JPH04336987A - Gripping device - Google Patents

Abstract

PURPOSE:To prevent a breakage or a slipping down of a substance being gripped by a variation of the gripping force. CONSTITUTION:When a substance is gripped by a fixed finger 3 and a movable finger 2 loaded on a hand board 1, its gripping force is detected by a gripping force sensor 5. The acceleration of the hand board 1 is detected by an acceleration sensor 6. This acceleration is input to a correcting signal generator 9, and a correction driving signal is generated. This correction driving signal is added to the output signal of a compensator 7 in an adder 11, and input to a finger driving amplifier 4.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gripping device for gripping an object with fingers.

0002

2. Description of the Related Art Object gripping devices, typified by parallel grippers, are used in various industrial fields, including object conveyance work by robot manipulators. Figure 6
1 shows an example of the configuration of a parallel gripper type robot hand, which is a conventional gripping device. This robot hand is composed of a hand base 1, movable fingers 2, a gripper drive amplifier 4, and the like. The movable finger 2 is driven in the direction of the arrow by a driving force generated from the gripper drive amplifier 4 based on a finger opening/closing command in order to grip the object shown with diagonal lines. The hand base 1 is usually attached to the tip of a spatial movement mechanism such as a manipulator. As described above, most conventional gripping devices grip rigid objects with relatively large force by opening and closing fingers with appropriate mechanical rigidity. However, in this method, the fingers are only passive mechanical elements, and it is impossible to actively control the force applied to the gripped object. Therefore, in some cases, an excessive gripping force acts on the object, causing damage to the object, or an insufficient gripping force causes the object to slide down. Furthermore, for similar reasons, it has been difficult to apply conventional gripping devices to gripping flexible objects, elastic objects, etc. that require precise control of gripping force.

[0003] In order to overcome these drawbacks, a technique has been proposed in which the gripping force of an object is controlled by actively driving the fingers. For example, JP-A-60-118480
The technique disclosed in the publication attempts to grip an object with a predetermined force by controlling the finger position by driving fingers, which are force applying means, based on a force applying command. However, since this method does not use a means to directly detect the gripping force, precise control of the gripping force is impossible in the first place, and the actual force applied may differ greatly from the command value depending on the dimensional error of the object. The disadvantage is that it is highly possible. In addition, this method has the disadvantage that there is no means for correcting errors in gripping force that occur after gripping the object.

[0004] In the technique disclosed in Japanese Patent Application Laid-open No. 172484/1984, out of the force applied to the two fingers,
The drive of the fingers is controlled so that the smaller force matches the force setting value for gripping the object, thereby preventing the object from falling. Furthermore, the technique disclosed in Japanese Patent Application Laid-Open No. 120990/1983 controls the position of one finger and the force of the other finger to grip an object at a predetermined position with a predetermined force. Aiming. However, the former method does not take into account the case where an excessive force is applied to the remaining fingers other than the one on which the minimum force is applied, and the latter method also has the disadvantage that the gripping force cannot be controlled on the side of the position-controlled fingers. The drawbacks of the prior art as described above become even more apparent when viewed from the following viewpoints.

As mentioned above, the gripping device is usually attached to the tip of a spatial movement mechanism such as a manipulator, and the gripped object is conveyed at high speed by the movement of the manipulator. When the manipulator starts and stops, a large acceleration change occurs in the gripping device, and at the same time, a corresponding inertia force is generated in the gripped object. A similar phenomenon is also seen when an impact disturbance is applied to the hand base of the gripping device due to a collision with the environment. As a result, a difference occurs between the inertial force of the object and the gripping force by the movable fingers, resulting in dynamic fluctuations in the set object gripping force. More specifically,
For example, in the case of two movable fingers facing each other, the gripping force applied to one finger increases rapidly and the gripping force applied to the other finger decreases. Phenomena caused by the dynamics of the object/grip system are often pointed out,
It can also be easily inferred from considerations using physical models. In order to absorb such rapid dynamic fluctuations, it is possible to increase the feedback gain of the gripping force control system to improve the response of the control system, but this is generally not possible due to mechanical resonance in the movable finger system. There is a limit to the increase in gain.

[0006]

[Problem to be solved by the invention] From the above,
Conventional gripping devices proactively compensate for fluctuations in gripping force that occur when the hand base is driven at high speed, or due to impact disturbances that are applied to the hand base due to interaction with the environment during work. Since no absorption means is provided, the gripped object may be damaged or even fall off.

It is an object of the present invention to reduce gripping force caused by fluctuations in gripping force that occur when the hand base on which the fingers are mounted is driven at high speed, or by impact disturbances that occur due to interaction with the environment during movement of the hand base. It is an object of the present invention to provide a gripping device in which there is no possibility that an object being gripped will be damaged or fall off due to fluctuations in force.

