JP2005326340A - Image sensor using apparatus, optical displacement gage, and optical information reading device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image sensor using apparatus capable of utilizing sufficiently a dynamic range, while avoiding saturation of the accumulated charge of the image sensor. <P>SOLUTION: The image sensor is equipped with a plurality of pixel constitution parts having charge generation parts PD0, PD1 for generating the charge corresponding to the light receiving quantity and charge accumulation parts C0, C1 for accumulating the generated charge, shutter means TR20, TR21 for controlling simultaneously accumulation start and accumulation stop of the charge in the plurality of pixel constitution parts, a plurality of comparators CMP0, CMP1 for comparing individually the accumulated charge with a reference value in each pixel constitution part, a control input terminal of the shutter means, and a terminal for outputting a logic sum signal of output signals from the plurality of comparators. A control part is constituted so that accumulation stop of the charge in each pixel constitution part is executed by controlling the shutter means of the image sensor when at least one of outputs from the plurality of comparators of the image sensor shows that the accumulated charge becomes larger than the reference value. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an apparatus using an image sensor to which an automatic charge accumulation time control function is added in order to avoid saturation of each pixel.

  As this type of image sensor device, an optical displacement meter that measures the displacement of an object using an image sensor, an optical reader such as a barcode reader that reads an image pattern using an image sensor, and other optical devices Includes electronics. In these image sensor utilizing devices, it is important to appropriately adjust the charge accumulation time in each pixel component of the image sensor. The charge accumulation time (sometimes simply the accumulation time) corresponds to the exposure time (shutter time). If this is not appropriate, the image of the object will be too dark or conversely too bright, and the object will be displaced. It becomes difficult to accurately perform measurement and image pattern recognition. In addition, since the amount of light received by the image sensor varies depending on the intensity of illumination light and the reflectance of an object, it is necessary to set an appropriate charge accumulation time according to them.

  In general, the greater the maximum amount of light received, the more fully the dynamic range of the image sensor can be utilized, so the accuracy of displacement measurement and image pattern recognition is improved. However, if the maximum amount of received light is set large, saturation of the amount of received light for each pixel (saturated accumulated charge) is likely to occur. When saturation occurs, for example, in the case of an optical displacement meter using the principle of triangulation, the peak position of the light distribution waveform obtained from the linear image sensor becomes unclear, and the displacement of the object can be detected correctly. Disappear. Similarly, in an optical reader, there is a risk of erroneous recognition of an image pattern due to saturation.

As a conventional method for avoiding the saturation of the accumulated charge as described above, for example, in the optical displacement meter described in Patent Document 1, the light emission amount of the laser diode based on the light reception amount data obtained from the linear image sensor. Control is performed. That is, saturation is prevented by controlling the peak output or light emission time (pulse width) of the laser diode based on digital data obtained by AD conversion of the output signal of the linear image sensor. Alternatively, saturation is prevented by controlling the accumulation time (exposure time or shutter time).
JP-A-10-267648

  Control of the light emission amount or accumulation time for avoiding saturation in the conventional optical displacement meter as described above is performed based on the received light waveform obtained from the linear image sensor. The received light waveform, which is a one-dimensional received light amount distribution, is obtained by calculating the received light amount data obtained from the linear image sensor. After reading this received light waveform for one frame, it is determined whether or not it is saturated after the next frame, and the light emission amount or the accumulation time is controlled based on the determination result. Delay occurs. Specifically, when transfer and waveform calculation are performed simultaneously, a delay of 2 frames may be sufficient, but when transfer and waveform calculation are not simultaneous, a delay of 3 frames or more is required.

  Due to this delay in feedback control, if the sampling period is shortened (high-speed sampling), saturation may not be avoided accurately. For example, when the control for reducing the light emission amount or the accumulation time is executed based on the data when the light reception amount is sufficiently large (light reception waveform), the actual light reception amount has already greatly decreased due to the change in the reflectance of the object. There may be. On the contrary, when the control for increasing the light emission amount or the accumulation time is executed based on the data (light reception waveform) when the light reception amount is small, the actual light reception amount greatly increases due to the change in the reflectance of the object. May have. In this case, saturation occurs and correct measurement values cannot be obtained.

  Further, the peak position cannot be determined from the received light waveform when saturation occurs, and it is also difficult to determine the degree of saturation. For this reason, when the control for decreasing the light emission amount or the accumulation time is executed step by step, the saturation state may continue for several frames.

  In addition, when controlling the light emission amount by the light emission time (pulse width) of the laser diode, since the pulse width is normally controlled in units of clocks, saturation cannot be avoided even if the light emission amount is reduced to the minimum pulse width. There is. For example, such a situation is likely to occur when the surface of the object is a highly reflective mirror surface.

  The above-described problems become particularly noticeable when a CMOS image sensor is used as the image sensor. The CMOS image sensor has an advantage that it can be systematized by adding an on-chip function, but the dynamic range is narrower than that of the CCD and saturation is likely to occur. In addition, the above-described problem relating to saturation is not limited to an optical displacement meter, but is a problem common to various image sensor-utilizing devices such as an optical reading device and an imaging device.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an image sensor utilizing device to which an accumulation time automatic control function for avoiding saturation of accumulated charge for each pixel is added. On the other hand, it is an object of the present invention to optimize the operation of the signal processing circuit when the accumulated charge is small.

  A first configuration of an apparatus using an image sensor according to the present invention includes an image sensor that receives light from an object and generates an image signal, and a control unit that processes a signal from the image sensor. In the application device, the image sensor includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge, and a plurality of pixels Shutter means for controlling the start and stop of charge accumulation in accordance with the amount of received light in the components substantially simultaneously for all pixel components, and values corresponding to accumulated charges in a plurality of pixel components separately from a common reference value A plurality of comparators for comparison, a control input terminal of the shutter means, and a terminal for outputting a logical sum signal of the output signals of the plurality of comparators; When at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value, the control unit controls the shutter means of the image sensor to control the charge of each pixel component. The storage is configured to be stopped.

