JPS58160093A - Gravity balancer for rocking arm - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a gravity balance device for a swinging arm, and more particularly to a gravity balance device suitable for an arm of a teaching/playback type multi-joint robot.

For example, in an articulated robot, a gravitational moment acts on each swinging arm, and most of the driving force of electric motors and hydraulic equipment is used to cancel out this gravitational moment. Therefore, it is necessary to take measures to reduce the gravitational moment, but most of the conventional examples have a structure in which a tension spring is installed. Figure 1 shows the modeled configuration.

In the figure, 1 is an arm whose swing center is a fulcrum B at a fixed position, and 2 is an arm connected between a fixed position C, which is vertically upwardly separated by a distance a from the fulcrum B, and a certain position A on the arm 1. It is a tension spring. For arm 1, the length between A and 8 is R2, and the current length of tension spring 2 is l. Also, A of arm 1
The load at the point is W, the tensile force of the tension spring 2 pulling the point A is F, the angle between the arm 1 and the horizontal line is θ, and the angle between the tension spring 2 and the horizontal line is α. The overturning moment 1-Ml due to gravity of the swing arm 1 defined in this way is given by equation (1).

M,=WR focus θ (1) On the other hand, the moment M2 generated by the tension spring 2 is as follows: M2=p a cma ·--(2). Here, if the free length of the tension spring 2 is calculated and the spring constant is k, then the tensile force F is given by equation (3).

F=k・(l−L) ・・・・・・・・・(
3) Here, W=59 (kyf) as a practical value.

+t 1ooo(m), ni=t(kyf/m), a-
200 (mr), the graph shown in FIG. 2 can be drawn. The horizontal axis is the arm tilt angle θ and the vertical axis is the moment) (k
g f −m ), the solid line indicates the gravitational moment M1, and the dotted line indicates the moment M2 due to the tension spring 2. In this graph, the free length of the spring 2 is set in advance so as to be balanced at θ-0'' and 90''.

In Figure 2, the shaded area indicates the remaining amount that cannot be balanced, but as you can see from this graph, the maximum amount is 16 kgf, m
Some degree of imbalance remains.

In this way, in the conventional example using the tension spring 2, although the swing arm l can be approximately balanced, perfect balance is not possible. That is, in Fig. 1, if we examine it further, we will first find that in terms of length, zcosα=Rcosθ...River...(4
). Since the conditions for perfect balance are M, -M2, Eri, Rcosθ(
W-a・7)-〇 ......(5) In formula (5), R\Q, 008θ are not 0, so
As a perfect balance condition, ~■-a ・-=0
10901119, (6) where W,
Since a is a constant, that is, it is a necessary condition that F l.

In other words, perfect balance cannot be achieved unless a tensile force F proportional to the length t is applied. However, in the tension spring 2, the tension force F is 0 at the close contact length, and when 1=0, F
= Q cannot be satisfied.

This is the reason why the swing arm l cannot be perfectly balanced in the conventional example.

A system that perfectly balances the gravitational moment of the swinging arm is particularly required for so-called direct teaching, which involves cutting off the power source and teaching by holding the tip of the robot arm. In other words, when manually operating a robot's multi-jointed arm, it is desirable to be able to do so with light force regardless of the direction of movement, but a typical robot arm itself has considerable weight. Therefore, it is undeniable that it is light in the descending direction and heavy in the ascending direction, which causes a problem of lack of smoothness during manual teaching operation, and also requires unnecessary torque during servo control. Another problem is that positioning reproducibility accuracy decreases.

The present invention has been made in view of the above-mentioned problems, and its basic purpose is to provide a novel gravity balance device that can balance the weight of a swinging arm regardless of the tilting position of the arm. By using a balance device, the weight of a robot's multi-jointed arm or other arm can be constantly balanced regardless of the arm tilt position, reducing movement during teaching and further contributing to improving the reproducibility accuracy of servo control. It is particularly suitable for robot arms.

