JP6141466B2 - Work identification device and identification method - Google Patents

Description

  The present invention relates to an identification device and an identification method for identifying a workpiece on a conveyance line. More specifically, when a plurality of types of workpieces having different specifications are mixed and conveyed on a conveyance line, the identification apparatus and identification method for identifying workpieces for each specification (or type) are particularly contactless. Suitable for what to do.

  In recent years, customer requests for product specifications have been diversified, and in order to meet diversified demands, there are an increasing number of cases in which product specifications differ for each product destination. At the same time, new models have been added to meet the needs of users, and the number of product types is increasing.

  For this reason, it is necessary to remodel conventional equipment that has been used for small-quantity and high-volume production, and to manufacture small-quantity and high-variety models without reducing the operating rate (for multi-variety small-volume manufacturing).

  When manufacturing various types of products mixed with conventional equipment (lines), there are various problems, but the biggest problem is that it is possible to judge multiple types of workpieces flowing through the lines (for example, assembly lines) without error. Thus, it is definitely to execute different assembly or processing operations for each type of product.

  For example, an automobile engine manufacturing factory has a cylinder block transfer line such as a casting, and a plurality of types of cylinder blocks often flow in the transfer line as workpieces. For this reason, at the entrance or exit of the transfer line, it is necessary to determine the type of cylinder block and sort it by type. In general, instead of a contact-type displacement sensor, a bar code including a convex portion is formed on a casting or the like flowing through a conveyance line, and this bar code is irradiated with light obliquely from a light source. It is known that a shadow of a bar code is formed and the type of the casting is discriminated by photographing the shadow with a TV camera and performing predetermined information processing.

  In addition, a bar code consisting of convex portions is integrally cast with a reference bar on the outer peripheral surface of the cylinder block, which is a casting to be discriminated, and the model number and mold number are expressed by the number of convex portions and the interval between them, This is detected by a TV camera.

  Furthermore, in order to reduce the number of protrusions that are integrally cast, that is, the number of reference bars, the width and height of the bar are determined to determine the casting, and the height or width of the bar is changed for each type of casting. It is known that a plurality of types of castings and the like are discriminated by this, for example, described in Patent Document 1.

  It is also known that the distance to the workpiece surface can be determined without error by using a displacement laser sensor, which is an optical measuring device, so that various types of workpieces placed on the conveyor can be identified without error. For example, it is described in Patent Document 2.

Furthermore, it is known that, instead of using a contact-type displacement sensor, the outer shape is optically inspected in a non-contact manner, so that it can be detected with high accuracy without being adversely affected by the displacement of the workpiece. It is described in.
Furthermore, in the ultrasonic sensor, in order to avoid erroneous detection due to the fact that the amount of reflected or transmitted ultrasonic waves varies depending on the material of the object, and to enable stable detection, reflection from the timing of ultrasonic irradiation is performed. The distance calculation unit calculates the distance to the object based on the time until the wave is detected, and detects the type of the object based on the calculated distance and the received amount received by the ultrasonic transmission / reception unit. For example, it is described in Patent Document 4.

JP-A-8-287175 JP 2008-119786 A JP 2004-294095 A JP 2006-292634 A

  In the above-mentioned prior art, a workpiece that is discriminated by contact in the assembly or processing conveyance line is not only difficult to detect with high accuracy due to the displacement of the workpiece, etc., but also may be damaged or destroyed by impact. Yes, not realistic.

  In addition, in the case of using an optical TV camera or a displacement laser sensor, it is affected by the environment where the transfer line is placed. For example, a machine tool such as a machining center that has an automatic tool change function and performs different types of machining such as milling, boring, drilling and tapping according to the purpose needs to identify the model immediately before machining. In the equation, in the environment of oil mist or dust, which is fine particles, light and laser are diffused by the influence thereof, and accurate discrimination is difficult, and it is very difficult to discriminate multiple models.

  Furthermore, when using an eddy current displacement sensor that uses a high-frequency magnetic field that is strong against dust, water, oil, etc., the accuracy and response speed are fast, but the measurable distance is as short as a few millimeters, and it can be used for machining centers, etc. It is not suitable for use in a transport line.

