JPH07205068A - Coordinate system setting method of robot - Google Patents

Abstract

PURPOSE:To generate easily a right-angled crossing coordinate system necessary for force control and at the time improve the safety of operation and action precision at the time of regeneration. CONSTITUTION:This is a coordinate system setting method applied to an articulated robot possesses the freedom degree of more than 2 and can be set at a free position and posture and is equipped at its arm tip portion a force sensor 3 to detect the force of each direction of parallel advance and rotation in regard to three axial directions and is furnished at the tip side portion of this force sensor with a finger effect tool and whose action is possible by means of force control. A rectangular coordinate system is necessitate by the instruction in the force direction under force control and set by single directional vector 41 and position parameter for production by a target track of work and in addition, the setting of one direction vector 41 is conducted by pressing the finger effect tool 32 against a work 35 or adding force by hand.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for setting a coordinate system of a robot, and more particularly, a control means executes a force control together with a position control, and an operation is performed based on the control so that the position and the posture are set arbitrarily. The present invention relates to a coordinate system setting method which is applied to an articulated robot having a degree of freedom and is easy to set.

[0002]

2. Description of the Related Art As a document disclosing a conventional example of a coordinate system setting method for a robot, Japanese Patent Laid-Open No. 61-49205 is cited. In the robot control method disclosed in this document,
As a component, it includes means for defining one local coordinate system (that is, an arbitrary coordinate system) by using two points in the robot absolute coordinate system.

[0003]

According to the method of setting an arbitrary coordinate system in the above-mentioned robot control method, two points are arbitrarily selected while operating the robot body, and based on the teaching of the coordinate information of these two points. It is necessary to teach the coordinate axis direction. Since the robot body is operated, the operation for setting the arbitrary coordinate system is generally complicated. Also,
It may be difficult to teach the coordinate information of two points due to the installation position of the work. In such a case, 1
There was a problem that it became impossible to set the direction vector of the axis.

An object of the present invention is to set a 1-axis direction vector with a simple operation and in a short time without actually teaching a plurality of points by operating a robot so as to take an appropriate posture. To provide a coordinate system setting method for a robot, which generates a Cartesian coordinate system required for force control from position parameters for generating a target trajectory related to work and improves operation safety and motion accuracy during playback. is there.

[0005]

A robot coordinate system setting method according to the present invention has two or more degrees of freedom and can be set to an arbitrary position and posture. The arm tip portion is translated in three axial directions. It is a method that is equipped with a force sensor that detects the force in each direction of rotation, and a hand effector is attached to the tip side of this force sensor, and is a method applied to an articulated robot that can operate by force control. The Cartesian coordinate system required for the indication of the inside force direction is set by the vector in one direction and the position parameter for generating the target trajectory related to the work, and the setting of the vector in the one direction is pressed against the workpiece. It is a method of doing it.

In the above method, instead of pressing the end effector against the work, the operator himself can press the end effector by hand to set the vector in one direction.

[0007]

In the robot coordinate system setting method according to the present invention,
In a robot equipped with a force sensor equipped with a hand effector on the wrist of an arm of the robot body, and a control means capable of controlling position and force with respect to the operation of the robot body,
By applying a force to the force sensor in one direction, the force sensor and the control means obtain a vector relating to the force in the pressed direction from the value of the applied force, use this vector, and perform work. The orthogonal coordinate system required for force control is set using the position parameters (taught before work) for generating the desired trajectory for

[0008]

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

FIG. 1 is a block diagram conceptually showing the configuration of a robot control apparatus to which the coordinate system setting method according to the present invention is applied. In this figure, a mechanical configuration portion and a hardware configuration such as a sensor portion are also shown. Is shown. FIG. 2 is an external perspective view of the robot body.

In FIG. 1, reference numeral 1 denotes a robot mechanism (or a robot main body), a mechanical mechanism portion, a drive device arranged at each movable portion (joint portion) of the mechanical mechanism portion, and the mechanical mechanism. It is composed of a work tool (generally a hand effector) attached to the arm tip of the section. The robot mechanism 1 is controlled as a whole by receiving various control signals for determining the posture and movement of the robot mechanism 1 given by the force control calculation unit 20 from each drive device arranged in the movable portion, through the servo circuit 2. It operates according to the signal, and the work tool performs the necessary work on the work (not shown). The work operation by the robot mechanism 1 and the work tool includes a force work operation based on force control. Therefore, when the work tool performs a force work such as grinding on the work, the work tool receives a reaction force from the work. Since the work tool is fixed to the front side portion of the force sensor 3 due to its mounting structure, the force (including the moment) applied to the work tool is detected by the force sensor 3.

