TWI500950B - Optical displacement sensor - Google Patents

Description

Optical displacement sensor

The present invention relates to an optical displacement sensor comprising: a light projection portion that projects light for detecting; and a light receiving portion that receives reflected light from an object to be measured, the light Projecting from the light projection portion to the object; and a measurement processing portion measuring a displacement of the object to be measured based on a light receiving state of the light receiving portion to output the measurement result.

The optical displacement sensor based on the triangulation measurement includes: a light projection portion including a light emitting device such as a laser diode; and a light receiving portion including a light receiving device in a one-dimensional or two-dimensional configuration . The light receiving portion receives the reflected light from the object to be measured, and the light is projected from the light projecting portion to the object. Then, the coordinates of the peak of the light reception amount distribution data are then detected and converted into displacements for output.

Other examples of optical displacement sensors include: sensors using a Time of Flight (TOF) system that uses the length of time from light projection to light reception; sensing using a phase difference ranging system The phase difference ranging system uses a phase difference between the projected light and the received reflected light; a sensor using a PN code ranging system that projects light that undergoes intensity modulation by a PN code and The measurement is performed using the results of the correlation calculation between the projected light and the received light; and the like.

In order for the above optical displacement sensor to perform stable measurement, it is necessary to frequently adjust The sensitivity is adjusted to maintain a certain amount of light received regardless of the reflectivity of the object to be measured or its reflection state. In this regard, for example, Japanese Unexamined Patent Publication No. 2006-133051 describes an optical displacement sensor based on triangulation to adjust a shutter open time (exposure time) to saturate the amount of reflected light and detect light. The technique of the center position of the saturated pixel group in the received amount data as the peak position of the light receiving amount and converting the peak position into the height data.

There is also a method of applying the above-described principle of displacement measurement to determine whether an object is present at a predetermined reference distance. For example, Japanese Unexamined Patent Publication No. Publication No. 2007-221491 describes the use of a plurality of light receiving devices arranged in at least one direction to receive reflected light from an object projected by light from a light projecting portion, in contrast to each light. A technique of determining a peak position of a light reception amount distribution in a device and a predetermined reference position to determine the presence/absence of an object. Japanese Unexamined Patent Publication No. 2007-221491 further describes that a plurality of reflections are determined to have occurred when a plurality of peaks are detected from the light reception amount distribution.

In order for the above-described optical displacement sensor to ensure measurement accuracy, it is necessary to guide only the reflected light from the measurement area of the sensor to the light receiving portion. However, depending on the state of use of the sensor or the condition of the surrounding environment, light from outside the detection area may enter the light receiving portion, resulting in erroneous processing. This example will be described with reference to FIGS. 6 to 8.

Figure 6 illustrates an example of an application using an optical displacement sensor based on triangulation. This application is intended to detect a plate-like workpiece at a predetermined height position, which The plate-like workpieces are arranged in two columns in a state of being mounted on the palette 20 and moving downward. The sensors 1 and 1 are mounted laterally with respect to the detection positions of the respective columns. In each column, two workpieces W1 and W2 having different thicknesses are transferred in a random order. The sensor 1 is configured to measure the distance between the edge surface of the object (the workpiece W1, the workpiece W2, and the palette 20) passing through the detection position and the sensor 1, and has transferred the workpieces W1 and W2. One is determined based on the length of time during which the measured value corresponding to the workpiece is obtained.

7 and 8 illustrate an example of error detection that can occur in the above applications. In one example of Figure 7, the absence of a workpiece occurs in the right column. Therefore, the light traveling obliquely upward from the right sensor 1 is sequentially reflected in the palette 20 above the missing portion, the workpiece W2 in the adjacent column, and the workpiece W1 below the missing portion, and the reflected light (Stray light) enters the right sensor 1.

In an example of FIG. 8, the workpieces W1 and W2 are arranged in a row, and a member (mirror body) 30 having a high reflectance is disposed at a position opposite to the sensor column with respect to the workpiece row. In this example, the lack of configuration occurs in the configurations of workpieces W1 and W2. Therefore, light emitted from the sensor 1 and passing through the missing portion of the workpiece W is regularly reflected at the surface of the mirror body, and the regularly reflected light enters the sensor 1.

The examples of Figures 7 and 8 illustrate the absence of conditions that occur in the configuration of workpieces W1 and W2. However, in the absence of a defect, similar noise light can enter the sensor in a state where the workpiece to be measured has not yet reached the detection position. In addition, there may be cases where light suddenly generated in the surrounding area may enter the sensor. In addition, in the case where the detection position is near the window, sunlight entering through the window can enter the sensor in a certain time zone.

If the noise light enters the sensor 1, the sensor 1 outputs distance data corresponding to the object different from the object to be measured. In the case where the distance data does not indicate the distance to the workpiece W1 or the workpiece W2, the failure may not occur; however, in the case where the noise light enters around the position indicating the distance to the workpiece W1 or the workpiece W2, the sensor 1 The output corresponds to the measured value of one of the workpieces W1 and W2, which may result in error handling.

