JP2580502B2 - Force / torque control method for motor with reduction gear - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Object of the Invention [Industrial Application Field] The present invention relates to a force / torque control method for a motor with a speed reducer, such as a drive for a joint of a robot. It can be applied to all fields that require force / torque control.

[Related Art] Control of a joint of a robot arm requires high-precision position control, and also requires control of torque and force. That is, it is often required to appropriately switch and use the position control and the torque control according to the work content to be dealt with. Therefore, the drive system of the joints of the robot arm needs to have a control structure that can control both of them stably with high speed and high accuracy. Such joint drive systems usually use an electric motor with a reduction gear.

Commonly used motors have many rotations per minute
Since it rotates about 3000 to 8000 times and the output torque is low, when using it as a drive system for a robot joint, reduce the number of rotations to, for example, several tens to several hundredths, and make it easy to control, Accordingly, the output torque is increased in inverse proportion.

Conventionally, when controlling the position and torque of such a motor with a reduction gear, an actuator system 101 composed of elements as shown in FIG. 2 has been used.

That is, a torque sensor 105 is attached to an output shaft 104 of a motor 103 having a speed reducer 102, a position (angle) detector 106 is attached to a tip of the output shaft 104, and a position (angle) of a load 107 such as a robot arm or a hand. And torque). Then, as shown in FIGS. 3 (a) and (b), the torque,
By applying position feedback, both control modes are realized.

Here, as the torque sensor 105, a sensor having a structure such as a strain gauge attached to an elastic body 110 that can generate a small twist due to a rotational force is used. Then, when performing torque control on the load 107 side, as shown in FIG. 3B, a signal 109 of the torque sensor 105 is fed back and compared with a torque target value, and the difference is sent to the motor 103 through the amplifier 111. And a torque control system 114 for adjusting the current i to the motor 103 so that the difference becomes zero. On the other hand, when performing position control, as shown in FIG. 3 (a), the signal 112 of the position detector 106 is fed back, compared with the position target value, and the difference is added to the amplifier 111. To be a position servo system 113.

[Problems to be Solved by the Invention] However, in the position servo system 113 configured as described above, when the inertia of the load 107 increases, the resonance frequency of the position control system decreases, and stable control at high speed is realized. There is a problem that it is difficult to do. That is, even if an electric current is applied to the motor and the output shaft of the motor is moved to position the load 107 at a certain position so that the elastic body 110 enters between the motor 103 and the load 107, the load immediately moves. not because the phase lag occurs between the output rotation amount theta _r rotation amount of the load 107 theta, stable position control becomes difficult. The phase delay increases as the elasticity of the elastic body 110 increases, that is, as the rigidity decreases, and as the inertia of the load increases. However, a torque sensor is required to form a torque servo system, and an elastic body 110 must be used for that purpose.
For this reason, when performing position control in a system that includes a torque sensor, it is not applicable to a considerably low-speed work in which the influence of this phase shift is reduced or a somewhat rough work in which a force error is allowed. There is a problem that it cannot be applied to work or precision work.

Looking at this phase delay problems on formula, the reduction ratio of the decelerator 102 n: 1, the stiffness of the elastic body 110 k, the inertia of J _r of the motor 103 side, and the inertia of load 107 and J _L , The transfer function G (s) which receives the torque _Tr generated by the motor 103 as input and outputs the rotational displacement θ of the load 107 as θ / T _r = G (s) = [1 / ｛(n ² J _r + J) _L ) s ² ｝] × [1 / {(s2 / ω _n ² ) +1}] (1)

Here, the first term of the equation (1) is a transfer characteristic in the case where the elastic body 110 is not present, and the second term is a higher order element generated by inserting the elastic body 110. Communication will be good.