[0008]

[Means for Solving the Problems] The gripping device of the present invention includes a hand base, and one movable finger and one fixed finger or two movable fingers mounted on the hand base to grip an object. a gripping force sensor that detects the gripping force of the movable finger on the object; a gripping force control system that controls the gripping force based on a feedback amount based on a signal from the gripping force sensor; and a correction based on the hand acceleration. It has a correction signal generator that generates a drive signal, and an adder that adds a feedforward amount based on the correction drive signal to an input signal of a finger drive amplifier that drives the movable finger.

[0009]

[Operation] The present invention controls the gripping force with high precision by adding a correction drive input based on the acceleration of the hand base on which the movable finger is mounted to the finger drive input in the gripping force control system of the movable finger. .

0010

[Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings. Fig. 1 is a diagram showing a gripping device according to a first embodiment of the present invention, and Fig. 1 (1) shows the mechanism configuration. Figure, same figure (2)
FIG. 2 is a diagram showing a control system configuration. The gripping device of this embodiment is
A hand base 1, a movable finger 2, a fixed finger 3, a gripping force sensor 5 that detects the gripping force fs of the object by the movable finger 2, an acceleration sensor 6 that detects the acceleration of the hand base 1, and the acceleration The gripping force fs applied to the object by the movable fingers 2 is the gripping force target value. fr
The gripping force feedback control system drives and controls the movable fingers 2 of the movable finger system dynamics 8 so as to match ef.

Next, the operation of this embodiment will be explained. first,
The movable finger 2 is driven to grip an object between it and the fixed finger 3. At this time, a gripping force feedback control system is configured by the gripping force sensor 5, compensator 7, drive amplifier 4, etc., and the movable fingers 2 are controlled so that the acting force applied to the object by the movable fingers 2 matches the gripping force target value fref. Drive control. At the same time, the acceleration α of the hand base 1 is detected by the acceleration sensor 6, branched and inputted to the correction signal generator 9, and a correction drive signal based on the acceleration α is output from the compensator 7 of the finger grip force control system. The signals are added and input to the drive amplifier 4. As a result, in addition to the local gripping force feedback control system of the fingers, a feedforward control system based on the base acceleration α is configured as a whole. Note that the broken line in FIG. 1 (2) indicates the hand base 1.
This shows that an acceleration disturbance is inevitably mixed into the moving finger system dynamics 8 due to the movement of the moving finger system.

The flow of control shown above becomes even clearer when the dynamics of fingers and objects are explicitly described. FIG. 2 is a model of grasping an object by a hand introduced for the purpose of explanation. In the figure, m, c, and k represent mass, damping, and stiffness, respectively, and subscripts a, s, e, and o represent movable finger 2, gripping force sensor 5, finger tip (part that contacts the object), and object, respectively. represent. In addition, since the movable finger 2 vibrates when it moves at high speed, in this case,
It is modeled as consisting of two parts (mass ma1 and ma2).

When this model is applied to the control system shown in FIG. 2, the state equations of the system become the following equations (1) and (2). dx/dt=Ax+Bu...(1) y=Cx...(2) Here, x=[xa1, dxa1/dt, Xa2, dxa2/d
t, xe, dxe/dtxe, Xo, dxo/d
t] Tu=fa, y=fs, A: 8×8 characteristic matrix, B=8×1 input vector C
: 1×8 output vector, fa : Movable finger input, f
s: Sensor detection force Now, the force proportional feedback gain in the finger's local gripping force control system compensator 7 is Hb, and the proportional acceleration feedforward gain in the correction signal generator 9 is H
When f is the input to the movable finger 2, the input to the movable finger 2 is given by the following equation (3).

fa=fref-Hb (fref-fs)
+Hf α...(3) The model in Fig. 2 is a one-actuator, one-sensor system, and the gripping force fluctuation fL on the left side, that is, the movable finger 2 side, and the gripping force fluctuation fR on the right side, that is, the fixed finger 3 side, are respectively expressed as follows. cannot be controlled independently. However, by adjusting the proportional feedback gain Hb and the proportional acceleration feedforward gain Hf, it is possible to make the gripping force approximately equal between the movable finger 2 side and the fixed finger 3 side. That is, assuming that the low frequency fluctuation components of the left and right gripping force fluctuations fR and fL from the gripping force target value fref are equal, the following equation (4) is obtained.

pHf + qHb = 1 (4) where p = (ko1 + ko2)/r, q = -ko1 (me +
mo )/r, r=ko1M+Ko2(mo1+mo2), M=mo1
+mo2+me +mo Therefore, if the proportional feedback gain Hb is determined under certain constraints, the proportional acceleration feedforward gain Hf can be determined by equation (4). Of course, the reverse is also possible.