An application similar to the examples of FIGS. 6 to 8 is disclosed in Japanese Unexamined Patent Publication No. 2007-221491. In this application, in the case where a plurality of peaks are observed in the light receiving amount distribution, it is determined that the peak reflects multiple reflections, and the edge of the workpiece is not detected (see Japanese Unexamined Patent Publication No. 2007-221491 No., paragraphs 0073 to 0074 and Figure 19). However, by this processing, if the noise light enters around the position indicating the distance to the workpiece W1 or the workpiece W2 without the occurrence of a plurality of peaks, erroneous detection occurs.

The same problem can occur in the case where the noise light as described above is received in a sensor for measuring the displacement of the object. That is, if the measurement system is performed for the noise light, the measurement accuracy cannot be ensured.

The present invention has been made to focus on the above problems, and its object is to prevent false measurement from being performed due to noise light entering the light receiving portion to ensure measurement accuracy.

The present invention is applicable to an optical sensor comprising: a light projection portion that projects light for measurement; and a light receiving portion that receives reflected light from an object to be measured, the light from The light projection portion is projected to the object; and a measurement processing portion that measures the object to be measured based on a light receiving state of the light receiving portion and outputs a result of the measurement. The measurement processing section according to an aspect of the present invention includes: a determination section that determines a value indicating a change in one of the light reception amounts received by the light receiving section or indicates a value to be received according to the light reception amount Whether one of the values of one of the parameters of the sensitivity of the adjustment is increased or decreased falls within a predetermined tolerance; and a controller that performs control such that the determination portion determines that the value of the parameter to be determined falls within The measurement result is outputted within the allowable range, and the measurement result is not output when the determination portion determines that the value of the parameter to be determined falls outside the allowable range.

Typically, in this type of sensor, the sensitivity is adjusted prior to the start of the measurement so that the reflected light from the object to be measured is received at an intensity suitable for the measurement, and the sensitivity is also The measurement is adjusted as needed based on the amount of light received. Therefore, as illustrated in FIG. 6, in the case where the measurement system is executed by the normalized object (workpiece W1, workpiece W2, and palette 20) set as the detection target, the reflected light from the object is properly received. During the state, a large change in the amount of light received is unlikely to occur.

On the other hand, the noise light entering the sensor after being reflected at various positions as illustrated in FIG. 7 becomes more than that from the workpiece W1, the workpiece W2, or the palette 20. The light of reflection is weak. In addition, the specular reflection light from the scope 30 as illustrated in FIG. 8 is considered to be stronger than the reflection from the workpiece W1, the workpiece W2, or the palette 20.

As described above, a large difference between the intensity of the reflected light from the measurement area of the sensor and the intensity of the noise light from outside the measurement area is likely to occur. In view of this, in the present invention, the control is performed such that when determining a parameter indicating a change in the amount of received light (for example, a change in a peak value in a light receiving amount distribution obtained by the one-dimensionally configured light receiving device) Or the value of the parameter indicating the sensitivity to be adjusted according to the increase or decrease of the light receiving amount falls within the allowable range, and the measurement result is output, and the measurement result is not output when the determined parameter value falls outside the allowable range . According to the above method, when the noise light enters the light receiving portion, a large change in the amount of light received and the sensitivity based on the amount of received light is generated, thereby preventing the measurement data corresponding to the noise light from being output.

The above sensor is configured to perform the measurement when, for example, the determination portion determines that the parameter value falls within the allowable range, and outputs the obtained measurement data. Alternatively, the sensor may be configured to perform measurement each time light projection and light reception are performed, and stop outputting the measurement result only when the determination portion determines that the parameter value falls outside the allowable range.

In a specific example of the sensor, the measurement processing portion further includes a sensitivity adjustment portion that changes and defines the light projection portion according to the increase or decrease of the light reception amount acquired by the light receiving portion. An exposure time of one of the operation periods of the light receiving portion, a light emission intensity of the light projection portion, and the light At least one of the light receiving gains of one of the receiving sections. In response to the processing performed by the sensitivity adjusting portion, the determining portion uses the exposure time obtained after the processing of the sensitivity adjusting portion, the light projection intensity, and the light receiving gain to calculate the indication to be used by the exposure time And an estimated value of the light projection intensity and the sensitivity of the light receiving gain adjustment, and comparing the calculated evaluation value with a predetermined upper limit value and a lower limit value of the allowable range to determine whether the evaluation value is Fall within this tolerance.

According to the above specific example, whenever at least one of the three sensitivity parameters (exposure time, light emission intensity, and light receiving gain) is changed, the level of sensitivity to be adjusted by the parameters is indicated after the change. The evaluation is worth calculating, and the determination as to whether the evaluation value falls within the allowable range is made. Thus, for example, by varying the evaluation of the sensitivity of the sensitivity to be adjusted in the state in which the reflected light from the detection area is received, and defining the upper and lower limits to cause the change The range is included in the allowable range, and the evaluation value of the sensitivity adjusted with the reception of the noise light is determined to fall out of the allowable range with a high degree of certainty, thereby preventing the erroneous measurement result from being output.

In the above specific example, the measurement processing section further includes a setting portion that performs a process of repeatedly operating the light projection section, the light receiving section, and the adjustment section to respectively make the light receiving amount, the exposure time, the light emission intensity, and the light a process of receiving a stable value of the gain; a process of calculating a reference value of the evaluation value using the stabilized exposure time, the stabilized light emission intensity, and the stabilized light receiving gain; and determining the allowable range based on the calculated reference value Limit and lower limit The processing of values. According to the setting portion, the sensitivity can be adjusted before the measurement processing so that the light receiving amount suitable for the measurement can be obtained, and then the upper limit value and the lower limit value of the allowable range are determined based on the estimated value of the adjusted sensitivity.

