News Column

Patent Issued for Displacement Sensor

July 23, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- A patent by the inventors Iida, Yusuke (Ayabe, JP); Takimasa, Hiroaki (Ayabe, JP), filed on March 17, 2011, was published online on July 8, 2014, according to news reporting originating from Alexandria, Virginia, by VerticalNews correspondents.

Patent number 8773668 is assigned to OMRON Corporation (Kyoto-Shi, JP).

The following quote was obtained by the news editors from the background information supplied by the inventors: "A conventional displacement sensor includes a light projecting unit including a light emitting element such as a laser diode and a light receiving unit including a light receiving element such as a PSD, a CCD, and a CMOS, and repeatedly performs processing for emitting light to an object to be detected from the light projecting unit and receiving reflected light from the object to be detected (this process being referred to as 'detection processing' herein) and processing for measuring a displacement of the object by using light receiving amount data generated by the light receiving unit. Triangulation which uses a position in a light receiving element on which reflected light is incident is often adopted as a measurement method. However, in addition thereto, a TOF (Time of Flight) method which uses a length of time from light projection to light reception, a phase difference ranging method which makes use of a phase difference between the projected light and the received reflected light, a PN code ranging method in which light subjected to intensity modulation with a PN code is projected and measurement using a result of correlation operation between that light and reflected light is conducted, and the like are available.

"In addition, some conventional displacement sensors, being provided in a path where an object to be detected moves, have a function to adjust detection sensitivity in accordance with a state of reception of reflected light while it repeats detection processing and measurement processing. Patent Literature 1 (PTL 1) is exemplified as a literature showing that conventional example.

"In the displacement sensor described in PTL 1, a laser diode is introduced as a light emitting element and a CCD is introduced as a light receiving element. An image signal output from the CCD is processed by an amplifier circuit or an AD conversion circuit and used for measurement processing.

"This PTL 1 describes adjustment of a parameter (gain of the amplifier circuit, a time period and intensity of light emission from the laser diode, a shutter time of the CCD) for determining sensitivity for detection processing based on a calculated ratio between a peak value of a light receiving amount that appeared in an image (specifically, an average value of maximum values of density along horizontal lines) and an optimal value for that peak value.

"In addition, according to the description in PTL 1, in the case where the peak value of the light receiving amount in the image has reached a saturation level, the peak value is estimated by calculation and a ratio of an optimal value for the peak value to an estimated value of the peak value is used to perform sensitivity adjustment processing, and in the case where the peak value is insufficient, sensitivity is reset to an initial state."

In addition to the background information obtained for this patent, VerticalNews journalists also obtained the inventors' summary information for this patent: "Technical Problem

"In a conventional displacement sensor having a sensitivity adjustment function, each time when detection processing is performed, a ratio between light receiving amount data obtained in the processing and an optimal value is calculated and sensitivity for next detection processing is adjusted based on that ratio. This adjustment method, however, is on the premise that reflected light having substantially the same intensity as previous reflected light is also incident on light receiving unit in next detection processing. If an object to be detected changes and a quantity of light incident on the light receiving unit significantly fluctuates, appropriate sensitivity adjustment becomes difficult.

"The problem above will specifically be described with reference to FIG. 7.

"FIG. 7 (1) shows an example where a displacement sensor 300 is arranged above a conveying path where a substrate 200 on which a plurality of components 201 is mounted and the moving substrate 200 is subjected to measurement. FIG. 7 (2) shows in a graph, of a measurement value varying along a time axis obtained in the processing above. It is noted that a measurement value shown here is a value obtained by converting a distance from sensor 300 to an object to be detected to a height when viewed from a prescribed reference plane, with a portion in the graph where the value is low representing the measurement value in connection with substrate 200 and a portion in the graph where the value is high representing the measurement value in connection with component 201.

"In this example, since substrate 200 and component 201 are significantly different from each other in reflectance, sensitivity adjusted immediately before will be inappropriate when the object to be detected by sensor 300 changes from substrate 200 to component 201 or the object to be detected changes from component 201 to substrate 200.

"For example, when it is assumed that component 201 is higher in reflectance than substrate 200 and when the object to be detected is changed to component 201 while high sensitivity is set for adaptation to substrate 200, significantly increased reflected light is detected at high sensitivity and hence light receiving amount data may be saturated. Alternatively, when the object to be detected is changed to substrate 200 while low sensitivity is set for adaptation to component 201, a value for light receiving amount data becomes very low and hence it becomes difficult to recognize whether reflected light is incident or not.