Furthermore, an ultrasonic displacement sensor that uses sound waves as a medium is suitable for use in a conveyance line because of its long measurement distance, but its accuracy is low compared to other methods simply by using it, and the measurement surface. In order to distinguish many models, the workpiece measurement surface had to be increased accordingly.
In particular, when distinguishing multiple models using an ultrasonic displacement sensor, a threshold is set for each model and the rank is compared by comparing the arrival time with the arrival time of the ultrasonic wave reflected from the workpiece surface. Judging.

  In addition, the one described in Patent Document 4 is simply set by a setting unit to identify a reception amount threshold and a distance threshold as thresholds, and takes into account that arrival time varies depending on the measurement environment. Not. Therefore, even if each threshold value is specified as a constant value and set within a range, it is difficult to distinguish many models depending on the measurement environment such as temperature. In particular, when a value is set as a threshold value in a range that simply allows variation, the threshold value has a margin larger than necessary. In that case, it is necessary to reduce the number of models that can be discriminated when discriminating a plurality of models.

  The object of the present invention is to solve the above-mentioned problems of the prior art, even in the case where a plurality of types of work flows in the assembly or processing conveyance line, and also in an environment where oil mist and dust exist. The purpose is to reliably determine the type at the entrance or exit of the line. In particular, in cylinder block transfer lines in automobile engine manufacturing factories, many models are identified, and the process of changing the process for each model or sorting it for each model is made more accurate, improving reliability. There is.

  In order to achieve the above object, a workpiece identification device according to the present invention is a workpiece identification device for identifying a model of a workpiece provided with an identification unit at a predetermined position, and transmits an ultrasonic wave toward the identification unit and receives a reflected wave. And a master sensor and a slave sensor that measure the time from transmission to reception, and distinguishing the model using a difference between values measured by the master sensor and the slave sensor.

  Since model discrimination is performed using the difference between the values measured by the master sensor and slave sensor, the effects of temperature, oil mist, dust, etc. in measuring the distance from the sensor to the workpiece identification unit can be offset. . Therefore, even in an environment such as a cylinder block production line, it is possible to accurately discriminate many models while setting a sufficient operating distance that does not hinder processing.

  Further, in the above, the master sensor and the slave sensor are arranged at positions facing the identification unit, and a surface of the identification unit facing the master sensor and a surface of the identification unit facing the slave sensor. It is desirable to discriminate the model by detecting a step.

Thereby, the measurement range can be clarified by making the identification part a step, and more models can be identified.
Furthermore, in the above, it is preferable that the transmission of the ultrasonic wave is alternately performed by the master sensor and the slave sensor.
It is possible to avoid the ultrasonic waves from interfering with each other between the master sensor and the slave sensor.

Furthermore, in the above, it is desirable that the oscillation frequency of the ultrasonic wave be 200 to 400 kHz.
Thereby, the beam size of an ultrasonic wave can be made small and the area of an identification part can be reduced.

Furthermore, in the above, it is preferable that a clock signal serving as a reference time for transmitting an ultrasonic wave is generated by the master sensor, and an ultrasonic wave is transmitted by the slave sensor in synchronization with the clock signal.
Even if the measurement is repeated many times, the transmission timing of the ultrasonic waves is not shifted, and interference can be avoided for a long time.

Furthermore, in the above, it is preferable that a distance from the master sensor and the slave sensor to the identification unit is 150 to 200 mm.
In the cylinder block production line, it is not necessary to bring the sensor close to each other. Therefore, the position control for stopping the workpiece is easy, and the sensor position does not become an obstacle to machining.

Furthermore, in the above, it is preferable that the workpiece is a cylinder block, and the transfer line is used for processing the cylinder block.
In the manufacturing process of the cylinder block, it can be made suitable in terms of environment, accuracy, measurement area, and the like.

Furthermore, in the above, it is desirable to identify the workpiece model by measuring the step difference changed by a predetermined amount for each workpiece model.
Thereby, the number of model discrimination | determination can be increased.

  According to the present invention, an ultrasonic wave is transmitted to an identification unit provided at a predetermined position of a workpiece by a master sensor and a slave sensor, and a time from transmission to reception of a reflected wave is measured and measured. Since the model is discriminated using the difference in values, the type of workpiece can be reliably discriminated without being affected by the temperature, oil mist, dust and the like. In particular, it is possible to accurately discriminate a plurality of models in a cylinder block transfer line in an automobile engine manufacturing factory and improve reliability.