The data regarding the force detected by the force sensor 3 is sent to the force control calculation unit 20 and used as force data regarding the control situation in the subsequent force control. Similarly, each movable part of the robot mechanism 1 is provided with a sensor for detecting an operation amount, and when the movable part is operated by a corresponding drive device, each sensor measures the operation amount and the servo circuit is operated. It is sent to the force control calculation unit 20 as motion amount data via 2. These motion amount data are used as actual position data for subsequent position and force control.

A block 5 indicated by a chain line is a part of the robot controller. A robot playback system to which this robot control device is applied employs a teaching playback system. Therefore, the robot control device 5 in FIG. 1 has a portion (teaching / setting unit) related to teaching and setting of a plurality of control parameters and a portion (control execution unit) that takes out the set plurality of control parameters and executes control. Composed of and. Robot controller 5
In regard to the transfer route of the taught programs and data, the teaching / setting unit is basically located in the front stage on the left side of the drawing, and the control execution unit is located in the rear stage of the right side.
That is, the teaching / setting unit stores the force control parameter 1
4, a user program storage unit 13, a position parameter storage unit 10, a coordinate system parameter storage unit 11, a work coordinate system axial direction storage unit 12, and a pressing force direction calculation unit 21. On the other hand, the control execution unit includes a user program analysis unit 16, a force control parameter transfer unit 17, a position parameter transfer unit 15,
The work coordinate system calculation unit 18, the force control calculation preprocessing unit 19, and the force control calculation unit 20 described above are included.

In each of the force control parameter storage unit 14, the user program storage unit 13, the position parameter storage unit 10, and the coordinate system parameter storage unit 11, an operator of the user operates the robot mechanism 1 including the robot control device 5. When trying to perform the required work (work that requires position control and force control regarding the operation of the work tool), by performing teaching operation in advance, each of the force control and position control necessary for controlling the work is performed. Data regarding control parameters and necessary user programs are stored. In the teaching operation by the operator, for example, the handy type teaching operation device 4 is used. The teaching operation device 4 has an input function unit 4a for inputting a control command and a plurality of data using a programming language, and has a predetermined display area and allows the operator to visually recognize the contents of the control command and the like. It has a display function unit 4b for confirmation. This teaching operation device 4
By using, the robot mechanism 1 is made to perform a trial operation just like the actual work before the actual work, and the data required for each section during the work regarding a plurality of control parameters is stored in the force control parameter storage. It can be given to each of the unit 14, the user program storage unit 13, the position parameter storage unit 10, and the coordinate system parameter storage unit 11.

The setting of the work coordinate system axial direction in the work coordinate system axial direction storing unit 12 is performed by the pressing force direction calculating unit 21 based on the force signal detected by the force sensor 3 by a predetermined pressing operation, as described later. This is performed by obtaining a force direction vector and transferring this force direction vector to the work coordinate system axial direction storage unit 12.

Position parameter transfer unit 15, force control parameter transfer unit 17, work coordinate system calculation unit 18 for calculating the work coordinate system, force control calculation preprocessing unit 19, force control calculation unit 2.
0 and the like are activated based on the user program obtained by the user program analysis unit 16 that extracts the user program from the user program storage unit 13 and analyzes the user program when executing the control.

Next, the structure and operation of each section of the teaching / setting section will be described in detail with reference to FIGS.

The parameters stored in the force control parameter storage unit 14 include set values of a plurality of various control parameters as shown in FIG. 4, for example. These control parameters are force control coordinate system designation, feed rate, force target value, virtual spring constant, virtual viscosity coefficient, and dead zone of force. The feed rate, the force target value, the virtual spring constant, the virtual viscosity coefficient, and the dead zone of the force are given set values a, b, c, d, and e, respectively. These control parameters are examples when the virtual compliance control described in JP-A-61-7905 is used as the force control method. The relationship between each control parameter such as the feed rate, the target force value, the virtual spring constant, and the virtual viscosity coefficient and the image of the control state is shown in FIG. In FIG. 5, 51 is a work tool,
52 is a robot wrist at the end of the arm of the robot mechanism 1,
53 is a work.

