JPH1026204A - Nip mechanism for servo motor drive type end effector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize strong nipping force, speed of speedy operation, and the reduction of weight of a whole device simultaneously by constituting a means which converts rotary movement into linear movement by a crank mechanism in a nip mechanism of an end effector which nips an article by converting rotary movement of a servo motor into linear movement. SOLUTION: When a nip mechanism of a servo motor drive type end effector is applied to a rod push-out mechanism of a spot welding gun 100, a conversion means 2 for converting rotary movement of a servo motor M into linear movement is provided with a crank plate 3 which is rotated and driven by the servo motor M and incorporates a decelerator and an arm 4 of which one end part is fixed at a position away from the center O of the crank plate 3 by a predetermined dimension. A basic part of a rod 102' provided with an electrode 101 on movable side which comes into contact with and leaves an electrode 108 on fixed side is fixed on a node B provided at the other end of the arm 4. The direction of travel of this rod 102' is regulated by a linear bush 110 fixed on a spot welding gun main body. Accordingly, it is possible to realize high speed operation and the reduction of weight of a device.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a clamping mechanism of a servo motor driven end effector.

[0002]

2. Description of the Related Art Conventionally, an air cylinder has generally been used as a drive source for operating a clamping mechanism of an end effector. A clamping mechanism using a servomotor has been proposed to satisfy the demand.

As an end effector for converting a rotary motion of a servomotor into a linear motion to press an article, a rod pushing mechanism of a spot welding gun and a robot hand for article handling are known.

FIG. 6 is a conceptual diagram schematically showing a rod pushing mechanism of a conventional spot welding gun as an example.

The spot welding gun 100 is a kind of an end effector used by being mounted on the tip of a robot arm. Inside the spot effecting gun, a rod 102 to which a movable electrode 101 is attached is projected and retracted in an axial direction. A servo motor M 'and conversion means 103 for converting the rotary motion of the servo motor M' into a linear motion are provided.

A main part of the conversion means 103 is a ball screw 102a engraved on a base of a rod 102 attached to the main body of the spot welding gun 100 so as to be axially movable and non-rotatable, and is screwed to the ball screw 102a. And a ball nut 104 that is axially immovable and rotatably attached to the main body of the spot welding gun 100. Reference numeral 109 denotes a bearing for pivotally supporting the ball nut 104 on the body of the spot welding gun 100, and reference numeral 110 denotes a linear bush that guides the linear movement of the rod 102 and also serves as a detent.

A driven sparger 106 meshing with a driving sparger 105 on the servo motor M 'side is provided integrally with an outer peripheral portion of the ball nut 104, and rotates the ball nut 104 driven by the servo motor M'. The rod 102 is converted into linear motion by a ball nut & screw mechanism to project the rod 102 in the axial direction, and the fixed side electrode 10 located at the tip of the clamp arm 107 of the spot welding gun 100.
The welding operation is performed by pressing the object to be welded between the movable electrode 8 and the movable-side electrode 101.

According to such a configuration, there are advantages that the protrusion amount and the moving speed of the rod 102 can be accurately controlled, and that the clamping pressure can be easily controlled.

However, in order to increase the clamping pressure, the servomotor M 'must be replaced with a high output one, or
The reduction ratio of the ball nut and screw mechanism must be increased. If the servo motor M 'has a large output, the manufacturing cost naturally increases, and the weight of the device also increases. On the other hand, if the reduction ratio of the ball nut and screw mechanism is increased, the rod 102 is increased. However, there is a problem that the projecting speed and the degenerating speed are reduced.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to achieve a servo motor driven type which can simultaneously achieve a strong clamping force, a quick operation speed and a light weight of the whole apparatus. An object of the present invention is to provide an end effector clamping mechanism.

[0011]

The object of the present invention has been attained by the present invention in which a means for converting a rotary motion into a linear motion is constituted by a crank mechanism.