"When saturation or shortage in the light receiving amount data thus occurs, a ratio between the light receiving amount data and an optimal value cannot correctly be calculated and hence adjustment of sensitivity becomes difficult. Therefore, sensitivity adjustment over a plurality of cycles when required may lead to unstable measurement during that period or occurrence of a measurement error.

"The graph in FIG. 7 (2) shows with an extra-thick solid line, measurement data obtained with sensitivity being appropriately adjusted, and shows with a dotted line, a measurement value that should theoretically be obtained during periods a, b, c, d, e, and f during which measurement becomes unstable or a measurement error is caused because of insufficient adjustment of sensitivity. As shown with these two types of lines, immediately after change in the object to be detected, measurement may become unstable due to inappropriate sensitivity. Therefore, as these periods a to e during which measurement is unstable are longer, it becomes difficult to correctly recognize variation in the shape of the surface of the substance. In addition, in the case where a substance moves at a high speed or in the case where a small substance is the object to be measured, the substance may move out of a detection area of sensor 300 while sensitivity is being adjusted and measurement may completely be missed.

"According to the invention described in PTL 1, when the light receiving amount is saturated, the light receiving amount is estimated so as to adjust sensitivity, however, a result of estimation is not necessarily correct and it is likely that sensitivity cannot be quickly adjusted. In addition, even though resetting to initial sensitivity is made in the case where the light receiving amount is insufficient, it is less likely that a light receiving amount suitable for measurement is obtained. Therefore, the invention described in PTL 1 cannot completely solve the problems above.

"The present invention pays attention to the problems above, and it is an object of the present invention to make such sensitivity adjustment that light receiving amount data promptly returns to an appropriate state even when saturation or shortage in the light receiving amount data to be used in measurement processing may occur due to change in the object to be detected or the like.

"Solution to Problem

"A displacement sensor according to the present invention includes a light projecting unit configured to project light for detection, a light receiving unit configured to receive reflected light from an object reflecting the light from the light projecting unit and generate light receiving amount data indicating a light receiving state thereof, a measurement unit configured to repeat detection processing by the light projecting unit and the light receiving unit and measure a displacement of the object using the light receiving amount data obtained by each detection processing, and a sensitivity adjustment unit configured to adjust sensitivity in the detection processing.

"The light receiving unit includes a light receiving element and a plurality of signal processing units, each of the plurality of signal processing units generating the light receiving amount data by applying different magnifications to a light receiving amount signal output from the light receiving element. The measurement unit performs measurement processing of the displacement using the light receiving amount data generated by a specific signal processing unit of the plurality of signal processing units.

"The sensitivity adjustment unit selects one of the light receiving amount data generated by the plurality of signal processing units according to the detection processing based on a prescribed rule. Then, the sensitivity adjustment unit determines a correlation between a value of the light receiving amount data generated by the specific signal processing unit and a predetermined appropriate value based on a ratio of a magnification applied to a signal processing unit generating the selected light receiving amount data to a magnification applied to the specific signal processing unit and the selected light receiving amount data, and adjusts sensitivity in subsequent detection processing based on the correlation. It is noted that a ratio or difference between the light receiving amount data and the appropriate value can be determined as the correlation.

"According to the configuration above, by processing the light receiving amount signal output from the light receiving element with the plurality of signal processing units, the plurality of pieces of light receiving amount data to which different magnifications are applied respectively are generated. Since the light receiving amount data generated by the specific signal processing unit is used in measurement processing, each measurement result can be consistent and stable measurement can be conducted unless the light receiving amount data is saturated or greatly lowers.

"On the other hand, in sensitivity adjustment processing, light receiving amount data generated by a signal processing unit other than the specific signal processing unit is selected, a correlation between a value of the light receiving amount data generated by the specific signal processing unit and the appropriate value is determined based on the ratio of the magnification applied to the selected signal processing unit to the magnification applied to the specific signal processing unit and the selected light receiving amount data, and sensitivity in next detection processing can be adjusted based on this relation. Therefore, even when saturation or shortage in the light receiving amount data generated by the specific signal processing unit occurs, sensitivity in subsequent detection processing can appropriately be adjusted by selecting light receiving amount data in which reflected light incident on the light receiving element is represented with the appropriate value.