  According to such a configuration, by setting the reference value to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. Therefore, saturation can be avoided while fully utilizing the dynamic range of the image sensor.

  According to a second configuration of the image sensor using device according to the present invention, in the first configuration, when the control unit has passed a predetermined upper limit time from the start of charge accumulation in each pixel configuration unit of the image sensor. Further, the shutter means is controlled to stop the accumulation of electric charges in each pixel constituent unit.

  According to such a configuration, if for some reason the amount of received light is small and the elapsed time from the start of accumulation becomes abnormally long, the charge accumulation is forcibly stopped in each pixel component, so the charge accumulation is completed There is no need to wait for a long time for reading. Whether or not the elapsed time has exceeded a predetermined upper limit time may be determined by the control unit by software, or may be determined by an output signal of a timer circuit provided separately.

  According to a third configuration of the image sensor of the present invention, in the second configuration described above, an AD converter that converts an analog voltage signal from the image sensor into a digital signal and supplies the digital signal to the control unit; A maximum value acquisition unit that acquires a voltage corresponding to the maximum value, and a reference voltage that determines a conversion voltage range of the AD converter can be changed and set according to an output of the maximum value acquisition unit.

  According to such a configuration, when the charge accumulation stop in each pixel component is executed as the upper limit time elapses before the accumulated charge in any pixel component is saturated, a plurality of pixel components The conversion voltage range (reference voltage) of the AD converter can be changed and set according to the maximum value of the accumulated charge at. For example, when the voltage corresponding to the maximum value is 3V with respect to the accumulated charge saturation voltage of 5V, the conversion voltage range of the AD converter is changed from 0 to 5V (reference voltage 5V) to 0 to 3V (reference voltage 3V). ). By doing so, the dynamic range of the signal processing circuit obtained from the image sensor can be optimized. The maximum value acquisition unit may be provided outside the image sensor or may be built in the image sensor. In the case of a CMOS image sensor, it is relatively easy to incorporate a circuit corresponding to the maximum value acquisition unit in the image sensor as an on-chip function.

  According to a fourth configuration of the image sensor of the present invention, in the second configuration, a binarization circuit that binarizes the analog voltage signal from the image sensor by comparing it with a threshold voltage and supplies the binarization circuit to the control unit; A maximum value acquisition unit that acquires a voltage corresponding to the maximum value of accumulated charge in a plurality of pixel components, and a threshold value that changes and sets the threshold voltage of the binarization circuit according to the output of the maximum value acquisition unit And a setting circuit.

  According to such a configuration, in an optical reader such as a barcode reader, for example, the analog voltage signal from the image sensor is binarized and input to the control unit, and the binarized image (monochrome image) is input by the control unit. ), The threshold value for binarization can be set optimally. This improves the reading accuracy (pattern discrimination accuracy) of barcodes and the like. As in the third configuration, the maximum value acquisition unit may be provided outside the image sensor or may be built in the image sensor.

  According to a fifth configuration of the image sensor of the present invention, in any one of the configurations described above, the image sensor further includes a light-emission element with a variable light emission amount for irradiating the object with light. When the time from the start of charge accumulation to the stop of accumulation is shorter than a predetermined lower limit time, control for reducing the light emission amount of the light emitting element is performed.

  According to such a configuration, if the accumulation time is shorter than the lower limit time as a result of the automatic control of the charge accumulation time in each pixel component of the image sensor by the control unit as described above, it is considered that the light emission amount is too large. Therefore, the control unit can contribute to a reduction in power consumption by performing control to reduce the light emission amount.

  A sixth configuration of the image sensor according to the present invention includes a light emitting element with variable light emission for irradiating the object with light, an image sensor for receiving light from the object and generating an image signal, In an apparatus using an image sensor having a control unit that processes a signal from the image sensor, the image sensor includes an array including a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge. A plurality of pixel components arranged in a shape, shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components, and the plurality of pixel components A plurality of comparators for individually comparing the value corresponding to the accumulated charge in the common reference value, and a terminal for outputting a logical sum signal of the output signals of the plurality of comparators And the control unit controls to reduce the light emission amount of the light emitting element when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value. It is characterized by.

  According to such a configuration, the control unit performs the automatic control of the light emission amount of the light emitting element instead of the automatic control of the charge accumulation time in each configuration described above (or together with the automatic control of the charge accumulation time). By setting the reference value to the value just before saturation, the amount of light emitted from the light emitting element is reduced just before the charge accumulated in any pixel component is saturated, and saturation is avoided while fully utilizing the dynamic range of the image sensor. can do. Further, according to this configuration, even when automatic control of the charge accumulation time by the shutter means is difficult from the viewpoint of the S / N ratio, saturation can be effectively avoided by controlling the light emission amount of the light emitting element. It becomes possible. For example, when the light emitting element is pulse-driven, the light emission amount can be controlled by changing the pulse width or the duty ratio, or by changing the peak voltage.

  According to a seventh configuration of the image sensor of the present invention, in any one of the configurations described above, a plurality of pixel configurations that are provided with a selection unit that sets each of the plurality of pixel configuration units to be valid or invalid are enabled. The operation of the comparator is effective for the part.

  According to such a configuration, for example, the comparison with the common reference value by the comparator is enabled for the pixel configuration unit in the effective pixel range excluding the peripheral portion, not the pixel configuration unit of the entire pixel range of the image sensor. be able to. Furthermore, even within the effective pixel range, it is possible to make effective comparison with a common reference value by, for example, every other comparator instead of all pixel components.

  According to an eighth configuration of the image sensor of the present invention, in the third or fourth configuration, a selection unit that sets each of the plurality of pixel components is set to be valid or invalid. The maximum value acquisition unit functions with respect to the pixel configuration unit.