Further, since the clamping operation is adjusted so as to start when the crank mechanism rotates near the bottom dead center, the clamping operation can be performed in a portion where the amplification factor of the crank mechanism is the largest. A large clamping pressure can be obtained even with a low-output servomotor. In addition, since the clamping mechanism can be operated at a high speed during the approach and retreat operations,
The time required for opening and closing the clamping mechanism can be shortened as a whole.

This clamping mechanism can be applied not only to a rod pushing-out mechanism of a spot welding gun, but also to a robot hand for article handling.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram showing an example in which the clamping mechanism of the present invention is applied to a rod pushing mechanism of a spot welding gun. The body structure of the spot welding gun is the same as that of the conventional example shown in FIG. 6 and therefore will not be described here. In FIG. The outline of the configuration of the conversion means 2 for converting the data into.

Reference numeral 3 denotes a crank plate having a built-in reduction gear that is rotationally driven by a servo motor M, and has a radius r
Is provided with a node A to which one end of an arm 4 having the entire length L is pivotally mounted. A node B is provided at the other end of the arm 4, and the node B has a movable electrode 101.
The base of a rod 102 ′ with is pivotally mounted. The total length of the rod 102 ′ is x including the movable electrode 101.
The movement direction is regulated by a linear bush 110 fixed to the main body of the spot welding gun, similarly to the conventional example shown in FIG. In this embodiment, the positional relationship between the linear bush 110 and the crank plate 3 is determined such that the rotation center O of the crank plate 3 is located on an extension of the rod 102 '.

FIG. 2 is a plan view showing the principle of operation by further simplifying the structure of the clamping mechanism 1.

Next, the relationship between the rotation angle θ of the crank plate 3 and the position x of the tip of the movable electrode 101 and the pressing force F acting on the tip of the movable electrode 101 will be described.
The rotation angle θ is the state when the arm 4 and the rod 102 ′ are aligned and the rod 102 ′ projects most.
In other words, it is the value of the rotation angle measured in the counterclockwise direction from the state where the crank mechanism is at the bottom dead center, and the tip position x of the movable electrode 101 is the distance from the rotation center O of the crank plate 3. .

First, the distance x from the rotation center O of the crank plate 3 to the tip of the movable-side electrode 101 is, as apparent from FIG.

[0019]

(Equation 1) It is. Among them, the value of x0 is a constant, and only the term of x 'changes corresponding to the rotation angle θ.

The term x 'is a function of the rotation angle θ,

[0021]

(Equation 2) Indicated by In short, the line segment OC and the line segment C in FIG.
B and the sum.

Accordingly, the tip position x of the movable electrode 101 is calculated as a function of the rotation angle θ as follows:

[0023]

(Equation 3) Will be indicated by

The pressing force F acting on the tip of the movable electrode 101 due to the rotation of the crank plate 3 is represented by T which is the rotational torque acting on the crank plate 3 itself. If the angle between 4 and φ is φ,

[0025]

(Equation 4) Can be indicated by

Equation (4) indicates that the force [T / r] acting at the node A in the tangential direction of the crank plate 3 is [sin
(Θ + φ)] acts along the axis of the arm 4, and when the force acting in the axial direction of the arm 4 is multiplied by [cos φ], the force acting in the axial direction of the rod 102 ′ In short, this means that the pressing force F is determined. The conversion from the first row to the second row of the equation (4) is based on the sine addition theorem.

At this stage, since the value of φ is unknown, it is considered that the term of φ is deleted from the equation of Equation 4 and the equation of Equation 4 is described using only the rotation angle θ.

Here, focusing on the virtual line a in FIG.

[0029]

(Equation 5) Can be obtained. Therefore,

[0030]

(Equation 6) It is.

Further, x 'in FIG. 2 and the line segment OC (= r
cos θ) and the relationship between L and φ,

[0032]

(Equation 7) Is obtained.

Therefore, by substituting the values of sin φ and cos φ obtained by the equations (6) and (7) into the equation (4) and replacing the term x ′ by the equation (1), A functional expression expressing the pressing force F acting on the tip of the movable-side electrode 101 only by the rotation angle θ,

[0034]

(Equation 8) Is obtained.