The block diagram which shows the case where the workpiece identification device concerning embodiment of this invention is applied to a machine tool etc. The block diagram which shows the discrimination | determination process in one Embodiment Explanatory drawing which shows the identification shape and process of the workpiece | work in one Embodiment. Explanatory drawing which shows the assignment (mastering) of the work number in one Embodiment Explanatory drawing which shows discrimination | determination of the work number in one Embodiment Graph showing the relationship between beam spot diameter, oscillation frequency and distance of ultrasonic displacement sensor Graph showing relationship between energy density, oscillation frequency and distance of ultrasonic displacement sensor The graph which shows the relationship between the beam spot diameter of the ultrasonic displacement sensor in one embodiment, an oscillation frequency, and distance Graph showing output value versus time in a conventional ultrasonic displacement sensor The graph which shows the output value versus time in the ultrasonic displacement sensor in one embodiment Explanatory drawing of the discrimination effect with respect to the temperature change in the ultrasonic displacement sensor in one embodiment Explanatory drawing which shows the measurement interval in the ultrasonic displacement sensor in one Embodiment The flowchart which shows the setting method of the threshold value in one Embodiment The graph which shows the allocation state of the threshold value with respect to each workpiece | work number in one Embodiment

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

  In the production of automobiles, in order to meet the diversification of consumer needs for automobiles, multi-model small-volume production is desired. Under such multi-model low-volume production, from the viewpoint of production efficiency, total line length, cost of incidental equipment, line availability, etc., it corresponds to multiple models rather than assembling products with dedicated lines for each model. It is preferable to assemble products on a multi-model mixed line that can be made. However, the type of work required for product assembly, the number of work required to complete the product, the time required for each work, and the like vary greatly depending on the model.

  FIG. 1 is a configuration diagram in which a workpiece identification device according to an embodiment of the present invention is applied to a machining center that is a machine tool. Reference numeral 6 denotes a workpiece, which is a cylinder block in which a plurality of pistons are accommodated and a crankshaft is attached to a lower crankcase portion.

  As the cylinder block, cast iron or aluminum alloy casting is generally used, and a wide variety of workpieces 6 are mixedly introduced into the transfer line. There are cylinder block transfer lines in automobile engine manufacturing factories, and there are many cases where a plurality of types of cylinder blocks flow as a work in the transfer line. For this reason, it is necessary to determine the type of cylinder block at the entrance or exit of the transfer line.

  The machining center is a numerically controlled machine tool that performs various processes such as milling, drilling, boring, and tapping without changing the attachment of the workpiece (workpiece). In FIG. 1, for example, 5 performs drilling. It is a machine tool. Furthermore, the tool magazine stores a large number of cutting tools, automatically performs processing according to computer numerical control commands, and has an automatic tool changer. Furthermore, there are known ones in which a work table can be rotated at high speed and turning can be performed by attaching a cutting tool to the spindle, a grinding wheel can be used in place of a milling tool, and a probe for measuring dimensions is mounted. Since machining is the main purpose, therefore, the environment where the machining center is installed contains oil mist and dust, which are fine particles, and an ultrasonic displacement sensor is used to identify castings such as cylinder blocks. It is desirable.

  The cylinder block which is the workpiece 6 is placed on the transfer line, is sent in the direction of arrow A, and stops. Reference numerals 1 and 2 are ultrasonic displacement sensors, 1 is a master sensor, 2 is a slave sensor, and transmits ultrasonic waves to an identification unit provided at a predetermined position of the workpiece 6 when the workpiece 6 is stopped. The model is identified by receiving the reflected wave.

  Reference numeral 3 denotes a sensor unit that performs measurement and discrimination by the master sensor 1 and the slave sensor 2, and receives a measurement start instruction from the machine tool controller 4 and transmits a discrimination result. After receiving the determination result, the machine tool controller 4 instructs the workpiece 6 to move to a workable position indicated by a broken line. Then, the discrimination result received from the sensor unit 3, that is, the machining instruction depending on the model is given to the machine tool 5. The processing instruction is, for example, the size and position of a hole as a specification in drilling, and a rotational speed as a processing condition.

  Here, since the ultrasonic wave is excellent in focusing and directivity and is a dense wave of air, the influence of scattering by fine particles in the air is small compared to the optical type, and oil mist and dust on which the machine tool 5 is installed Stable measurement is possible even in the environment. In addition, if ultrasonic waves are used, the measurement object (work 6) can be measured in a non-contact manner, such as metal, wood, glass, rubber, powder, liquid, and several hundred mm from the work 6. Can be done long distances away.