  According to such a configuration, for example, not the pixel configuration unit in the entire pixel range of the two-dimensional image sensor but only the pixel configuration unit in the effective pixel range excluding the peripheral portion can be set as the target for obtaining the maximum value. Furthermore, even within the effective pixel range, the maximum value can be acquired, for example, every other pixel component, instead of every other pixel component.

  A first configuration of an optical displacement meter according to the present invention includes a light projecting unit for irradiating light on an object, an image sensor that receives reflected light from the object and generates an image signal for each sampling, In the optical displacement meter having a control unit that calculates the displacement to the object based on the peak position or the center of gravity position of the signal from the image sensor, the image sensor generates a charge according to the amount of received light. A plurality of pixel components arranged in an array having a charge accumulating unit for accumulating the generated charges, and all pixel configurations for starting and stopping charge accumulation according to the amount of received light in the plurality of pixel component units A shutter unit that controls substantially the same part, a plurality of comparators that individually compare values corresponding to accumulated charges in a plurality of pixel components with a common reference value, and a control of the shutter unit And a terminal for outputting a logical sum signal of the output signals of the plurality of comparators, and the control unit has at least one of the outputs of the plurality of comparators of the image sensor having a larger accumulated charge than the reference value. When it is shown, the shutter means of the image sensor is controlled to stop the charge accumulation in each pixel component.

  According to such a configuration, by setting the reference value to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. Therefore, saturation can be avoided while fully utilizing the dynamic range of the image sensor.

  A second configuration of the optical displacement meter according to the present invention is characterized in that, in the first configuration, the image sensor is a CMOS image sensor in which a plurality of pixel components are arranged one-dimensionally or two-dimensionally. . As described above, since the CMOS image sensor has a narrow dynamic range and is likely to be saturated, the effect of the configuration of the present invention as described above is enhanced.

  The first configuration of the optical information reader according to the present invention includes an image sensor that receives light from an object and generates an image signal for each sampling, and a binarization circuit that binarizes the signal from the image sensor. And an optical information reader having a decoder that decodes the binarized signal, the image sensor includes a charge generation unit that generates a charge corresponding to the amount of received light and a charge storage unit that stores the generated charge. A plurality of pixel components arranged in an array, shutter means for controlling the accumulation start and stop of charge according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components, and a plurality of pixels A plurality of comparators that individually compare a value corresponding to the accumulated charge in the component with a common reference value, a control input terminal of the shutter means, and an output signal of the plurality of comparators A terminal for outputting a logical sum signal, and the control unit indicates that when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value, The present invention is characterized in that the shutter unit is controlled to stop charge accumulation in each pixel component.

  According to such a configuration, by setting the reference value to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. Therefore, saturation can be avoided while fully utilizing the dynamic range of the image sensor.

  According to a second configuration of the optical information reading device of the present invention, in the first configuration, a trigger input means for inputting a timing for starting sampling and a battery for supplying power to the optical information reading device are provided. Furthermore, it is characterized by having. As an optical information reading apparatus having such a configuration, for example, there is a handy type bar code reader, and the effect of achieving both the utilization of the dynamic range and the avoidance of saturation according to the present invention is particularly effective in such an apparatus.

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

  FIG. 1 is a diagram showing the measurement principle of an optical displacement meter that is an example of an apparatus using an image sensor of the present invention. This optical displacement meter is also called a laser displacement meter, and is used to measure the displacement of a measurement object in a non-contact manner using the principle of triangulation. Laser light emitted from the laser diode 12 under the control of the LD driver 11 passes through the light projecting lens 13 and irradiates the measurement object WK. Part of the laser light reflected by the measurement object WK passes through the light receiving lens 14 and is received by the linear image sensor 15.

  When the measurement object WK is displaced as indicated by a broken line in FIG. 1, the optical path of the laser light that is reflected by the measurement object WK and reaches the linear image sensor 15 changes as indicated by the broken line. As a result, the position of the light receiving spot on the light receiving surface of the linear image sensor 15 moves.

  The linear image sensor 15 has a structure in which a plurality of pixel configuration units are arranged in a line, and each pixel configuration unit generates a charge according to the amount of received light and a charge storage unit that stores the generated charge. And have. Accumulated charges corresponding to the amount of received light in each pixel component of the linear image sensor 15 are read out by the readout circuit 16 and a received light waveform that is a one-dimensional received light amount distribution is obtained by signal processing. The displacement of the measuring object WK is obtained from the peak position or the center of gravity position of the received light waveform.

  2A and 2B show the appearance of the optical displacement meter, FIG. 2A is a plan view, and FIG. 2B is a side view. The optical displacement meter includes a sensor head unit 21 and a controller unit 22. The sensor head unit 21 incorporates the LD driver 11, the laser diode 12, the light projecting lens 13, the light receiving lens 14, the linear image sensor 15, and the readout circuit 16. The controller unit 22 includes a microprocessor (control unit), controls the output (light emission amount) of the laser diode 12 via the LD driver of the sensor head unit 21, and uses signals read from the linear image sensor 15. A process for obtaining the displacement of the measuring object WK is executed.

  The sensor head unit 21 and the controller unit 22 are connected by an electric cable 23 to exchange electric signals with each other, and a power supply voltage is supplied from the controller unit 22 to the sensor head unit 21. The sensor head unit 21 is fixed to a predetermined mounting base 25 using two bolts 24. Two mounting holes through which the bolts 24 are inserted are provided along the reference surface 26 of the sensor head portion 21. The reference surface 26 is a surface on which the laser beam for measurement is emitted and the reflected light from the measurement object WK is incident.

  FIG. 3 is a block diagram showing a main circuit configuration of the optical displacement meter. The sensor head unit 21 includes a laser diode 12 and its drive circuit (LD driver) 11, a linear image sensor 15 and its readout circuit 16, a light projecting lens 13 and a light receiving lens 14. The controller unit 22 includes a low-pass filter (LPF) 41, a peak hold circuit 42, AD converters (A / D) 43 and 47, a microprocessor (MPU) 44, a DA converter (D / A) 45, and an AGC (automatic gain control) amplifier. 46 and a reset / control circuit 48.