Next, each force control parameter will be described. “Force control coordinate system designation” designates a reference coordinate system for performing force control. Each control parameter of the force target value, the virtual spring constant, the virtual viscosity coefficient, and the force dead zone is set for each axial direction of the reference coordinate system. As the force control coordinate system, a base coordinate system set on a base on which the main body of the robot mechanism 1 is installed, a tool coordinate system set on a work tool (also referred to as a work tool), and preset corresponding to an arbitrary position Any of the arbitrary coordinate system and the work coordinate system that can be performed is appropriately selected. The “feed speed” is a speed for moving the work tool 51 in a direction taught in advance. In this case, the “taught direction” is the moving direction determined by the position data stored in the position parameter storage unit 10. The “force target value” is the work tool 51 and the work 53
It is a target value for pressing against. The "virtual spring constant" and the "virtual viscosity coefficient" are characteristic parameters in virtual compliance control, and are springs and dampers realized by software as shown in FIG. 5, respectively. The “force dead zone” is for setting a dead zone for the force data from the force sensor 3 in order to ensure the stability of the operation.

The coordinate system parameter storage unit 11 stores several kinds of coordinate system data necessary for the operation of the robot mechanism 1. As described above, the coordinate system data includes the base coordinate system fixed to the base of the robot mechanism 1 and the operation of the robot mechanism 1 fixed to the work tool attached to the arm tip (wrist section) of the robot mechanism 1. It includes a tool coordinate system whose position and orientation change accordingly, an arbitrary coordinate system which can be arbitrarily set by the user, and the like.

The work coordinate system axial direction storage unit 12 has a function of storing the direction of one of the coordinate axes x, y, z of the work coordinate system in the axial direction as a vector <k> as shown in FIG. Have. Here, the symbol "<>" represents a vector. This <k> is arbitrarily set by the user. In the example of FIG. 6, the z-axis direction of the work coordinate system is <k>. The work coordinate system axis direction storage unit 12 outputs <k> in consideration of convenience in calculating the work coordinate system. In this way, in the work coordinate system axial direction storage unit 12,
Which coordinate system of the coordinate systems stored in the coordinate system parameter storage unit 11 is used to designate <k> and the designation information of one axis among the x, y, and z axes of the work coordinate system. Set whether to specify the axis as <k>. In the following description, for convenience of explanation of these set values, it is assumed that the <k> vector for calculating the z-axis direction of the work coordinate system is given by the z-axis direction vector of the base coordinate system.

The position parameter storage unit 10 is a unit for storing data such as the position or orientation of each part of the mechanism and the work tool required for the operation of the robot mechanism 1 during work. The position parameter storage unit 10 has the same configuration as the storage unit for the teaching position data provided in the conventional position control robot, and is a known unit. This robot control device is applied to a robot system that performs work based on force control. However, since position control is required in addition to force control, the position parameter storage unit 10 is naturally provided. There is.

Next, the configuration and operation of each part of the control execution part will be described. The control execution unit has a function of performing a reproduction operation using a program and a set value such as force related to the work taught and stored by using the teaching / setting unit, and actually performing the work. The user program analysis unit 16 reads the user program stored in the user program storage unit 13, decodes the user program, and activates necessary processing. For example, when the deciphered user program includes a description regarding the position, the position parameter transfer unit 15 is activated, necessary position data is taken out from the position parameter storage unit 10 and transferred to the force control calculation preprocessing unit 19. When the decrypted user program includes a description about the force control parameter, the force control parameter transfer unit 17 is activated and the necessary force control parameter is sent to the force control calculation preprocessing unit 19. In this case, when the work coordinate system is designated in the force control coordinate system designation of the force control parameter, the work coordinate system calculation unit 18 is activated.

Next, the flow of processing in the work coordinate system calculation unit 18 will be described with reference to the flowchart of FIG.

When the processing is started, first, the work coordinate system axial direction storage unit 12 is referenced (step S1). Here, it is assumed that the set value is instructed to set the z-axis direction of the work coordinate system to be the z-axis direction of the base coordinate system. Based on this content, the z-axis direction vector of the base coordinate system is acquired from the coordinate system parameter storage unit 11 and set as <k> (step S2). Next, the position target value relating to the operation of the robot mechanism 1 is acquired from the position parameter storage unit 10 through the position parameter transfer unit 15, and this is set as Pn (step S3). Although there are position and orientation target values as position parameters, in this case only the position target values need be acquired. Furthermore, it is assumed here that the position parameter acquired last time is Pn-1 (step S3). At this time,
At the stage immediately after the work coordinate system calculation unit 18 is started, P
Since n-1 cannot be defined, Pn-1 may be the current position. Next, the unit vector <n> in the x-axis direction of the work coordinate system is calculated using Pn and Pn-1 by the following equation (step S4).