  The ultrasonic displacement sensor detects the presence or absence of an object and the distance to the object by transmitting an ultrasonic wave toward the object with a transmitter and receiving the reflected wave with a receiver. Ultrasonic elements are used to transmit and receive ultrasonic waves. Ultrasonic elements are elements that generate ultrasonic waves by applying electrical energy or convert ultrasonic vibration energy into electrical signals. A barium titanate vibrator using a piezoelectric phenomenon can be used.

  A piezoelectric element vibrates efficiently when an alternating voltage is applied, the element vibrates, has a unique frequency, and an alternating voltage having the same frequency as that frequency is applied. Generally, a frequency of 40 kHz is often used. A low frequency is used to measure a long distance, and a high frequency is used to accurately measure a short distance.

  In addition, the ultrasonic displacement sensor can measure all materials including metal, wood, glass, rubber, etc., powder and liquid, and is non-contact, so there is no problem of viscosity and corrosion. It has features such as long-distance detection that does not interfere with moving objects in the transport line, and stable level measurement in adverse environments.

  Further, the ultrasonic displacement sensor measures the length by measuring the time from transmission to reception of sound waves. Therefore, since the ultrasonic displacement sensor does not change the arrival time even if the surface roughness of the object to be measured is large or the strength changes, it is not affected by the surface roughness unlike the optical type and is stable. Measurement is possible. In particular, when the workpiece 6 is a cast cylinder block, this advantage can be utilized, and even if the cylinder block is heated, it is not affected.

  In addition, the speed of sound in the air varies depending on the temperature, and the measurement result of the ultrasonic displacement sensor is affected by atmospheric changes. Therefore, each of the master sensor 1 and the slave sensor 2 is an ultrasonic displacement sensor that measures the time from transmission to reception, and the sensor unit 3 uses the difference between the measurement values of the pair of master sensor 1 and slave sensor 2. Make a decision.

  Since the model discrimination is performed using the difference between the values measured by the master sensor 1 and the slave sensor 2, the temperature, oil mist, dust, etc. at the distance from the master sensor 1 and the slave sensor 2 to the identification part of the workpiece 6 are determined. The effect can be offset. Therefore, even in an environment such as a cylinder block production line, it is possible to accurately discriminate many models while setting a sufficient operating distance that does not hinder processing.

  FIG. 2 is a block diagram showing the discrimination process. The master sensor 1 and the slave sensor 2 are configured to measure the distance to the workpiece 6. FIG. 3 shows the shape of the identification portion that becomes the measurement surface of the workpiece 6. The shape of the identification portion is integrated with the workpiece 6, and a step is provided between the surface facing the master sensor 1 and the surface facing the slave sensor 2, and the unevenness is several mm.

  In the measurement, the measurement surface needs to face the master sensor 1 and the slave sensor 2 as shown in FIG. 3 at the stop position of the workpiece 6, and the size of the measurement surface depends on the stop position accuracy and the ultrasonic displacement sensor. Determined by beam size. However, the cylinder block is a casting and is required to have a smaller measurement area. By making the identification part a step, it becomes possible to distinguish more models by clarifying the measurement range.

  Further, by taking the difference between the measured values of the master sensor 1 and the slave sensor 2, the length measurement process between the sensor and the workpiece 6 is canceled, and the measurement is limited to the measurement of only the unevenness. If two ultrasonic sensors are simply used side by side, the sound waves interfere with each other, resulting in a measurement error. However, the master sensor 1 and the slave sensor 2 alternately oscillate ultrasonic waves so as to avoid interference. Therefore, it is possible to avoid the ultrasonic waves from interfering with each other between the master sensor 1 and the slave sensor 2.

  As shown in FIG. 2, the master sensor 1 and the slave sensor 2 have the same configuration, and have ultrasonic elements 31 and 32, respectively, and are switched by the CPUs 33 and 34 to perform transmission and reception. The memories 35 and 36 temporarily store measurement data, and the CPUs 33 and 34 control the storage and reading. The master sensor 1 and the slave sensor 2 are connected to each other, and the ultrasonic element 32 of the slave sensor 2 is oscillated in synchronization with a clock signal generated by the master sensor 1. The measurement data of the slave sensor 2 is transmitted to the CPU 33 of the master sensor 1. Thereby, even if the measurement is repeated many times, the transmission timing of the ultrasonic wave is not shifted, and interference can be avoided for a long time.

