the laser diode can be accurately compensated even under laser diode aging issue. 
         [0005]    According to one embodiment of the present invention, a method for controlling a power of a laser emitting unit comprises: receiving a reflected light from an object, where the object reflects light emitted from the laser emitting unit; determining a power of the reflected light; and determining a control signal by referring to a level of the power of the reflected light to control the power of the laser emitting unit. 
         [0006]    According to another embodiment of the present invention, an apparatus for controlling a power of a laser emitting unit comprises a photo detector integrated circuit and power control circuit. The photo detector integrated circuit is arranged for receiving a reflected light from an object, where the object reflects light emitted from the laser emitting unit. The power control circuit is coupled to the photo detector integrated circuit, and is arranged for determining a power of the reflected light, and determining a control signal by referring to a level of the power of the reflected light to control the power of the laser emitting unit. 
         [0007]    These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]      FIG. 1  is a diagram illustrating a SLS machine according to one embodiment of the present invention. 
           [0009]      FIG. 2  is a diagram showing a power-control signal curves generated off-line and on-line. 
           [0010]      FIG. 3  is a diagram illustrating an optical disc drive according to one embodiment of the present invention. 
           [0011]      FIG. 4  is a flow chart of a method for controlling a power of the LD according to a first embodiment of the present invention. 
           [0012]      FIG. 5  is a diagram showing a power-control signal curves generated off-line and on-line. 
           [0013]      FIG. 6  is a diagram illustrating how to obtain the power of the reflected light of the plastic layer. 
           [0014]      FIG. 7  is a flow chart of a method for controlling a power of the LD according to a second embodiment of the present invention. 
           [0015]      FIG. 8  shows LBAs and corresponding powers of the reflected light. 
           [0016]      FIG. 9  is a flow chart of a method for controlling a power of the LD according to a third embodiment of the present invention. 
           [0017]      FIG. 10  shows the current of the LD when the optical disc drive  300  writes data into the optical disc, and the sampling signals for the sample and hold circuit. 
           [0018]      FIG. 11  is a flow chart of a method for controlling a power of the LD according to a fourth embodiment of the present invention. 
           [0019]      FIG. 12  is a flow chart of a method for controlling a power of the LD according to a fifth embodiment of the present invention. 
           [0020]      FIG. 13  is a flow chart of a method for controlling a power of the LD according to a sixth embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0021]    Certain terms are used throughout the following description and claims to refer to particular system components. As one skilled in the art will appreciate, manufacturers may refer to a component by different names. This document does not intend to distinguish between components that differ in name but not function. In the following discussion and in the claims, the terms “including” and “comprising” are used in an open-ended fashion, and thus should be interpreted to mean “including, but not limited to . . . ” The terms “couple” and “couples” are intended to mean either an indirect or a direct electrical connection. Thus, if a first device couples to a second device, that connection may be through a direct electrical connection, or through an indirect electrical connection via other devices and connections. 
         [0022]    Please refer to  FIG. 1 , which is a diagram illustrating a SLS machine  100  according to one embodiment of the present invention, where the SLS machine uses a laser as the power source to sinter powdered material (e.g. metal powder), aiming the laser automatically at points in space defined by a 3D model, binding the powdered material together to create a solid structure. In this embodiment, the SLS machine  100  comprises a PDIC  110 , a power control circuit  120 , a laser driver  130 , a light emitting unit (in this embodiment, a laser diode (LD)  140 ), two lens  152  and  154 , and a component  160 , where the component  160  can be any component having a suitable surface or smooth surface for reflecting light emitted from the LD  140 . 
         [0023]    In the operations of the SLS machine  100 , the power control circuit  120  is arranged for generating a control signal S c , and the laser driver  130  receives the control signal S c  to control a current of the LD  140  (i.e. control a power of the LD  140 ). Then, the LD  140  emits light to the powdered material via the lens  150  and  154  to sinter the powdered material. However, because the relationship between the control signal S c  generated by the power control circuit  120  and the power of the LD  140  may not be always the same, therefore, the PDIC  110  and the power control circuit  120  provide a mechanism to accurately compensate/adjust the power of the LD  140 . It is noted that the control signal S c  generated by the power control circuit  120  can be implemented by many types. For example but not limited to, the control signal can be a control voltage, a control current or a DSP (digital signal processor) parameter for the laser driver  130 , and the DSP parameter can be an auto power control parameter saved in a DAC (digital analog converter) register. 