  The laser light emitted from the laser diode 12 passes through the light projection lens 13 and irradiates the measurement object WK. Part of the laser light reflected by the measurement object WK passes through the light receiving lens 14 and enters the linear image sensor 15. The charge accumulated in each pixel component of the linear image sensor 15 is read out by the readout circuit 16. The readout circuit 16 obtains a time-series voltage signal corresponding to a one-dimensional received light amount distribution by applying a pixel selection signal that is a readout pulse signal to the linear image sensor 15 and sequentially scanning each pixel component. For example, when the linear image sensor 15 is composed of 256 pixels and the transfer rate for each pixel is 1 microsecond, the accumulated charge of all the pixel components is read out in 256 microseconds, and the time series voltage is read from the readout circuit 16. Output as a signal. The time required to read the accumulated charges of all the pixels is the sampling period. The output signal of the readout circuit 16 is passed to the controller unit 22, and the high frequency component is first removed by the low pass filter 41. This high frequency component includes the frequency component of the pixel selection signal given to the linear image sensor 15.

  FIG. 4 is a diagram schematically illustrating how the voltage signal output from the readout circuit 16 changes via the low-pass filter 41 and the peak hold circuit 42. As shown in FIG. 4, the output signal 31 of the readout circuit 16 is a continuous rectangular wave, and the frequency of this rectangular wave corresponds to the frequency of the pixel selection signal. When the output signal 31 passes through the low pass filter 41, the high frequency component corresponding to the frequency of the pixel selection signal is removed, and the voltage signal 32 includes only the low frequency component corresponding to the envelope. The voltage signal 32 includes information on the distribution of the amount of received light related to the pixel position in the linear image sensor 15. The higher the voltage value, the greater the amount of light received at that pixel position. Therefore, the peak position of the voltage signal 32 corresponds to the pixel position having the largest amount of received light that changes according to the displacement of the measurement object WK.

  The voltage signal 32 output from the low pass filter 41 is given to the peak hold circuit 42. The peak hold circuit 42 holds the peak value Vp of the voltage signal 32 and outputs it to the first AD converter 43. The AD converter 43 converts the peak value Vp into a digital value and gives it to the microprocessor 44. As shown in FIG. 3, the voltage signal 32 output from the low-pass filter 41 is also supplied to the AGC amplifier 46. The voltage signal amplified by the AGC amplifier 46 is converted into a digital value by the second AD converter 47, and the digital value is sequentially given to the microprocessor 44. The gain of the AGC amplifier 46 is automatically controlled so that the amplified voltage value falls within a predetermined range.

  The microprocessor 44 determines the position of the barycentric value of the amount of received light based on the peak data input through the first AD converter 43 and the sequential data input through the second AD converter 47. When the position of the barycentric value of the amount of received light is obtained, the distance or displacement to the measurement object WK is obtained from the principle of triangulation described above. The distance or displacement to the measurement object WK determined in this way is given from the microprocessor 44 to the DA converter 45, converted into an analog voltage and output.

  In FIG. 3, the intensity (light emission amount) of the laser light emitted from the laser diode 12 is controlled by the microprocessor 44 via the LD driver 11. If the intensity of the laser beam changes, the amount of light (the amount of received light) reflected by the measurement object WK and incident on the linear image sensor 15 also changes. Therefore, by adjusting the intensity of the laser light emitted from the laser diode 12 according to the light reflectance (brightness) of the measurement object WK, the dynamic range of the received light amount of the linear image sensor 15 can be fully utilized. I have to. Specifically, the intensity of the laser beam is adjusted by changing the pulse width or duty ratio of a pulse for driving the laser diode 12. Of course, the intensity of the laser beam may be adjusted by changing the pulse voltage (peak value).

  Next, automatic accumulation time control of the linear image sensor 15 in the optical displacement meter of the present embodiment will be described. In this embodiment, a CMOS image sensor is used as the linear image sensor 15. The CMOS image sensor has an advantage that it can be systemized by adding an on-chip function, but has a disadvantage that the dynamic range is narrower than that of the CCD and the stored charge is likely to be saturated. When saturation occurs, the peak position (or centroid position) of the received light amount obtained from the linear image sensor becomes unclear, and the displacement of the object cannot be detected correctly.

  FIG. 5 is a circuit configuration diagram of the linear image sensor 15 used in the optical displacement meter according to the first embodiment of the present invention. This linear image sensor 15 is a global shutter (shutter means) that controls the start and stop of charge accumulation in accordance with the amount of light received in each pixel component substantially simultaneously for all pixel components, and the accumulated charge in each pixel component. A plurality of comparators for individually comparing corresponding values with a common reference value, terminals for outputting a logical sum signal of their output signals, and the like are provided. When at least one of the outputs of the plurality of comparators of the image sensor 15 indicates that the accumulated charge is larger than the reference value, the optical displacement meter microprocessor 44 (control unit) 44 The global shutter is controlled to stop charge accumulation in each pixel component. As a result, the dynamic range can be fully utilized while avoiding saturation of accumulated charges in each pixel component.

  The linear image sensor 15 shown in FIG. 5 includes photodiodes PD0, PD1,... That are electric charge generation units that generate electric charges according to the amount of received light, and capacitors C0, that are electric charge storage units that accumulate the generated electric charges. A plurality of pixel components having C1,... Are arranged in a line. Although only two pixel components are illustrated in FIG. 5, the actual linear image sensor has as many pixel components as the number of pixels (for example, 256).

  Charges generated by the photodiodes PD0, PD1,... According to the amount of light received are accumulated in the capacitors C0, C1,. The transistors TR20, 21,... Are simultaneously turned on / off by a common global shutter signal GS. This realizes a global shutter function that controls the start and stop of charge accumulation in accordance with the amount of received light in a plurality of pixel components substantially simultaneously for all the pixel components.

