JP2012196717A - Method and device for controlling robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the workload of a user for setting a value of a variable for determining the direction of a tool at a target position and furthermore to reduce the movement time of a robot.SOLUTION: When a user sets a rotational angle of the tool around a predetermined axis as an optional variable, a controller sets the rotational angle around the predetermined axis as the optional variable settable to an optional value by the controller side. The controller sets an evaluation index which is based on the movement time required when a leading end of the tool moves from the present position to the target position, and determines the value of the optional variable by optimizing the evaluation index. Since each of the above processing is executed by the controller, the direction of the tool at the target position is automatically determined to a direction for minimizing the movement time of the robot.

Description

  The present invention relates to a robot control method and a robot control device for moving a tip of a tool attached to a hand of a robot having a plurality of axes from a current position toward a target position.

  The purpose of introducing robots in factories and the like is to improve production efficiency, that is, to shorten production tact time. In order to shorten the production tact time, it is necessary to shorten the operation time in each work performed by the robot. Therefore, teaching (teaching) is performed by an operator so that the operation time of the robot is as short as possible. That is, in the present situation, the work for shortening the operation time of the robot greatly depends on the individual ability of the worker in charge of teaching.

  In teaching performed to move the tip of the tool attached to the hand of the robot from the current position toward the target position, the value of each variable for determining the tip position and orientation of the tool at the target position is determined by the operator. All are specified. Each of the above variables is a rotation angle around a predetermined axis of the tool (hand) in addition to each coordinate value of the tool tip (for example, a rotation angle around the fourth axis in the case of a 4-axis horizontal articulated robot) That's it.

  Now, depending on the type of tool attached to the hand of the robot and the work content, there are cases where the work can be achieved regardless of the direction of the tool (= the direction of the hand). For example, when an air chuck is used as a tool in a 4-axis horizontal articulated robot, the workpiece can be gripped regardless of the direction of the tool (the direction around the fourth axis). As described above, the specific direction of the tool at the position where the workpiece can be gripped (target position) may be any direction.

  FIG. 7 schematically shows an aspect of the robot when the tool tip is moved from the current position toward the target position. The robot shown in FIG. 7 is a 4-axis horizontal articulated robot, and an air chuck is attached as a tool to the hand. In FIG. 7, each axis (each joint) and each link are indicated by a circle and a straight line, respectively, and the tip of the tool is indicated by an arrow. In FIG. 7, the tool tip is moved from the current position indicated by the solid line to the target position indicated by the dotted line or the broken line, and the work is gripped by the air chuck that is a tool.

  When the robot is in a state indicated by a broken line, the tip of the tool is oriented to face the front of the workpiece (the lower surface in FIG. 7). On the other hand, when the robot is in a state indicated by a dotted line, the tool tip is inclined with respect to the front surface of the workpiece. In each of these states, the rotation angles of the respective axes (joints) are different from each other. That is, the posture of the robot changes according to the direction of the tool. Therefore, in each of the above states, the movement times from the current position are different from each other. Specifically, the movement time from the current position to the target position is shorter when the posture of the robot at the target position is the state indicated by the broken line than when the posture is indicated by the dotted line. The reason is that the amount of movement (rotation amount) of the first axis that takes the longest movement time is smaller in the dotted line state than in the broken line state.

  Even in the teaching in the case where the orientation of the tool (hand) at the target position is not questioned, the values of variables for determining the tip position and orientation of the tool at the target position are all designated by the operator. In other words, the posture of the robot at the target position (the rotation angle of each axis) is determined by the operator. However, as described above, in the case where the direction of the tool at the target position is unquestioned, there are many postures of the robot where the tip position of the tool is the same target position. The worker needs to select and determine the optimum posture from the many postures. That is, the operator needs to set the value of a variable for determining the direction of the tool at the target position so that the operation time of the robot is as short as possible. In the case of FIG. 7, teaching work is required so that the posture of the robot (the direction of the tool) at the target position is not the state indicated by the broken line but the state indicated by the dotted line.

  In this way, in cases where the orientation of the tool at the target position is unquestioned, the task of finding the robot posture (rotation angle of each axis) at the target position where the operation time is the shortest from among the many robot postures that exist It is very difficult, and even a skilled worker often requires a lot of time for the work, and the work load is very large.

  By the way, as a prior art for shortening the cycle time of the operation | work using a robot, the technique described in patent document 1 is mentioned, for example. The technique described in Patent Document 1 does not perform position control for a predetermined direction or rotation direction, but instead performs control based on force or torque value.

JP-A-5-23982

  However, the technique described in Patent Document 1 is based on the premise that position information, force, and torque value information are given by the user so that the target position can be calculated correctly. For this reason, it is considered necessary to obtain the posture of the robot at the target position. That is, the technique described in Patent Document 1 requires the same work load only by using a different method from the conventional technique, and it is considered that the work load on the user is unlikely to be reduced. It cannot be said that it is a means.

  The present invention has been made in view of the above circumstances, and its object is to reduce the work load on the user when setting the value of a variable for determining the direction of the tool at the target position, while moving the robot. It is an object of the present invention to provide a robot control method and a robot control apparatus capable of shortening the length of the robot.

  According to the means of claim 1 or 3, in the control for moving the tip of the tool attached to the hand of the robot having a plurality of axes from the current position toward the target position, an arbitrary variable setting process, a variable A value determination process is executed. In general teaching work, the values of the variables for determining the tip position and orientation of the tool are all specified by the user. Note that the values of each variable are the coordinate values (X-axis coordinates, Y-axis coordinates, and Z-axis coordinates) of the tool tip and the rotation angle (for example, four-axis horizontal multiples) around a predetermined axis of the tool (hand). In the case of an articulated robot, this is the value of the rotation angle around the fourth axis (Z axis). However, depending on the type of tool attached to the hand and the work content, the work may be able to be achieved regardless of the orientation of the tool (= the orientation of the hand). For example, when an air chuck is used as a tool in a 4-axis horizontal articulated robot, the workpiece can be gripped regardless of the direction of the tool (the direction around the fourth axis). In this case, it can be said that the orientation of the tool at the target position may be any orientation. Conventionally, even in such a case, the user has specified a variable (for example, a rotation angle around the Z axis) for determining the direction of the tool.

  On the other hand, according to the present means, one or two variables designated by the user among variables for determining the direction of the tool are set as arbitrary variables that can be set to arbitrary values (arbitrary variables Setting process). Then, an evaluation index based on the movement time required for the tool tip to move from the current position to the target position is set, and the evaluation index is optimized to determine the value of an arbitrary variable (variable value determination process). For example, when an air chuck is attached to the tip of a 4-axis horizontal articulated robot, if the rotation angle around the Z axis of the tool (hand) is specified as an arbitrary variable, the tool around the Z axis of the tool at the target position The rotation angle is automatically determined to a value that minimizes the movement time of the tool.

  That is, in the variable value determination process, all numerical ranges that can be set as values of arbitrary variables are set as variable value ranges. For example, in the case of the rotation angle around the Z axis of the tool (hand), the numerical range that can be set due to the mechanical limitations of the robot is “−180 degrees to +180 degrees”, and that range is set as the variable value range. The Then, a predetermined number of numerical values within the set variable value range are extracted, and an evaluation index when each of the extracted numerical values is set as the value of the rotation angle around the Z axis of the tool at the target position is calculated. The

  Based on each evaluation index calculated in this way, the variable value range is narrowed by a predetermined range and reset so that the numerical value that minimizes the evaluation index (the value of the rotation angle around the Z axis of the tool) is included. Is done. As a technique for narrowing the variable value range so as to include the minimum value of the evaluation index, for example, the golden section method is cited. When the reset variable value range exceeds the predetermined required accuracy range, each calculation for narrowing the variable value range is executed again. On the other hand, when the reset variable value range is equal to or less than the required accuracy range, a predetermined numerical value within the variable value range is determined as the value of the rotation angle around the Z axis of the tool at the target position. That is, any one numerical value within the finally set variable value range is set as the value of the arbitrary variable at the target position. Therefore, as the required accuracy range is narrowed, the variable value range to be finally set becomes narrower and the accuracy with which the value of an arbitrary variable that minimizes the evaluation index is obtained increases. However, the number of repetitions of each of the above operations increases. Therefore, the calculation time required for the variable value determination process becomes longer. In addition, the wider the required accuracy range, the wider the variable value range to be finally set and the lower the accuracy with which the value of an arbitrary variable that minimizes the evaluation index is obtained, but the number of repetitions of each of the above operations is small. Thus, the calculation time required for the variable value determination process is shortened. The required accuracy range may be appropriately set in consideration of such a trade-off relationship.

  The value of the rotation angle (arbitrary variable) around the Z axis of the tool determined in this way is a value that minimizes the evaluation index based on the movement time, or a value that conforms to the value. That is, the determined value of the rotation angle around the Z-axis is a value that minimizes the movement time of the tool (robot) when moving from the current position to the target position. Since the above-mentioned control is automatically executed on the robot side, the user performs the teaching operation by specifying each coordinate value of the tool tip at the target position and setting the rotation angle of the tool (hand) around the Z axis. Just specify it as an arbitrary variable. Then, in addition to the X, Y and Z axis coordinate values of the tool tip at the specified target position, the rotation angle of the tool around the Z axis at the target position automatically determined as described above (arbitrary variable) Based on this value, the tool tip is moved from the current position toward the target position, thereby reducing the work load on the user (operator) during teaching and shortening the movement time of the robot. .

  Here, the case of a 4-axis horizontal articulated robot has been described as an example. However, for example, the case of a 6-axis vertical articulated robot is as follows. That is, if any one or two of variables for determining the direction of the tool (respective rotation angles around the X, Y, and Z axes) are designated as arbitrary variables, the tool at the target position The rotation angle of the (hand) around a specific axis is automatically determined to a value that minimizes the movement time of the robot. As a result, the same effects as those of the above-described 4-axis horizontal articulated robot can be obtained. That is, according to this means, the above-mentioned operation and effects can be obtained for all robots having a plurality of axes.

  In the variable value determination process, an evaluation index based on the movement time required when the tool tip moves from the current position to the target position is used. Therefore, for example, it is possible to use a detailed (accurate) moving time considering acceleration as an evaluation index, and it is also possible to use an approximate value of moving time considering only speed as an evaluation index. Among these, if an evaluation index is set as in the former, the accuracy in determining an arbitrary variable increases. That is, it is possible to set an arbitrary variable value that can shorten the operation time of the robot more reliably. On the other hand, if the evaluation index is set as in the latter case, the calculation can be performed relatively easily, and therefore the calculation time can be shortened.

  In the variable value determination process described above, the larger the number of values to be extracted within the variable value range, and the smaller the range that narrows the variable value range at one time (predetermined range), the smaller the numerical value that minimizes the evaluation index is Although the probability of being determined as the value of an arbitrary variable in (in the following, referred to as the accuracy of minimization) increases, the calculation time required for the variable value determination process becomes longer. The smaller the number to be extracted and the wider the predetermined range, the lower the accuracy of minimization, but the shorter the computation time required for the variable value determination process. In consideration of such a trade-off relationship, the user can set a desired accuracy and calculation time by appropriately setting the above-described required accuracy range in addition to the number to be extracted and the predetermined range. Can be set to meet the specifications.

  Now, an evaluation index is calculated for all possible values of an arbitrary variable (for example, the rotation angle around the Z axis of the tool) at the target position, and expressed as a function of the arbitrary variable (hereinafter referred to as an evaluation function) (graphed). The following can be understood. That is, in the evaluation function, the minimum value (optimum value) part of the evaluation index is the bottom of the valley, and other values that are not the minimum value of the evaluation index (values according to the minimum value, and in the following, local values and Say) also becomes the bottom of the valley. The reason for this is as follows.

  Even if the position of the tool tip (each coordinate value) is the same, the robot may have a completely different posture. Therefore, various postures that can be taken by the robot are usually divided into a plurality of forms. For example, in the case of a 4-axis horizontal articulated robot, there are two types of forms (arm forms) with different polarities of the rotation angle of the second axis. That is, the posture of the 4-axis horizontal articulated robot is classified into two types. Further, in the case of a 6-axis vertical articulated robot, two types of configurations (arm configuration) in which the rotation angle of the first axis is 180 degrees different from each other, and two types of configurations (elbow) in which the polarities of the rotation angle of the third axis are different from each other There are two forms (wrist forms) in which the rotation angle of the fourth axis and the fourth axis are different from each other by 180 degrees. That is, it is classified into 8 types in total by the combination of these arm forms, elbow forms, and wrist forms.

  If such a form is the same, the posture of the robot does not change much. However, if the form is different, the posture of the robot is greatly different. The fact that the postures of the robots are greatly different means that the tendency of changes in the evaluation index based on the movement time is also greatly different. Therefore, there is a valley of evaluation functions for each robot form. In other words, the evaluation function has a valley portion on both sides of a singular point that is a boundary where the form of the robot changes. For this reason, for example, in the case of a 4-axis horizontal articulated robot, the evaluation function has at least two valleys, and in the case of a 6-axis vertical articulated robot, the evaluation function has at least 8 valleys. It will be.

  In the variable value determination process, if the local value instead of the minimum value is set as the value of the arbitrary variable at the target position, the effect of shortening the robot operation time as much as possible is slightly reduced. As a countermeasure, it is preferable to increase the probability that the minimum value is set by increasing the number of numerical values extracted within the variable value range described above. However, focusing on this point alone and excessively increasing the number to be extracted lead to an increase in computation time, which is not desirable. In order to improve such a point, the means described in claim 2 or 4 may be employed.

  According to the means of claim 2 or 4, in the variable value determination process, when the process of extracting a predetermined number of numerical values within the variable value range is executed for the first time, the process is executed for the second time or later. The number of numerical values to be extracted is increased as compared with the case where the numerical values are within the variable value range. When the process of extracting numerical values within the variable value range is first executed, all numerical value ranges that can be set as values of arbitrary variables are set as variable value ranges. Therefore, at this time, if a relatively large number of values are extracted evenly (evenly) over the variable value range, the range in which the numerical value (minimum value) that minimizes the evaluation index exists is based on them. Judgment can be made easily and reliably. That is, it is possible to easily and reliably avoid the local value. On the other hand, when the same processing is performed after the second time, although the number of numerical values to be extracted is relatively small, a problem regarding minimization accuracy is unlikely to occur because local values have already been avoided. In this means, since a relatively large number of values are extracted when the above process is executed for the first time, the calculation time required for the variable value determination process is increased while improving the accuracy of minimization. It can prevent becoming long.

The 1st Embodiment of this invention is shown, The schematic block diagram of a robot system Flow chart showing the contents of variable value decision processing A figure that represents an evaluation index as a function of an arbitrary variable A diagram schematically showing the robot mode at the current position and target position FIG. 4 equivalent view when the target position is set at any position within the target area FIG. 1 equivalent diagram showing a second embodiment of the present invention FIG. 4 equivalent diagram showing the prior art

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described with reference to FIGS.
FIG. 1 shows a system configuration of a general industrial robot. A robot system 1 shown in FIG. 1 includes a robot 2, a controller 3 that controls the robot 2, and a teaching pendant 4 connected to the controller 3.

  The robot 2 is configured as, for example, a 4-axis horizontal articulated robot. The robot 2 includes a base 5 fixed to the installation surface, a first arm 6 connected to the base 5 so as to be rotatable about a first axis J1 having an axis in the Z-axis (vertical axis) direction, A second arm 7 that is rotatably connected around a second axis J2 having an axis center in the Z-axis direction on the tip of the first arm 6 and can be moved up and down to the tip of the second arm 7 And a shaft 8 that is rotatably provided. The axis when moving the shaft 8 up and down is the third axis J3, and the axis when rotating the shaft 8 is the fourth axis J4. A flange 9 is positioned and attached to the tip (lower end) of the shaft 8 so as to be detachable.

  The base 5, the first arm 6, the second arm 7, the shaft 8 and the flange 9 function as an arm of the robot 2. Although not shown in the drawing, a tool such as an air chuck is attached to the flange 9 (corresponding to the hand) that is the tip of the arm. A plurality of axes (J1 to J4) provided in the robot 2 are driven by motors (not shown) provided corresponding to the respective axes. In the vicinity of each motor, a position detector (not shown) for detecting the rotation angle (rotation position) of each rotation shaft is provided.

  In general, an industrial robot operates according to a predetermined operation program created by performing teaching or the like in advance. The controller 3 (corresponding to a control device for the robot) performs feedback control of the motor drive based on the operation program and controls the operation of the arm of the robot 2.

  The teaching pendant 4 is, for example, a size that can be operated by being carried by a user or carried by a hand, and is formed in, for example, a thin, substantially rectangular box shape. The teaching pendant 4 is provided with various key switches, and the user performs various input operations using these key switches. The teaching pendant 4 is connected to the controller 3 via a cable, and performs high-speed data transfer with the controller 3 via a communication interface. An operation input by operating a key switch Information such as signals is transmitted from the teaching pendant 4 to the controller 3.

  In general, when a teaching operation is performed in which the tip of a tool attached to the flange 9 that is the hand of the robot 2 is moved from the current position toward the target position, the posture of the robot 2 at the target position is set to any type. Whether to do so is determined by the user. That is, in such teaching work, variables for determining the target position of the tool tip (X-axis coordinate value, Y-axis coordinate value and Z-axis coordinate value of the tool tip) and the tool (hand) at the target position All variables for determining the direction (the rotation angle of the tool around the Z axis) are specified by the user. However, depending on the type (shape) of the tool attached to the flange 9 and the content of work using the tool, the direction of the tool can be made unquestioned. For example, when an air chuck is used as a tool, the workpiece can be gripped regardless of the orientation of the tool around the Z axis (fourth axis J4).

  In the robot system 1 of the present embodiment, in the case where the orientation of the tool can be made unquestioned, the user only has to specify the values of the X, Y, and Z axis coordinates indicating the target position of the tool tip. The value of the rotation angle Rz around the Z axis of the tool at the target position need not be specified. Instead, the user specifies the rotation angle Rz about the Z axis of the tool as an arbitrary variable. Receiving this, the controller 3 sets the rotation angle Rz as an arbitrary variable that can be set to an arbitrary value on the controller 3 side (arbitrary variable setting process). Although details will be described later, the controller 3 sets an evaluation index based on the movement time required when the tip of the tool moves from the current position to the target position, and optimizes the evaluation index to set the value of the arbitrary variable. Is determined (variable value determination processing). Thus, the controller 3 functions as an arbitrary variable setting processing unit and a variable value determination processing unit. In the present embodiment, the controller 3 executes the processes described above, so that the direction of the tool at the target position is determined such that the movement time of the robot 2 is as short as possible.

  FIG. 2 is a flowchart showing the contents of variable value determination processing. As shown in FIG. 2, when the variable value determination process is started (start), all numerical value ranges that can be set as values of arbitrary variables are set as variable value ranges (step S1). In the present embodiment, the settable numerical range of the rotation angle Rz around the Z axis of the tool, which is an arbitrary variable, is −180 degrees to +180 degrees due to the mechanical limitation of the robot 2. In step S2, N (predetermined numbers) numerical values within the set variable value range are extracted. Although the reason will be described later, N may be an integer of 3 or more. In step S3, an evaluation index is calculated when each numerical value extracted in step S2 is set as the value of the rotation angle Rz around the Z axis of the tool at the target position.

  In step S4, based on the value of each evaluation index calculated in step S3, the variable value range is narrowed and reset by a predetermined range so that the numerical value that minimizes the evaluation index is included. In the present embodiment, the variable value range is reset as follows. For example, assume that three numerical values of −90 degrees, +30 degrees, and +150 degrees are extracted in step S2 (N = 3). And as a value of the evaluation index corresponding to these numerical values, +30 degrees is the smallest, +150 degrees is the second smallest, and -90 degrees is the largest.

  In such a case, the numerical value with the smallest evaluation index is around +30 degrees where the evaluation index is the smallest among the extracted numerical values, that is, in the range of -90 degrees to +30 degrees, or in the range of +30 degrees to +150 degrees. Is likely to exist in any of the. The numerical value with the smallest evaluation index is unlikely to exist in a range away from +30 degrees where the evaluation index is smallest, that is, within a range of +150 degrees to -90 degrees. Therefore, a range of −90 degrees to +30 degrees to +150 degrees (240 degrees range) is set as a new variable value range. That is, a range that is narrowed by a range of 120 degrees (predetermined range) from the original variable value range (range of 360 degrees) is set as a new variable value range. Here, for the sake of explanation, the case where N = 3 has been described. However, even when N ≧ 4, the variable value range is reset by the same method.

  In step S5, it is determined whether or not the reset variable value range is equal to or less than a predetermined required accuracy range. As a result, when the variable value range exceeds the required accuracy range (“NO” in step S5), the process returns to step S2. And in order to narrow a variable value range further, the process of step S2-S5 is performed again. On the other hand, when the variable value range is equal to or less than the required accuracy range (“YES” in step S5), the process proceeds to step S6. In step S6, the numerical value at the center within the variable value range reset in step S4 is determined as the value of the rotation angle Rz (arbitrary variable) around the Z axis of the tool at the target position. For example, if the variable value range is +12 degrees to +14 degrees, +13 degrees is determined as the value of the rotation angle Rz around the Z axis of the tool at the target position. In step S6, a predetermined numerical value within the variable value range may be determined as the value of the arbitrary variable at the target position. Therefore, for example, the minimum value or the maximum value within the variable value range may be determined as the value of the arbitrary variable at the target position.

  By executing such processing, any one numerical value within the finally set variable value range is set as the value of the arbitrary variable at the target position. Therefore, the narrower the required accuracy range, the narrower the variable value range that is finally set and the greater the accuracy with which the value of an arbitrary variable that minimizes the evaluation index is obtained, but the above processing (steps S2 to S5). The number of repetitions increases and the computation time required for the variable value determination process becomes longer. In addition, the wider the required accuracy range, the wider the variable value range to be finally set, and the lower the accuracy with which the value of an arbitrary variable that minimizes the evaluation index is obtained, but the number of repetitions of the above processing decreases. Thus, the calculation time required for the variable value determination process is shortened. The required accuracy range may be appropriately set in consideration of such a trade-off relationship.

  The value of the rotation angle Rz (arbitrary variable) around the Z axis of the tool determined in this way is a value that minimizes the evaluation index based on the movement time, or a value very close to it. That is, the determined value of the rotation angle Rz about the Z axis is a value that minimizes the movement time of the tool (robot 2) when moving from the current position toward the target position. Since the above-described control is automatically executed by the controller 3, the work performed by the user during teaching is to specify each coordinate value of the tool tip at the target position as described above, and to rotate the tool around the Z axis. It is only necessary to specify Rz as an arbitrary variable. Then, the controller 3 rotates the tool around the Z axis at the target position automatically determined by the above-described processes in addition to the X, Y, and Z axis coordinate values of the tool tip at the target position where the value is specified. Based on the value of the angle Rz (tool direction), the tool tip can be moved from the current position toward the target position. As a result, the burden on the user (operator) during teaching is reduced, and the movement time of the robot 2 is shortened.

  In the variable value determination process, an evaluation index based on the movement time required when the tool tip moves from the current position to the target position is used. Therefore, for example, detailed (accurate) travel time considering the acceleration of each axis can be used as an evaluation index, and for example, an approximate value (approximate value) of travel time considering only the speed of each axis is evaluated. It can also be used as an index. That is, the degree of freedom in setting the evaluation index is high. Among these, if an evaluation index is set as in the former, the accuracy in determining an arbitrary variable increases. That is, it is possible to set the value of an arbitrary variable that can shorten the operation time of the robot 2 more reliably. On the other hand, if the evaluation index is set as in the latter case, the calculation for obtaining the evaluation index can be performed relatively easily, so that the calculation time can be shortened.

  In the variable value determination process, the larger the number of values to be extracted within the variable value range, and the narrower the range (predetermined range) that narrows the variable value range at a time, the smaller the numerical value at which the evaluation index is at an arbitrary Although the probability of being determined as a variable (hereinafter referred to as the accuracy of minimization) increases, the computation time required for the variable value determination process becomes longer. The smaller the number to be extracted and the wider the predetermined range, the lower the accuracy of minimization, but the shorter the computation time required for variable value determination processing. In consideration of such a trade-off relationship, the user can set a desired accuracy and calculation time by appropriately setting the above-described required accuracy range in addition to the number to be extracted and the predetermined range. Can be set to meet the specifications. Thus, it can be said that the robot system 1 of this embodiment is a user-friendly system.

  FIG. 3 calculates evaluation indexes for all possible values of the rotation angle Rz (arbitrary variable) of the tool around the Z-axis at the target position, and represents it as a function of the arbitrary variable (hereinafter referred to as an evaluation function) (graph). ). As shown in FIG. 3, the evaluation function has two valleys, and the minimum value (optimum value) portion of the evaluation index is located at the bottom of one valley and is not the minimum value of the evaluation index. The portion of the value (which is a value according to the minimum value, hereinafter referred to as a local value) is located at the bottom of the other valley. The reason why such two valleys exist in the evaluation function is as follows.

  Even if the position of the tool tip (X, Y, Z coordinate values) is the same, the robot may have a completely different posture. For this reason, various postures that can be taken by a robot are usually divided into a plurality of forms. For example, the robot 2 (four-axis horizontal articulated robot) of this embodiment is classified into two forms. That is, it is classified into an arm form in which the rotation angle of the second axis J2 is plus (+) and an arm form in which the rotation angle of the second axis J2 is minus (−). If such a form is the same, the posture of the robot 2 does not change much. However, if the form is different, the posture of the robot 2 is greatly different. The fact that the posture of the robot 2 is greatly different also means that the tendency of change in the evaluation index based on the movement time is greatly different. Therefore, the valley of the evaluation function exists for each form of the robot 2. In other words, the evaluation function includes valley portions on both sides of a singular point that is a boundary where the form of the robot 2 switches. For this reason, in the case of the robot 2 of the present embodiment, the evaluation function has at least two valleys.

  In the variable value determination process, if the local value instead of the minimum value is set as the value of the arbitrary variable at the target position, the effect of shortening the operation time of the robot 2 as much as possible is slightly reduced. As a countermeasure, it is preferable to increase the probability that the minimum value is set by increasing the number of numerical values extracted in the variable value range in step S2 (increasing the value of N). However, focusing on this point alone and excessively increasing the number to be extracted lead to an increase in computation time, which is not desirable. In order to improve such a point, the variable value determination process may be changed as follows.

  That is, after the variable value determination process is started, when the step S2 is executed for the first time, the number to be extracted is increased (the value of N is increased) compared with the case where the step S2 is executed for the second time and thereafter. ) And change so that numerical values within the variable value range are evenly extracted. When step S2 is executed for the first time, all numerical value ranges that can be set as values of arbitrary variables are set as variable value ranges. Therefore, at this time, if a relatively large number of values are extracted evenly (evenly) over the variable value range, the range in which the numerical value (minimum value) that minimizes the evaluation index exists is based on them. Judgment can be made easily and reliably. That is, it is possible to easily and reliably avoid the local value.

  On the other hand, when step S2 is executed after the second time, although the number of numerical values to be extracted is relatively small, a local value is already avoided, so that a problem regarding the accuracy of minimization hardly occurs. Further, when steps S2 to S4 are executed after the second time, as a method of narrowing the variable value range so as to include the minimum value of the evaluation index, for example, a method such as a golden division method can be used. is there. When the golden section method is used, the number to be extracted may be two or more (N ≧ 2). In this way, by extracting a relatively large number of values evenly when step S2 is executed for the first time, it is possible to prevent the calculation time required for the variable value determination process from becoming unnecessarily long while improving the accuracy of minimization. it can.

Next, specific effects obtained by the robot system 1 of the present embodiment will be described with reference to FIGS. 4 and 5 as well.
FIG. 4 schematically shows an aspect of the robot when the tool tip is moved from the current position Pc toward the target position Pd. The robot shown in FIG. 4 is a four-axis horizontal articulated robot, and an air chuck is attached as a tool to the hand. In FIG. 4, each axis and each link are indicated by a circle and a straight line, respectively, and the tool tip is indicated by an arrow. In addition, the state of the robot at the current position is indicated by a dotted line, and the state of the robot at the target position is indicated by a solid line. Here, it is assumed that the tool tip is moved from the current position Pc to the target position Pd and the work is gripped by an air chuck that is a tool.

  The teaching work in the above case is performed as follows according to the conventional method. That is, the worker in charge of teaching first examines the states (postures) shown in FIGS. 4A, 4B, and 4C. That is, the worker roughly changes the direction of the tool and estimates which direction is likely to be good. As a result, when it is determined that the state of (c) looks good, the direction of the tool is gradually changed from the state of (c) based on the state of (c) ((d) of FIG. 4). , (E), and (f)). As a result, it is determined that the state of FIG. 4F is optimal (movement time is shortened). Here, in order to simplify the description, the number of states examined by the operator is reduced, and the optimum state can be found with a small number of repeated operations. In practice, more states may be considered or the number of repetitions may increase.

  On the other hand, according to the robot system 1 of the present embodiment, the direction of the tool at the target position Pd is automatically determined by the controller 3 so that the movement time of the robot 2 is as short as possible. Therefore, the result of the state (tool direction) in FIG. 4 (optimum) (optimized movement time can be shortened as much as possible) can be easily obtained without going through an iterative process as in the conventional method.

  Thus, according to the conventional method, the state (posture) of the robot at the target position is changed little by little based on the experience and guess of the worker in charge of teaching. Then, as a result of repeating the operation several times (for example, five times), for example, the operation time of the robot is larger than the posture of the robot having the same tool orientation at the current position and the target position ((a) in FIG. 4). It has become possible to obtain a tool orientation that is shorter (for example, an improvement of about 25%). On the other hand, according to the robot system 1 of the present embodiment, the same effect as that obtained by the conventional method can be obtained regardless of the experience of the worker in charge of teaching. Further, at that time, the operator does not need to specifically examine the posture of the robot at the target position, so that the work load is greatly reduced.

  FIG. 5 is a view corresponding to FIG. 4 when the tool tip is moved from the current position Pc toward an arbitrary target position in the target area Ad. In this case, the position to be moved in the target area Ad shown in FIG. 5A is given from an external device such as a camera during actual work, and the worker cannot know at the time of teaching. And In such a case, the optimum direction of the tool changes depending on the position in the target area Ad where the target position is set. Therefore, in the conventional method, as shown in FIG. 5B, the target area Ad is divided into a plurality of small areas, and an optimum tool orientation is taught for each of the small areas. It was. Also, depending on how the target area Ad is divided, whether or not the optimum tool orientation can be obtained changes, and therefore there is a part that depends greatly on the individual ability of the worker in charge of teaching.

  On the other hand, according to the robot system 1 of the present embodiment, even in a case where a target position is given from an external device such as a camera for the first time during actual work, the controller 3 The optimum tool orientation at the target position is automatically determined. For this reason, it is possible to save the time-consuming work of dividing the target area Ad into small areas and teaching for each small area as in the conventional method.

(Second Embodiment)
Hereinafter, a second embodiment in which the type of the target robot is changed with respect to the first embodiment will be described with reference to FIG.
FIG. 6 is a view corresponding to FIG. 1 in the first embodiment, and the same parts as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. The robot system 21 of this embodiment shown in FIG. 6 differs from the robot system 1 of the first embodiment shown in FIG. 1 in that a robot 22 is provided instead of the robot 2.

  The robot 22 is configured as, for example, a 6-axis vertical articulated robot. In other words, the shoulder portion 26 is coupled to the base 25 so as to be rotatable in the horizontal direction via a first axis J21 having an axis in the Z-axis direction. A lower end portion of a lower arm 27 extending upward is connected to the shoulder portion 26 via a second axis J22 having an axis in the Y-axis direction so as to be rotatable in the vertical direction. A first upper arm 28 is connected to the distal end portion of the lower arm 27 via a third axis J23 having an axis in the Y-axis direction so as to be rotatable in the vertical direction. A second upper arm 29 is connected to the distal end portion of the first upper arm 28 via a fourth axis J24 having an axis in the X-axis direction so as to be able to rotate. A wrist 30 is connected to the tip of the second upper arm 29 via a fifth axis J25 having an axis in the Y-axis direction so as to be rotatable in the vertical direction. A flange 31 is connected to the wrist 30 via a sixth axis J26 having an axis in the X-axis direction so as to be able to rotate.

