JPS6116598B2 - - Google Patents

Description

[Detailed Description of the Invention] This invention provides, for example, a spot welding gun,
The present invention relates to a control device for an industrial robot that allows a working tool such as a painting gun to face a workpiece in a free position.

When controlling the position of a working tool in this type of industrial robot, it is desirable to perform linear control. However, in actual industrial robots, it is difficult to perform such ideal control, and there are cases where only nonlinear control can be performed.

An example of this type of industrial robot will be described with reference to FIG.

This industrial robot accurately follows a product 1 such as a car flowing on a conveyor (not shown) and automatically performs work such as welding, painting, and applying filler, and 2 is its working tool. This working tool 2 is attached horizontally and axially to the tip of a second arm 6 whose base end is pivotally connected to the upper end of a first arm 4 which will be described later and whose base end is pivotally connected to a support stand 3 via a shaft 5. It is supported so that it can rotate around the center.

The support stand 3 is supported by the base 7 so as to be rotatable within a horizontal plane. And this support stand 3
The first arm 4 is supported rotatably (swingably) in the vertical direction. first arm 4
A bracket 8 is provided near the upper end of the
A linear actuator 9, which is a hydraulic cylinder, is installed between the bracket 8 and the support base 3. A bracket 10 is also attached near the lower end of the first arm 4, and a linear actuator 11, which is a hydraulic cylinder, is also attached between this bracket 10 and the second arm 6.

The support base 3 is provided with a rotation angle detector 12 that detects the rotation angle (swing angle) of the first arm 4 . This rotation angle detector 12 is connected to the servo valve 1.
A trajectory command signal is given to 9 from the control device 13,
As the linear actuator 9 operates, the rotation angle of the first arm 4, which changes angle, is detected, and a trajectory feedback signal is returned to the control device 13. A computer 14, which is a storage device for work information, is connected to the control device 13, and receives a trajectory feedback signal from the rotation angle detector 12 through the control device 13, and transmits trajectory data corresponding to the feedback signal to the control device 13. It is becoming more and more common to give money to people.

The control device 13 sends control commands to the hydraulic device 15 that match the operation contents while reconfiguring the work information as necessary. The hydraulic device 15 supplies power to a servo valve that adjusts the hydraulic flow rate, and the servo valve sends hydraulic pressure to the linear actuator 9 in response to a command from the control device 13.

This industrial robot configured in this way is
Although two axes are used as arms, the first arm 4 and the second arm 6, this invention
This is related to a control device for controlling the movement of the tip (point P) of the first arm 4 in a one-axis mechanism as shown in FIG. I will only explain the points.

Conventionally, hydraulic pressure has been supplied to the linear actuator 9 that controls the first arm 4 shown in FIG. 2 through the following circuit. To explain this with reference to FIG. 3, 16 and 17 are D/A converters, and the D/A converter 16 has a built-in attenuation circuit and receives the speed command θi from the computer 14. The A converter 17 is the computer 14
It receives a position command θi from. The signals converted into analog quantities by these D/A converters 16 and 17 are added together and applied to an amplifier 18, where they are amplified to a required current value.

A servo valve 19 is connected to the output side of the amplifier 18, and a linear actuator 9 is connected to the control side of the servo valve 19. The linear actuator 9 is connected to a link mechanism 20 consisting of the linear actuator 9 and the first arm 4,
The rotation angle (momentum) of the linear actuator 9 is detected by the rotation angle detector 12. This detection signal is then fed back to the position command signal.

Here, the gain constant in the link mechanism 20 of the control device will be considered.

In FIG. 2, the distance between the pivot points of the first arm 4 and the linear actuator 9 to the support base 3 is a, and the base end pivot point of the second arm 6 at the upper end of the first arm 4 is P. The distance between and the pivot point of the linear actuator 9 to the bracket 8 is b, the distance between the vertical pivot point of the linear actuator 9 is C, and the input (cylinder displacement) to the linear actuator 9 is d. The rotation angle output of the first arm 4 is θ, a straight line from the pivot point of the lower end of the first arm 4 to the pivot point of the second arm 6 of the first arm 4, and a straight line. If the angle between the actuator 9 and the straight line leading to the pivot point of the bracket 8 is α, then C=√ ² + ² −2(−) = f(θ) …(Formula 1) The input at the steady operating point is θ ₀ , output C ₀ ,
Letting the minute fluctuations be Δθ and ΔC, C ₀ +ΔC=
Expand the right side of f(θ+Δθ), omit terms of (Δθ) ² or more, condition C ₀
= f(θ ₀ ), ΔC=[d/dθf(θ)] _{= 0}・Δθ In other words, the gain constant of the link mechanism, arm rotation angle output/actuator input (=Δθ/Δ
C) is It can be approximated as follows, and a proportional (linear) relationship between Δθ and ΔC can be obtained. Furthermore, when the operating range of θ is large, the cylinder stroke becomes long, and considering a≪d, gain constant = Δθ/ΔC = [1/a・sin(θ−α+β)] ₌ = ₀ …(Equation 3) It can be approximated as Note that β is a correction term.

Here, among the gain constants K ₁ to K ₆ , K ₃ .K ₄・K ₅ .
If K ₆ /a=K, the steady speed deviation e(∞), which is the delay angle of point P, is e(∞)=1/K ₂・[sin(θ ₀ −α+β)/K−
K ₁ ]θi... (Formula 4).

Such conventional control devices have the following problems. That is, in such a servo mechanism, the delay angle (steady speed deviation) e(∞) of the first arm 4 can be approximated by equation 4, but sin(θ
₀ −α+β) is a variable that changes depending on the rotation angle of the first arm 4, so in the feedforward loop, 1/K・sin(θ ₀ −α
+β) It is difficult to obtain a constant K ₁ that makes −K ₁ 0, and highly accurate control is difficult. In particular, link mechanisms with large arm rotation angles (swing angles),
This tendency becomes more pronounced when servo systems with two or more axes are combined singly.

Therefore, if the servo mechanism is controlled by detecting the cylinder stroke rather than by the rotation angle of the first arm 4, there will be no nonlinear elements in the servo mechanism, and accuracy can be improved. However, there are problems with the mounting structure of the stroke detector in creating position data, durability, etc., and position detection based on rotation angle is common.

This invention solves the above-mentioned problem.In a servo mechanism that uses a rotation angle detector to detect the operating position of an arm of an industrial robot, the gain constant Δθ/ΔC of the link mechanism is a sine at a steady operating point. Focusing on the fact that it can be approximated to a characteristic value with a waveform, by providing a gain switching circuit whose characteristic is a sine waveform, the steady speed variation e(∞) can be theoretically made zero (0),
This is intended to improve the accuracy of velocity trajectory control at the arm tip (point P).

FIG. 4 is a block diagram embodying this. In this figure, 21 and 22 are D/A converters, 23 is a gain sine switching circuit, and 24 is a transfer function from the amplifier to the rotation angle detector. In the case of this circuit, the steady speed deviation e(∞) is e(∞)=1/ _K2・[sin(θ ₀ −α+β)/K −K ₁・sin(θ ₀ −α+β)]×θi, If K ₁ =1/K is chosen, e(∞)=0 can be obtained.

The circuit shown in FIG. 5 is representative of the invention. To explain this, 25 is a D/A converter, 26 is a gain sine switching circuit, 27 is a subtracter,
28 is a D/A converter, 29 is an adder, 30 is an amplifier, 31 is a servo valve, 9 is a linear actuator, 32 is a link mechanism, and 33 is a rotation angle detector, which are connected as shown in the figure. ing. In this circuit, the rotation angle detector 33 currently detects the rotation angle.
A gain command signal, which is a feedback signal, is supplied from the gain sine switching circuit 26 to the gain sine switching circuit 26.

FIG. 6 shows the gain sine switching circuit 26 of the circuit shown in FIG. As shown in this figure, this gain sine switching circuit 26 produces an output V ₀ for an input Vi, and the gain of the gain sine switching circuit 26 is expressed by the following equation.

Gain=V ₀ /Vi=[sin (θ ₀ −α+β)] ₀ FIG. 7 is a diagram illustrating the operating characteristics of the gain sine switching circuit 26. As is clear from this figure, when the current rotation angle signal (gain command signal) θ ₀ is changed as a parameter, a sine waveform is obtained. By this gain sine switching circuit 26,
By theoretically setting the steady speed deviation to zero, the accuracy of speed trajectory control at the tip of the first arm 4 is improved.

Next, what is shown from FIG. 8 onwards are modifications and applied examples of this invention. These are changes in which position the gain sine switching circuit 26 is placed and where the gain command signal is taken from.

To explain this one by one, the one in Figure 8 is D/
A converters 34, 35, gain sine switching circuit 36,
It consists of a configuration 37 from an amplifier to a rotation angle detector, and the gain command signal is currently applied to the gain sine switching circuit 36 not from the rotation angle θ ₀ but from the position command θi.

Then, according to the position command θi, the gain is switched so that V ₀ /Vi=gain=sin(θi−α+β). This compensates for the nonlinearity of arm rotation angle/cylinder displacement≈1/[a·sin(θ−α+β)] _{= 0} , and makes the deviation e(∞) due to nonlinearity zero.

e(∞)=1/ _K2・[sin( _θ0 −α+β)/K− _K1 sin(θi−α+β)]θi Here, if the gain is set so that _K1 =1/K, then e( ∞)=0.

The one in FIG. 9 consists of D/A converters 38, 39, an amplifier 40 with a gain sine switching circuit, and a configuration 41 from the servo valve to the rotation angle detector, and the gain command signal is set to the current rotation angle θ. ₀ to the amplifier 40. In this circuit, the nonlinear relationship (arm rotation angle/cylinder displacement) in the feedback loop is compensated for by the amplifier 40 in the feedback loop, and the relationship between the current rotation angle θ ₀ /amplifier input is made into a linear characteristic. Then, the deviation e(∞) will be made zero by feedforward compensation. In this circuit, e(∞)=1/K ₂ [1/K ₃ sin (θ ₀ −α+β) × sin (θ ₀ −α+β)/K′−K ₁ ]×θi = 1/K ₂ [1/ K ₃ K'-K ₁ ]×θi K ₁ =1/K ₃ K', so e(∞)=0.

The operating characteristics of the amplifier 40 (with a gain sine switching circuit) in this circuit are similar to those shown in FIG.

The one in FIG. 10 is a modification of the one in FIG. 9, and the circuit configuration is exactly the _same as that in FIG.
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The one in FIG. 11 includes D/A converters 42, 43,
It consists of an attenuator 44, a configuration 45 from an amplifier to a rotation angle detector, and instead of a gain sine switching circuit, an analog rotation angle detector with sine output characteristics having characteristics as shown in FIG. 12 is used as an attenuator. 46 (see FIG. 13) and is installed in parallel with the rotation angle detector 12 to obtain substantially the same characteristics as each of the above-mentioned circuits.

The one in FIG. 14 includes D/A converters 47, 48,
It consists of an amplifier 49, a structure 50 from a servo valve to a rotation angle detector, and is a modification of the one shown in FIG. In this circuit, the amplification variable resistor shown in FIG. 13 is used as the amplification variable resistor of the amplifier 49, thereby obtaining an amplification corresponding to the rotation angle of the first arm 4.

The one in Fig. 15 consists of D/A converters 51, 52, an amplifier 53, an attenuator 54, and a configuration 55 from the servo valve to the rotation angle detector, and has almost the same effect as the one in Fig. 14. It is something that does.

Each of the circuits described above is connected to the tip of the first arm 4 (P
This was a device that controlled the movement of points), but what will be explained next is a further development of it.

To explain this, in FIG. 16, reference numeral 56 is a rotation angle detector which detects the rotation angle ψ ₀ of the linear actuator 9. The rotational axis of this linear actuator 9 and the rotational axis of the first arm 4 are aligned in the vertical direction.

In FIG. 17, 57 and 58 are D/A converters;
59 is a gain sine switching circuit, 60 is an amplifier, 61
is a servo valve, 62 is a linear actuator, 63
is a link mechanism, and 64 is a rotation angle detector. In this circuit, a gain command signal is given from the ψ ₀ rotation angle detector 65 to the gain sine switching circuit 59. In this circuit, e(∞)=1/K ₂ [sinψ ₀ /K−K ₁ sinψ ₀ ]θ
If i K=K ₃ · K ₄ · K ₅ · K ₆ /a K ₁ =1/K, then e(∞)=0.

The one in FIG. 18 includes D/A converters 66, 67,
Gain sine switching circuit 68, configuration 69 from servo valve to rotation angle detector, and ψ ₀ rotation angle detector 7
0, and the gain command signal is supplied from the ψ ₀ rotation angle detector 70 to the gain sine switching circuit 68.