  The charges accumulated in the capacitors C0, C1,... Pass through the buffers BF20, 21,... And the transistors TR30, TR31, etc., and are read as the output voltage Vout through the common output buffer BF3. The pixel selection signals Add0, Add1,..., Which are readout pulse signals, are sequentially applied, so that the transistors TR30, TR31,... Are sequentially turned on, and the capacitors C0, C1,. The charge is read out as a time-series voltage signal Vout.

  The outputs of the buffers BF20, 21,... Are connected to comparators CMP0, CMP1,... Via transistors TR40, TR41,.・ Is connected. In the process of accumulating charges in the capacitors C0, C1,..., The transistors TR40, TR41,... Are turned on by a common comparator switching input (CMP switching input) signal. A common reference voltage Vref is input to the other input of each of the comparators CMP0, CMP1,. Each of the comparators CMP0, CMP1,... Is an open drain output, and is connected in common to form a wired OR output (WOR) line. A pull-up resistor Rup is connected to the wired OR output line WOR.

  With the circuit configuration as described above, when at least one of the outputs of the plurality of comparators indicates that the accumulated charge is larger than the reference value, the microprocessor 44 controls the global shutter to Realizes automatic accumulation time control to stop charge accumulation. Hereinafter, the operation of the circuit of FIG. 5 will be described in order. Note that the reset (RESET) input signal, global shutter (GS) input signal, pixel selection input signals (Add0, Add1,...) And comparator switching (CMP switching) input signals in FIG. It is included in the signal that the microprocessor 44 of the section 22 gives to the sensor head section 21 via the reset / control circuit 48.

  First, the comparator switching (CMP switching) input is set to L level, and the transistors TR40, TR41,... Are turned on. Also, the pixel selection signal inputs (Add0, Add1,...) Are all set to the H level, and the transistors TR30, TR31,. In this state, the reset input signal is set to L level and the global shutter input signal is set to L level. Since the transistors TR20, 21,... Are simultaneously turned on, charges corresponding to the power supply voltage Vcc are accumulated in the capacitors C0, C1,. As a result, the outputs of all the comparators CMP0, CMP1,...

  When the reset input signal is set to H level (the reset state is released), the transistors TR10, 11,... Are turned on, and the photodiodes PD0, PD1,. The generation of the corresponding charge is started. At this time, the outputs of all the comparators CMP0, CMP1,... Remain at the H level, the global shutter signal GS is maintained at the L level, and the transistors TR20, 21,. Therefore, charge accumulation in the capacitors C0, C1,.

  As the charge accumulation in each capacitor C0, C1,... Progresses, the input voltage of each comparator CMP0, CMP1,. Eventually, when the accumulated charge of the capacitor of any of the pixel components having the largest amount of received light becomes larger than the reference value, the input voltage of the comparator becomes smaller than the reference voltage Vref, and the output of the comparator is inverted to the L level. . As a result, the wired OR output (WOR) becomes L level, and the microprocessor 44 inverts the global shutter signal GS to H level according to the inversion of the wired OR output. As a result, the transistors TR20, 21,... Are turned off at the same time, and the accumulation of charge in each capacitor C0, C1,... Is executed, and the accumulated charge in each pixel component at that time is stored in the capacitors C0, C1. , ... are stored.

  Subsequently, the accumulated charge in each pixel component is read out. First, the comparator switching input is set to H level, and the transistors TR40, TR41,. Then, by sequentially scanning the pixel selection signal inputs (Add 0, Add 1,...) To the L level, the accumulated charges of the capacitors C 0, C 1,. Is read as After the accumulated charges of all the capacitors C0, C1,... Are read, the comparator switching input is again set to the L level, and the pixel selection signal inputs (Add0, Add1,. return.

  With the operation as described above, in the optical displacement meter of this embodiment, the charge accumulation in all the pixel components stops when the accumulated charge in any pixel component of the linear image sensor 15 exceeds the reference value. , The accumulated charge at that time is stored. Therefore, by setting the reference value (reference voltage Vref) to a value immediately before saturation, the charge accumulation in each pixel component can be stopped immediately before the accumulated charge in any pixel component is saturated. In this way, saturation can be avoided while fully utilizing the dynamic range of the image sensor.

  Note that the above-described automatic storage time control is not limited to a device that uses a linear image sensor (one-dimensional image sensor) in which each pixel configuration unit is arranged in a row, but each pixel configuration unit is arranged in a matrix. It can also be applied to devices that use area image sensors (two-dimensional image sensors). Further, the present invention is not limited to the optical displacement meter, and can be applied to various devices using an image sensor such as an optical reader and an imaging device.

  FIG. 6 is a circuit configuration diagram of the linear image sensor 15 used in the optical displacement meter according to the second embodiment of the present invention and its periphery. In this embodiment, the automatic accumulation time control executed by the microprocessor 44 in the first embodiment is realized by a circuit built in the linear image sensor 15. In other words, the linear image sensor 15 includes (a part of) a control unit that performs automatic accumulation time control. As an on-chip additional circuit of the CMOS image sensor, in addition to such a circuit for automatic storage time control, a circuit for an additional function as described below is configured. However, whether part or all of these circuits are incorporated in the linear image sensor 15 or realized by an external circuit including the microprocessor 44 can be changed as appropriate.

  In FIG. 6, the charge generation units PD0, PD1,... Correspond to the photodiodes PD0, PD1,. The charge storage units C0, C1,... Correspond to the capacitors C0, C1,. The shutter means 50 corresponds to the transistors TR20, 21,. Further, the address means 52 corresponds to the transistors TR30, 31,.