If it is desired to know the moving speed V of the movable electrode 101 when the rotation angle of the crank plate 3 is θ, the distance x in Expression 3 can be differentiated with respect to the rotation angle θ.

[0036]

(Equation 9) An example of the relationship between the position x of the movable electrode 101 corresponding to the rotation angle θ, the pressing force F (however, the amplification factor with respect to the rotation torque T), and the moving speed V is shown in FIGS.

However, the movable side electrode 10 represented by the equation (3)
The value of the tip position x of 1 is also the pressing force F expressed by the equation (8).
Is also a function formula based on the rotation angle θ of the crank plate 3 and the rotation torque T acting on the crank plate 3 itself. To adjust the force F, θ
And the value of T need to be replaced by a function of the rotation angle of the servo motor M and the driving torque.

Here, assuming that the reduction ratio between the servomotor M and the crank plate 3 is G, the rotation angle of the servomotor M is θm, and the driving torque of the servomotor M is Tm, the relational expressions of Expressions 10 and 11 are obtained. Is led.

[0039]

(Equation 10)

[0040]

[Equation 11] Therefore, when these values θ and T are substituted into the expressions of Expressions 3 and 8, they are transformed into Expressions of Expressions 12 and 13, respectively.
By controlling the position and torque with respect to the servo motor M, the tip position x of the movable electrode 101 and the movable electrode 1
01 can be adjusted.

[0041]

(Equation 12)

[0042]

(Equation 13) Next, a configuration for optimizing the tip position x and the pressing force F of the movable electrode 101 in the pinching mechanism 1 of the spot welding gun will be described.

The simplest method is as follows.
The pressing force F acting on the tip of the crank plate 3 rapidly increases near the bottom dead center of the crank plate 3, and the moving speed V of the movable-side electrode 101 relatively increases when the rotation angle θ of the crank plate 3 is around 90 degrees. This is a design method utilizing the structural characteristics itself such as being large and very small near the bottom dead center (θ = 0), and does not necessarily require strict control of the position and torque of the servo motor M.

As shown in FIG. 2, the maximum value of the tip position x of the movable electrode 101 is determined by the distance r from the center O of the crank plate 3 to the node A, the total length L of the arm 4 and the rod 10
This is the sum of 2 'and the total length x0. However, in order to clamp the welding target when the maximum pressing force F is exerted when the crank plate 3 reaches the bottom dead center and the thickness of the welding target is Δt1, the center O of the crank plate 3 is set. The distance S from the head to the tip of the fixed side electrode 108 is [r + L + x
[0 + Δt1] is erroneous to design the clamp arm 107. In such a design, the movable-side electrode 101 and the object to be welded only come into contact with the fixed-side electrode 108 without any gap, and in fact, no pressing force acts between them. This is because when the movable electrode 101 comes into contact with the surface of the welding target supported by the fixed electrode 108, the projecting operation of the rod 102 'stops.

That is, as shown in FIG.
1 shows the maximum pressing force F (theoretical infinity) when the crank plate 3 reaches the bottom dead center, but the reaction force against the pressing force F is generated in proportion to the pressing force F until it gets tired. When the movable electrode 101 comes into contact with the surface of the welding target as described above,
If the protrusion of 2 'reaches the limit and stops, no reaction force is generated and the pressing force F eventually becomes zero.

Therefore, before the arm 4 and the rod 102 'are completely aligned and extended, the movable electrode 101 is brought into contact with the surface of the object to be welded. 107, or by forcibly stopping the projecting operation of the rod 102 ′ due to the rigidity of the clamp arm 107, the pressing force F from the side of the clamp arm 107.
It is necessary to generate a reaction force proportional to.