In a specific example of the setting section, the calculated reference value is multiplied by a predetermined coefficient α greater than 1, whereby the upper limit of the allowable range can be calculated, and the reference value is multiplied by the inverse of the coefficient α by 1/α, thereby The lower limit of the allowable range can be calculated. In addition, the input portion of the value of the input coefficient α can be set. In this case, the allowable range can be adjusted until the state in which the error processing is not performed is reached, or the allowable range can be changed in response to the change of the object to be measured.

In another specific example of the sensor, the determination section sets the value of the parameter indicating the change in the amount of received light or the value of the parameter to be adjusted according to the increase or decrease in the amount of received light, and the upper limit of the allowable range. The value and the lower limit are compared to determine whether the parameter value falls within the allowable range. The sensor of this specific example includes: an input portion that inputs data for setting the upper limit value and the lower limit value; and a setting portion that is set based on the input data in the determination portion Limit and the lower limit.

The change in the amount of light received during reception of the received light from the object to be measured depends on various environmental elements (such as the material of the object to be measured, the surface of the substrate measured (the surface that has not been displaced) The distance from the sensor varies, and the state of the sensitivity adjustment changes correspondingly. In the above specific example, the upper limit value and the lower limit value for defining the allowable range to be used by the determination portion can be set according to the input, thereby improving the convenience of the sensor and more. Feature.

According to the present invention, the output of the measurement result due to the incidence of the light (noise light) different from the incident light from the object to be measured can be prevented with respect to the light receiving portion, whereby the measurement is stably performed.

Figure 1 illustrates one configuration of an optical displacement sensor to which the present invention is to be applied.

The optical displacement sensor 1 (hereinafter simply referred to as "displacement sensor 1" or "sensor 1") of the specific example of the present invention includes: a light projection portion 101 including a light-emitting device (laser) A diode 11; and a light receiving portion 102 including a one-dimensionally arranged light receiving device 12 (in this embodiment, CMOS). In addition to the light-emitting device 11, the light projecting portion 101 also includes a light projection control circuit 13. In addition to the light receiving device 12, the light receiving portion 102 also includes a signal processing circuit 14 and an A/D conversion circuit 15 for processing image signals generated by the light receiving device 12.

Further, the sensor 1 includes a CPU 10, a memory 16, a display portion 17, an operation portion 18, an I/O interface 19, and the like. The light projection unit 101 and the light receiving unit 102 are included in the sensor head 100 illustrated in Fig. 2, and other components are provided in an auxiliary casing (not illustrated) called an "amplifier unit". The configuration of the sensor is not limited thereto, and all components may be disposed in one housing.

The CPU 10 performs measurement processing and processing regarding sensitivity adjustment based on the program stored in the memory 16. The result of the measurement is displayed on the display unit 17, and is output to the external device via the I/O interface 19. The operation unit 18 is configured to detect Make various settings before processing.

FIG. 2 exemplarily illustrates the principle of one configuration and measurement processing of the sensor head 100.

The sensor head 100 in this example is arranged such that the optical axis of the illumination device 11 is set to a detection position on the path L of the workpiece W. In the case where the workpiece to be moved up and down is measured, the sensor head 100 can be laterally mounted relative to the workpiece path (as illustrated in FIG. 6) to measure the edge surface of the workpiece and the sensor head 100. The distance between them.

The laser light emitted from the light-emitting device 11 passes through the light-projecting lens 111, is reflected at the object to be detected, and enters the light-receiving device 12 via the light-receiving lens 122. Therefore, the peak appears at a position corresponding to the incident position of the reflected light in the light receiving amount distribution indicated by the one-dimensional reflected light image (which is generated by the light receiving device 12). The peak position varies depending on the height of the surface of the object that reflects the laser light.

Based on the above principle, the CPU 10 cyclically moves the light projecting portion 101 and the light receiving portion 102 at a constant interval, and measures the centroid of the maximum peak which appears in the light receiving distribution pattern generated by the light receiving portion 102 in a period, The coordinates are converted into distance data using a conversion table temporarily stored in the memory 16. In addition, each time the light is projected and the light is received, the CPU 10 adjusts the sensitivity in accordance with the increase or decrease of the maximum peak value of the light receiving amount to perform the measurement in a stable manner.

Distance data from the coordinates of the centroid of the largest peak will be from the light The distance between the object reflected by the projection portion toward the centroid position and the sensor head 100, and the relationship between the coordinates of each of the light receiving devices 12 and the distance data is temporarily stored in the conversion table. Note that the coordinates of the centroid of the largest peak can be converted not only into distance data, but also into data representing the height of the object that reflects the laser light.

The above measurement processing makes it possible to distinguish between the state in which the workpiece W does not exist in the environmental region and the state in which the workpiece W exists. Further, in the case where the workpiece W to be measured has a step as illustrated in the example of Fig. 2, the difference in height between the two surfaces constituting the step can be detected.

However, all of the peaks appearing in the light receiving amount distribution are not necessarily generated by the reflected light from the measuring region, but there may be a case where the peak is due to the incidence of the noise light generated in the surrounding region.

