JP3201170B2 - Exploration distance setting method for industrial robots - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an industrial robot for assembling a part to a work object by fitting the part into the work object, inserting the part into the work object, or tightening the screw to the work object.

[0002]

2. Description of the Related Art Conventionally, in an industrial robot or the like for assembling parts to the same place each time, a point at which the success rate of assembling is considered to be the maximum is taught as a work center point, but the success rate is further improved. Japanese Patent Laid-Open No.
In No. 1701, when assembling at the work center was not successful, assembling at several search points around the work center was attempted, and a search point having a success rate better than that at the work center was determined. In some cases, the search point is changed to a new work center.

Here, the search point is set in a plurality of directions separated by a search distance from the work center point, and the search distance is determined by performing a test operation prior to the actual operation of the industrial robot. The success rate distribution of the work is measured in advance, the distance between the work point having a higher success rate than the work center point taught and the work center point taught is estimated, and the distance is set as the search distance. , Having a fixed value.

[0004]

As described above, conventionally, since the exploration distance is set based on the success rate distribution of the work measured by performing the test operation using the actual product,
A large number of products are required for measuring the distribution of the success rate, and many products are wasted, resulting in a large loss.

The present invention relates to an industrial robot that attempts to work at a search point separated by a search distance when the work has failed at a certain work center, without increasing the number of work failures. The purpose is to set the exploration distance to a point appropriately.

[0006]

According to a first aspect of the present invention, there is provided a work performing unit comprising a mechanical part of a robot for performing a work on a work target, and a work center which is a position where the work is to be performed in the work performing unit. A robot controller comprising: means for setting a point; and control means for controlling the operation of the work performing unit based on the work center point, wherein the means for storing the work center point to be set is stored. Work instructing means for moving the work performing unit toward the work central point to perform the work, and grasping the success rate of the work by dividing the number of successful works by the number of work at the work central point Work determination means, search command means for moving the work performing section toward a plurality of preset search points around the work center point, and performing the search as the work, the work at each of the search points The quality of it Search determination means for determining the success rate obtained by dividing the number of successes of the work at each search point by the number of work times, the success rate of the work at the work center point and the success rate at each search point In an industrial robot having a correction means for correcting the work center point from a relative relationship based on the difference between the work object and the work object gripped by the work object, the distribution of the relative position variation and the work Create a success rate distribution function of the work from the range of the allowable error to succeed, the success rate distribution of the work in the success rate distribution function, and the success rate at the work center point, in the success rate distribution of the work The technical means is to calculate the distance between the point where the success rate is maximum and the work center point, and to set the calculated distance as the search distance between the work center point and the search point.

According to a second aspect of the present invention, in the first aspect of the present invention, the position where the success rate is maximum in the success rate distribution of the work, and the work object and the work object which the work object grasps the success rate distribution of the work. The technical means is to use, as the success rate distribution function, a function obtained by connecting a position between 2 and 4 times the variance of the distribution of the relative position with a straight line.

According to the present invention, the success rate distribution function is a function in which the position where the success rate is maximum and the position where the success rate is 0 in the success rate distribution of the work are connected by a straight line. Its use is a technical measure.

According to a fourth aspect of the present invention, in the first aspect of the present invention, in the first aspect, when the work performing unit fails in the work, the work is performed again around the work, and the work is performed based on the position where the work was successful. Creating a success rate distribution is a technical measure.

According to a fifth aspect of the present invention, in the first aspect, the number of corrections when the work center point is corrected by using a function that approximates a predetermined success rate distribution, and a predetermined success rate are set. By comparing the value of the function approximating the rate distribution with the number of corrections when correcting the work center point using a function having a coefficient that differs by a small amount, it is possible to change the value of the coefficient with the smaller number of corrections. Repeating is a technical measure.

According to a sixth aspect of the present invention, in the third aspect, the work center is calculated using a variance value representing the distribution of the relative positions set in advance and a function calculated from the value of the allowable error. The number of corrections when a point is corrected, a variance value representing the distribution of the relative position set in advance, and the work center point using a function calculated from a coefficient different from the value of the allowable error by a small amount. The technical means is to compare the number of corrections at the time of correction and change the value of the permissible error to a coefficient having a smaller number of corrections.