The fact that the movable electrode 101 comes into contact with the surface to be welded before the arm 4 and the rod 102 'extend completely means that the crank plate 3 is not located at the bottom dead center at the contact stage, but there is a practical problem. As a result, even when the crank plate 3 is at a position slightly deviated from the bottom dead center, the pressing force F of the movable electrode 101 is considerably large. Therefore, even after the movable electrode 101 comes into contact with the surface of the welding target, the rod 10
The protruding operation 2 ′ continues, and the pressing force F increases as the crank plate 3 approaches the bottom dead center. However, if a material having sufficiently large rigidity is applied to the clamp arm 107, it will eventually change. Is the pressing force F and the clamp arm 107
Of the clamp arm 1
The projecting operation of the rod 102 'is forcibly stopped while 07 is elastically deformed.

The internal force acting between the members in this state is a substantial clamping force. At this time, the clamp arm 107
Assuming that the amount of flexure occurring at Δt2 is Δt2, the most desirable value as the separation distance S from the center O of the crank plate 3 to the tip of the fixed electrode 108 is [r + L + x0 + Δt1-Δt
2]. Of course, the value of the pressing force F represented by the amount of deflection Δt2 varies depending on the driving torque Tm of the servomotor M, the rotation angle θ of the crank plate 3 and the material and shape of the clamp arm 107, so that the actual Δt2
Must be determined at the design stage by calculation or experiment.

In practice, the movable electrode 101 is worn due to repetition of welding and clamping operations, and it will eventually need to be replaced. In any case, the movable electrode 101 is placed on the surface to be welded. Since it is necessary to avoid that the arm 4 and the rod 102 ′ extend completely before the 101 comes into contact, if the maximum amount of wear that can occur before the movable electrode 101 is replaced is Δt 3, As a result, from the center O of the crank plate 3 to the fixed-side electrode 1
The most desirable value as the separation distance S to the tip of 08 is
[R + L + x0 + Δt1-Δt2-Δt3].

Of these, the amount of wear is a variable value. In this case, the maximum value Δt3 is used as a design value. However, the moving position x of the movable-side electrode 101 suitable for the actual clamping operation. Is relatively wide, for example, about 5 to 7 mm as shown in the example of FIG. 3, so that there is no problem that abrasion of the movable electrode 101 causes a significant variation in the clamping pressure.

As shown in FIG. 4, in this embodiment, the range in which the power amplification factor is 3 to 4 times is defined as a practical range. However, as shown in FIG. Great power amplification is possible. The practical range is defined as a section where the amplification factor is 3 to 4 times. In a section where the amplification factor is larger than that, the shift of the moving position of the movable-side electrode 101 or the variation in the thickness of the welding target or the like. Movable electrode 1
This is because the clamping pressure may fluctuate significantly due to various errors such as the degree of wear of No. 01, and furthermore, the clamping pressure may become excessive and cause damage to the mechanism, and the amplification factor may be smaller than that. The reason why the section is not set is to achieve an intended purpose such as an increase in clamping pressure.

According to such a design policy, an optimum clamping pressure can be obtained by the structure of the mechanism itself, so that strict control of the position and torque with respect to the servomotor M is not always necessary. The simplest control method is to limit the driving torque to such an extent that the servomotor M is not overloaded, and to apply a movement command to the servomotor M to a position where the rotation angle θ of the crank plate 3 becomes zero at the time of clamping. Output and also
When the clamping operation is released, the rotation angle θ of the crank plate 3 is set to a position corresponding to the retracted position of the movable electrode 101, for example, 90 °.
That is, a movement command for rotating the motor to the maximum speed is output to the servo motor M.

When the rigidity of the clamp arm 107 is sufficiently larger than the pressing force F of the movable electrode 101, that is, when the clamp arm 107 is not easily bent when the movable electrode 101 is protruded. Below, since a reaction force proportional to the pressing force F is generated from the moment the movable electrode 101 comes into contact with the welding target,
Substantially, the pressing force F of the movable-side electrode 101 changes depending only on the driving torque Tm of the servo motor M and its rotation angle θm as shown in the equation (13).