However, ω _n in the expression (1) is _{expressed as} follows: ω _n ² = k ｛(n ² J _r + J _L ) / n ² J _r J _L … (2) = (k / J _L ) + (k / n ² J _r )... (3) From the equation (2), ω _n decreases as k decreases, that is, as the rigidity of the elastic body 110 decreases, and (3)
NJ _r in J _r is small even for n the higher the reduction ratio than the expression is to die becomes ω _n to large decreases. When ω _n becomes small, the denominator of the second term of the equation (1) becomes large, and the second term becomes small. Then, G (s) becomes small, and eventually even if _Tr is changed (that is, even if the motor current i is changed), θ does not change much and a phase lag occurs, and position control becomes difficult. Also, this ω _n is generally called a natural frequency,
When ω _n is small, the resonance frequency becomes low and oscillation occurs at a low frequency, so that there is a problem that it is difficult to perform position control with high rigidity. In this case, if a stable position control is to be performed, it can only be used at a low frequency and is not practical.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described circumstances, and uses only a position servo without using a torque sensor, and realizes the power and torque of a motor with a speed reducer that can simultaneously realize stable torque control and highly rigid position control. It is intended to provide a torque control method.

(B) Configuration of the Invention [Means for Solving the Problem] In response to this object, the force / torque control method of the motor with a reduction gear of the present invention applies a load to the output shaft of the reduction gear connected to the motor. A force / torque control method of an actuator that is connected, wherein an output shaft of the speed reducer and the load are integrally connected via an elastic element having rigidity k so that an output shaft of the speed reducer and the load are connected to each other. other rotation angle r ₂ of detecting the rotation angle r ₁ of the output shaft of the reduction gear in a state where a force to said load so as to rotate about the same rotation shaft is applied with the position detector and said load And a control system for controlling the position of said actuator using said r ₂ by detecting with said position detector, and said r ₁
Feedback of the r ₂ the angle r ₁ -r ₂ constitutes a servo system to follow the quotient T _r / k between the target value T _r and k of the torque around the rotation axis of the load and, thereby the The load is controlled so that the torque k (r ₁ -r ₂ ) around the rotation axis follows the target value _Tr .

Hereinafter, details of the present invention will be described with reference to the drawings showing an embodiment.

In FIG. 1, reference numeral 1 denotes an actuator. The actuator 1 includes a motor 2, a speed reducer 3 connected to an output of the motor 2 and having a reduction ratio of n: 1, and a load 6 connected to an output shaft 4 of the speed reducer 3 via an elastic element 5. The load 6 includes an operation shaft 7 connected to a rigid, and when a current i is input to the motor 2, the output shaft 4, the elastic element 5, and the operation shaft 7 rotate around the same rotation axis l, and the work object Approaching 8, force F
And attempts to control the force F so as to follow a target value.

For such force / torque control of the actuator 1, a first position detector 11 is attached to the output shaft 4 and a second position detector 12 is attached to the working shaft 7. The servos that feed back the original signals r ₁ and r ₂ of the detected positions so that the torque of the load 6 follows the target value _Tr corresponding to F so as to detect the rotation angles r ₁ and r ₂ of system
13

That is, the servo system 13, the first amplifier 14 to a target value T _r by 1 / k times the T _r / k, it adds the detected values r ₂ to T _r / k, the (T _r / k) + _{r 2} is compared with the detected value r ₁ to obtain a control operation signal 16 that makes the error zero, and this is amplified A times by the amplifier 15 to obtain a current i. The detected values r ₁ , r ₂ fluctuating according to i are fed back to obtain the actual value of the load 6 that gives rise to (T _r / k) + r ₂ = r ₁ , that is, the displacement r ₁ −r ₂ before and after the elastic element 5. Torque k
(R ₁ −r ₂ ) becomes equal to the target value _Tr , and _Tr = k (r ₁ −
to achieve r _2), it arranged to momentarily control.

[Operation] In the force / torque control method of the motor with the speed reducer configured as described above, r ₁ −r ₂ is controlled to always follow T _r / k, and the actual torque k (r ₁ −r ₂ ) follows the torque target value _Tr corresponding to the force F.

On the other hand, when using the first view: (a) as a position servo system position r ₂ of the feedback loop as in Fig. 1 (b)
Construct a system with 17 added.