In order to achieve the above object, the gist of the present invention is to provide a fixed point that is vertically above or approximately vertically above the fulcrum of an arm that can swing in a vertical plane and is separated by a distance a; A gravity balance device that is suspended between a point and balances the gravity of the arm is equipped with a compression spring, and the spring constant k of this compression spring is calculated by dividing the arm load W at the point on the arm by the distance a. In addition, the free length of the compression spring is determined by the length t between the predetermined fixed point and the point on the arm, and the length ts of the compression spring when suspended at this length t. The tensile force due to the repulsive force of the compression spring is configured to be proportional to the distance between the fixed point and a point on the MiJ arm.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 3 is a diagram showing the principle of the embodiment. 8 is a gravity balance device for the arm 1 that swings in place of the fulcrum B (hereinafter referred to as
This is called a spring unit). As shown in FIG. 4, the structure of the spring unit 3 is similar to that of a hydraulic cylinder, and includes a cylindrical case 81, a compression spring 82 provided inside the case 31, and a compression spring 82 that penetrates one end surface of the case 31. It is composed of a movable rod 33 that appears and retracts, and a fixed rod 34 fixed to the outside of the other end surface of the case 31. The compression spring 32 is interposed and supported between a lid portion 31a forming one end surface of the case 31 and a flange-shaped portion 88a formed at the end of the movable rod 33. Further, 85 is a fixed rond attachment portion corresponding to a point 0 which is vertically above the swinging fulcrum B by a distance a, and 36 is a movable rond attachment portion corresponding to a point A on the arm 1.

The attachment portions 85 and 86 are attached to point 0 and point A, respectively, with respect to the initial posture of arm 1 shown in FIG. The distance (=AC) between the attachment parts 85 and 86 in this initial posture is t, which is a predetermined value. For this distance t, the length of the compression spring is set to t8.

Regarding the constant of this compression spring 32 (determining method will be described later)
, the spring constant is k −W / based on the above-mentioned theoretical formula.
Choose a. On the other hand, the free length is chosen as L=t+ts. The principle diagram of FIG. 3 explains how this spring unit 3 achieves perfect balance.

Now, assume that arm 1 rotates counterclockwise from the initial position shown in FIG. 3, and the distance between AC increases by Δt and becomes lx. The compression spring compresses by Δts, and the spring length becomes tsx
becomes. The tensile force FX exerted by the gravity balance device 3 on point A on the arm is Fx-(L-t8X)=((1+18)-(1s-Δt8'))-=(1
+Δt8)・k ・Old・・・・・・(7) By the way, Rondo 88.84 itself is rigid and does not expand or contract, so Δt8−Δt・・・・・・・・・(8)
When this is substituted into equation (7), FX - (l + Δt) · k = / = X -, that is, tX a , and the perfect balance condition is satisfied. In other words,
The swinging arm 1 can be balanced at any position regardless of the tilting position θ, and the external force required to make it stand still or move at any position can be reduced to almost zero.

A more specific structure of this spring unit 3 is shown in a sectional view of a main part in FIG.

The movable rod 33 is passed through a through hole 87 formed in the lid portion 31a, and is supported by a bearing 38 that forms the through hole 37.

The compression spring 32 is interposed and supported between a stepped portion 81b on the back side of the lid portion 81a and a stepped portion 88b of the collar portion 88a. The cylindrical case atti constituting the winding drum of this compression spring 82 is formed to have a rectangular cross section. That is, four side plates forming four sides are assembled, and lid parts 81a and 81c are attached at both ends.
Fit together. Nuts are screwed onto the threaded rods 39 (plurality) passing through the lids 81a and 81c from both sides and fixed.

On the other hand, the fixing rod 34 provided with the attachment part 35 is screwed into the lid part 81C and fixed with a presser nut. Then, the mounting portion 36 is screwed onto the tip of the movable rod 38 and fixed with a holding nut. Shaft holes 40.degree. and 41 are formed in each of the mounting portions 35.degree. and 36 to receive the shaft portion of the mounted portion, and flanged bushings 40a and 41a are fitted therein. In addition, 88
a is a bush of the bearing 38; Further, in this specific example, the cylindrical case 31 has a rectangular cross section, but it may have a cylindrical shape.

When designing the spring unit 3, it is necessary to modify the specifications by modifying various arms (C), and each constant string of the compression spring 32 is determined as follows. ■Spring constant: +i4A/+4
: 6'l tlL"+1m!tFII '14'
C water gap JL, Vl'llll&- is given in advance by the mounting structure. k = W/a (k, y/am). Further, the mounting length l of the spring unit 3 is determined by the arm. It is set between the minimum value of t (θ=90°) and the maximum value of t determined by the movable range θ of the arm.

■From the spring constant k, the spring dimensions are the strand diameter d(w) and the winding diameter D(a+).

Find the number of turns N (turns): where d, D, and N are one k
Since it cannot be determined uniquely, an appropriate value should be selected based on the design. ■Determine the spring contact length: Spring installation length t
This is because 8 must be larger than the contact length.

■ Find the free length of the spring: Return L = t + ts, and structurally (10/-8) is always a constant length.

Next, adjustment of the spring unit 3 will be explained.

When the spring unit 8 as described above is actually manufactured, due to manufacturing errors of each member, it may not always work as planned. That is, since the mounting length t, the support +5, and the distance a between the spring unit mounting positions are machined, the error is less than 0.1%. Regarding the load W, if it is a machined product, there will be almost no error, but if a molded product is used with grooves in the cast surface, it is necessary to allow for an error of about several percent. Regarding the tensile force F, first of all, it is due to the variation in free length, the winding diameter, and the variation in wire diameter d (
There are variations in the constants. Each of these needs to be expected to be around several percent.

Here are eight ways to make fine adjustments.

The first is a means for adjusting the spring length t8. As shown in FIG. 6, a threaded portion 33C is formed at the other end of the movable rod 33, and a female-threaded collar-shaped spring receiver 88d is screwed into this threaded portion 33C. By rotating the spring receiver 88d, the spring length ts can be changed. In other words, the generated tensile force F is adjusted by changing ts without changing the attachment length t of the spring unit 3.

The second method is to adjust the distance a to adjust the variation in F/l, that is, the spring constant. FIG. 7(a) is a detailed view of the lower part of the spring unit 3, and FIG. 7(b) is a sectional view of the main part thereof. The fixed rod 84 is rotatably attached to the shaft member 52 provided with the flange 51.
1 is firmly fixed to the fixing base 28a with screws 53 (plurality). A hole drilled in the flange 51 through which this screw 53 is passed is made into a vertically elongated hole 54. This elongated hole 54 allows the distance a
can be adjusted. Preferably, the upper end of the fixed base 23a may be bent in an inverted shape, and an adjustment screw 55 may be attached to this portion, and the flange 51 may be adjusted by sliding on the upper surface of the fixed base 28a. . This has the advantage of allowing minute adjustments.

Normally, the range of motion is a few percent of the set distance a (
If a = 200 (1111), ±5 to ±10
Level (a) is sufficient.

The third is means for adjusting the spring constant k. FIG. 8 is a sectional view of the main part thereof. A cylindrical member 56 having a female thread that matches the shape of the inside of the compression spring 32 is provided at the end of the movable rod 33, so that the movable rod 33 is screwed into the compression spring 32.

When the movable rod 33 is turned in the direction of the arrow in the figure, the cylindrical member 56 moves to the left from the illustrated position. casing 81
The compression spring 3 between the lid portion 81a and the rod end 57
The number of turns of 2 is reduced.・Kune constant is inversely proportional to the number of turns, so
The spring constant becomes large.