  The configuration shown in FIG. 2 is an example, and any configuration can be adopted as long as the configuration exhibits the same function. For example, instead of using two CPUs 33 and 34, a configuration in which the master sensor 1 and the master sensor 2 are controlled by one CPU can be adopted, or the master sensor 1 and the master sensor can be used by one memory. A configuration for operating 2 may be adopted.

  The CPU 33 of the master sensor 1 is connected to the machine tool controller 4, the machine tool controller 4 instructs the start of measurement, and the determination result is transmitted from the CPU 33 to the machine tool controller 4. After receiving the discrimination result, the machine tool controller 4 moves and stops the workpiece 6, and gives a machining instruction according to the discrimination result to the machine tool 5.

  In order to avoid interference, the master sensor 1 and the slave sensor 2 generate a clock signal serving as a reference time for transmitting an ultrasonic wave by the master sensor 1, and the slave sensor 2 synchronizes with the generated clock signal on the master sensor 1 side. The master sensor 1 and the slave sensor 2 oscillate alternately so as to transmit ultrasonic waves, and the oscillation / transmission interval is set to a time sufficient to eliminate reverberation due to the reflected wave from the work 6. Since the reverberation due to the reflected wave depends on the operating distance between the master sensor 1, the slave sensor 2, and the workpiece 6, the operating distance is determined by setting the transmission (transmission) interval.

  The measurement is started by first transmitting an ultrasonic wave from the ultrasonic element 31 of the master sensor 1 and then transmitting an ultrasonic wave from the ultrasonic element 32 of the slave sensor 2. With this as one set, the transmission is stopped after repeating a predetermined number of sets. The identification shape that becomes the measurement surface of the workpiece 6 is an uneven pattern shape provided on the surface as shown in FIG. In the example of FIG. 3, the distance from the master sensor 1 to the workpiece 6 is 200 mm as the operating distance, the distance from the slave sensor 2 to the workpiece 6 is 197 mm, and the slave sensor 2 side has a convex step toward the 3 mm ultrasonic displacement sensor side. It has become.

  The value of the step is preferably about 1/40 to 1/200 of the operating distance from the viewpoint of measurement error. Thereby, even when the number of models to be distinguished is large, the resolution of the sensor can be ensured. An ultrasonic wave is transmitted from the ultrasonic element 31 of the master sensor 1, and the time until the reflected wave from the concave portion of the workpiece 6 reaches the master sensor 1 is counted as measurement data and stored in the memory 35. Next, the ultrasonic wave is transmitted from the ultrasonic element 32 of the slave sensor 2 at different timings so as not to interfere with each other, and the time until the reflected wave returns to the slave sensor 2 is counted and stored in the memory 36.

  After stopping transmission, the slave sensor 2 outputs the measurement data stored to the master sensor 1. The master sensor 1 calculates the difference between its own measurement data stored in the memory 35 and the measurement data output from the slave sensor 2. Then, the CPU 33 of the master sensor 1 determines that the slave sensor 2 side is 3 mm convex as the measurement surface pattern.

  FIG. 4 is an explanatory diagram for explaining a mode (mastering mode) in which a memory number is assigned and a threshold value used as a criterion for determination is stored in the memory 35. For the cylinder block actually mounted on the conveyance line to be measured, a master work 11 serving as a reference is separately prepared for the necessary types and set in the master sensor 1 and the slave sensor 2. The measurement unit measures the master work 11 by placing the master work 11 corresponding to the work number 1 on the conveyance line of the work to be actually measured. The difference value between the read master sensor 1 and slave sensor 2 is stored, and is registered as the work number 1 as shown in the discrimination data table 12 as a discrimination reference in correspondence with the work number 1. The determination data table 12 is stored in the memory 35 of the master sensor 1 as a table structure.

  In addition, since the arrival time varies depending on the measurement environment, the measurement unit performs a plurality of measurements on the master work 11 corresponding to each work number. In order to increase the number of discriminating models, it is desirable to set the threshold value with a predetermined range from the statistics of the obtained data group.

  FIG. 5 is an explanatory diagram illustrating a discrimination mode in which the discrimination of the work number is shown and the cylinder block (work 6) placed on the transfer line is measured and identified. The workpiece 6 is measured as described above, and the measured difference value between the master sensor 1 and the slave sensor 2 is compared with the discrimination data table 12 to obtain a matching workpiece number. When it matches with the work number 1, it outputs that the work number is 1 to the machine tool controller 4. The machine tool controller 4 executes a processing instruction or the like corresponding to the work number 1.