         [0024]    In the operations of the PDIC  110  and the power control circuit  120 , the PDIC  110  receives the reflected light from the powdered material, and the power control circuit  120  determines a power of the reflected light, and determines the control signal in response to the power of the reflected light to control the power of the LD  140 . In detail, referring to  FIG. 2 , which is a diagram showing a power-control signal curves generated off-line and on-line. When the SLS machine  100  is in the production line, the power control circuit  120  generates at least two control signals S c1  and S c2  to control the power of the LD  140 , and the PDIC  110  receives the reflected light (from the powdered material) corresponding to the control signals S c1  and S c2 , respectively. Then, the power control circuit  120  can build an off-line power-control signal curve. It is noted that, in the embodiment it is assumed that the relationship (e.g. the ratio) between the power of the LD  140  and the power of the reflected light from the powdered material is determined and is always the same, therefore, the term “power” shown in  FIG. 2  can refer to the power of the LD  140  or the power of the reflected light sensed by the PDIC  110 . In other words, in the production line, the relationship between power of the LD  140 /reflected power/control signal S c  are known. 
         [0025]    When the SLS machine  100  is in use, because the off-line power-control signal curve may not be appropriate for use to compensate/adjust the power of the LD  140  due to the environment issue or laser diode aging issue, the power control circuit  120  generates at least two control signals S c1H  and S c2H  to control the power of the LD  140 , and the PDIC  110  receives the reflected light (from the powdered material) corresponding to the control signals S c1H  and S c2H , respectively. Then, the power control circuit  120  can build an on-line power-control signal curve. Therefore, when the SLS machine  100  is in use, the PDIC  110  may continuously receive the reflected light, and the power control circuit  120  may continuously determine the power of the reflected light received by the PDIC  110 , or may periodically determine the power of the reflected light received by the PDIC  110 , to generate the control signal S c  by referring to a level of the power of the reflected light to compensate/adjust the power of the LD  140 . 
         [0026]    For example, assuming that the LD  140  is required to emit light having power PW 1 , and because the power of the reflected light from the powdered material is determined and is always the same, the target power of the reflected light is known (hereafter PW 2 ). Therefore, the power control circuit  120  may refer to the power of the reflected light to compensate/adjust the power of the LD  140  to make the power of the reflected light equal to or closer to PW 2 , and at this time the LD  140  should have the required power PW 1 . 
         [0027]    In addition, in the above-mentioned embodiment, the power control circuit  120  generates the control signal S c  by referring to a level of the power of the reflected light from the powdered material. However, in other embodiment, the power control circuit  120  may generate the control signal S c  by referring to a level of the power of the reflected light from the component  160  such as an metal sheet within the SLS machine  100 , that is when the power of the LD  140  is intended to be compensated/adjusted, the LD  140  will emit light to the component  160 , and the PDIC  110  will receive the reflected light from the component  160 . This alternative design shall fall within the scope of the present invention. 
         [0028]    Please refer to  FIG. 3 , which is a diagram illustrating an optical disc drive  300  according to one embodiment of the present invention. As shown in  FIG. 3 , the optical disc drive  300  comprises a PDIC  310 , a power control circuit  320 , a laser driver  330 , a light emitting unit (in this embodiment, a laser diode (LD)  340 ), two lens  352  and  354 , and a component  360 , where the component  360  can be any component having a suitable surface or smooth surface for reflecting light emitted from the LD  340 . In addition, the optical disc drive  300  is arranged for writing data into an optical disc  370  or reading data from the optical disc  370 , where the optical disc  370  mainly includes a reflective layer  372  for recording data and a plastic layer  374 . 
         [0029]    In the operations of the optical disc drive  300 , the power control circuit  320  is arranged for generating to a control signal S c , and the laser driver  330  receives the control signal to control a current of the LD  340  (i.e. control a power of the LD  340 ). Then, the LD  340  emits light to the optical disc via the lens  350  and  354  to read data from the optical disc  370  or to write data into the optical disc  370 . However, because the relationship between the control signal generated by the power control circuit  320  and the power of the LD  340  may not be always the same, therefore, the PDIC  310  and the power control circuit  320  provide a mechanism to accurately compensate/adjust the power of the LD  340 . 
