Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B25—HAND TOOLS; PORTABLE POWER-DRIVEN TOOLS; MANIPULATORS
  • B25J—MANIPULATORS; CHAMBERS PROVIDED WITH MANIPULATION DEVICES
  • B25J19/00—Accessories fitted to manipulators, e.g. for monitoring, for viewing; Safety devices combined with or specially adapted for use in connection with manipulators
  • B25J19/0008—Balancing devices
  • B25J19/002—Balancing devices using counterweights

Definitions

• the invention relates to a counterbalancing device for the arm system of an industrial robot.
• Known devices of this kind consist, inter alia, of springs or hydraulic power units.
• these solutions are expensive and often bulky and have therefore sometimes been replaced by a simple counterweight. In those cases where the robot arm is articulated, this solution has the drawback that both the primary and the secondary arm cannot be counterbalanced with one weight.
• the present invention solves the above problem in a very elegant way.
• the robot according to the invention comprises a stand with a first shaft and a primary arm which, at one end, is pivotably mounted on the first shaft.
• a second shaft is arranged and on this second shaft a secondary arm is pivotably mounted at a first bearing point.
• a bracket arranged in parallel with the primary arm is, at one end, pivotably connected to the rear part of the secondary arm, which part projects from the first bearing point.
• a crank arm which is substantially parallel to the rear part of the secondary arm is, at one end, pivotably mounted on the first shaft and, at the other end, pivotably connected to the other end of the bracket by means of a third shaft.
• the invention is characterized in that a second bearing point is rigidly connected to the primary arm and on the opposite side of the first shaft in relation to the principal extent of the primary arm.
• This second bearing point is connected, by means of a lever, to a counterweight at a third bearing point.
• the counterweight in its turn, is at a fourth bearing point pivotably mounted on the third shaft in such a way that the first shaft, the second and third bearing points and the third shaft form a tetragon.
• both of the robot shafts may become completely counterbalanced with one weight within the entire working range.
• Figure 1 shows the design principle and Figures 2-9 form the basis of the calculations carried out in the description.
• Figures 10-13 show an embodiment of the robot.
• FIG 1 designates the first shaft mounted in the stand which is not shown in the figure.
• a primary arm 2 is pivotably mounted.
• a second shaft 3 is arranged.
• a secondary arm 4 has a first bearing point 5 and is at this point pivotably mounted on the second shaft 3.
• a bracket 6 has been arranged in parallel with the primary arm 2 and is, at one end, pivotably connected, at a point 8, to the rear part 7 of the secondary arm 4, which rear part projects from the first bearing point 5.
• a crank arm 9, which is substantially parallel to the rear part 7 of the secondary arm 4, is at one end pivotably mounted on the first shaft 1 and at the other end pivotably connected, by means of a third shaft 10, to the second end of the bracket 6.
• a second bearing point 11 is rigidly connected to the primary arm 2 and on the opposite side of the first shaft 1 in relation to the principal extent of the primary arm 2.
• This second bearing point 11 is pivotably connected, by means of a lever arm 12, to a counterweight 13 at a third bearing point 14.
• This counterweight 13 or a rod 15 rigidly connected to the counterweight 13 is pivotably connected, at a fourth bearing point 16, to the third axle 10.
• the primary arm 2, the rear part 7 of the secondary arm 4, the bracket 6 and the crank arm 9 form a parallel system.
• the first shaft 1, the second and third bearing points 11, 14 and the third shaft 10 form a tetragon, the sides of which are suitably formed so as to form a second parallel system.
• the novel feature of the invention is that the counterweight 13 is pivotably suspended from the third shaft 10 and also pivotably connected to the extension of the primary arm 2 at the second bearing point 11 by means of an extra lever 12.
• m 2 the mass of the primary arm 2 at the centre of gravity of the primary arm
• m 3 the mass of the secondary arm 4 at the centre of
• L 1 the total length of the primary arm 2
• L 2 the length of the rear part 7 of the secondary arm 4
• L 2 the length of the lever 12
• L 3 the distance between the third 14 and fourth 16 bearing points
• L 3 the distance between the first shaft 1 and the second bearing point 11
• L 4 the shortest distance between m 1 and the fourth bearing point 16