[0012]

The operation success rate distribution indicates whether or not the operation succeeds when the industrial robot is actually operated, within a certain range, and whether the operation succeeds at a certain operation point. The success rate indicating whether or not the work is successful is determined by the relative variation between the two parts, the work target and the work target, and the allowable error for the successful work. Therefore, the success rate distribution of the work itself considers how the relative position between the work target and the work target is dispersed with no actual operation of the industrial robot. It is only necessary to be able to measure.

[0013] Variations in the relative positions of the work target and the work target can be measured by a distance sensor and a visual device.
A normal distribution or a distribution function equivalent thereto can be assumed, and an allowable error for successful operation is set in advance for each component. As a result, a work success rate distribution function can be obtained from the variation in the relative position between the work target and the work target and the allowable error for the successful work.

The above is performed prior to the actual working process.
Then, after teaching a certain point as a work center point, the industrial robot is operated. When a task is performed at a certain work center and the success rate at that point is calculated, if the success rate distribution function for that work is known, the highest point of the success rate in the success rate distribution and the work center point Can be estimated. Therefore, by using that distance as the search distance, when moving from a certain work center to the search point, there is a high probability that the search point is a work point with a higher success rate than the initial work center point, and it is easy to succeed. The work center point can be corrected to a work point with a high rate.

[0015]

According to the present invention, the distribution of the variation in the relative position between the work object and the work object obtained by measurement or the like in advance and the success rate distribution of the work determined by the allowable error of the success of the work are given. By doing so, an appropriate search distance can be set at the time when the success rate at the work center point is measured, so that the work center point can be easily corrected to a point having the best work success rate. In this case, since the work success rate distribution does not require actually operating the industrial robot, a large number of products are not required to measure the work success rate distribution,
Product defects will not occur, and even if work at the taught work center point fails, the distance from that point to the search point will be set appropriately, minimizing product defects that occur during the search. Can be minimized. Therefore, it is possible to greatly reduce the loss due to product failure due to the failure of the operation as compared with the related art.

In the second aspect of the present invention, the position where the success rate is maximum in the success rate distribution of the work and the success rate distribution of the work are determined by calculating the variance of the distribution of the relative position between the work target and the work target gripped by the work target. Since the function connecting the positions between 2 and 4 times with a straight line is used as the work success rate distribution function, the calculation formula for calculating the search distance can be simplified. Therefore, the program can be simplified.

According to a third aspect of the present invention, a function connecting a position where the success rate is maximum and a position where the success rate is zero with a straight line in the success rate distribution of the work is defined as a success rate distribution function. The equation can be further simplified, the program can be simplified, and the measurement of the distribution of the variation in the relative position between the work target and the work target can be simplified, so that the adjustment load is reduced. Can be.

According to the present invention, after the work center point is corrected, the distance between the new work center point and the point with the highest success rate is calculated based on the success rate at the corrected work center point. Since a new search distance is set, a search for a point having the highest success rate can be performed with a small number of corrections.
Thus, the points with a better success rate are quickly searched and the work center point is easily modified to a point with a better success rate. As a result, the number of work failures can be reduced.

According to a fifth aspect of the present invention, for the function approximating the success rate distribution function, the work center point is corrected using a function having a coefficient that differs only slightly, and as a result of comparing the numbers of corrections, the number of corrections is small. Since the coefficient is used, a coefficient suitable for the actual operation is selected, and the number of times the operation fails is reduced. According to claim 6, the distribution of the work success rate is calculated using two values having different coefficients as an allowable error for the work to be successful, and the number of corrections when the work center point is corrected is compared. Is selected as the allowable error, the convergence of the correction to the most suitable point is quickly performed. Therefore, the number of work failures is reduced.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described based on an assembling operation in an industrial robot 1. FIG. An industrial robot 1 whose functional configuration is shown in FIG. 1 is a teaching playback robot for assembling a lamp 5 into a hole 4 of a substrate 3 as shown in FIG. 2, and a robot control circuit 10 includes a CPU 11 and a RAM 1
2, the ROM 13, the drive circuit 14, the sensor 15, and the interface 16, and the work performing unit 20 includes a servomotor 21 and a robot hand 22.