  The identification shape that becomes the measurement surface of the workpiece 6 is convex toward the ultrasonic displacement sensor side by 3 mm with respect to the master sensor 1 side on the slave sensor 2 side. Each work number is assigned in 4 steps of 1 mm each.

  Since the cylinder block is a casting made by pouring metal into a mold, it cannot be as accurate as 0.1 mm or 0.01 mm as required for metal cutting products. The predetermined amount for stepping the step is 0.7 to 1.4 mm, preferably about 1 mm because it is rough and uneven. Thereby, manufacture of a cylinder block becomes easy even if the number of model discrimination increases.

4 types of identification can be made with respect to the convex pattern on the side of the slave sensor 2 such that the step 3 mm is workpiece number 1, 4 mm is workpiece number 2, 2 mm is workpiece number 3, and 1 mm is workpiece number 4. At this time, it is desirable not to assign the work numbers in the order of the size of the steps, but to approach the center value of the steps in which the work numbers of a large number of models are set. In other words, when there are many models of the work number 1, it is preferable to assign it to 3 mm that is close to the center value of the step (or the center value when five steps are used).
The reason is that it is more reliable to distinguish large steps than to distinguish small steps. For example, it is more reliable to identify 3 mm and 5 mm than to identify 5 mm and 4 mm as steps. Therefore, exception determination can be easily performed by assigning a large number of models to the center value of the step, for example, 3 mm, and assigning an exceptional model to 5 mm.

As another pattern, a pattern in which the unevenness is reversed on the master work 11 and the step difference is similarly prepared by making the master sensor 1 side convex with respect to the slave sensor 2 side is prepared. Thereby, 4 × 4 = 16 types of model discrimination can be performed. Thereby, the input / output system of the master sensor 1 and the machine tool controller 4 can be reduced to 4 bits (2 ⁴ = 16 types can be handled with 4 bits). Of course, in order to increase the number of model discrimination, the number of steps may be increased, or a pattern without steps may be provided.

  FIG. 13 is a flowchart illustrating a threshold value setting method, and the measurement unit performs a plurality of measurements on the master work 11 corresponding to each work number. The calculation unit obtains a threshold value for identifying the model. The threshold is set with a range. First, the master work 11 serving as a discrimination reference is installed, for example, at the start of operation of the cylinder block transfer line in an environment for model discrimination (S1). Next, the measurement of the time D is repeated a plurality of times, for example, 32 times (S2) every predetermined time for one master work 11 corresponding to the work number 1, and is stored in the memory 35 as a data group of the times D1 to D32. (S3).

  The calculation unit obtains the average value Da and the standard deviation σ from the times D1 to D32 of the obtained data group (S4). The threshold value for the work number 1 is set in the determination data table 12 as ± 3σ around the average value Da, that is, Da ± 3σ (S5). For the workpiece 6 placed on the transport line, the master sensor 1 and the slave sensor 2 transmit ultrasonic waves to the identification unit and receive reflected waves, and the identification determination unit determines the difference between the measured values. If it falls within the threshold range set in the data table 12, the work 6 is determined to be work number 1. If the workpiece 6 is known as the workpiece number 1, the fact that the workpiece number is 1 is output to the machine tool controller 4. The machine tool controller 4 executes a processing instruction or the like corresponding to the work number 1.

  FIG. 14 is a graph showing the assignment state of the threshold value for each work number. As an example, work numbers 1 to 6 are assigned as a step of 1 mm. Prepare six master workpieces 11 with different steps for each workpiece number, obtain the data group, average value Da, and standard deviation σ according to FIG. 13, respectively, and the threshold is centered on the average value indicated by the black circle of each workpiece number Is set to a range indicated by a vertical line. In the case of a casting such as a cylinder block, it is shown that each set value can be determined so as not to overlap if the step is 0.7 to 1.4 mm, preferably about 1 mm.

  According to the determination of the threshold value as described above, the threshold value is determined based not only on the numerical value but also on the basis of the value measured at the start of operation of the transfer line of the workpiece 6 in the actual measurement environment using the master workpiece 11. In addition, due to the fact that measurement values vary in the measurement environment, and statistical errors are taken into account, the threshold does not become more than necessary, and it is possible to handle a large number of models and improve reliability. Can do.