In view of the above, in this specific example, before the peak position in the light receiving amount pattern is detected for measurement, the evaluation value indicating the sensitivity based on the peak adjustment is calculated. When the evaluation value falls within a predetermined allowable range, the measurement process is performed to output the distance data. On the other hand, when the evaluation value falls outside the allowable range, the distance data is not output, but the error output is performed.

The sensitivity adjustment performed in this specific example is described below.

In this specific example, three parameters (exposure time, intensity of laser light to be projected (hereinafter referred to as "light projection intensity"), and gain of light reception amount (hereinafter referred to as "light receiving gain") are The adjustment is made to adjust the sensitivity such that the amount of light received exhibits a value close to a predetermined target value. In addition, before the measurement starts, in the workpiece In a state where W is mounted in the measurement area, light projection and light reception are repeated to adjust each sensitivity parameter so that the peak of the light reception amount based on the reflected light from the workpiece W exhibits sufficient intensity. This adjustment is performed in the "tuning process" to be described later.

After the tuning process, even after the start of the measurement process, the sensitivity parameter is adjusted depending on the maximum peak value of each light reception amount distribution.

In this specific example, the light projection period of the light projection unit 101 and the light reception period of the light receiving unit 102 are overlapped with each other, and the length of the period in which light projection and light reception are performed is defined as the exposure time. However, it is not necessary to always make the two cycles coincide with each other. For example, the light projection period may begin earlier than the light reception period, and the light reception period may terminate later than the light projection period. In this case, the length from the start of the light projection period to the end of the light receiving period is defined as the exposure time.

In the process of adjusting the light projection intensity, the light projection intensity is gradually decreased from the maximum value 1 by a predetermined ratio. In the process of adjusting the light receiving gain, the light receiving gain is gradually increased from the minimum value 1 by a predetermined ratio. In this specific example, the adjustment control data is represented by a magnification ratio for both the light projection intensity and the light reception gain.

In principle, sensitivity adjustments are performed based on adjustments in exposure time. Specifically, when the maximum light receiving amount in the light receiving amount distribution is decreased, the exposure time is increased according to the decreasing rate thereof, and when the maximum light receiving amount is increased, the exposure time is decreased according to the increasing rate thereof. However, the exposure time needs to be projected from the light / Minimum time required for light reception to be adjusted within the range of the maximum length of time corresponding to the intended use of the process. Hereinafter, the upper limit of the adjustment range is referred to as "maximum exposure time", and the lower limit is referred to as "minimum exposure time". In this specific example, the light projection intensity or the light reception gain is reduced even if the exposure time is set to the minimum exposure time and the maximum light reception amount is saturated, and is maximized even if the exposure time is set to the maximum exposure time In the case where the amount of light received does not exhibit sufficient intensity, the light projection intensity or the light receiving gain increases.

Figure 3 illustrates the procedure to be performed in order to derive the processing of the three parameters for sensitivity adjustment. This derivation process is integrated into the portion of the detection process as illustrated in FIG. 4 and is executed repeatedly. In this specific example, the sensitivity parameter is adjusted based on a ratio between the maximum light receiving amount P(t) detected in the current processing cycle and the predetermined light receiving amount target value, and the result of the adjustment is applied to the subsequent The second detection processing loop.

The parameter derivation process will be described with reference to the flowchart of FIG. 3, where ST is the exposure time, D is the light projection intensity, and G is the light reception gain. The values of the respective sensitivity parameters to be applied to the current processing loop (the values calculated in the penultimate processing loop) are defined as ST(t), D(t), and G(t), and are to be applied to The values of the next second processing loop are defined as ST(t+2), D(t+2), and G(t+2).

In step S101, the CPU 10 multiplies the exposure time ST(t) applied to the current processing cycle by the value P0/P obtained by dividing the light reception amount target value P0 by the current maximum light reception amount P(t) ( t) to calculate the exposure of the second cycle Light time ST(t+2).

Subsequently, the CPU 10 compares the thus calculated exposure time ST(t+2) with the above-mentioned minimum exposure time and maximum exposure time. When ST(t+2) falls within the range between the minimum exposure time and the maximum exposure time ("NO" in both steps S102 and S103), the CPU 10 determines the value of ST(t+2), And setting D(t) and G(t) in the light projection intensity D(t+2) of the second cycle and the subsequent light receiving gain G(t+2) of the second cycle (step S108). ).

That is, the exposure time is adjusted in accordance with the percentage change of the peak light receiving amount P(t), and the value of the light projection intensity or the light receiving gain is set to the same value as the value of the penultimate cycle.

On the other hand, when the exposure time ST(t+2) is smaller than the minimum exposure time (YES in step S102), the CPU 10 changes the value of ST(t+2) to the minimum exposure time (step S104). Further, the CPU 10 sets the light projection intensity D(t+2) and the light reception gain G(t+2) to be lower than its current value according to the degree of deviation of ST(t+2) before the change with respect to the minimum exposure time. The magnification (step S105).

When the exposure time ST(t+2) is greater than the maximum exposure time (NO in step S102 and YES in step S103), the CPU 10 changes the value of ST(t+2) to the maximum exposure time. (Step S106). In addition, the CPU 10 sets the light projection light intensity D(f+2) and the light reception gain G(t+2) to be higher than its current value according to the degree of deviation of ST(t+2) before the change with respect to the maximum exposure time. The magnification of the value is high (step S107).