The one in FIG. 19 includes D/A converters 71, 72,
It consists of an amplifier 73 and an attenuator 74, and the 20th
The ones shown are D/A converters 75, 76 and amplifier 7.
7. Consists of a configuration 78 from the servo valve to the rotation angle detector. The one in FIG. 21 consists of D/A converters 79, 80, an amplifier 81, an attenuator 82, and a structure 83 from a servo valve to a rotation angle detector. Similar to the circuits shown in FIGS. 11, 14, and 15, these circuits do not use a gain command signal, but instead use an analog rotation angle detector consisting of a variable resistor. This is done by an attenuator 74 in the figure, an amplifier 77 in the figure 20, and an attenuator 82 in the figure 21.

Since the present invention is configured as described above, it has the advantage of being able to perform high-speed and highly accurate velocity trajectory control. That is, regardless of θi, theoretically e(∞)=1/K ₂ [sin(θ ₀ −α+β)/K−K ₁
]≒0. Also, the larger the rotation angle (swing angle) of the arm, the greater the advantage. That is, as θ becomes larger, the cylinder stroke becomes longer, and a<<d. This means that the gain constant of the link mechanism is Δθ/ΔC≒[1/a・sin(θ−α+β)]
This is the premise for approximating ₌ 〓 ₀ .

[Brief explanation of the drawing]

Figure 1 is a system diagram showing an example of an industrial robot.
2 is an enlarged side view of the main part of FIG. 1, FIG. 3 is a circuit diagram showing an example of a conventional control device for an industrial robot, and FIG. 4 is a circuit diagram showing the principle circuit of the present invention. FIG. 5 is a circuit diagram showing a typical example of the present invention, FIG. 6 is a circuit diagram showing a part of the circuit in FIG. 5,
FIG. 7 is an explanatory diagram showing the operating characteristics of the circuit in FIG. 6;
8 to 10 are circuit diagrams of modified embodiments of the present invention, FIGS. 11, 14, and 15 are circuit diagrams of other modified embodiments of the present invention, and FIG. 12 is a circuit diagram of a modified embodiment of the present invention.
Explanatory diagram showing some operating characteristics of the one in Figure 1, Part 1
FIG. 3 is a circuit diagram showing a specific example of a part of the circuit shown in FIG. 11, FIG. 16 is a side view of a partially modified version of the circuit shown in FIG. 2, and FIGS. FIG. 6 is a circuit diagram of a modified embodiment. 2...Work tool, 3...Support stand, 4...First arm, 6...Second arm, 7...Base, 8...Bracket, 9,62...Linear actuator, 12,3
3, 64... Rotation angle detector, 20, 32, 63... Link mechanism, 21, 22, 25, 28, 34, 3
5, 38, 39, 42, 43, 47, 48, 5
1, 52, 57, 58, 66, 67, 71, 7
2, 75, 76, 79, 80...D/A converter, 2
3, 26, 36, 59, 68...gain sine switching circuit, 30, 40, 49, 53, 60, 73, 7
7, 81...Amplifier, 31, 61...Servo valve.

Claims (1)

[Scope of Claims] 1. A first arm is supported swingably in a vertical direction on a support stand rotatably supported in a horizontal plane on a base, and the first arm and the first A link mechanism is formed by a linear actuator, which is a hydraulic cylinder, installed between a bracket provided near the upper end of the arm and a support base, and a power tool is attached to the tip of the upper end of the first arm of the link mechanism. Second supported
In an industrial robot in which the base end of the arm is pivotally connected, the relationship between the angle of the first arm of the link mechanism and the length of the linear actuator is such that the first arm and the linear actuator are pivoted to the support base. The distance between the landing points is a, the distance between the base end pivot point of the second arm at the upper end of the first arm and the pivot point of the linear actuator to the bracket is b, and the distance between the top and bottom of the linear actuator is The distance between the pivot points is C, the cylinder displacement which is the input of the linear actuator is d, the rotation angle output of the first arm is θ, the first
The angle formed by the straight line from the pivot point of the lower end of the arm to the pivot point of the second arm of the first arm and the straight line to the pivot point of the linear actuator to the bracket is α. Then, the formula C=√ ² + ² −2(−) is satisfied, and a rotation angle detector for detecting the rotation angle of the first arm is provided on the support base, and the rotation angle detection a servo valve that controls the hydraulic pressure supplied to the linear actuator based on the rotation angle of the first arm detected by the device; A control device that issues a matched control command is provided, the gain constant of the link mechanism is approximated to a characteristic value having a sine waveform at a steady operating point, and a gain sine switching circuit having a characteristic of the sine waveform is controlled by a trajectory from the computer. A control device for an industrial robot, characterized in that it is provided between a D/A converter that receives a command signal and an amplifier that sends a signal to a servo valve.