  In addition, although the description has been made centering on the average value of the data group, the mode value may be the center of the threshold. Furthermore, the standard deviation σ is obtained and set in the determination data table 12 as the average value Da ± 3σ. However, it is possible to use ± σ and ± 2σ instead of ± 3σ depending on the numerical distribution status of the data group. Furthermore, it is also effective to learn a large number of measurement values obtained by each master work 11 or a number of measurement values at the time of identification / determination of the work 6, and use the results as experience values to determine the threshold value and range from the experience values. .

  In general, the ultrasonic wave has a tendency that the measured value is not only influenced by the air temperature, but also the beam size is widened with respect to the workpiece 6 which is a measurement object. As a result, the measurement area must be increased, and in the case of a cylinder block, the influence is great due to the surface shape of the casting and the roughness, making it difficult to put it to practical use. In addition, an ultrasonic horn, which is a reflector for focusing and emitting or receiving ultrasonic waves in a certain direction, can be provided to reduce the beam size, but only a sound wave that travels straight from the object to be measured can be received. Therefore, it is desirable to utilize the fact that the ultrasonic wave can increase in linearity in proportion to the height of the frequency and can reduce the beam size.

  In addition, when the frequency is the same and the transducer dimensions are different, the directivity becomes sharp when the transducer size is large, and the beam width is large at a short distance, but the ultrasonic beam is not so wide at a long distance. On the other hand, if the size of the transducer is small, the directivity becomes dull and the beam width is small at a short distance, but the beam divergence becomes large at a long distance, and the echo height is significantly lowered due to the distance.

  FIG. 6 shows the relationship between the beam size, the oscillation frequency, and the distance of the ultrasonic displacement sensor, where the alternate long and short dash line is 40 kHz, the broken line is 100 kHz, and the solid line is 300 kHz. On the other hand, FIG. 7 shows the relationship between the energy density of the ultrasonic displacement sensor, the oscillation frequency, and the distance, and the energy density related to the output intensity attenuates as the oscillation frequency increases as shown in the figure. As in FIG. 6, the alternate long and short dash line is 40 kHz, the broken line is 100 kHz, and the solid line is 300 kHz.

  FIG. 8 shows the actual measurement value of the beam size when the oscillation frequency is 40 kHz and 300 kHz. When the frequency is 300 kHz, the operation distance is 200 mm from the workpiece 6 (cylinder block) to the master sensor 1 and 20 mm corresponding to an appropriate measurement area. It can be. The oscillation frequency can be 200 to 400 kHz, the operating distance can be 150 to 250 mm, and the beam size can be 15 to 25 mm, which is a practical value for the cylinder block. Further, since the distance from the master sensor 1 and the slave sensor 2 to the identification unit is set to 150 to 200 mm, it is not necessary to bring the sensor close to each other in the cylinder block production line, so that the position control for stopping the workpiece 6 can be easily performed. Also, the sensor position does not become an obstacle to machining the workpiece 6.

  In addition, since the cylinder block is a casting, the unevenness of the measurement surface is limited to producing a step of about 1 mm. On the other hand, when the oscillation frequency is 40 kHz and the beam size is about 60 to 80 mm as in the conventional ultrasonic displacement sensor, the resolution is about 1 mm, and a step of 1 mm cannot be measured.

  If the oscillation frequency is 200 to 400 kHz and the operating distance is 150 to 250 mm, the resolution can be improved to about 0.1 mm, and the identification of the limit of 1 mm that can be stepped with the casting takes into account the influence of the surface roughness of the casting. Even it will be possible enough. By setting the ultrasonic oscillation frequency to 200 to 400 kHz, the ultrasonic beam size can be reduced, and the area of the identification unit can be reduced. In addition, since the beam size at the identification part of the ultrasonic wave to be transmitted is set to 15 to 20 mm, the production of the identification part does not become an obstacle even if the object has a complicated shape such as a casting like a cylinder block. However, when an electric signal close to the resonance frequency is applied to the ultrasonic elements 31 and 32 in a pulsed manner, even after the electric signal disappears, a phenomenon in which ultrasonic vibration mechanically lasts for a short time occurs, and the reflection type is used. Therefore, if this phenomenon continues for a long time, detection becomes difficult.