"It is noted that sensitivity adjustment above is desirably made for each detection processing, however, substantial sensitivity adjustment processing may be skipped during a period in which the light receiving amount data generated by the specific signal processing unit is within a prescribed numerical range including the appropriate value.

"In one preferred embodiment of the displacement sensor above, when the value of the light receiving amount data generated by the specific signal processing unit is in a range from a prescribed acceptable value to a saturation level, the sensitivity adjustment unit selects the light receiving amount data. On the other hand, when the value of the light receiving amount data generated by the specific signal processing unit is lower than the prescribed acceptable value, the sensitivity adjustment unit selects light receiving amount data generated by a signal processing unit for which a magnification higher than that of the specific signal processing unit is set. Alternatively, when the value of the light receiving amount data generated by the specific signal processing unit reaches the saturation level, the sensitivity adjustment unit selects light receiving amount data generated by a signal processing unit to which a magnification lower than that of the specific signal processing unit is applied.

"According to the configuration above, when a value of the light receiving amount data used for measurement processing can correctly be obtained, that light receiving amount data is selected to adjust sensitivity, so that the light receiving amount data can be maintained in an appropriate state. On the other hand, in the case where the light receiving amount data used in measurement processing is lower than the acceptable value or saturated and it is difficult to obtain a correct value of the light receiving amount data, appropriate sensitivity adjustment can be made by using light receiving amount data for which an appropriate value has been obtained as a result of signal processing at magnification different from that of the specific signal processing unit.

"In another preferred embodiment, the sensitivity adjustment unit selects light receiving amount data closest to the appropriate value from the light receiving amount data generated by the plurality of signal processing units. By doing so, data most suitable for sensitivity adjustment among the plurality of pieces of light receiving amount data can be selected so as to make sensitivity adjustment of high accuracy.

"The displacement sensor according to another preferred embodiment is provided with an imaging element having a plurality of pixels as the light receiving element. In addition, light receiving amount data representing light receiving amounts of all pixels of the imaging element is generated in the specific signal processing unit, and light receiving amount data representing at least a peak value of the light receiving amounts of the pixels of the imaging element is generated in other signal processing units.

"The sensitivity adjustment unit determines correlation between a peak value of the light receiving amount data generated by the specific signal processing unit and the appropriate value based on a peak value of the selected light receiving amount data and the ratio of the magnification applied to the signal processing unit generating the selected light receiving amount data to the magnification applied to the specific signal processing unit. In addition, the measurement unit specifies a position where the peak value of the light receiving amount is obtained in the imaging element using the light receiving amount data generated by the specific signal processing unit, and measures the displacement based on the specified position.

"According to the configuration above, light receiving amount data in which the peak value of the light receiving amount indicates appropriate intensity is selected from the plurality of pieces of light receiving amount data so as to perform sensitivity adjustment processing, so that a peak value in the light receiving amount data generated by the specific signal processing unit can be adjusted to sufficient magnitude. Therefore, a position in the imaging element corresponding to this peak value can accurately be specified and high-accuracy displacement measurement can be conducted.

"Advantageous Effects of Invention

"According to the present invention, adjustment processing can be performed in such a manner that a plurality of pieces of light receiving amount data to which different magnifications are applied are generated from a light receiving amount signal output from a light receiving element and data suitable for adjustment of sensitivity is selected from these pieces of light receiving amount data. Therefore, even though light receiving amount data suitable for measurement can no longer be obtained with sensitivity adjusted immediately before due to change in the object to be detected or the like, sensitivity can promptly be changed so that the light receiving amount data can be recovered to an appropriate state. Therefore, even in the case where a substance moving at a high speed or a small substance is to be detected, measurement processing can be performed without any difficulty."

URL and more information on this patent, see: Iida, Yusuke; Takimasa, Hiroaki. Displacement Sensor. U.S. Patent Number 8773668, filed March 17, 2011, and published online on July 8, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8773668.PN.&OS=PN/8773668RS=PN/8773668

Keywords for this news article include: Electronics, Laser Diodes, OMRON Corporation, Signal Processing.

Our reports deliver fact-based news of research and discoveries from around the world. Copyright 2014, NewsRx LLC


For more stories covering the world of technology, please see HispanicBusiness' Tech Channel



Source: Electronics Newsweekly


Story Tools






HispanicBusiness.com Facebook Linkedin Twitter RSS Feed Email Alerts & Newsletters