         [0030]    Please refer to  FIG. 4 , which is a flow chart of a method for controlling a power of the LD  340  according to a first embodiment of the present invention. It is noted that in the production line, the optical disc drive  300  has built an off-line power-control signal curve as shown in  FIG. 5 . In detail, referring to  FIG. 4 , in the production line, the power control circuit  320  generates at least two control signals S c1  and S c2  to control the power of the LD  340 , and the PDIC  310  receives the reflected light (from the plastic layer  374  of the optical disc  370  or from the component  360 ) corresponding to the control signals S c1  and S c2 , respectively. Then, the power control circuit  320  can build an off-line power-control signal curve. It is noted that, in the embodiment it is assumed that the relationship (e.g. the ratio) between the power of the LD  340  and the power of the reflected light from the plastic layer  374 /component  360  is determined and is always the same, therefore, the term “power” shown in  FIG. 4  can refer to the power of the LD  340  or the power of the reflected light sensed by the PDIC  310 . In other words, in the production line, the relationship between power of the LD  340 /reflected power/control signal S c are known. Referring to  FIGS. 3-5  together, the flow is described as follows. 
         [0031]    In Step  400 , the flow starts. In Step  402 , the power control circuit  320  compensates a power-control signal curve by determining at least two control signals and corresponding powers of the reflected light of the plastic layer  374  of the optical disc  370  or corresponding powers of the reflected light from the component  360  of the optical disc drive  300 . In detail, because the off-line power-control signal curve may not be appropriate for use to compensate/adjust the power of the LD  340  due to the environment issue or laser diode aging issue, the power control circuit  320  generates at least two control signals S c1H  and S c2H  to control the power of the LD  340 , and the PDIC  310  receives the reflected light (from the powdered material) corresponding to the control signals S c1H  and S c2H , respectively. Then, the power control circuit  320  can build an on-line power-control signal curve. 
         [0032]    Then, in Step  404 , when the optical disc drive is in use, the PDIC  310  receives the reflected light of a plastic layer  374  of the optical disc  370  or the reflected light from the component  360  of the optical disc drive  300 . In Step  406 , the power control circuit  320  determines a power of the reflected light of the plastic layer  374  or a power of the reflected light from the component  360 . Finally, in Step  408 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to compensate/adjust the power of the LD  340 . 
         [0033]    It is note that the steps  404 - 408  can be continuously performed or periodically performed to compensate/adjust the power of the LD  340 . 
         [0034]    In addition, referring to  FIG. 6 , which is a diagram illustrating how to obtain the power of the reflected light of the plastic layer  374 . Referring to  FIG. 6 , by moving the lens to adjust the focus position, the power of the reflected light of the plastic layer  374  and the power of the reflected light of the reflective layer  372  are obtained. Because the power of the reflected light of the plastic layer  374  should be much smaller than the power of the reflected light of the reflective layer  372 , therefore, the power of the reflected light of the plastic layer  374  can be obtained by determining the powers of the reflected light sensed by the PDIC  310 . 
         [0035]    Please refer to  FIG. 7 , which is a flow chart of a method for controlling a power of the LD  340  according to a second embodiment of the present invention. Referring to  FIG. 3  and  FIG. 7  together, the flow is described as follows. 
         [0036]    In Step  700 , the flow starts. In Step  702 , the PDIC  310  senses the reflected light of the reflective layer  372  from many different areas of the optical disc  300 , and the power control circuit  320  records the powers of the reflected light of the reflective layer  372  from many different areas of the optical disc  300 . For example, referring to  FIG. 8 , the optical disc  370  has four logical block addressing LBA 1 -LBA 4 , and the power control circuit  320  records the powers RFL 1 -RFL 4  of the reflected light from the LBA 1 -LBA 4 . In addition, for the boundary between two LBAs such as LBAX 1 -LBAX 5 , an interpolation method can be performed to generate the power of the reflected light. 
         [0037]    Then, in Step  704 , when the power of the LD  340  is to be compensated/adjusted, the power control circuit  320  measures the power of the reflected light of the reflective layer  372  of the optical disc  370 . In Step  706 , the power control circuit  320  determines whether the reflected light is from a data area or a blank area of the reflective layer  372  of the optical disc  370 , for example, in  FIG. 8 , “Blank 1 = 0 ” means that the LBA 1  is data area, and “Blank 3 = 1 ” means that the LBA 3  is blank area. Then, in Step  708 , the power control circuit  320  determines the power of the reflected light of the reflective layer  372  by adjusting the measured power with a parameter corresponding to the data area or with another parameter corresponding to the blank area. Finally, in Step  710 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to compensate/adjust the read power of the LD  340 . 