[0025]

[Equation 1]

Next, the unit vector <o> in the y-axis direction is calculated. At this time, if it is assumed that the <n> vector is parallel to the <k> vector, calculation cannot be performed, so whether or not it is parallel is first determined by the following equation (step S5).

[0027]

<N> · <k><α where the symbol “·” means the inner product and | α | <
It is 1.

When the above conditions are satisfied, <o>
And the unit vector <a> in the z-axis direction are calculated by the following equation (steps S6 and S7).

[0029]

## EQU3 ## <o> = <k> * <n> <a> = <n> * <o> However, the symbol "x" means an outer product.

When the above condition (Equation 2) is not satisfied, exception processing is performed (step S8). The contents of the exception processing include stopping the operation of the entire robot, notifying the user that the setting is inappropriate, or using the previously calculated <n>, <o>, and <a> unit vectors. , A method of using a unit vector in each of the x, y, and z directions of the coordinate system (work coordinate system in this example) designated by the work coordinate system axis direction storage unit 12 can be considered, and can be appropriately used. . After the calculation is completed, each vector of <n>, <o>, and <a> obtained as a result is transferred to the force control calculation preprocessing unit 19 as coordinate data of the work coordinate system (step S9).

In the above example, the teaching data stored in the position parameter storage unit 10 was used as the position parameter, but the data created by the arithmetic processing based on the position data stored in the position parameter storage unit 10, Alternatively, it is possible to use data which has been subjected to interpolation processing and data which is sent from outside the robot control device 5 by communication by a workstation or the like. The above process is executed at regular sampling intervals after the start-up, and is repeated until the end command comes.

In the work 53 having the shape shown in FIG. 6, when the work tool 51 moves along the trajectory (target trajectory) indicated by the reference numeral 54, for example, when polishing work is performed,
At each of the positions P001 to P010, the above-described calculation (flowchart in FIG. 8) is executed by using the position parameter of each position to obtain <n>, <o>, <a>. 7A,
As is apparent from (B), according to the robot control method of the above embodiment, for example, the coordinate system at the position P002 and the coordinate system at the position P007 face the same direction, and the force is always applied to the work 53.
Acts toward.

As described above, the uniaxial force vector,
The orthogonal coordinate system (work coordinate system) required for indicating the force direction during the force control is set by the position parameter for generating the target trajectory regarding the work.

The force control calculation preprocessing unit 19 receives the given position parameters, the force control parameters for executing the force control, and the control parameters related to the coordinate system from the force control calculation unit 2.
The process for converting to a format that can be used with 0 is executed.

The force control calculation unit 20 has a configuration that can execute virtual compliance control and is well known, so a detailed description of its configuration and operation will be omitted.

Next, a process of generating one axial direction of the work coordinate system by the pressing force direction calculation unit 21 will be described.

First, a robot to which the coordinate setting method according to the present invention is applied will be described with reference to FIG. The above-mentioned robot body 1 attached to the base portion (base) 31 has the force sensor 3 attached to the tip portion thereof, and the work tool 32 is attached to the tip side portion of the force sensor 3. The operation of the robot body 1 is controlled by the robot controller 5 described above. The robot controller 5 includes the configuration described in FIG.
The robot body 1 is a mechanism unit having a plurality of joints inside and at least two degrees of freedom, and the joints are provided with a drive device. The robot body 1 can take various postures by the operation of each drive device, and the work tool 32 can be moved to an arbitrary position.

As shown in FIG. 2, a base coordinate system 33, which is a fixed coordinate system, is set in the base unit 31 of the robot body 1, and a force sensor coordinate system 34 is set in the center of the force sensor 3. There is. Both the translational force and the rotational force are detected by the force sensor.
It is represented by 4 x, y, and z components. Now, assume that ^s F ₁ = (f _x1 , f _y1 , f _z1 ) is detected as the translational force. ^It is assumed that ^s F ₁ means the force expressed in the force sensor coordinate system 34. Regarding the force (translational force) ^s F ₁ detected by the force sensor 3 by the force sensor coordinate system 34, the force (translational force) ^s F ₁ is transferred to the work coordinate system axial direction storage unit 12 and is stored therein by the base coordinate system 33. It is necessary to convert it into the representation of the unit vector shown and transfer it. Therefore, ^s F ₁ represented by the above equation is converted into a unit vector representation as the following equation.