According to the above processing, when the maximum light receiving amount P(t) is considerably increased, the exposure time ST(t+2) is reduced to the minimum exposure time, and the values of the light projection intensity and the light receiving gain are decreased. On the other hand, when the maximum light receiving amount P(t) is considerably reduced, the exposure time ST(t+2) is increased to the maximum exposure time, and the values of the light projection intensity and the light receiving gain are increased. In either case, when the laser light having the same intensity as P(t) has been received after two cycles, the sensitivity is adjusted so that the light receiving amount at that time becomes the target value P0.

The larger the increase or decrease rate of the maximum light receiving amount P(t), the larger the change in the magnification of each of the light projection intensity and the light receiving gain becomes.

The procedure of one cycle of the measurement process will be described below with reference to FIG.

In step S1, the CPU 10 reads out the sensitivity parameters ST(t), D(t), and G(t) to be applied to the current cycle from the memory 16, and causes the light projecting portion 101 and the light receiving portion 102 to The sensitivity is adjusted by the adjustment of such parameters (steps S1 and S2).

Subsequently, the CPU 10 inputs the reflected light image generated by the light receiving device 12 thereto, and the light receiving amount distribution detected by the freely reflected light image detects an amplitude (small amplitude) larger than a predetermined value (step S3). After the peak is detected (YES in step S4), the CPU 10 acquires the maximum light reception amount P(t) corresponding to the maximum peak value between the detected peaks (step S5).

Step S6 indicates the processing illustrated in Fig. 3 (steps S101 to S108). By this processing, the sensitivity parameter ST(t+2), D(t) of the second cycle that follows +2), and G(t+2) are derived based on the ratio between the maximum light receiving amount P(t) acquired in step S5 and the predetermined light receiving amount target value P0.

In step S7, the CPU 10 multiplies the sensitivity parameters ST(t+2), D(t+2), and G(t+2) calculated in the above processing to calculate the sensitivity parameter adjustment The evaluation value of the sensitivity level R. In step S8, the CPU 10 compares the evaluation value R with the predetermined lower limit value R _A and the upper limit value R _B . When the evaluation value R falls within the range between the lower limit value R _A and the upper limit value R _B (YES in step S8), the CPU 10 calculates the position including the occurrence of the maximum light receiving amount P(t). The centroid g(t) of the centroid of the largest peak (step S9). Further, the CPU 10 converts the coordinate g(t) into the distance data using the conversion table mentioned above (step S10), and outputs the distance data (step S11).

When the evaluation value R is smaller than the lower limit value R _A or larger than the upper limit value R _B (NO in step S8), the CPU 10 does not execute steps S9, S10, and S11, but performs error output (step S12). When the reflected light of the laser light projected from the light projecting portion 101 cannot be received for some reason, no peak is detected in the processing of step S3 (NO in step S4). Also in this case, the CPU 10 proceeds to step S12 and performs error output as described above.

In order to achieve stable measurement of the workpiece W, in this specific example, after the sensitivity parameter is adjusted in advance, the process illustrated in FIG. 4 is started so that the peak of the light receiving amount based on the reflected light from the workpiece W is optimal. strength. Therefore, the maximum peak value of the light reception amount taken in the processing of S3 or S5 is reflected light from the object (workpiece W or its supporting surface) in the measurement area. When produced, the maximum light receiving amount P(t) does not change significantly, except immediately after the change in the type of the object causing the reflection. In addition, changes occurring immediately after the change in the type of the object causing the reflection can be maintained to a relatively small range. Therefore, in the case where the maximum peak of the light receiving amount is generated from the light from the measurement area, in most cases, only the adjustment of the exposure time ST is sufficient, and in the case where the light projection intensity or the light receiving gain needs to be adjusted. The adjustment range is small.

However, in the case where the reflected light is not from the workpiece W but the noise light enters, a significant change in the maximum peak height may occur. For example, as in the above example of FIG. 7, in the case where the weak light traveling away from the main light of the sensor 1 is reflected back at a plurality of positions and returned to the sensor 1, based on the peak of the noise light The light receiving amount P(t) becomes significantly low, with the result that the exposure time ST(t+2) calculated based on the ratio between the target values P0 and P(t) significantly exceeds the maximum exposure time. Therefore, in this case, the exposure time ST(t+2) is changed to the maximum exposure time, and the light projection intensity D and the light receiving gain G are significantly increased. From this, it can be seen that the evaluation value R of the integrated value as the sensitivity parameter becomes large.

In addition, in the case where regular reflected light having high intensity enters (as in the example of Fig. 8), the maximum peak may be saturated, so that the exposure time ST to be derived by the saturation as the maximum peak of P(t) (t+2) is significantly lower than the minimum exposure time. Therefore, in this case, the exposure time ST(t+2) is changed to the minimum exposure time, and the light projection intensity D and the light receiving gain G are significantly reduced. It can be seen that the evaluation value R becomes small.