  The voltages corresponding to the stored charges in the charge storage units C0, C1,... Are individually compared with the reference voltage Vref by comparators (comparators) CMP0, CMP1,. The wired OR signal WOR output from the comparators CMP0, CMP1,... Passes through the buffer BF5 to become the global shutter signal GS and is given to the shutter means 50. Therefore, the function of controlling the shutter unit 50 to stop the charge accumulation in all the pixel components when the accumulated charge in any pixel component of the linear image sensor 15 exceeds the reference value does not go through the microprocessor 44. Has been realized. Of course, similarly to the first embodiment, the wired OR signal WOR may be input to the microprocessor 44, and the microprocessor 44 may output the global shutter signal GS. Note that the reset signal REST also becomes the global shutter signal GS through the buffer BF4.

  Further, in this embodiment, as shown in FIG. 6, a timeout signal Tout is externally connected to the line of the wired OR signal WOR output from the comparators CMP0, CMP1,. This time-out signal Tout is for controlling the shutter unit 50 to stop the accumulation of charges in each pixel component when the elapsed time (charge accumulation time) from the start of accumulation of each charge has exceeded a predetermined upper limit time. Signal. In this embodiment, the microprocessor 44 outputs a timeout signal Tout. As a result, when the amount of received light is small and the elapsed time from the start of accumulation becomes abnormally long, the charge accumulation is forcibly stopped in each pixel component, so that charge accumulation is completed and read out for a long time. No need to wait. Whether the elapsed time has exceeded a predetermined upper limit time may be determined by the microprocessor 44 by software, or may be determined by an output signal of a timer circuit provided separately.

  Further, when the charge accumulation stop in each pixel component is executed by the timeout signal Tout, the accumulated charge does not reach saturation in any pixel component, and corresponds to the accumulated charge read from each pixel component. The maximum voltage may be quite low. In such a case, in this embodiment, the dynamic range related to signal processing is optimized by changing (narrowing) the conversion voltage range of the AD converter 47 according to the maximum value of the voltage.

  That is, as shown in FIG. 6, a voltage corresponding to the accumulated charge obtained from each pixel component is input to the maximum value acquisition unit 53 via the buffers BF70, BF71,. .. Are connected between the charge storage units C0, C1,... And the buffers BF70, BF71,. A CDS (Collected Double Sampling) circuit is a circuit for compensating for variations in residual charges (voltage) when the accumulated charges in the charge accumulation units C0, C1,. . Details of the CDS circuit will be described later. As shown in FIG. 6, each CDS circuit CD0, CD1,... Is supplied with a reset signal RESET and a sample hold signal S & H generated by the timing generation unit 51 from the wired OR signal WOR.

  The maximum value acquisition unit 53 acquires a voltage corresponding to the maximum value of accumulated charges in each pixel configuration unit, and outputs the voltage as a reference voltage AVref that determines the conversion voltage range of the AD converter 47. For example, when the accumulated charge reaches saturation in any pixel component, the voltage output from the pixel component is the maximum voltage, which is the maximum of the reference voltage AVref that determines the conversion voltage range of the AD converter 47. Equal to a value (eg 5V). At this time, the AD converter 47 converts the input voltage into a digital value (for example, a value of 0 to 255 in the case of an 8-bit AD converter) corresponding to a conversion voltage range of 0 to 5V.

  On the other hand, if the charge accumulation stop in each pixel component is executed by the timeout signal Tout and the maximum voltage obtained by the maximum value acquisition unit at this time is 3 V, the reference voltage AVref of the AD converter 47 Is set to 3V. As a result, the input voltage of the AD converter 47 is converted into a digital value corresponding to a conversion voltage range of 0 to 3V. That is, the voltage width per step is reduced, and the output value from the AD converter 47 can take a value within the full scale range. For example, in the case of an 8-bit AD converter, it is also converted to a value of 0 to 255. In this way, even when the accumulated charge of each pixel component is small as a whole, the dynamic range of the processing circuit after the AD converter 47 can be fully utilized. Note that the maximum voltage obtained by the maximum value acquisition unit is not necessarily used as the reference voltage AVref of the AD converter 47 as it is. Each voltage in the above description is merely an example.

  FIG. 7 is a circuit diagram showing a configuration example of the CDS circuits CD0, CD1,... In FIG. CDS circuits CD0, CD1,... And transistors C40, TR41,... And capacitors C10, C11,. , And capacitors C20, C21,... And transistors C60, TR61,... And capacitors C30 for transferring the accumulated charges when accumulation is stopped according to the sample hold signal S & H. C31,... Are provided. Further, a differential amplifier that amplifies a difference voltage between the voltage of the capacitors C20, C21,... Corresponding to the accumulated charge at the reset and the voltage of the capacitors C30, C31,. AMP10, AMP11,... The voltage corresponding to the accumulated charge at the time of stopping the accumulation in each pixel component after compensating for the variation in the residual charges (voltage) of the charge accumulation units C0, C1,... At the time of reset is the differential amplifiers AMP10, AMP11, Is obtained as an output voltage.

  Returning to FIG. 6, the voltage corresponding to the accumulated charge at the time of accumulation stop in each pixel component is sequentially read by the address means 52 through the respective CDS circuits CD0, CD1,. Value AV input. That is, the timing signal TIM1 corresponding to the pixel selection signal input (Add0, Add1,...) In the first embodiment of FIG. 5 is given from the microprocessor (or gate array) 44 to the address means 52 and selected pixel configuration. The voltage (analog value AV) corresponding to the accumulated charge of the part is sequentially read. The read analog value AV is applied to the AD converter 47, and the converted digital value DV is input to the microprocessor 44 in accordance with the timing signal TIM2 applied from the microprocessor 44 to the AD converter 47.

  FIG. 8 is a timing chart showing an operation example of the circuit shown in FIGS. In this example of operation, at time t1, the accumulated charge of one of the pixel components reaches saturation, the input voltage of the comparator becomes larger than the reference voltage Vref, and the charge accumulation stops when the output is inverted to the L level. ing. On the other hand, at time t2, the charge accumulation is stopped by the timeout signal Tout indicating a time-out before the accumulated charge in any of the pixel components reaches saturation. Therefore, the reference voltage AVref of the AD converter 47 is set to full scale in the readout period of the (n−1) th frame from time t1 to time t2, and in the readout period of the nth frame starting from time t2, the AD converter 47 is set. The reference voltage AVref is set to a value lower than the full scale.