  The base 25, the shoulder portion 26, the lower arm 27, the first upper arm 28, the second upper arm 29, the wrist 30 and the flange 31 function as an arm of the robot 22. Although not shown, a tool such as an air chuck is attached to the flange 31 (corresponding to the hand) that is the tip of the arm. The plurality of axes (J21 to J26) provided in the robot 22 are driven by motors (not shown) provided corresponding to the respective axes, similarly to the robot 2 of the first embodiment. Further, in the vicinity of each motor, a position detector (not shown) for detecting the rotational position of each rotating shaft is provided.

  Also in the configuration of the present embodiment, the controller 3 can execute the same arbitrary variable setting process and variable value determination process as in the first embodiment. For example, if any one or two of the variables for determining the direction of the tool (the rotation angles Rx, Ry, Rz around the X, Y, and Z axes) are designated as arbitrary variables, The designated variable is set as an arbitrary variable (arbitrary variable setting process). Then, the controller 3 performs variable value determination processing. Thereby, the value of the arbitrary variable (tool direction) at the target position is automatically determined to a value that minimizes the movement time of the robot 22. As a result, also in the configuration of the present embodiment, the same operations and effects as those of the first embodiment can be obtained.

(Other embodiments)
The present invention is not limited to the embodiments described above and illustrated in the drawings, and the following modifications or expansions are possible.
In each of the above embodiments, the example in which the present invention is applied to the 4-axis horizontal articulated robot 2 or the 6-axis vertical articulated robot 22 has been described. However, the present invention is a robot having a plurality of axes. Applicable in general.

  In the drawing, 2 and 22 are robots, 3 is a controller (robot control device, arbitrary variable setting processing means, variable value determination processing means), 9 and 31 are flanges (hands), and J1 to J4 and J21 to J26 are axes. Show.

Claims (4)

A method for controlling a robot when moving the tip of a tool attached to the hand of a robot having a plurality of axes from a current position toward a target position,
Arbitrary variable setting processing for setting one or two variables designated by the user as arbitrary variables that can be set to arbitrary values among the variables for determining the orientation of the tool after movement,
A variable value determination process for setting an evaluation index based on a movement time required when the tip of the tool moves from the current position to the target position, and optimizing the evaluation index to determine a value of an arbitrary variable at the target position; ,
Including
The variable value determination process includes:
A first step of setting all numerical ranges that can be set as values of the arbitrary variable as variable value ranges;
A second step of extracting a predetermined number of numerical values within the variable value range;
A third step of calculating the evaluation index when each of the extracted numerical values is set as the value of the arbitrary variable at the target position;
A fourth step of narrowing and resetting the variable value range by a predetermined range so as to include the numerical value that minimizes the evaluation index, based on the calculated evaluation indices;
Including
When the reset variable value range exceeds a predetermined required accuracy range, the second to fourth steps are executed again,
When the reset variable value range is less than or equal to the required accuracy range, a predetermined numerical value within the variable value range is determined as the value of the arbitrary variable at the target position. The variable value determination process includes:
When performing the second step for the first time,
The number of the numerical values to be extracted is increased as compared to when the second step is executed after the second time, and the numerical values within the variable value range are uniformly extracted. Robot control method. A control device for a robot that moves a tip of a tool attached to a hand of a robot having a plurality of axes from a current position toward a target position,
Of the variables for determining the orientation of the tool after movement, one or two variables designated by the user are set as arbitrary variables that can be set to arbitrary values, arbitrary variable setting processing means,
Variable value determination processing means for setting an evaluation index based on a movement time required when the tip of the tool moves from the current position to the target position, and optimizing the evaluation index to determine a value of an arbitrary variable at the target position When,
With
The variable value determination processing means includes:
All numerical ranges that can be set as the value of the arbitrary variable are set as variable value ranges,
Extract a predetermined number of numerical values within the variable value range,
As the value of the arbitrary variable at the target position, the evaluation index when each of the extracted numerical values is set is calculated,
Based on each of the calculated evaluation indexes, the variable value range is narrowed and reset by a predetermined range so as to include the numerical value that minimizes the evaluation index,
When the reset variable value range exceeds a predetermined required accuracy range, each calculation for narrowing the variable value range is executed again,
When the reset variable value range is less than or equal to the required accuracy range, a predetermined numerical value within the variable value range is determined as the value of the arbitrary variable at the target position. The variable value determination processing means includes:
When first executing a process of extracting a numerical value within the variable value range,
4. The robot according to claim 3, wherein the number of numerical values to be extracted is increased as compared with a case where the process is executed after the second time, and the numerical values within the variable value range are uniformly extracted. Control device.

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