For the allowable range of the evaluation value R, the range of variation of the evaluation value R is calculated based on the change in the respective sensitivity parameter generated under the condition that the maximum peak of the light reception amount is generated from the reflected light from the measurement region. Next, the upper lower limit value R _A and the upper limit value R _B are determined such that the change is included in the allowable range, and thereafter, the determined R _A and R _B are temporarily stored in the memory 16 . By performing the measurement processing of FIG. 4 using the temporary lower limit value R _A and the upper limit value R _B , the light receiving amount based on the noise light is detected as the maximum light receiving amount. In this case, even if the sensitivity parameter adjusted based on the detection result exhibits a significant change, the determination of "NO" is performed in step S8 so that there is no error distance data due to the incidence of the noise light. The possibility of being calculated and output. Therefore, stable and accurate measurement can be performed.

As described above, in the present specific example, the sensitivity parameter of the next second cycle is derived based on the ratio between the maximum light receiving amount and the target value in each cycle at the time of repeating light projection and light reception. At the same time, the evaluation value for determining whether the derived sensitivity parameter is appropriate is calculated, and it is determined whether the calculated evaluation value falls within the allowable range. However, the sensitivity parameter of the second loop that follows is derived so that the sensitivity adjustment measure is stably performed when the loop of the detection processing is relatively short, and if the operating speed of the CPU 10 is allowed, then the sensitivity of the loop is subsequently The parameter can be derived and it can then be determined whether the evaluation value R based on these sensitivity parameters falls within the allowable range.

In the process of FIG. 4, in the case where the change in exposure time falls outside the allowable range defined between the lower limit value R _A and the upper limit value R _B , the measurement process itself is not performed. However, alternatively, the measurement process itself is always executed, but if the evaluation value R deviates from the allowable range R, a configuration in which the output of the measurement data is stopped may be possible.

In addition, the following methods can be used to improve measurement accuracy. That is, the calculation of the distance data measured by the single light projection/light receiving operation is not performed by the calculation of the average value of the distance data measured by the plurality of previous cycles (the moving average calculation), and the calculation is performed. The average value is output as a measurement result. Moreover, in this case, it is necessary to perform the sensitivity adjustment and the calculation of the evaluation value R each time the light projection and the light reception are performed, and stop the moving average calculation or the output of the average value if the evaluation value R falls outside the allowable range. . In the case where the evaluation value R returns to the allowable range once it is outside the allowable range, the output of the moving average calculation or the average value can be recovered, but the distance data obtained during the time during which the evaluation value R is outside the allowable range needs to be Excluded from moving average calculations.

The sensor 1 of this specific example is provided with a function of determining conditions required for measurement while repeating light projection and light reception before the measurement processing. The processing based on this function is the "tuning" process mentioned above.

The tuning process includes a process of adjusting the sensitivity such that the maximum peak of the light receiving amount stays around the above target value P0. Therefore, by performing the tuning process in a state where the model of the workpiece W is mounted in the measurement region, the peak value of the light receiving amount based on the reflected light from the workpiece W can be brought close to the target value P0.

In addition, the sensor 1 of this specific example has a plurality of measurement models, and the same amount The measurement model has different response times, and the preset measurement conditions are temporarily stored for each measurement model. The response time is the length of time required for the CPU 10 to output a measurement result in response to light projection and light reception performed at a certain point, and depends on the period during which light projection and light reception are performed (hereinafter referred to as "measurement period" "), the maximum exposure time, the number of times the above moving average is calculated, or the like. Depending on the measurement mode, the sensitivity parameters set by the above tuning process are different.

Further, in this particular embodiment, the lower limit value of the upper limit value of R _A and R _B may be performed based on a result of the sensitivity adjustment processing in the tuner is calculated, for temporary storage.

FIG. 5 is a flow chart for explaining the tuning process and the temporary storage process of the lower limit value R _A and the upper limit value R _B . The processing flow of each process will be described below with reference to FIG.

Before performing the tuning process, the user selects one of the operating modes, mounts the workpiece W at the detecting position, and instructs the start of the tuning process via the operating portion 18. As a result, the process of Figure 5 begins.

In a first step S20 of this process, the preset measurement conditions corresponding to the selected measurement mode are read. The measurement conditions include a measurement period, a minimum exposure time, a maximum exposure time, and a maximum magnification of each of the light projection intensity and the light receiving gain (the maximum magnification that can be adjusted in the selected measurement mode).

In step S21, the exposure time ST, the light projection intensity D, and the light receiving gain G are initialized within the range of the preset measurement conditions. For example, the preset minimum exposure time is set to the exposure time ST, and the light projection intensity D and light The reception gain G is set to 1 respectively.

Thereafter, until the maximum light receiving amount stays around the target value P0 and the sensitivity parameters ST, D, and G respectively stay at substantially certain values, the light projection/light receiving processing and the sensitivity adjustment processing are repeated (and The processing of steps S101 to S108 of Fig. 3 is the same processing).

After the maximum light receiving amount and the sensitivity parameter have become stable (YES in steps S23 and S24), the flow proceeds to step S26, in which the stabilized exposure time ST and the stabilized light projection are performed. The intensity D and the stabilized light receiving gain G are set to ST0, D0, and G0, respectively, and the measurement conditions are determined based on the values. The measurement conditions determined at this time also include a measurement period, a minimum exposure time, a maximum exposure time, and a maximum magnification of each of the light projection intensity and the light receiving gain. In addition to this, the number of data (the number equal to or greater than 1) calculated by the moving average mentioned above is also added to the measurement condition.