  FIG. 9 shows the time change of the output voltage from oscillation to reception when the oscillation frequency is about 40 kHz as in the prior art. The peak on the rightmost graph in FIG. 9 is obtained by detecting multiple reflected ultrasonic waves. As described above, since the ultrasonic wave having a low frequency has a small attenuation after transmission, it is easy to cause multiple reflection, and the conventional ultrasonic distance measuring device may erroneously detect the multiple reflection. On the other hand, when the oscillation frequency is 200 to 400 kHz, since the attenuation of the ultrasonic wave is large, the reflected wave is large as in the peak (the one in which the reflected wave is detected) in the rightmost graph in FIG. Attenuation and influence of multiple reflection can be reduced, and variation in measurement can be reduced.

  FIG. 11 shows the discrimination effect on the temperature when the master sensor 1 and the slave sensor 2 are used as one set. If the temperature rises by 10 ° C, the speed of sound will rise, so if you do not compensate for the increase in temperature by 10 ° C, the distance of 200 mm is measured as 196.5 mm, but this difference is measured and calculated, so this effect is ignored It can be made as small as possible. In practice, the change in temperature by 10 ° C. with a step of 1 mm is about 0.017 mm.

  FIG. 12 shows the timing of oscillating ultrasonic waves when the master sensor 1 and the slave sensor 2 are used as one set. The oscillation of the slave sensor 2 is delayed with respect to the oscillation of the master sensor 1 by a sufficient time during which the two ultrasonic waves do not interfere with each other and a time longer than the time for reciprocating the operating distance of 200 mm and at the same time when no transmission is performed. In order to synchronize with the common clock so that the two timings are not shifted, the CPUs 33 and 34 control each other. Moreover, in order to reduce the variation in the measured values, it is desirable to repeat the measurement times 32 to 64 times with one identification. Moreover, it is desirable to calculate the median of repeated measurement values like a median filter and to stabilize by excluding different values.

  In the above embodiment, the discrimination target is a casting. However, the discrimination target is not particularly limited as long as it can form irregularities. For example, a plastic molded product can be formed integrally with the workpiece 6.

DESCRIPTION OF SYMBOLS 1 Master sensor 2 Slave sensor 3 Sensor unit 4 Machine tool controller 5 Machine tool 6 Work 11 Master work 12 Discrimination data table 31, 32 Ultrasonic element 33, 34 CPU
35, 36 memory

Claims (10)

In the workpiece identification device for identifying the type of workpiece on the conveyance line, the identification unit being provided at a predetermined position,
A master sensor and a slave sensor that transmit ultrasonic waves toward the identification unit, receive reflected waves, and measure a time from transmission to reception,
The workpiece identification apparatus, wherein the model is determined using a difference between values measured by the master sensor and the slave sensor. The master sensor and the slave sensor are arranged at positions facing the identification unit,
The workpiece identification apparatus according to claim 1, wherein the model identification is performed by detecting a step between a surface of the identification unit facing the master sensor and a surface of the identification unit facing the slave sensor.   The workpiece identification apparatus according to claim 1, wherein the transmission of the ultrasonic wave is alternately performed by the master sensor and the slave sensor.   The work identification apparatus according to any one of claims 1 to 3, wherein an oscillation frequency of the ultrasonic wave is 200 to 400 kHz.   5. The clock signal as a reference time for transmitting an ultrasonic wave by the master sensor is generated, and the ultrasonic wave is transmitted by the slave sensor in synchronization with the clock signal. The workpiece identification device described in 1.   6. The workpiece identification apparatus according to claim 1, wherein a distance from the master sensor and the slave sensor to the identification unit is 150 to 200 mm.   The workpiece identification apparatus according to claim 1, wherein the workpiece is a cylinder block, and the conveyance line is used for machining the cylinder block.   8. The workpiece identification apparatus according to claim 2, wherein the workpiece type is identified by measuring the step changed by a predetermined amount for each workpiece type. 9. A workpiece identification method for identifying the type of workpiece on a transfer line,
An identification unit is provided at a predetermined position of the workpiece, and a master sensor and a slave sensor transmit ultrasonic waves toward the identification unit and receive a reflected wave to measure a time from transmission to reception. A workpiece identification method, wherein the model is identified using a difference between values measured by a slave sensor.   The work identification method according to claim 9, wherein the transmission of the ultrasonic waves is alternately performed by the master sensor and the slave sensor.