Of course, by turning it in the opposite direction, the spring constant k can be made smaller. The above fine adjustments can be made by means of l or 2 as desired.
The above means may be used in combination.

The spring unit 3 described above is suitable for a swinging arm of an articulated robot. Next, a specific application example will be given.

FIG. 9 is a side view of the first application example, in which the articulated robot 20 employs a parallelogram link mechanism. To briefly describe the robot 20, 22 is a box part, 23 is a turning pace, 24 is a first arm, 25 is a second arm, 26 is a wrist part, 27 is an upper arm link, 28 is a parallel link for the first arm, and 29 is a This is a parallel link for the second arm. robot 2
For example, the first arm motor M2 moves the lever in the parallel link and moves the lever in the first arm via the first arm parallel link 28. A lever fixed at right angles to the arm 24 is moved to drive the first arm 24. The second arm motor M3 is provided on the opposite side of the motor M2 (corresponding to the back side of the paper), and this motor M3 moves the lever in the parallel link, and also moves the lever in the parallel link 29 to move the lever in the second arm parallel link 29. The second arm 25 is driven by moving the upper arm link 27 in the two parallel links. The motor M4 (with the motor M5 on the opposite side) and the motor M6 correspond to the three axes of the wrist portion 26. Note that the motor M1 (not shown) corresponds to the turning pace 23.

In such a robot, in the first application example, a spring unit 3 as a gravity balance device is provided on the first arm 24. The mounting portion 35 at the tip of the fixed rod 34 is attached to the upper end of the fixed base 28a that integrally extends above the rotating pace 23, and the mounting portion 36 at the tip of the movable rod 33 is attached to the upper end of the first arm 24. attached to the 1st arm 2 at all times.
Apply tensile force to the upper end of 4.

FIG. 10 is a side view showing the second application example, and FIG. 11 is a rear view thereof. In this industrial articulated robot 20, a spring unit 8 is provided along the upper arm link 27. That is, the fixed rod 34 of the spring unit 3 is attached to the extension part 29' where the parallel link 29 for the second arm extends vertically upward, and the movable rod of the spring unit 8 is attached to the connecting part between the second arm 25 and the upper arm link 27. Install 88. Of course, both mounting portions 85 and 86 are rotatably supported. The distance a along the vertical line is the distance between the axis of the motor M6 and the mounting portion 85 of the fixed rod 34.

When the spring unit 3 is attached in this manner, there is an effect of offsetting the moment based on the own weight of the upper arm link 27 and the gravitational moment of the first arm 24 as well. Also,
The dead weight (Wl) of the spring unit 3 itself is the second arm 25
and the first arm 24. It acts as a counterbalance for the second arm 25, and also produces an advantageous secondary effect in terms of moment balance. Note that, as shown in FIG. 11, it is preferable to provide two spring units 3 symmetrically. This is for the sake of balance and design effect. However, it goes without saying that the spring constant should be 1/2 of the previously calculated value.

Further, the aspect in which the spring units 3 are provided symmetrically is the first
The same applies to application examples.

Furthermore, as a modification, such a spring unit 8 may be attached to both the arm 24 and the upper arm link 27.

FIG. 12 is a side view of the eighth application example. In this example, two spring units 3 (four if left-right symmetry is considered) are used. There are two types: a first arm spring unit 3a and a second arm spring unit 8b.

The first arm spring unit 3a is the same as in the first application example.

In the second arm spring unit 3b, a mounting portion 85 of the fixed rod 34 is rotatably supported on one end of the triangular plate 42, and a mounting portion 36 of the movable iron 33 is a connecting portion between the second arm 25 and the wrist portion 26. It is rotatably supported on the shaft. The triangular plate 42 has one end pivoted on the first arm 24 and the fixed base 28a, and is supported by a link 43 parallel to the first arm 24, so that it does not tilt even when the first arm 24 rotates. ing. The distance a on the vertical line about the second arm 25 is the distance between the attachment part 35 of the second arm spring unit 8b on the triangular plate 41 and the connection point of the first arm 24 and the second arm 25. These two points are configured so that they are always on the vertical line even if the second arm 25 rotates in the parallel link mechanism.