  As another method for avoiding the saturation of the accumulated charge in each pixel component, as shown in FIG. 6, the microprocessor 44 outputs the output of the laser diode 12 via the LD driver 11 (based on the wired OR signal WOR ( It is also possible to perform control to reduce the (light emission amount). Also in this case, if the reference voltage Vref given to the comparators CMP0, CMP1,... Of each pixel component is set to a voltage just before saturation, the laser diode 12 is output before saturation occurs in any pixel component. Since the output is reduced, the dynamic range of the linear image sensor 15 can be fully utilized while avoiding saturation.

  Alternatively, as a result of automatic control of the charge accumulation time based on the wired OR signal WOR, when the charge accumulation time in each pixel component of the linear image sensor 15 becomes shorter than a predetermined lower limit time, the microprocessor 44 Control may be performed to reduce the output (light emission amount) of the laser diode 12 via the LD driver 11. By setting the lower limit time to an appropriate value, if the charge accumulation time becomes shorter than the lower limit time, it is determined that the light emission amount is too large, and control for reducing the light emission amount contributes to the reduction of power consumption. be able to. In this embodiment, an example is shown in which the input voltage of the comparator increases when charge is accumulated. However, as shown in the first embodiment, the input voltage of the comparator is decreased when charge is accumulated. Also good. In that case, it is preferable to invert the signal waveform by the CDS circuit.

  FIG. 9 is a circuit configuration diagram of the linear image sensor 15 used in the optical displacement meter according to the third embodiment of the present invention and its periphery. This embodiment differs from the second embodiment shown in FIG. 6 in that selection means 61 is provided for selecting whether the input signals of the comparators CMP0, CMP1,... The selection means 62 is provided for selecting whether the input signal of the value acquisition unit 53 is valid or invalid for each pixel configuration unit.

  By the action of these selection means 61 and 62, it is determined whether or not there is saturation with respect to the accumulated charge in the selected pixel component instead of all the pixel components, or the maximum accumulated charge in the selected pixel component. The conversion voltage range (reference voltage AVref) of the AD converter 47 can be set by acquiring the value. For example, not the pixel configuration unit of the entire pixel range of the image sensor but the pixel configuration unit within the effective pixel range excluding the peripheral part is selected to determine the presence or absence of saturation and to set the conversion voltage range of the AD converter 47 Is possible. For example, when the object to be measured is a glass plate and not only the reflected light from the surface to be acquired but also the reflected light from the back surface is incident on the image sensor, the effect of the reflected light from the back surface is reduced by narrowing the effective pixel range. (Second voltage peak) can be removed. Thereby, the displacement measurement accuracy of the measurement object is improved.

  FIG. 10 is a circuit configuration diagram of an image sensor used in the bar code reader according to the fourth embodiment of the present invention and its periphery. The function of the automatic accumulation time control is realized by a circuit built in the image sensor, as in the case of the optical displacement meter of the second embodiment shown in FIG. Also in this embodiment, it is possible to appropriately change whether the circuit for the automatic accumulation time control and the additional function described below is built in the image sensor or realized by an external circuit.

  In FIG. 10, elements having the same functions as those of the components of the optical displacement meter shown in FIG. The operation of the circuit of FIG. 10 will be described focusing on the differences from the circuit of the optical displacement meter shown in FIG. In the bar code reader shown in FIG. 10, the voltage AV corresponding to the accumulated charge of each pixel component read out via the address means 52 is input to the binarization circuit 54. The binarization circuit 54 compares the input voltage AV with the threshold voltage AVth and inputs the obtained digital value DV of 0 or 1 to the microprocessor 44. The microprocessor 44 recognizes the binary pattern of the barcode read from the input time-series binary data.

  A trigger signal for instructing the start of barcode reading is input from the trigger input means 56 to the microprocessor 44. Further, in order to perform the same control as the circuit of the optical displacement meter shown in FIG. 5, the wired OR signal WOR is input to the microprocessor 44 and the control signal for the LD driver 11 is output from the microprocessor 44. Yes. The microprocessor 44 can control the output (light emission amount) of the laser diode or LED that emits light to the barcode via the LD driver 11.

  In the circuit of FIG. 10, a maximum value acquisition unit 53 that acquires the maximum value of the voltage corresponding to the accumulated charge obtained from each pixel component, and a threshold value setting that sets the threshold voltage AVth of the binarization circuit 54 A circuit 55 is provided. The maximum value acquisition unit 53 gives the maximum value of the acquired voltage to the threshold setting circuit 55. The threshold setting circuit 55 sets an appropriate threshold voltage AVth based on the applied voltage corresponding to the maximum value of the accumulated charge of each pixel component, and supplies this to the binarization circuit 54.

  According to such a configuration, even when the analog value AV obtained from each pixel component changes due to the light reflectance of the barcode printing surface to be read, the change follows the change. Since the threshold voltage AVth of the binarization circuit 54 is appropriately changed and set, the binarization processing is optimized. This improves the barcode reading accuracy (pattern discrimination accuracy). Note that the circuit configuration example of the barcode reader shown in FIG. 10 can be applied to other optical readers.

  As described above, the configuration of the present invention can be widely applied to devices using an image sensor such as an optical displacement meter, a barcode reader, and other optical readers, and is stored in each pixel configuration unit of the image sensor. An effect is obtained in which the dynamic range can be fully utilized while avoiding charge saturation. Note that the specific circuits shown in the drawings are merely configuration examples. The specific circuit configuration can be changed or reconfigured as appropriate. The present invention is not limited to the above embodiment, and can be implemented in various forms.

It is a figure which shows the measurement principle of the optical displacement meter which is an example of the image sensor utilization apparatus of this invention. It is a figure which shows the external appearance of an optical displacement meter. It is a block diagram which shows the main circuit structures of an optical displacement meter. It is the figure which drawn typically a mode that the voltage signal output from the read-out circuit changed through a low-pass filter and a peak hold circuit. It is a circuit block diagram of the linear image sensor used for the optical displacement meter which concerns on 1st Example of this invention. It is a circuit block diagram of the linear image sensor used for the optical displacement meter which concerns on 2nd Example of this invention, and its periphery. FIG. 7 is a circuit diagram illustrating a configuration example of a CDS circuit in FIG. 6. 8 is a timing chart illustrating an operation example of the circuit illustrated in FIGS. 6 and 7. It is a circuit block diagram of the linear image sensor used for the optical displacement meter which concerns on 3rd Example of this invention, and its periphery. It is a circuit block diagram of the image sensor used for the barcode reader which concerns on 4th Example of this invention, and its periphery.

Explanation of symbols

12 Laser diode (light emitting element)
15 Image sensor 44 Microprocessor (control unit)
47 AD converter 50 Shutter means 53 Maximum value acquisition unit 54 Binarization circuit 55 Threshold setting circuit C0, C1,... Capacitors (charge storage units)
CMP0, CMP1, ... Comparator (comparator)
PD0, PD1, ... Photodiode (charge generation unit)
TR20, TR21, ... Transistors (shutter means)

Claims (12)

An image sensor using device having an image sensor for receiving light from an object and generating an image signal, and a control unit for processing the signal from the image sensor,
The image sensor includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing a value corresponding to the accumulated charge in the plurality of pixel components with a common reference value;
A control input terminal of the shutter means, and a terminal for outputting a logical sum signal of output signals of the plurality of comparators,
The control unit controls the shutter unit of the image sensor to control each pixel when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value. An apparatus using an image sensor, which is configured to stop charge accumulation in a component. The control unit controls the shutter unit to stop accumulating charge in each pixel component when the elapsed time from the start of charge accumulation in each pixel component of the image sensor exceeds a predetermined upper limit time. The image sensor using device according to claim 1, wherein the image sensor using device is configured as described above. An AD converter that converts an analog voltage signal from the image sensor into a digital signal and applies the digital signal to the control unit; and a maximum value acquisition unit that acquires a voltage corresponding to a maximum value of accumulated charges in the plurality of pixel components The image sensor utilization device according to claim 2, further comprising: a reference voltage that determines a conversion voltage range of the AD converter can be changed according to an output of the maximum value acquisition unit. A binarization circuit that binarizes the analog voltage signal from the image sensor by comparing it with a threshold voltage and gives it to the control unit, and obtains a voltage corresponding to the maximum value of accumulated charges in the plurality of pixel components And a threshold value setting circuit configured to change and set a threshold voltage of the binarization circuit in accordance with an output of the maximum value acquisition unit. The device using the image sensor described. The light emitting element having a variable light emission amount for irradiating the object with light is further provided, and the control unit has a time from the start of charge accumulation to the stop of accumulation in each pixel component of the image sensor shorter than a predetermined lower limit time. The apparatus using an image sensor according to any one of claims 1 to 4, wherein control for reducing a light emission amount of the light emitting element is executed. A light emitting element with a variable light emission amount for irradiating the object with light, an image sensor for receiving light from the object to generate an image signal, and a control unit for processing a signal from the image sensor An image sensor using device having
The image sensor includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing a value corresponding to the accumulated charge in the plurality of pixel components with a common reference value;
A terminal for outputting a logical sum signal of the output signals of the plurality of comparators,
The control unit controls to reduce the light emission amount of the light emitting element when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value. A device that uses an image sensor. A selection unit that sets validity or invalidity of each of the plurality of pixel components is provided, and the operation of the comparator is valid for the plurality of pixel components that are validated by the selection unit. Item 7. The image sensor using device according to any one of Items 1 to 6. The selection means for setting each of the plurality of pixel components to be valid or invalid is provided, and the maximum value acquisition unit functions for the plurality of pixel components validated by the selection unit. The apparatus using the image sensor according to 3 or 4. A light projecting unit for irradiating the object with light, an image sensor that receives reflected light from the object and generates an image signal for each sampling, and a peak position or a gravity center position of the signal from the image sensor In an optical displacement meter having a control unit that calculates the displacement to the object based on
The image sensor includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing a value corresponding to the accumulated charge in the plurality of pixel components with a common reference value;
A control input terminal of the shutter means, and a terminal for outputting a logical sum signal of output signals of the plurality of comparators,
The control unit controls the shutter unit of the image sensor to control each pixel when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value. An optical displacement meter configured to execute charge accumulation stop in a component. The optical displacement meter according to claim 9, wherein the image sensor is a CMOS image sensor in which a plurality of pixel components are arranged one-dimensionally or two-dimensionally. An image sensor that receives light from an object and generates an image signal for each sampling, a binarization circuit that binarizes the signal from the image sensor, and a decoder that decodes the binarized signal; In an optical information reader having
The image sensor includes a plurality of pixel configuration units arranged in an array having a charge generation unit that generates a charge according to the amount of received light and a charge storage unit that stores the generated charge;
Shutter means for controlling the start and stop of charge accumulation according to the amount of received light in the plurality of pixel components substantially simultaneously for all the pixel components;
A plurality of comparators for individually comparing a value corresponding to the accumulated charge in the plurality of pixel components with a common reference value;
A control input terminal of the shutter means, and a terminal for outputting a logical sum signal of output signals of the plurality of comparators,
The control unit controls the shutter unit of the image sensor to control each pixel when at least one of the outputs of the plurality of comparators of the image sensor indicates that the accumulated charge is larger than the reference value. An optical information reading apparatus configured to stop charge accumulation in a component. 12. The optical information reader according to claim 11, further comprising trigger input means for inputting timing for starting sampling and a battery for supplying power to the optical information reader.

Images