         [0038]    Please refer to  FIG. 9 , which is a flow chart of a method for controlling a power of the LD  340  according to a third embodiment of the present invention. In addition, in the flow chart of  FIG. 9 , it is assumed that the relationship between power of the LD  340 /reflected power/control signal S c  are obtained. Referring to  FIG. 3  and  FIG. 9  together, the flow is described as follows. 
         [0039]    In Step  900 , the flow starts. In Step  902 , the power control circuit  320  determines the power of the reflected light of the reflective layer  372  of the optical disc  370  when the optical disc drive  300  writes data into the optical disc  370 . For example, referring to  FIG. 10 , which shows the current of the LD  340  when the optical disc drive  300  writes data into the optical disc  370 , that is I LD  or I LD ′, and the power control circuit  320  may use a sample and hold (S/H) circuit to use the sampling signals P 1 , P 2  or P 3  to sample the signal from the PDIC  310  (the waveform of the signal from the PDIC  310  is similar to I LD  or I LD ′) to obtain the power of the of the reflected light of the reflective layer  372  of the optical disc  370 . Then, in Step  904 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to compensate/adjust the write power of the LD  340 . 
         [0040]    Please refer to  FIG. 11 , which is a flow chart of a method for controlling a power of the LD  340  according to a fourth embodiment of the present invention. In addition, in the flow chart of  FIG. 11 , it is assumed that the relationship between power of the LD  340 /reflected power/control signal S c  are obtained, and the optical disc  370  is a Digital Versatile Disc Random Access Memory (DVD-RAM). Referring to  FIG. 3  and  FIG. 11  together, the flow is described as follows. 
         [0041]    In Step  1100 , the flow starts. In Step  1102 , the power control circuit  320  determines a power of the reflected light from a header of a reflective layer  372  of the optical disc when the optical disc drive writes data into the DVD-RAM. Then, in Step  1104 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to compensate/adjust the read/write power of the LD  340 . 
         [0042]    Please refer to  FIG. 12 , which is a flow chart of a method for controlling a power of the LD  340  according to a fifth embodiment of the present invention. In addition, in the flow chart of  FIG. 12 , it is assumed that the relationship between power of the LD  340 /reflected power/control signal S c  are obtained. Referring to  FIG. 3  and  FIG. 12  together, the flow is described as follows. 
         [0043]    In Step  1200 , the flow starts. In Step  1202 , the power control circuit  320  determines a power of the reflected light of a reflective layer  372  of the optical disc  370  when the optical disc drive  300  reads data from the optical disc  370 . Then, in Step  1204 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to pre-compensate/pre-determine the write power of the LD  340  for further use. 
         [0044]    Please refer to  FIG. 13 , which is a flow chart of a method for controlling a power of the LD  340  according to a sixth embodiment of the present invention. In addition, in the flow chart of  FIG. 13 , it is assumed that the relationship between power of the LD  340 /reflected power/control signal S c  are obtained. Referring to  FIG. 3  and  FIG. 13  together, the flow is described as follows. 
         [0045]    In Step  1300 , the flow starts. In Step  1302 , the power control circuit  320  determines a power of the reflected light of a reflective layer  372  of the optical disc  370  when the optical disc drive  300  writes data into the optical disc  370 . Then, in Step  1304 , the power control circuit  320  determines the control signal S c  by referring to a level of the determined power to pre-compensate/pre-determine the read power of the LD  340  for further use. 
         [0046]    For the above-mentioned embodiments about the step of determining the control signal S c  by referring to a level of the determined power to compensate the power of the LD  340 , for example, assuming that the LD  340  is required to emit light having power PW 1 , and because the power of the reflected light from the powdered material is determined and is always the same, the target power of the reflected light is known (hereafter PW 2 ). Therefore, the power control circuit  320  may refer to the power of the reflected light to compensate/adjust the power of the LD  340  to make the power of the reflected light equal to or closer to PW 2 , and at this time the LD  340  should have the required power PW 1 . 
         [0047]    In light of above, in the method and associated apparatus of the present invention, a power of the reflected light is used to determine the control signal to control the power of the laser diode, therefore, the FMD and the temperature sensor are not used to save the manufacturing cost. In addition, the method and apparatus of the present invention does not need to build models and the power of the laser diode can be accurately compensated even under environment issue or laser diode aging issue. 
         [0048]    Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims.