JPH0760667A - Weaving control device for robot - Google Patents

Abstract

PURPOSE:To improve weaving amplitude accuracy by carrying out operation on a strain quantity of a driving mechanism by substituting an operating quantity, a driving position and driving speed in an equation of motion of a robot driving mechanism, feeding back these strain quantity and driving position, and inputting the operating quantity according to deviation between a target value and a feedback quantity to a driving source. CONSTITUTION:An observer 8 models a robot mechanism part 15 as a system composed of a spring and a rigid body, and finds an equation of motion of the robot mechanism part 15. Operation is carried out on a strain quantity between an electric motor 5 and an arm 7 by substituting an electric current (i) inputted to the electric motor 5, an output turning angle thetaM of the electric motor 5 and the rotational speed G. M in the equation of motion. This strain quantity is multiplied by a control gain Kps by a gain multiplier theta. The sum of this multiplied result and a rotational position thetaM is fed back to the input side of a servo operation part 3 as a feedback quantity. The servo operation part 3 outputs an operating quantity according to a target value and this feedback quantity to a driving part 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for controlling an industrial robot, and more particularly to a controller applied to a robot for weaving welding and capable of accurately drawing a weaving waveform.

[0002]

2. Description of the Related Art In the field of industrial robots, weaving welding is generally used in which the torch attached to the tip of the robot is oscillated at a predetermined weaving frequency, for example, in a direction perpendicular to the direction of the welding line for welding. This weaving welding is performed by driving all the operating axes of the robot and weaving the torch tip.

Here, as a robot, for example, 1 in FIG.
A 6-axis vertical articulated robot as shown in 3 is used, but since this type of robot has an axis with low rigidity, it exhibits resonance characteristics with respect to the weaving frequency and with respect to the command amplitude of the weaving waveform. The phenomenon that the actual amplitude becomes large occurs.

Further, since the above-mentioned resonance characteristics greatly change with a change in posture of the robot, there is also a problem that the resonance ratio of the actual amplitude with respect to the command amplitude changes depending on the operating position. Therefore, in order to solve such a problem, an invention has been made in which the resonance ratio due to the weaving motion of the robot mechanical system is obtained, and the reciprocal of the resonance ratio is used to correct the weaving amplitude command value at the torch tip (working point), It is disclosed in Japanese Patent Laid-Open No. 3-207576.

FIG. 5 is a block diagram schematically showing the invention described in this publication. Referring to this figure, as shown in FIG. 5 (a), the target of the torch tip in the weaving waveform calculator 1 is shown. The trajectory is calculated, and the inverse transformation calculation unit 2 mechanically performs the inverse transformation based on the target trajectory of the torch tip, whereby the target value (target angle) of each axis of the robot is calculated. Based on the target value, the servo operation unit 3 outputs an operation amount such that each axis follows the target value to the drive unit 4 including an amplifier, which drives the mechanism unit 5 including the speed reducer and the arm. The torch tip is weaving operated. Here, in the weaving waveform calculation unit 1, the command value of the weaving amplitude at the tip of the torch is shown in FIG.
The correction is made as shown in (b).

FIG. 5B shows a weaving waveform calculator 1.
Is shown in detail in blocks. Now, the axis that needs correction is the vertical axis having the lowest mechanical rigidity and natural frequency, that is, the first axis J in the case of the robot 13 in FIG.
1 and it is assumed that the correction is performed only on this axis J1.

Then, first, the weaving vector calculation means 11 generates a weaving vector at the tip of the torch, and the J1 axis command amplitude calculation means 22 obtains the command amplitude converted to the J1 axis based on the weaving vector.
On the other hand, the J1 axis resonance rate calculation means 23 obtains the J1 axis resonance rate from the weaving frequency and the robot posture.
Next, the J1 axis correction amplitude calculating means 24 calculates the correction amplitude by multiplying the J1 axis command amplitude obtained by the calculating means 22 by the reciprocal of the resonance rate obtained by the calculating means 23. The weaving vector at the torch tip is re-synthesized by the weaving vector synthesizing means 25 by the corrected amplitude, and the weaving waveform computing means 26 computes the weaving target locus using the re-synthesized vector to obtain the weaving amplitude command value at the torch tip. Correcting.

FIG. 7 is a diagram for explaining the processing contents of FIG. 5, in which weaving welding is performed while linearly interpolating from point P1 to point P2 in FIG. 7, and the command amplitude at point P on the way is corrected. Shall be. Note that point O is the robot center position and XY is the coordinate system fixed to the robot.