The work operation of the industrial robot 1 is as follows. The robot hand 22 is driven by the servomotor 21 to insert the lamp 5 into the hole 4 of the substrate 3 and the claw 6 of the lamp 5 inserted into the hole 4 The assembly is completed when it is locked to the substrate 3. The sensor 15 is turned on when the robot hand 22 grips the lamp 5 at the chuck position,
Is in the off state when is not left in the robot hand 22.

The robot control circuit 10 stores in the RAM 12
A register R0 that stores the number of operations and the number of successes at the operation center point P0, and the number of operations at the search points P1 to P4;
ROM having registers R1 to R4 for storing the number of successes
The work performed by the work performing unit 20 is performed according to the control procedure of the operation program in the control unit 13. The robot control circuit 10
The signal of the sensor 15 for determining the pass / fail of the work is converted and fetched by the interface 16, and the success of the work is determined when the sensor 15 changes from the on state to the off state. .

The industrial robot 1 having the above configuration is
By the operation program incorporated in the robot control circuit 10, the assembling operation is performed at the work center point P0 taught in advance, and when the work at the work center point P0 is unsuccessful, the work is performed at a nearby search point. It has a learning program for sequentially correcting the work center point P0, which is the work target position, to a work point with a higher work success rate. Here, as shown in FIG. 3, the plurality of search points P1 which are separated from the work center point P0 by the search distance L in the X-axis direction and the Y-axis direction are modified by the learning program.
To P4, and the correction is performed based on the respective work success rates at the work center point P0 and the search points P1 to P4.

Prior to the assembling work by the industrial robot 1 having the above-described configuration, first, a variation in a relative position between the work target and the work target is measured. The measuring device may be any device that can measure the position, such as a visual device, even with a distance sensor.

FIG. 4 shows an example in which the visual device 50 is used.
The visual device 50 is attached to the robot hand 22 to flow the product, and each time the product is positioned, the work target position of the product is measured. In this example, the lamp 5 is assembled to a resin product, so that the position of the lamp assembly hole of the resin product is measured. With this measurement, it is possible to measure the variation in the relative position of the work target position between the industrial robot 1 and the product.

If the positioning accuracy of the industrial robot 1 is high and the positioning error of the product is sufficiently small compared to the variation in the position of the product and the dimensional error, only the variation in the working position of the product may be measured. For example, there are a method of measuring a hole position at a work position using a laser displacement meter, and a method of measuring an arbitrary position at which a product is easy to measure and a dimensional variation from the arbitrary position to the work position, and adding both. In the latter case, the variation at any position where the product is easy to measure is represented by σ1,
Assuming that the dimensional variation from an arbitrary position to the work position is σ2, the product work position variance σ is

[0027]

(Equation 1) It is represented by The variation in the work position of the product (probability density distribution) assumes a normal distribution or another distribution function equivalent thereto. Normally, a normal distribution function is sufficient. The normal distribution function of the variation (probability density distribution) of the work position of the product is shown in FIG.
As shown in (a), the horizontal axis represents the position and the vertical axis represents the probability density.

Next, the allowable range in which the operation is successful is measured. In the case of assembling and inserting work, this is usually a clearance, for example, a difference between the diameter of a part to be inserted (the insertion part of the lamp) and the diameter of the hole 4 to be inserted.
In the case of work such as soldering or application of an adhesive, even if the material is shifted, it is within a range that can be determined as a good product.

When the above measurement is completed, a success rate distribution function is created. The success rate distribution function integrates the normal distribution function within the allowable range 2α in which the operation is successful while shifting the position from one end of the normal distribution function indicating the variation of the work position of the product to the other end. Thus, the success rate at each position can be obtained. Figure 5 shows the result of integration.
(B). FIG. 6 shows a success rate distribution function created based on this result.

Next, the search distance L is calculated using the success rate distribution function shown in FIG. To calculate the search distance L, the success rate P (a) at the taught work center point a is measured, and the value is applied to the success rate distribution function to estimate the distance L to the point at which the success rate is maximized. And set it as the search distance L. The success rate is determined based on the success or failure of the assembly operation performed by operating the industrial robot 1. The assembling work of the industrial robot 1 will be described later.