[0039]

[Equation 4]

Next, the equation (4) is converted into an expression in the base coordinate system. In order to perform this transformation, when the rotational transformation from the base coordinate system to the force sensor coordinate system is expressed by the following (Equation 5), based on the equation of ^B F ′ ₁ = ^B T _s ^s F ₁ ′, Can be calculated.

[0041]

[Equation 5]

The above calculation is executed by the pressing force direction calculating unit 21 which takes in the force signal output from the force sensor 3, and the pressing force direction is calculated in this way. Finally obtained value ^B F '
₁ is transferred from the pressing force direction calculation unit 21 to the work coordinate system axial direction storage 12, and is stored as the axial direction of the work coordinate system.

Although the above description relates to the translational force, the same applies to the rotational force.

In FIG. 3, the force vector 41 in the one-axis direction is shown.
An example of the operation for obtaining is shown. For example, when the blade portion of the work tool 32 equipped on the force sensor 3 at the arm tip of the robot body 1 is pressed against the work piece of the work 35 while maintaining the work posture, the force sensor 34 produces a reaction force 42. The force vector 41 is detected based on the force sensor coordinate system 34, and the pressing force direction calculation unit 21 calculates the data.
Further, the pressing force direction calculation unit 21 converts the force vector 41 in the one-axis direction into the base coordinate system 33 and expresses it, and transfers this data to the work coordinate system axial direction storage unit 12 for storage. In FIG. 3, the blade portion of the work tool 32 is pressed against the work 35, but the worker applies a force to the work tool 32 to generate a reaction force 42, and thus a force vector in the uniaxial direction can be obtained. It is possible.

[0045]

As is apparent from the above description, according to the present invention, the vector of the uniaxial direction is set, the position parameter is taught to generate the target trajectory relating to the work, and the direction of the force is controlled during the force control. Since the required orthogonal coordinate system can be set, the coordinate system can be set by a simple operation by the user, and automation can be performed. In particular, the vector setting in the 1-axis direction can be performed by pressing a grinding tool or the like against the work piece or by causing the operator to manually apply a force to generate the required reaction force. It can be done easily and the work is safe.

[Brief description of drawings]

FIG. 1 is a block diagram showing an overall configuration of a robot system to which the present invention is applied.

FIG. 2 is an overall perspective view of a robot.

FIG. 3 is a diagram showing an example of an operation for generating a reaction force.

FIG. 4 is a table showing the contents of force control parameters.

FIG. 5 is a diagram showing a correspondence relationship between an image of work and each control parameter.

FIG. 6 is a diagram showing a target trajectory in a work and a coordinate system generated at each position.

FIG. 7 is a diagram showing a coordinate system generated at two positions on a target trajectory.

FIG. 8 is a flowchart for explaining a coordinate system setting method.

[Explanation of symbols]

1 Robot Mechanism (or Robot Main Body) 3 Force Sensor 4 Manipulator 5 Robot Controller 32, 51 Work Tool 33 Base Coordinate System 34 Sensor Coordinate System (or Force Sensor Coordinate System) 35, 53 Work 41 Force Vector in One Axis 42 Reaction force 54 Target trajectory

Claims (2)

[Claims] 1. A force sensor having two or more degrees of freedom, capable of being set to an arbitrary position and posture, and equipped with a force sensor for detecting a force in a translational direction and a rotational direction with respect to three axis directions at an arm tip portion,
In the robot coordinate system setting method applied to the articulated robot that can be operated by force control, a hand effector is attached to the tip side of this force sensor, which is required for the force direction indication during force control. Cartesian coordinate system 1
A method for setting a coordinate system of a robot, characterized in that it is set by a vector of direction and a position parameter for generating a target trajectory for work, and the vector of the one direction is set by pressing the hand effector against a work. . 2. A force sensor having two or more degrees of freedom, capable of being set to an arbitrary position and posture, and equipped with a force sensor at an arm tip portion for detecting forces in translational and rotational directions with respect to three axial directions,
In the robot coordinate system setting method applied to the articulated robot that can be operated by force control, a hand effector is attached to the tip side of this force sensor, which is required for the force direction indication during force control. Cartesian coordinate system 1
A coordinate system setting of a robot, which is set by a vector of a direction and a position parameter for generating a target trajectory for work, and the vector of the one direction is set by pushing the hand effector with a hand. Method.