In the memory 16 of this specific example, the measurement condition table is temporarily stored, and from the measurement condition table, the empirically derived measurement condition can be read using the value of the exposure time as a key. In step S26, the measurement condition table is referred to by the stabilized exposure time ST0, and the measurement condition corresponding to ST0 is read out and temporarily stored for the measurement.

In any one of the measurement conditions temporarily stored in the measurement condition table, the minimum exposure time and the maximum exposure time are set so as not to fall outside the allowable range of the preset exposure time set in the corresponding measurement mode. . Similarly, the measurement cycle Or the light projection intensity is set to be smaller than its preset value. However, there may be cases where the light receiving gain exceeds its preset value. In addition, the number of pieces of data (equal to, greater than 1) calculated by the moving average is calculated in a range satisfying the response time or the maximum exposure time in the corresponding measurement mode, and is added to the measurement condition.

After the measurement condition is determined in step S26, the flow proceeds to step S27, in which the stabilized exposure time ST0, the stabilized light projection intensity D0, and the stabilized light reception gain G0 are multiplied to calculate sensitivity. The reference value R0 of the evaluation value R of the sexual parameter. The reference value R0 indicates a preferred sensitivity value.

In step S28, the reference value R0 is multiplied by a predetermined coefficient α (α>0) to calculate an upper limit value R _{B of the} evaluation value R. Further, the reference value R0 is multiplied by the reciprocal 1/α of α to calculate the lower limit value R _{A of the} evaluation value R. Next, in step S29, R _A and R _B are temporarily stored in the memory 16, whereby the routine ends.

After the above-described tuning process is shifted to the selected measurement mode, the measurement process is performed according to the procedure of FIG. The lower limit value R _A and the upper limit value R _B are calculated by the tuning process for determining the evaluation value R for each cycle sensitivity adjustment (step S8).

According to the processing of FIG. 5, the evaluation values R of the sensitivity parameters ST0, D0, and G0 obtained based on the completion of the sensitivity adjustment performed under the condition that the reflected light from the workpiece W is received are set as the reference value R0, and Then, values sufficiently larger than and smaller than the reference value R0 can be temporarily stored as the upper limit value R _B and the lower limit value R _{A , respectively} . Therefore, the light receiving amount which is extremely different from the light receiving amount based on the reflected light from the workpiece W falls outside the allowable range defined between the upper limit value R _B and the lower limit value R _A .

The value of α used to derive R _A and R _B can be varied as needed. For example, if the fault has occurred due to the experimental measurement performed after the calculation of R _A and R _B based on the preset value of α, the value of α is changed to recalculate R _A and R _B , followed by the experimental amount. Another implementation of the test. By repeating the above procedure, the values of R _A and R _B can be determined when the state in which the error measurement due to the noise light does not occur is reached.

Alternatively, the values of R _A and R _B may be determined based on a method in which experimental measurement is performed while α or R0 is not used but the values of R _A and R _{B are} changed after the tuning process.

In the case where the experimental measurement is performed while changing the value of α or the values of R _A and R _{B ,} the value to be newly set can be input via the operation unit 18. Alternatively, the value to be newly set may be input via an external device such as a personal computer while being connected via the I/O interface 19 illustrated in FIG. In this case, the input value can be changed during the experimental measurement while monitoring the detection signal input to the sensor of the external device, and is consistent with the presence/absence of the detection error.

In the case where the moving workpiece W is measured, sensitivity adjustment can be performed while moving the workpiece W under the same conditions as the normal measurement processing to calculate the evaluation value R and then determine R _A based on the change of the evaluation value R And the value of R _B . By this method, the values of R _A and R _B can also be determined by considering the change in sensitivity of the incidence of light from the support surface of the workpiece W. Further, in the case where the workpiece W has steps or portions having different reflectances, the values of R _A and R _B can be determined by considering the change in the amount of light received during the passage of a workpiece through the region to be detected.

In the case where a plurality of workpieces W are to be detected, the values of R _A and R _{B are} calculated for each type of the workpiece, and the combination of the values is temporarily stored in the memory 16 in association with the identification information of the workpiece. . By this method, when the workpiece to be measured is changed to the other, the user can appropriately set the measurement by selecting the identification information corresponding to the other workpiece.

In the above specific example, the level of sensitivity adjusted by the three sensitivity parameters is expressed as a parameter called the evaluation value R, and whether the evaluation value R falls within the allowable range is set as the measurement value with respect to the workpiece W. The judgment condition to be output. However, alternatively, instead of the evaluation value R, the change in the maximum light receiving amount between the plurality of measurement cycles can be calculated, and it can be determined whether the change falls within the allowable range. Examples of the parameter indicating the change in the amount of received light include the ratio between the maximum light receiving amount of the last cycle or the penultimate cycle and the most recent maximum light receiving amount, and the ratio between the target value and the maximum light receiving amount.

In the case where the determination is made using the change in the light receiving amount, another light receiving device different from the light receiving device 12 can be set to measure the light receiving amount.

The function of detecting the presence/absence of the workpiece W while determining the change of the evaluation value R or the amount of light reception does not always have to be active. For example, the operating portion 18 can be configured to receive operations that switch functions between active and inactive. In this case, steps S9, S10, and S11 of FIG. 4 may be employed. It is executed and the configuration of steps S7 and S8 is not performed when an operation that makes the function inactive is performed. The switching can be achieved not only in response to the operation via the operating portion 18 but also in response to the input of a switching signal from the external device.