The success rate distribution function has the same effect even if the distribution of the work success rate is expressed by a linear approximation for simplicity. As shown in FIG. 7, as a method of forming a first-order approximation formula, a succession rate distribution function uses a function connecting a position where the success rate is maximum and a position where the success rate is 0 in the success rate distribution of the work as a straight line. There is a method of expressing the entire area of the distribution by a linear function.

However, according to the teaching of a normal worker, as shown in FIG. 8, if a first-order approximation formula is created using a point 3 s away from the center of the success rate distribution, even if the search distance L is set to the first-order approximation formula, Performs accurately with little error. Since the teaching by the operator is usually performed within a range of 2σ to 3σ from the center of the success rate distribution, the error of the approximate expression in a range up to a point 3σ away from the center of the success rate distribution is reduced. What is necessary is just to set.

Using this linear approximation, the linear approximation P of the success rate distribution is

(Equation 2)

Therefore, when x = L is substituted, the search distance L becomes

(Equation 3) Therefore, if the success rate P at a certain work center point is calculated,
The distance L between the work center point for which the success rate has been calculated and the point having the best success rate is calculated by the above formula 2, and this distance L can be used as the search distance L.

Next, the control operation of the learning program for correcting the work center point P0, including the search distance setting program for setting the search distance L as described above, will be described with reference to FIG. First, it is determined whether the search distance L has been calculated (step S101). If not calculated (No), the assembling work is performed at the work center point P0 (step S102). It is determined whether the number of assembly operations has reached the required number of samples (step S103). If the required number of samples has not been reached (No), the process proceeds to step S108. If the required number of samples has been reached (Ye
s), calculate the success rate T0 at the work center point P0 (step S104), and further, based on the function of the work success rate distribution and the success rate T0 given as described above, the search distance L.
Is calculated (Step S105), one work operation is completed, and the routine goes to Step S101.

If the search distance L has been calculated in step S101 (Yes), the assembling work is performed at the work center point P0 or the search points P1 to P4 (step S1).
06). In this assembling work, the assembling work is first attempted at the work center point P0, and if successful, the other search points P1 to P4
The assembling work is not performed, and the assembling work is sequentially attempted at each of the search points P1 to P4 only in the case of failure. Regarding the success or failure of the work, the number of works and the number of successes are stored in registers R0 to R4 corresponding to the work center point P0 or the search points P1 to P4 where the work was performed. For the work center point P0, the success rate is calculated each time the assembly work is performed a predetermined number of times. Here, the success rate is
Each time the number of operations reaches a plurality of different required sample numbers N, for example, 20, 40, and 100, respectively, each success rate corresponding to each required sample number N is calculated.

After the assembling work in step S106, in step S107, if the success rate for the work center point P0 has been calculated, two successive success rates are compared. If no success rate has been calculated, the process proceeds to step S108. In step S107, it is determined whether or not the past success rate is equal to the current success rate. If there is a change between two consecutive success rates (No), the work lot is switched or the work site is changed. Due to the temperature change and the like, it is considered that the conditions of the work target have changed, so the work center under the different conditions, the work center point is corrected based on the success rate calculated by statistical data such as the number of successes, Since there is a possibility that work defects increase, each statistical data is initialized (step S
111) One working operation is completed, and step S10 is performed.
Move to 1.

In step S107, if there is no change in the success rate between two consecutive ones (Yes), there is a significant difference between the success rate at the work center point P0 and the success rates at the search points P1 to P4. It is determined whether or not (Step S108). In step S108, when there is no significant difference (No), one work operation ends, and the process proceeds to step S101. In step S108, when there is a significant difference (Yes), the search point P1 is determined from the success rate of the work center point P0.
It is determined whether the success rate of P4 to P4 is good (step S10).
9).

In step S109, the search points P1 to P
If the success rate of the work center point P0 is better than the success rate of No. 4 (No), one work operation is terminated, and step S10 is performed.
Move to 1. In step S109, when the success rate of the search points P1 to P4 is better than the success rate of the work center point P0 (Yes), the work center point is moved to the search points P1 to P4 with a success rate better than the work center point P0. Is changed (Step S110), one work operation is completed, and Step S1
Move to 01.

The determination of the significant difference in the success rate in step S108 and the comparison of the success rate in step S109 indicate that the assembling work as many times as the required number of samples at the work center point P0 has been completed at each of the search points P1 to P4. Done if done.

FIG. 10 shows a change in the assembly success rate when a search is performed based on the search distance L determined as described above and the work center point is corrected. As is clear from FIG.
Since the search distance L is different each time the correction is performed, when the correction is performed from a certain work center point, the search is not performed beyond the point having the highest success rate. Further, the larger the distance L between the work center point and the point with the highest success rate is, the larger the search distance L is given, so that the number of corrections can be greatly reduced.

When the work center point is corrected according to the present invention, the change in the deviation between the work center point and the point (target position) having the highest success rate is shown together with the change in the assembly work failure rate in FIG.
It is shown in FIG. As is clear from FIG. 11, it can be understood that the correction of the work center point surely reduces the magnitude of the deviation from the target position and also reduces the failure rate of the assembly work.

FIG. 12 shows a change in the cumulative number of failed assembly operations according to the present invention. According to the present invention, the number of failures of the work is almost eliminated during the time when the number of assembly work is small, and after a certain number of assembly work, a low failure rate is maintained. Therefore, even when used for a long time, the cumulative number of failures hardly increases. You can see that.

For comparison, FIG. 13 shows the change in the number of accumulated failures when the conventional search distance is fixed, and FIG. 14 shows the change in the displacement when the conventional search distance is fixed. In the case where the conventional search distance is fixed, as shown in FIG. 13, when the search distance is set to be small (0.05 m).
m) Although the cumulative number of failures does not increase as the number of times of assembly increases, the misalignment is large at the initial stage of the number of times of assembly, and the number of failures increases. Also,
When the search distance is set to be large (0.2 mm), the misalignment becomes small at the beginning of the number of assembly operations and the failure rate becomes relatively low. Since the same failure rate continues thereafter and the failure rate itself does not decrease, the cumulative number of failures always increases as the number of assembly times increases. in this way,
When the search distance is fixed, the number of failures in the initial stage of the assembly work is small, and it is not possible to set the search distance to improve the success rate of the assembly work, as in the present invention, From the success rate distribution and the success rate at the work center, if the search distance is set every time the work center is corrected, the initial success rate of the assembly work is relatively good, and the cumulative number of failures is small. can do.

FIG. 15 shows a second embodiment of the present invention. Second
In the embodiment, the substrate 103 is attached to the base 102 by the screw 101.
The torque sensor 105 determines that the operation has succeeded when the screw driver 104 has entered a predetermined torque range, and fails otherwise. Reference numeral 106 denotes a guide for guiding the screw 101 and the screw driver to the screw tightening position of the base 102.

FIGS. 16 and 17 show third and fourth embodiments of the present invention, respectively. In these embodiments, the integrated circuit component 1
11 is inserted into each of the holes 113 of the substrate 112, and in addition to the plane position, a search is performed for the six search points in which the rotation direction is added to find a point having the optimum work success rate. Reference numeral 114 denotes a sensor for determining whether or not the operation is successful.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a functional configuration of an industrial robot according to an embodiment of the present invention.

FIG. 2 is a diagram for explaining the operation of the industrial robot according to the embodiment of the present invention.

FIG. 3 is a diagram illustrating search points of the industrial robot according to the embodiment of the present invention.

FIG. 4 is an explanatory diagram of a visual device for measuring a relative position variation of a work target position between an industrial robot and a product for setting a search distance in the present invention.

FIG. 5A is a diagram showing a variation (probability density distribution) of a work position of a product for setting a search distance in the present invention, and FIG. 5B is a diagram showing an integration result with respect to FIG.

6 is a diagram showing a success rate distribution function created based on the variation (probability density distribution) of the work position of the product in FIG. 5;

7 is a diagram expressing a linear function obtained by approximating the entire region of the success rate distribution in FIG. 6 using a linear approximation formula.

FIG. 8 shows the success rate distribution of FIG. 6 as 3σ from the center of the success rate distribution.
FIG. 4 is a diagram illustrating a linear function expressed by a linear approximation using distant points.

FIG. 9 is a flowchart showing an operation program of the industrial robot according to the embodiment of the present invention.

FIG. 10 is a diagram showing a change in an assembly success rate when a search is performed based on a search distance determined according to the present invention to correct a work center point.

FIG. 11 is a diagram showing a change in a deviation between the work center point and a point (target position) having the highest success rate when the work center point is corrected according to the present invention, and a change in an assembly work failure rate.

FIG. 12 is a diagram showing a change in the cumulative number of failures in the assembling work according to the present invention.

FIG. 13 is a diagram showing a change in the number of cumulative failures in an assembly operation according to a conventional technique.

FIG. 14 is a diagram showing a change in deviation between a work center point of an assembling work and a point (target position) having the highest success rate in the conventional art.

FIG. 15 is a diagram showing an operation in the second embodiment of the present invention.

FIG. 16 is a diagram showing an operation in a third embodiment of the present invention.

FIG. 17 is a diagram showing an operation in the fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Industrial robot 10 Robot control circuit 20 Work execution part P0 Work center point P1-P4 Search point L Search distance

Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G05B 19/18-19/42 B25J 3/00-3/10 B25J 9/10-9/22 B25J 13/00-13 / 08 B25J 19/02-19/06

Claims (6)

(57) [Claims] 1. A work performing part comprising a mechanical part of a robot performing a work on a work target, means for setting a work central point, which is a position where the work is to be performed, in the work performing part, and A control means for controlling the operation of the work performing unit by means of a robot, comprising: means for storing the set work central point; and the work performing unit directed to the stored work central point. Work instructing means for moving the work to perform the work, work determining means for grasping the success rate of the work at the work center point by dividing the number of successes of the work by the number of work, and setting in advance around the work center point Search command means for moving the work performing unit toward the plurality of search points, thereby performing the search as the work,
Search determination means for determining the pass / fail of the work at each of the search points and grasping a success rate obtained by dividing the number of successes of the work at each search point by the number of work, In an industrial robot having a correction means for correcting the work center point from a relative relationship based on a difference between a success rate and a success rate at each of the search points, a relative relationship between a work target and a work target gripped by the work target. The success rate distribution function of the work is created from the distribution of the distribution of the positional deviation and the allowable error range of the success of the work, and the success rate distribution of the work in the success rate distribution function and the success at the work center point. From the rate, the distance between the point where the success rate in the success rate distribution of the work is maximum and the work center point is calculated, and the calculated distance is the search distance between the work center point and the search point. Set as Exploration distance setting method of work for robot. 2. The variance of the distribution of the position where the success rate is maximum in the success rate distribution of the work and the distribution of the relative position between the work target and the work target gripped by the work target. 2. A function obtained by connecting positions between double and four times with a straight line as the success rate distribution function.
The method for setting the exploration distance of the industrial robot described. 3. The industry according to claim 1, wherein a function connecting a position where the success rate is maximum and a position where the success rate is zero in the success rate distribution of the work by a straight line is used as the success rate distribution function. For setting the search distance of a robot for use. 4. The method according to claim 1, wherein when the work execution unit fails the work, the work is performed again around the work, and a success rate distribution of the work is created based on a position where the work was successful. Item 8. The search distance setting method for an industrial robot according to Item 1. 5. The number of corrections when the work center point is corrected by using a function that approximates a predetermined success rate distribution, and the value of the function that approximates a predetermined success rate distribution differs by a small amount. 2. The industry according to claim 1, wherein a comparison is made with the number of corrections when the work center point is corrected using a function having a coefficient, and changing to the value of the coefficient with the smaller number of corrections is repeated. For setting the search distance of a robot for use. 6. A variance value representing a distribution of the relative position set in advance, the number of corrections when the work center point is corrected using a function calculated from the value of the allowable error, and a preset value. The variance value representing the distribution of the relative positions and the number of corrections when the work center point is corrected using a function calculated from a coefficient different from the value of the allowable error by a small amount, and correction is performed. 4. The method for setting the search distance of an industrial robot according to claim 3, wherein changing the value of the allowable error to a coefficient having a smaller number of times is repeated.