By applying the spring unit 3 to each arm in this way, perfect balance can be achieved during direct teaching.

Note that the spring unit 3 of the above embodiment is preferably attached to the center of gravity of the arm, if possible.

Furthermore, although it is best to position the mounting part 35 of the spring unit 3 vertically above the swinging fulcrum of the arm, it is not necessary to position it strictly vertically above, but rather at a position approximately vertically above the pivot point of the arm. However, there is no problem in practical use, and the purpose can be fully achieved.

As is clear from the above description, according to the present invention, the repulsive force of the compression spring whose constant is selected to a predetermined value so that the tensile force applied to the vertically swinging arm is proportional to the installation distance of the spring unit. Since the structure is based on the following, there is an effect that the swing arm can be balanced regardless of its tilting position.

In addition, when this spring unit is applied to an articulated robot, direct teaching operations can be performed easily and smoothly, and the positioning repeatability accuracy of the servo control system can be improved without wasting unnecessary torque during servo control. be able to.

[Brief explanation of drawings]

Fig. 1 is a principle diagram of a conventional example using a tension spring, Fig. 2 is a graph for explaining the remaining amount of moment, Fig. 8 is a principle diagram of an embodiment of the present invention, and Fig. 4 is a diagram of an embodiment of the present invention. The basic configuration diagram of the embodiment, FIG. 5 is a specific configuration diagram, and FIG. 6 is the spring length t8.
7(al), (b) are explanatory diagrams of the means for adjusting the mounting length t of the spring unit, FIG. 8 is an explanatory diagram of the means for adjusting the spring constant, and FIG. 9 is an explanatory diagram of the means for adjusting the spring constant. A side view of an application example in which the embodiment of the present invention is applied to an articulated robot, Fig. 1θ is a side view of another application example, Fig. 11 is a rear view of Fig. 10, and Fig. 12 is a side view of another application example. It is a side view. 1... Arm, 8... Spring unit, 82...
・Compression spring, 8B...Movable rod, 34...
・Fixed rod, W...Arm load at point A,
a...Distance between swing fulcrum B and attachment point C, t...
Installation length of spring unit, 7g... Length of compression spring. Patent applicant: Agent of Kobe Steel, Ltd.
Patent Attorney Aoyama Ao Two idiots Figure 1 Figure 2 Figure 3 Figure 4 Figure 10 Figure 9 Figure 11 Procedural amendment form) July 7, 1981 Patent Application No. 43959 2 Name of the invention Swinging arm gravity balance device 3 Relationship to the case of the person making the amendment Contents of the patent applicant 4 attorney 7 amendment' Page 20, line 8, ``No. 11'' was replaced with ``Fig. 11'' I am corrected. Above 531

Claims (2)

[Claims] (1) A fixed point located vertically above or approximately vertically above a distance a from the fulcrum of the arm that can swing in a vertical plane;
A gravity balance device that is suspended between an arbitrary point on the arm and balances the gravity of the arm, wherein the gravity balance device includes a compression spring, and sets a spring constant k of the compression spring to a point on the arm. Arm load W at the point
is selected to be a value divided by the distance a, and the free length of the compression spring is a predetermined length t between the fixed point and a point on the arm, and when suspended at this length t. and the length ts of the compression spring, and the tensile force applied by the compression spring is configured to be proportional to the distance between the fixed point and a point on the arm. Arm gravity balance device. (2) The compression spring passes through the fixed-side inner end surface of the cylindrical case to which the fixed iron having the first mounting portion corresponding to the fixed point is fixed, and the other end of the cylindrical case. - The movable rod is interposed between the movable rod and the flange-shaped portion formed at the other end, which is provided with a second attachment portion corresponding to a point on the arm. Swing arm gravity balance device.