Alternatively, the above functions are typically kept inactive and when the predetermined conditions are met (eg, when the number of times the error occurs exceeds the allowable value), it may be possible to configure it in effect. In addition, or in the case that the noise light in a certain time zone (for example, sunlight coming in through the window) can enter, the above functions can be made active at regular time intervals or when the set time is reached based on the internal timer. And again make it inactive after the predetermined time period has elapsed.

Although the sensor 1 of the above specific example is a sensor based on triangulation, the type of sensor is not limited thereto. Even for a sensor that measures displacement according to a method different from the triangulation measurement, it is possible to determine a change in the amount of received light to be used in the calculation process or a change in sensitivity parameter adjusted according to a change in the amount of received light. Whether to fall within the allowable range and then perform calculations when determining that the above changes fall within the allowable range to accurately detect the object to be detected without being affected by the noise light.

1‧‧‧Optical sensor

10‧‧‧CPU

11‧‧‧Lighting device (laser diode)

12‧‧‧Light Receiver (CMOS)

13‧‧‧Light projection control circuit

14‧‧‧Signal Processing Circuit

15‧‧‧A/D conversion circuit

16‧‧‧ memory

17‧‧‧Display Department

18‧‧‧Operation Department

19‧‧‧I/O interface

100‧‧‧ sensor head

101‧‧‧Light Projection Department

102‧‧‧Light Receiving Department

111‧‧‧Light projection lens

122‧‧‧Light receiving lens

W‧‧‧Workpiece

1 is a block diagram showing a configuration example of an optical displacement sensor; FIG. 2 is an exemplary view illustrating a use example of the sensor and the detection principle; and FIG. 3 is a flow chart illustrating the sensitivity parameter deviation processing. Figure 4 is a flow chart illustrating a cycle of the measurement process; 5 is a flow chart illustrating a setting process performed before the measurement process; FIG. 6 is a view showing an example of an application using an optical displacement sensor; and FIG. 7 is an example illustrating the generation of noise light in the above application. FIG. 8 is a view illustrating another example in which noise light is generated.

1‧‧‧Optical sensor

10‧‧‧CPU

11‧‧‧Lighting device (laser diode)

12‧‧‧Light Receiver (CMOS)

13‧‧‧Light projection control circuit

14‧‧‧Signal Processing Circuit

15‧‧‧A/D conversion circuit

16‧‧‧ memory

17‧‧‧Display Department

18‧‧‧Operation Department

19‧‧‧I/O interface

101‧‧‧Light Projection Department

102‧‧‧Light Receiving Department

Claims (8)

An optical displacement sensor comprising: a light projection portion configured to project light for measurement; a light receiving portion configured to receive light reflected from an object; a measurement a processing portion configured to measure the object based on the received reflected light and output a result of the measurement, the measurement processing portion having a determination portion configured to determine a parameter Whether a value is within an allowable range, the value of the parameter has a value indicating a change in one of the light receiving amounts received by the light receiving portion or indicates that the value to be increased or decreased according to one of the light receiving amounts a value of one parameter of the sensitivity of the adjustment; and a sensitivity adjustment portion configured to change an exposure time according to the increase or decrease of the amount of received light received by the light receiving portion, and receive by the light At least one of a light emission intensity projected by the portion and a light receiving gain of the light receiving portion, wherein the exposure time defines an operation period of the light projection portion and the light receiving portion, and the determination portion is grouped State calculation And comparing the evaluation value with the upper limit value and the lower limit value of the allowable range to determine whether the evaluation value falls within the allowable range, and the evaluation value indicates that the exposure time is changed based on the sensitivity adjustment portion, The light emission intensity and the sensitivity of the light receiving gain are one of the levels. Such as the optical displacement sensor of claim 1 of the patent scope, the measurement section The management department further includes: a controller configured to control the output of the measurement, and when the value of the parameter is within the allowable range, the result of the measurement is output, and when the parameter is When the value is not within the allowable range, the result of the measurement is not output. The optical displacement sensor of claim 1, wherein the measurement processing portion further includes: a setting portion configured to perform a process to adjust the light projection portion, the light receiving portion, and the The sensitivity adjustment section stabilizes the value of the light receiving amount, the exposure time, and the light emission intensity. The optical displacement sensor of claim 3, wherein the setting portion performs a process to calculate a reference value of the evaluation value, and the reference value is obtained by the light receiving amount, the exposure time, and the The values of these stabilizations of the light emission intensity are calculated. The optical displacement sensor of claim 4, wherein the setting portion performs a process to determine the upper limit and the lower limit of the allowable range based on the reference value. The optical displacement sensor of claim 5, wherein the setting portion multiplies the reference value by a predetermined coefficient α greater than one to calculate the upper limit value of the allowable range, and the reference value is The inverse of the allowable range is calculated by multiplying the inverse of the coefficient α by 1/α. Such as the optical displacement sensor of claim 6 of the patent scope, further Contains: an input portion configured to input a value of the coefficient a. The optical displacement sensor of claim 1, further comprising: an input portion configured to input data for setting an upper limit value and a lower limit value to determine the allowable range, and a setting Partially configured to set the upper limit value and the lower limit value in the determination portion.