FI83175C - Procedure for path control of a robotic cell - Google Patents

Description

1 83175

The present invention relates to a method for orbital control of a robot cell, the robot cell comprising a robot of at least five degrees of freedom, a manipulator of at least two degrees of freedom and a control unit synchronously controlling them, the method comprising the steps of - bringing the robot and manipulator manually into the desired position at points relevant to the trajectory, and - storing information about the mutual position of the robot and the manipulator at said points in the control unit.

Robotic systems have been developed in which the movements of the robot and the manipulator 15, most commonly the turntable, can be controlled synchronously so as to provide a controlled path movement relative to the object on the turntable (e.g., a linear motion). The systems allow for complex trajectories compared to 20 tuna systems that lack synchronization. For example, during welding, the axes of the turntable cannot be turned in non-synchronized systems, because otherwise the path made by the tool is not controllable (e.g., direct movement is not straight with respect to the part on the turntable). In the current 25 synchronized systems, the robot and the turntable drive through the points taught in the teaching phase. As a result, the user, when teaching synchronized trajectories, must first turn the part to a position favorable to the work process and then teach the point 30 by means of a robot. When driving along the taught trajectory, the axes of the turntable rotate linearly from the starting position to the end position, during which the robot adapts to the movement of the table to achieve the desired trajectory. The problem is that the orientation of the tool does not necessarily remain in its most favorable position for the work process. In this case, even if the start and end points of the hit 2 83175 dry track were taught, the so-called in the foot position, synchronized movement may result in the welding torch not remaining in the foot position at all points of the trajectory.

It is an object of the present invention to provide a method for orbital control of a robot cell, which does not involve the said problems related to, for example, the control of the position of a tool in synchronized movements. The object of the invention is thus to provide a robotic cell in which the teaching of synchronized movements is rapid and the optimal position of the tool for the work process is more easily achieved. This is achieved by means of the method according to the invention, characterized in that - the control unit is provided with path optimization criteria, and - the optimal path is calculated on the basis of the information on the mutual position of the robot and the manipulator and the optimization criteria by the control unit.

Thus, in the method according to the invention, the position and positions of the robot and the body manipulator 20 with respect to the environment can be selected in the easiest way from the point of view of teaching. It is essential that during the teaching phase, the inventive position of the robot tool holder and the part manipulator is correct for performing the work step. It is this central-25 position that is stored in memory in addition to the desired trajectory points. Based on this mutual position and the optimization criterion fed to the control unit, which may concern, for example, the position of the welding torch during the welding process, the control unit can then calculate the final optimal trajectory 30 to be used during the actual work. In this way, the teaching phase can be speeded up and simplified, and yet the end result is a trajectory in which both the relative position of the tool and the workpiece and their positions relative to the environment are most advantageous for the performance of the work itself.

3,83175

Preferably, the relative position of the robot and the part manipulator is stored as the position of the coordinate system of the robot tool holder with respect to the coordinate system of the robot platform and as the angular position of the joints of the part manipulator. The method is further simplified by the possibility that the robot and the part manipulator are brought into the desired mutual position only by controlling the robot while the position of the manipulator remains unchanged.

The method according to the invention will now be described in more detail with reference to the accompanying drawings, in which Figure 1 schematically shows a robot cell assembly according to the invention, Figure 2 shows the locations and associated coordinate systems of the robot cell 15 of Figure 1 and Figure 3 shows a block diagram of the robot cell of Figure 1.

The method according to the invention requires that the ro-20 bot cell consists of a robot 1 of at least five degrees of freedom, a turntable 2 of at least two degrees of freedom and a control unit 3 controlling them. The control unit 3 is able to drive both the robot 1 and the turntable 2 simultaneously. The workpiece (not shown) is attached to the pivot-25 table 2 and the required tool (not shown) to the robot 1. The head joints J1, J2, J3 of the robot can be either rotary-type joints or linear joints. The wrist joints J4, J5, J6 must be of the rotational type so that the control unit 3 can change the orientation of the tool if necessary. The joints J7, J8 of the turntable 30 must be of the rotary type so that the control unit 3 can, if necessary, change the position of the part relative to the robot.

The point of intersection of the rotary table axes has a rectangular coordinate system T, the robot mounting base 35 has a rectangular coordinate system W and the tool tip has a rectangular coordinate system P. The position of the coordinate system T is determined by the articulation angles of the rotary table axes. When teaching the points of the trajectories, the position W or 5 T of the coordinate system relative to the coordinate system and the articulation angles J7, J8 of the turntable are stored in the memory of the control unit.