Then, the calculating means 11 generates a weaving vector b in a direction perpendicular to the welding line a,
The command amplitude c converted to the J1 axis is calculated by the calculation means 22.
Next, the calculating means 23 calculates the resonance ratio of the J1 axis, and the calculating means 24 calculates the corrected amplitude d of the J1 axis. Finally, the weaving vector is recombined by the calculating means 25 to obtain the vector e. The obtained vector e becomes the vector after the weaving amplitude command value correction.

[0010]

The above-mentioned conventional technique is
The resonance ratio is obtained for the J1 axis where the resonance phenomenon is remarkable, and the amplitude is corrected based on the reciprocal of the resonance ratio. Only the gain characteristic is corrected among the weaving command input and output frequency characteristics (resonance characteristics). However, the phase delay is not corrected.

Therefore, when the weaving frequency is in the high frequency range, the phase difference between the J1 axis and the other axes becomes large,
The phase mismatch between the J1 axis and other axes may lead to deterioration of the weaving amplitude accuracy of the torch tip.

Further, since it is not possible to cope with the change in the characteristics of the mechanical system caused by the disturbance during control, similarly, the weaving amplitude accuracy of the tip of the torch is deteriorated.

The present invention has been made in view of the above circumstances, and it is possible to correct the frequency characteristic with respect to the phase delay as well as with the disturbance during control.
It is an object of the present invention to provide a device capable of further improving the weaving amplitude accuracy of the torch tip and further improving the distortion of the weaving surface and the wavefront.

[0014]

In view of the above, the present invention has a robot drive mechanism in which the robot axis is driven by a robot axis drive source provided for each axis of the robot. By calculating a target position of the robot axis on the basis of the target position and inputting an operation amount according to a deviation between the target position and the current drive position fed back from the robot axis drive source to the robot axis drive source, In the weaving control device of the robot, which drives the robot axis via a robot drive mechanism and moves the welding torch tip along the weaving target locus to draw a predetermined weaving waveform, the operation amount and the driving amount. The robot showing the relationship between the position, the drive speed obtained by differentiating the drive position, and the strain amount of the robot drive mechanism. The current equation of the robot drive mechanism is calculated by obtaining the equation of motion of the dynamic mechanism, and substituting the present operation amount, the current drive position, and the drive speed obtained by differentiating the current drive position into the obtained equation of motion. A strain amount is calculated, the calculated current strain amount is fed back together with the current drive position, and an operation amount corresponding to the deviation between the target value and these feedback amounts is input to the robot axis drive source. ing.

[0015]

With this configuration, the operation amount, the drive position, and the drive speed are substituted into the equation of motion of the robot drive mechanism to calculate the strain amount of the robot drive mechanism, and the calculated strain amount is fed back together with the drive position. Since the operation amount according to the deviation between the target value and the feedback amount is input to the robot axis drive source for control, the influence of the distortion amount of the robot drive mechanism is removed, and the weaving command input and output The frequency characteristic of is completely corrected. Further, since the distortion amount is constantly fed back during the control, the influence of disturbance is removed.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a weaving controller for a robot according to the present invention will be described below with reference to the drawings. In addition, hereinafter, the same reference numerals as those shown in FIG. 5 indicate the same functions.

FIG. 1 is a block diagram showing the control apparatus of the embodiment, and FIG. 1B shows the details of the weaving waveform calculation unit 1 shown in FIG. As the robot applied to this embodiment, a vertical articulated robot 13 having six axes J1 to J6 shown in FIG.
1 is assumed, and the apparatus of the embodiment of FIG.
Each robot axis J so that the weaving waveform is accurately drawn by the torch 14 attached to the arm tip of the robot.
It is a control device that controls 1 to J6.

Although the embodiment assumes a 6-axis vertical articulated robot, the present invention is not limited to this, and the number of axes and the structure of the mechanical portion are arbitrary, and will be described below. The robot can be applied to other types of robots if the parts related to the mechanism of the contents are changed as needed.

The correction described below is ideally carried out for all the motion axes of the robot, but the correction is necessary when the processing capacity of the CPU for performing the correction calculation is limited or due to the structure of the mechanical section. If there is no axis, etc., some axes, that is, at least one predetermined axis (J1)
You may make it correct only about.