The effects of such a structure will be explained below, taking as an example the gripping and conveying work of the object/gripping device system. Figure 3 shows a conceptual diagram of the work. A gripping device 13 is mounted on the tip of the manipulator 12, and the gripping force of the gripping device 13 and the manipulator driving force are each independently controlled. The movement acceleration of the manipulator 12 can be regarded as a disturbance to the gripping force control system from the viewpoint of acting force control. Therefore, during the gripping and transporting work, the object 14
Grasping force fluctuation fR to prevent it from falling and being destroyed,
The following equation (5) can be considered as a working condition regarding fL.

fmin −fref <f<fmax −fref
...(5) Here, f=fR or -fL, fmin: Critical frictional force between the gripping device and the target object, fm
ax: Critical strength of the target object, fref: Grip force target value (constant value), From Fig. 2, the grip force fluctuation f is clearly given as a function of the manipulator hand acceleration α, so the working condition of equation (5) is the acceleration This is nothing but a condition that determines the permissible value of α. Note that the acceleration α can also be detected by an acceleration sensor attached to the manipulator's hand, but if the manipulator has a high-performance encoder in its joint, it is also possible to use it to estimate the hand acceleration.

In such work, for example, if the present invention is not used and the finger gripping force control system uses only simple feedback, the acceleration generated in the hand base due to the high-speed movement of the manipulator tip will cause The gripping force fluctuation of deviates significantly from the upper and lower limits of the working conditions. On the other hand, FIG. 4 shows fR and fL in the gripping device of the present invention superimposed on fref. It can be seen that both fluctuations are within the range of working conditions, and the magnitudes of both are approximately equal. In this way, according to the gripping force control method using both feedback and feedforward, and the compensator design method shown above, 1
Even in the case of a single actuator sensor, it is possible to make left and right gripping fluctuations almost equal and to keep them small. Therefore, dynamic fluctuations occurring in the gripping force are reduced.

FIG. 5 is a diagram showing a gripping device according to a second embodiment of the present invention, and FIG. 5 (1) is a diagram showing the mechanism configuration, and FIG.
FIG. 2 is a diagram showing a control system configuration. In this example, the object is 2
gripped by two movable fingers 2, gripping force sensor 5
are also attached to both movable fingers 2. Since gripping force fluctuations of equal magnitude and opposite directions act on both movable fingers 2 due to the action of acceleration α, the acceleration signal is sent to the correction signal generator 9 of one gripping force control system as it is, while the other For this purpose, the acceleration may be input through the sign inverter 9'. As described above, since this embodiment has a two-actuator, two-sensor system, it is possible to adjust the gripping force with the left and right movable fingers 2, respectively. Of course, in this case, it is assumed that the design is performed as a multivariable control system.

[0020]

Effects of the Invention As explained above, the present invention adds a correction drive signal based on the acceleration of the hand base to the drive input of the movable fingers in the object gripping force control system, thereby controlling the dynamic fluctuation of the gripping force. This greatly reduces the gripping force, so even if the hand base suddenly starts or stops, or there is an impact disturbance from the environment on the hand base, the gripping force will become excessive and the object will be damaged, or vice versa. This has the effect of reducing the risk of the object slipping off due to insufficient gripping force, and realizing stable object gripping that satisfies predetermined work conditions.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a gripping device according to a first embodiment of the present invention,
(1) of the same figure is a diagram showing the mechanism configuration, and (2) of the same figure is a diagram showing the control system configuration.

FIG. 2 is a diagram showing an object grasping dynamics model.

FIG. 3 is a conceptual diagram of an object gripping and conveying operation.

FIG. 4 is a graph showing fluctuations in gripping force.

FIG. 5 is a diagram showing a gripping device according to a second embodiment of the present invention,
(1) of the same figure is a diagram showing the mechanism configuration, and (2) of the same figure is a diagram showing the control system configuration.

FIG. 6 is a schematic diagram showing a conventional example of a gripping device.

[Explanation of symbols]

1 Hand base 2 Movable finger 3 Fixed finger 4 Finger drive amplifier 5 Grip force sensor 6 Acceleration sensor 7 Grip force control system compensator 8 Movable finger system dynamics 9 Correction signal generator 9' Sign inverter 10 Subtractor 11 Adder 12 Manipulator 13 Gripping device 14 Object

Claims (1)

[Claims] 1. A hand base, one movable finger and one fixed finger, or two movable fingers that are mounted on the hand base and grip an object, and a gripping force of the object by the movable fingers. a gripping force sensor that detects the gripping force, a gripping force control system that controls the gripping force with a feedback amount based on a signal from the gripping force sensor, and a correction signal generation that generates a correction drive signal based on the acceleration of the hand base. and an adder that adds a feedforward amount based on the corrected drive signal to an input signal of a finger drive amplifier that drives the movable finger.