When running synchronized movements, the motion-path calculation with respect to the T coordinate system takes place instead of the W coordinate system. The control unit 3 performs the necessary conversion operations from the W coordinate system to the T coordinate system and vice versa. In order to obtain an optimal trajectory, the control unit 3 moves the pivot table joints so that the direction of the z-axis of the tool remains in a predetermined position relative to the W-coordinate system during movement (e.g. in hit-15, it is desirable that the z-axis of the tool coordinate system points downwards, so-called foot position). During each calculation period, the control unit calculates - the values of 20 for the articulation angles J7, J8 of the turntable 2 with respect to the T-coordinate system 2 - the point Pi in the T-coordinate system turns to the optimum position (point Pi2), - the point Pi2 with respect to the W coordinate system Pi3) - based on the value of point Pi3, the robot's articulation angles 25 J1 ... J6 - the angles J1 ... J8 correspond to the position values of the encoders E1 ... E8 - instruct each articulation servo NS1 ... NS8 to drive to the calculated encoder value 30 Since the optimization is performed during each calculation period, it is possible to teach the points of the trajectories in the non-optimum position and also to maintain the optimum position throughout the trajectory while repeating the taught trajectory.

Figure 1 shows a system with which the track optimization according to the invention can be implemented. The robot 5 83175 is a six-degree-of-freedom articulation mechanism with all articulated joints. The axes of rotation of the joints are marked J1, J2 ... J6. The turntable 2 has two rotating joints, the axes of which are marked J7 (turn) and J8 (turn).

5 The axes of the turntable are perpendicular to each other and intersect at point A. The axis J8 is parallel to the x-axis of the W-coordinate system. Each joint has a motor M1 ... M8, which can be driven via the corresponding joint servo NS1 ... NS8. To read the position of the joint, the motor-10 motors have absolute encoders E1 ... E8, the signals of which are connected to the corresponding joint servo NS1 ... NS8. The workpiece is attached to the turntable 2, the tool is attached to the robot tool flange. For example, the cell can be used to weld pieces if welding equipment is connected to the robot.

Figure 2 shows a reduced model of the system of Figure 1. The direction W of the robot coordinate system is chosen so that the z-axis is the direction of the joint J1, the y-axis is the direction of J2 when the joint angle of J1 is 0, the x-axis is perpendicular to the above axes. The origin of the W coordinate system 20 is at the intersection of the J1 and J2 axes B. The z-axis of the turntable T coordinate system points in the J8 direction (* J1 direction) and the x-axis W in the x-axis direction of the W coordinate system when J7, J8 are at 0. The origin of the T coordinate system is located at the intersection of the J7 and J8 axes. 25 The position and orientation of the tool coordinate system P relative to the W coordinate system depend on the robot joint angles J1 ... J6, the origin of the tool coordinate system is located at the tool tip.

Figure 3 shows a cell control system. 30 The articulated servos NS1 ... NS8 are connected to the respective motors M1 ... M8 of the robot 1 and the turntable 2 and to the encoders E1 ... E8. The articulated servos are each able to control their own joint according to the instructions from the calculation unit 3. The calculation unit can, for example, instruct the articulated servo to drive to the desired encoder reading. When the robot is taught to drive from point 6 to 83175, the taught points are stored in the memory 7 of the control unit 3. At each point, the position of the P-coordinate system with respect to the W-coordinate system and the swivel angles J7, J8 of the turntable are stored. The task of the calculation unit 8 included in the control unit 3 is to calculate the interpolation points of the trajectory in the rotary table coordinate system, perform the orientation rotation to the desired optimal position by the rotary table, perform a conversion to the optimized point in the W coordinate system, calculate the joints 10 , J8 values calculated in the optimization phase) and control the articulated servos to the calculated position. To obtain sufficient orbital accuracy, the interpolation calculation interval must be a few tens of milliseconds.

During the training phase, the user can keep the position of the turntable-15 unchanged. The point is taught by driving the robot 1 with the hand control 4 to the desired point in the desired orientation with respect to the object. The position and orientation of the point as well as the articulation angles of the turntable are stored in memory. The position and orientation of the point can be recorded relative to the W coordinate system, the T coordinate system, or as robot articulation angles. The articulation angles 37, 38 at the time of teaching are stored on the turntable. Continuing in this way, all the points needed for the course are taught.