The weaving waveform computing unit 1 comprises a weaving vector computing unit 11 and a weaving waveform computing unit 12. The difference from the prior art is that the weaving amplitude command value at the tip of the torch 14 is not corrected. That's what it means.

Thus, the target locus of the tip of the torch 14 is calculated from the weaving waveform calculation unit 1. This target locus is (X, Y, Z (three-dimensional position), A, B, C (angle))
It is expressed by a parameter with 6 degrees of freedom. Now, in the inverse conversion calculation unit 2, each axis J1 is mechanically determined from the target locus of the torch tip, that is, the torch tip position (X, Y, Z, A, B, C).
By converting back to the position (angle) of J6, each axis J
Target values (target angles) θ1d to θ6d of 1 to J6 are calculated.

The servo operation unit 3, the drive unit 4, the electric motor 5, the speed reducer 6, and the arm 7 are present for each control axis number (6) of the robot 13, and the observer 8, the gain multiplication unit 9, and the inertia of each axis are provided. The calculation unit 10 exists only for the axis to be corrected in the embodiment.

However, since the content of the correction for each correction axis is the same, in the following description, the case where only the J1 axis (first axis) is corrected is taken as an example, and the calculation is performed by the inverse conversion calculation section 2 which will be further described. A deviation between the target value θ1d and a feedback amount described later is input to the servo calculation unit 3. Then, a command value corresponding to the deviation is output from the servo calculation unit 3 to the drive unit 4 including an amplifier so as to obtain the target value θ1d. The drive unit 4 outputs an operation amount corresponding to the input command value, that is, a current i to the electric motor 5.

The electric motor 5 drives the arm 7 via the speed reducer 6. That is, the electric motor 5 drives the corresponding J1 axis. A position detector (not shown) such as an encoder is attached to the electric motor 5 to detect the control amount of the electric motor 5, that is, the current position (angle) θM. The detected value θM is fed back to the input side of the servo calculator 3 as a feedback amount.

The electric motor 5, the speed reducer 6 and the arm 7 constitute a mechanical system for driving the robot axis J1 by the electric motor 5 which is a drive source. Hereinafter, these are collectively referred to as a robot mechanism section 15.

As will be described later, the observer 8 models the robot mechanism unit 15 as a system composed of a spring and a rigid body as shown in FIG. 3, obtains the equation of motion of the robot mechanism unit 15, and uses this equation of motion as the equation. The electric current i input to the electric motor 5, the rotational position θM output from the electric motor 5, and a differential value of the rotational position θM, that is, the rotational speed θ. By substituting M, a later-described distortion amount between the electric motor 5 and the arm 7 is estimated and calculated. The current i is detected by an output current detector (not shown) attached to the drive unit 4 and added to the observer 8. The rotational position θM is detected by the position detector and added to the observer 8, and the rotational speed θ. M is calculated and output by inputting the added rotational position θM into a not-shown differentiator attached to the observer 8.

The estimated distortion amount is added to the gain multiplier 9, multiplied by a predetermined control gain Kps, and fed back to the input side of the servo operation unit 3 together with the feedback amount θM.

After all, the sum of the rotational position θM and the distortion amount multiplied by the gain Kps is used as the feedback amount, and the deviation between the target value θ1d and these feedback amounts is input to the servo calculation unit 3. .

The axis inertia calculation section 10 outputs the output θ of each position detector of each electric motor 5 provided for each robot axis.
Input M and calculate the inertia JL of the first axis J1 online. The inertia JL calculated by each axis inertia calculation unit 10 is added to the observer 8 and, as will be described later, substituted into the above equation of motion, and the current robot 13
It is re-described in the equation of motion according to the posture of.

Here, the feedback control device of the embodiment will be described in comparison with the conventional feedback control device shown in FIG. 6. The feedback control device shown in FIG. 6 is obtained by the position detector of the electric motor 5 of each axis. Since it is a semi-closed loop that makes the rotational position follow the target value, a resonance phenomenon occurs due to the low rigidity of the speed reducer 6, and the weaving width of the actual trajectory of the torch tip with respect to the weaving target trajectory is There were cases where the weaving characteristics deteriorated due to the increase in size and the distortion of the waveform. But,
In the embodiment apparatus, as described above, the strain amount estimated by the observer 8 is fed back together with the rotational position obtained by the position detector of the electric motor 5 of each axis, and a full closed loop is configured. The resonance characteristics are significantly improved.

At this time, unlike the prior art, the robot 1
Since the state of the robot mechanism unit 15 is estimated online by the observer 8 during the control of 3, it is possible to immediately respond to a temporary change in the resonance characteristic due to disturbance.

Further, since the inertia around each operation axis of the robot 13 changes depending on the posture of the robot 13,
The equation of motion obtained by the observer 8 also needs to be changed accordingly.

Therefore, in each axis inertia calculation unit 10,
Since the inertia around each operation axis is calculated online during the control of the robot 13 and the above equation of motion is changed online, the weaving characteristics with high accuracy are always obtained regardless of the posture of the robot 13. To be obtained.

The details of the estimation calculation process executed by the observer 8 will be described below. Now, assuming that the J1 axis robot mechanism unit 15 is a mechanical system including a spring and a rigid body as shown in FIG. 3, a motion model is created. At this time, since the arm 7 and the electric motor 5 have sufficiently high rigidity with respect to the speed reducer 6, it may be assumed that the strain amount of the robot mechanism unit 15 occurs only in the speed reducer 6. Therefore, under this assumption, the following equation of motion is obtained for the above motion model.

JM · θ. ． M + DM · θ. M + Kc ・ η ・ θs / RG + DL2 ・ η ・ θ. s / RG = KT · η · i (1) JL · θ. ． L + DL1 · θ. L-Kc.theta.s-DL2.theta. s = 0 (2) θs = θM / RG−θL (3) where, i: motor current θM: motor rotation angle θL: robot arm rotation angle θs: reduction gear distortion angle KT: motor torque constant η: Reducer efficiency JM: Motor rotor inertia moment RG: Reducer gear ratio Kc: Reducer spring constant JL: J1 axis inertial moment DL1: J1 axis friction coefficient DL2: Reducer friction coefficient DM: Motor friction coefficient. In addition, "." Attached to the lower right of each θM, θL, and θs.
Is the first derivative of each θM, θL, θs, and each θM, θL,
“..” attached to the lower right of θs represents the second derivative of θM, θL, and θs. Also, in the following, the same expressions have the same meanings.

In the equation of motion represented by the above equations (1) to (3), if the state variable is taken as the following equation (4) and the output variable is taken as the following equation (5), the state equation, The output equations are as shown in equations (6) and (7) below.

X = [θ. M, θM, θ. s, θs] T (4) y = [θ. M, θM] T (5) x. = A · x + B · i (6) y = C · x (7) where Is.

Further, a11 = -DM / JM a13 =-[eta] .DL2 / (JM * RG) a14 =-[eta] * Kc / (JM * RG) a31 = DL1 / (JL * RG) -DM / (JM *) RG) a33 =-((DL1 + DL2) / JL + η ・ DL2 / (JM ・ R
G.RG)) a34 =-(Kc / JL + .eta.Kc / (JM.RG.RG)) b1 = .eta..KT / JM b2 = .eta..KT / (JM.RG).

When the state variable x in the above equation (6) is estimated by the same dimension observer, the following equation is obtained.

X ^. = A * x ^ + B * i + K (y-C * x ^) ... (8) Here, K shows the gain matrix of an observer.

However, among the estimated state variables, the output variables, that is, the rotation angle θM and the rotation speed θ. M
, Which are directly detectable, form a minimum-dimensional observer, and the strain angle θs and the strain angular velocity θ. s can be estimated. ω. = A ^ .omega. + B ^ .i + G.y (9) x ^ = C ^ .omega. + D ^ .y (10) In order for the above equations (9) and (10) to be the minimum dimension observer, a certain matrix F Exists, A ^ · F = F · A−G · C B ^ = F · B C ^ · F + D ^ · C = In (In is a unit matrix of order n, n is a system order), and A It is necessary that ^ be a stable matrix. The observer 8 calculates the above equations (9) and (10) online. The input to this minimum dimension observer is the current i of the motor 5 and the output variable y, that is, the motor 5
Rotation angle θM and rotation angular velocity θ. M, and the output is the distortion angle θ ^ s of the reduction gear, the distortion angular velocity θ ^. s.

In this embodiment, since the control is based on the fully closed arm position control method, only the distortion angle estimated value θ ^ s is used for the control. Therefore, this distortion angle estimated value θ ^ s is used as the distortion amount by the observer 8
Is added to the gain multiplication unit 9.

Next, details of the calculation contents of each axis inertia calculation unit 10 will be described.

The robot 13 is modeled as shown in FIG. 4, and the moment of inertia JL about the J1 axis is obtained by the following equations (11) to (13). In this embodiment, the J2 axis is considered as a concentrated mass and is set on the link of the J2 axis, the J3 axis to the J6 axis are collectively considered as a concentrated mass, and this is set on the link of the J3 axis, and the J1 axis is fixed. The model is based on mass. It is clear from FIG. 4 that r2 = L2G · sin (θ2d) (11) r3 = L2 · sin (θ2d) + L3G · cos (θ2d + θ3d) (12) JL = J10 + m2 · (r2) * 2 + m3 · (r3) * 2 ... (13) is obtained. Here, θ2d and θ3d are target values of the J2 and J3 axes, m2 is the mass of the J2 axis, m3 is the mass of the J3 to J6 axes,
L2G and L3G are the positions of the concentrated masses m2 and m3, L2 is the link length of the J2 axis, and r2 and r3 are the concentrated masses m from the J1 axis rotation center.
2, horizontal distance up to m3, J10 represents fixed inertia of J1 axis. It should be noted that "* 2" represents the square.

In each axis inertia calculation unit 10, the above formulas (11) to (13) are calculated online, and the calculated inertia JL around the J1 axis is substituted into the formula (2) of the above equation of motion. , The motion model of the observer 8 will be changed online.

In the past, the observer was used in combination with state quantity feedback in order to reduce vibration during operation. In this embodiment, however, the observer was used as means for estimating the position of the arm, and the estimated position was used. Full-closed control is performed by returning to this point, which is different from the conventional control method using an observer.

[0047]

As described above, according to the present invention, the strain amount of the robot drive mechanism is calculated from the equation of motion of the robot drive mechanism, and the calculated strain amount is fed back together with the control amount. The influence of the distortion amount of the robot drive mechanism is removed, and the frequency characteristics of the weaving command input and output are completely corrected.

Further, since the distortion amount is constantly fed back during the control, the influence of disturbance is eliminated.

As a result, the accuracy of the weaving amplitude is dramatically improved, and the distortion of the weaving surface and the waveform is dramatically improved.

[Brief description of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of a weaving control device for a robot according to the present invention.

FIG. 2 is a perspective view showing the external appearance of a robot applied to the embodiment.

FIG. 3 is a diagram showing a model of the robot mechanism unit shown in FIG.

FIG. 4 is a diagram showing the robot shown in FIG. 2 as a model.

FIG. 5 is a block diagram illustrating a configuration of a conventional control device.

FIG. 6 is a block diagram illustrating the configuration of a conventional feedback control device.

FIG. 7 is a diagram used for explaining a process performed by the control device shown in FIG. 5, and is a diagram showing a manner of correcting an amplitude converted into each axis from a weaving waveform.

[Explanation of symbols]

 5 Electric motor 8 Observer 10 Each axis inertia calculation unit 15 Robot mechanism unit

Claims (2)

[Claims] 1. A robot axis drive source provided for each axis of the robot, wherein the robot axis is driven by a robot axis drive mechanism, and a target position of the robot axis is calculated based on a weaving target locus at the tip of the welding torch. Then, by inputting an operation amount according to a deviation between the target position and the current drive position fed back from the robot axis drive source into the robot axis drive source, the robot axis is moved through the robot drive mechanism. A weaving control device for a robot which is driven to move a tip of the welding torch along the weaving target locus to draw a predetermined weaving waveform, wherein the operation amount, the driving position, and a driving speed obtained by differentiating the driving position. And an equation of motion of the robot drive mechanism showing the relationship between the strain amount of the robot drive mechanism and The present strain amount of the robot drive mechanism is calculated by substituting the present operation amount, the present driving position, and the driving speed obtained by differentiating the present driving position into the calculated equation of motion. A weaving control device for a robot, wherein a current distortion amount is fed back together with a current driving position, and an operation amount corresponding to a deviation between the target value and these feedback amounts is input to the robot axis drive source. 2. The equation of motion of the robot drive mechanism uses a moment of inertia about the robot axis as a variable, calculates the moment of inertia based on the current position of each axis of the robot, and calculates the calculated moment of inertia. 2. The weaving control device for a robot according to claim 1, wherein the amount of strain of the robot drive mechanism according to the current posture of the robot is calculated by substituting into the equation of motion.