Here, in order to examine the high-speed stability of the position servo system, a transfer function G (s) from the torque target value _Tr of the servo system 13 to the displacement (rotation angle) θ _a (= r ₂ ) of the load 6 is considered. Then, θ _a = T _r = G (s) = A / [｛n ² kJ _r + (A + k) × J _L ｝ s ² ] × [1 / ｛(s / ω _n ) ² +1}] (4) where ω _n ² = (k / J _L ) + {(k + A) / (n ² J _r )} (5), where J _r : inertia moment of motor with reduction gear J _a : Moment of inertia of load A: Amplification factor of amplifier 15 k: Rigidity of elastic element. Here, ω _n is a parameter that defines the stable response speed range of the position servo system at the natural frequency. If ω _n can be increased, the speed of the position servo system increases.

If the equation (5), the Obviously A in large, that is, Takamere servo rigidity of position servo systems for r ₁ in FIG. 1, for example when k is larger small a and n be J _r However, ω _n becomes large. Also, at this time, the second term of equation (4) approaches 1. On the other hand, at this time, the first term of equation (4) is 1 / J _L
Since approaches s ^2, G (s) is independent of the value as a whole J _r
1 / J _L s ² , and a transmission system independent of the dynamics of the motor drive system is realized. In this transmission system, the phase lag is small, the natural frequency is high, and stable torque control and rigidity are achieved. High position control is realized at the same time.

(C) Effects of the Invention As is clear from the above description, according to the present invention, the torque and the power of the motor which can simultaneously realize stable torque control and high-rigidity position control only with the position servo without using the torque sensor. A torque control method can be obtained.

[Brief description of the drawings]

FIG. 1 (a) is an explanatory view showing a force / torque control method of a motor with a reduction gear according to one embodiment of the present invention, and FIG. 1 (b).
Is an explanatory diagram showing a position control system of the actuator shown in FIG. 1 (a), FIG. 2 is an explanatory diagram showing a conventional actuator system, and FIG. 3 (a) is a position control method of the actuator system shown in FIG. FIG. 3B is an explanatory diagram showing a force / torque control method of the actuator system shown in FIG. 1 ... actuator, 2 ... motor, 3 ... reduction gear,
4 ... output shaft, 5 ... elastic element, 6 ... load, 7 ... working shaft, 8 ... work object, 11 ... first position detector, 12
… Second position detector, 13… servo system, 14… amplifier, 15… amplifier, 101 …… actuator system, 102 …… reducer, 103 …… motor, 104 …… output shaft, 1
05: Torque sensor, 106: Position detector, 107: Load, 108: Wall, 109: Signal, 110: Elastic body, 11 ...
Amplifier, 112 ... Signal, 113 ... Position servo system, 114 ...
Force / torque system

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Makoto Kaneko 1-2-2 Namiki, Sakuramura, Niigata-gun, Ibaraki Pref. Machinery Research Laboratory, Institute of Industrial Science and Technology (56) References JP-A-54-44714 (JP, A) JP-A-58-186549 (JP, A) JP-A-61-110668 (JP, A) JP-A-61-110669 (JP, A) JP-A-60-66659 (JP, A)

Claims (1)

(57) [Claims] 1. An actuator force / torque control system in which a load is connected to an output shaft of a speed reducer connected to a motor, wherein an output shaft of the speed reducer and the load are connected by an elastic element having rigidity k. The output shaft of the speed reducer in a state in which the output shaft of the speed reducer and the load rotate around the same rotation axis and a force is applied to the load so that the output shaft rotates and the load r the rotation angle r ₂ of the detecting and the load detected by the other of the position detector ₁ position detector, said constitute a control system for the position control said actuator to use r ₂ wherein r ₁ and r ₂ Forming a servo system that feeds back the angle r ₁ -r ₂ to the quotient T _r / k of the target value _Tr and k of the torque of the load around the rotation axis, and thereby the rotation of the load. control child so that the torque around the axis k (r ₁ -r ₂₎ follows the target value T _r Force-torque control scheme of the motor with reduction gear, wherein