When repeating the taught trajectory (e.g. a straight line from point P1 to point P2), the calculation unit 8 must convert the points P1 and P2 from the W coordinate system to the T coordinate system. The point stored in the memory can be represented in the form of a transformation matrix 30 nx ox ax px | | ny oy ay py | | nz oz the pz | | 0 0 0 0 | 35 where vector {px, py, pz} = position of point origin '83175 vector {ηχ, ηγ, ηζ} - x-axis of tool coordinate system at point Pw vector {ox, oy, oz} = y-axis of tool coordinate system at point Pw 5 vector { ax, ay, az} «z-axis of the tool coordinate system at point Pw

The transformation of the point Pw from the W coordinate system T to the coordinate system takes place by multiplying the point Pw T in the W coordinate system by the inverse matrix Τ 'of the 10 transformation matrices T describing the position and orientation of the coordinate system.

Pt = T '* Pw T The matrix can be easily determined by knowing the location of the origin of the ΤΙ 5 coordinate system in the W coordinate system and the articulation angles J7, J8 of the turntable axes.

| C8 -S8 0 px | | C7 * S8 C7 * C8 -S7 py | 20 | S7 * S8 S7 * C8 C7 pz | | 0 0 0 1 | where C7 = cos (J7) C8 * cos (J8) 25 S7 = sin (J7) S8 = sin (J8) vector {px, py, pz} Location of the origin of the T-coordinate system in the W-coordinate system 30 When the points P1 and P2 of the trajectory are known In the T-coordinate system, the interpolation calculation of the trajectory can be performed with respect to the T-coordinate system. For each trajectory interpolation point Pti, a corrected value is calculated to implement the optimum orientation. The body is obtained for the optior-35 entation as follows: β 83175

Calculate the T * Pti z vector | ...... C8 * ax - S8 * ay ... | I ...... C7 * S8 * ax + C7 * C8 * ay - S7 * az | 5 | ...... S7 * S8 * ax + S7 * C8 * ay + C7 * the ... | | 0 0 0 1 |

Let the T * Pti z vector be equal to the desired optimum orientation v, giving the condition 10 vx = C8 * ax - S8 * ay vy * C7 * S8 * ax + C7 * C8 * ay - S7 * az vx »S7 * S8 * ax + S7 * C8 * ay + C7 * az 15 where the unit vector {vx, vy, vz} = desired optimum orientation.

From this group of equations, the optimal values of J7 and J8 can be solved by remembering that C7 = cos (J7) and C8 = cos (J8).

20 The interpolation point Pti is converted from the T coordinate system to the W coordinate system as follows

Pwi - To * Pti

Pwi * path optimized point in W coordinate system 25 To - T coordinate system transformation matrix in optimized position

Pti = point on the trajectory with respect to the T coordinate system

Based on the point pwi, the angles J1 ... J6 of the robot ni-30 can be calculated at the optimum point. The control unit 3 converts the articulation angles to the position information of the encoders E1 ... E8 and drives the articulations through the articulation servos NS1 ... NS8. position.

The method according to the invention has been described above with the aid of only one exemplary embodiment, which is particularly directed to the application of the method in connection with welding β 83175. It will be appreciated that the method of the invention may be applied to other robot cell applications in which it is desired to provide either an optimizer or a boundary condition to either the robot or the body multiplier. Such boundary conditions may be related to the positions of either the robot or the body manipulator, possible obstacles in their trajectory, restrictions on the operating range of some joints, etc.

Claims (4)

10,831 75 A method for orbital control of a robot cell, the robot cell comprising a robot 5 (1) of at least five degrees of freedom, a body manipulator (2) of at least two degrees of freedom and a control unit (3) synchronously controlling them, the method comprising the steps of - a robot (1) and a manipulator (2) ) is brought manually (4) to the desired mutual position at points relevant to the trajectory 10, and - information on the mutual position of the robot (1) and the manipulator (2) at said points is stored in the control unit (3), characterized in that - the control unit (3) is - 15 optimization criteria, and - calculating the optimal trajectory on the basis of the optimization criteria and the information on the mutual position of the robot and the manipulator by means of the control unit (3). Method according to Claim 1, characterized in that the relative position of the robot (1) and the manipulator (2) is stored as the position of the coordinate system (P) of the tool holder (5) of the robot (1) in the coordinate system (W) of the platform (6) of the robot (1). ) and as angular positions of the manipulator joints (J7, J8). Method according to claim 1, characterized in that the optimization criterion comprises the position of the robot (1) or manipulator (2) in relation to the environment. A method according to claim 1, characterized in that the robot (1) and the manipulator (2) of my pieces are brought into the desired mutual position by controlling the robot (1) while the position of the manipulator (2) remains unchanged. 11 83175