That is, if the rotation angle θm of the servomotor M when the movable electrode 101 comes into contact with the welding object can be detected, the desired pressing force F can be obtained by adjusting the driving torque Tm of the servomotor M. Can be.

The current position and speed of the servomotor are constantly monitored by the encoder of the motor. The current position θm of the motor at the time when the speed becomes 0 is read, the term x in the equation obtained by solving the equation 13 with respect to Tm is replaced by the equation 12, and the desired pressing force F and the read θm
, The drive torque Tm of the servomotor M required to achieve the desired pressing force F can be obtained, and the thickness Δt1 of the welding object and the movable side can be obtained. Regardless of the variation or change in the amount of wear Δt3 of the electrode 101, the desired pressing force F is always obtained.
With this, it becomes possible to clamp the welding object. The control relating to the drive torque Tm of the servomotor M is performed by setting a torque limit value for limiting the torque command to the servomotor M. The target value of the movement command for the servomotor M at the start of clamping is determined by the crank plate 3. The rotation angle θθ may be set to a value that becomes zero.

That is, the servo motor M attempts to rotate to a position where the rotation angle θ of the crank plate 3 becomes zero, but comes into contact with the object to be welded and its movement is prevented. As a result, the positional deviation increases, the torque command increases, and the movable electrode 101 is moved.
Only the flexure of 07 can be moved, the positional deviation further increases, and the torque command also increases. When the torque command value exceeds the set torque limit value, the torque command value is limited to the torque limit value, so that the output torque does not increase any more and the movement of the movable electrode 101 stops. However, a pressing force F corresponding to the torque limit value is generated on the welding target.

[0057]

The clamping mechanism of the present invention employs a crank mechanism as a means for converting a rotary motion into a linear motion.
While the pinch operation is performed near the bottom dead center of the crank mechanism, that is, near the bottom dead center of the crank mechanism, the high-speed operation characteristics of the crank mechanism located far from the dead center of the crank mechanism are used. The approach operation at the start of clamping and the retracting operation at the time of release are performed, so that a large clamping pressure can be obtained even with a low output servo motor. Can be operated with

Therefore, there is no need to use a high-output servomotor or increase the reduction ratio in order to increase the clamping pressure, and it is possible to simultaneously increase the clamping pressure and increase the operating speed of the clamping mechanism. In addition, the size and cost of the mechanism can be reduced.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram schematically showing the configuration of a spot welding gun according to an embodiment to which a clamping mechanism according to the present invention is applied.

FIG. 2 is a plan view showing the principle of operation by simplifying the configuration of the clamping mechanism of the embodiment.

FIG. 3 is a diagram showing a relationship between a rotation angle θ of a crank plate and a position x of a movable electrode.

FIG. 4 is a diagram showing a relationship between a rotation angle θ of a crank plate and a pressing force F.

FIG. 5 is a diagram showing a relationship between a rotation angle θ of a crank plate and a moving speed V of a movable electrode.

FIG. 6 is a cross-sectional view schematically showing a rod extruding mechanism of a conventional spot welding gun.

[Explanation of symbols]

 Reference Signs List 1 clamping mechanism 2 conversion means 3 crank plate 4 arm A node B node M servomotor 100 spot welding gun 101 movable electrode 102 rod 102 'rod 102a ball screw 103 conversion means 104 ball nut 105 driving sparger 106 driven sparger 107 clamp Arm 108 Fixed side electrode 109 Bearing 110 Linear bush M 'Servo motor

Claims (3)

[Claims] 1. A clamping mechanism of an end effector for converting a rotary motion of a servomotor into a linear motion to press an article, wherein a means for converting the rotary motion into a linear motion is constituted by a crank mechanism. Pressure mechanism of the servo motor driven end effector. 2. The clamping of the servo motor-driven end effector according to claim 1, wherein the clamping operation is started when the crank mechanism rotates near the bottom dead center. mechanism. 3. A clamping mechanism for a servo motor driven end effector according to claim 1, wherein said clamping mechanism is a rod pushing mechanism of a spot welding gun.