• L 5 the distance between m 3 and the first bearing point 5
• ⁇ 1 the angle between the extension of L 1 and L 3
• ⁇ 3 the angle through which the secondary arm 4 has moved in Figure 3.
• F 3 (F 1 sin ⁇ 3 +F 2 sin ⁇ 3 +m 1 g) /cos ⁇ 2 F 1 cos ⁇ 3 + F 2 cos ⁇ 3 + F 1 sin ⁇ 3 sin ⁇ 2 /cos ⁇ 2 +
• Figure 6 shows the forces to which the secondary arm 4 is subjected. It is then assumed that the moment is calculated around the suspension point of the secondary arm 4 in the second shaft 3.
• Figure 7 shows the forces to which the primary arm 2 is subjected. It is then assumed that the moment is calculated around the shaft 1.
• the angle ⁇ 1 and the length L 3 do not affect the balancing capacity.
• the force F 1 is inversely proportional to the length L 3 . By increasing L 3 , F 1 is decreased.
• the link arm system with the counterweight 13 must then be a parallel arm system with right angles in the initial position. Otherwise, the working range, within which full balancing takes place, will be limited.
• the first shaft 1 rests on two parallel columns 18 (one of them being concealed) belonging to the stand 17.
• the primary arm 2 is mounted and provided at its upper end with a second shaft 3, on which the secondary arm 4 is mounted at a first bearing point 5.
• the rear part 7 of the secondary arm 4 is pivotably connected, at a point 8, to a bracket 6 which is parallel to the primary arm 2.
• the bracket 6 is pivotably connected, over a third shaft 10, to the first shaft 1 by means of a crank arm
• a second bearing point 11 is rigidly connected to the primary arm 2 and on the opposite side of the first shaft 1 in relation to the principal extent of the primary arm 2.
• This second bearing point 11 is pivotably connected, by means of a lever 12, to a counterweight 13 at a third bearing point 14.
• This counterweight 13 is also pivotably connected, at a fourth bearing point 16, to the third shaft
• connection between the counterweight 13 and the third shaft 10 may, of course, also consist of a rod rigidly connected to the counterweight 13.
• a rod designated 15, is schematically shown in Figure 1.
• Figure 10 also shows a suspended motor 19 with a gear box 21 for driving the arm system of the robot.
• the motor 20 belongs to the stand 17 and is intended for the rotation of the robot arm and the column 18 around a vertical shaft.
• Figure 11 shows the robot in Figure 10 seen from behind, that is, from the left. The same designations as in Figure 10 have been used. From Figure 11 it is clear that the columns 18 have between them a space 22 through which the counterweight 13 is able to swing. The counterweight 13 is dividable and is kept together by a bar 23.
• the counterweight 13 is dividable and is kept together by a bar 23.
• Figure 12 shows the robot from the side, a section being made in the lower part along the symmetry axis in Figure 13 so as to clearly illustrate the suspension of the dividable counterweight 13.
• Figure 13 shows the dividable counterweight 13.
• the primary arm 2 is operated and the angle between this and the secondary arm 4 is not changed, the parallel systems remain completely rigid and the counterweight 13 accompanies the primary arm 2 in the rotation around the first shaft 1 as if the counteweight 13 had been rigidly connected to the primary arm 2.
• the primary arm 2 is completely inoperative in its upright position and only the secondary arm 4 is operated, the counterweight 13 moves substantially straight up and down as the parallel systems adopt a rhomboid shape. Accordingly, when the mentioned robot arms operate simultaneously, a movement pattern for the counterweight 13 is obtained which is a combination of the two movement patterns described. Further, since the counterweight 13 is able to swing in between the columns 18 of the stand, the range of movement of the robot arm is not limited by the counterweight 13, which is very important. Also the primary arm 2 is provided with a certain longitudinal recess 26 to prevent the bracket

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• Engineering & Computer Science (AREA)
• Robotics (AREA)
• Mechanical Engineering (AREA)
• Manipulator (AREA)

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Publications (1)

Family

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Family Applications (1)

Country Status (2)

Cited By (1)

Citations (3)

• 1990
  • 1990-02-28 SE SE9000717A patent/SE466244B/sv not_active IP Right Cessation
• 1991
  • 1991-02-14 WO PCT/SE1991/000104 patent/WO1991012936A1/en active Search and Examination

Patent Citations (3)

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