Machine element or mechanism – Control lever and linkage systems – Multiple controlling elements for single controlled element
Reexamination Certificate
2002-07-29
2004-06-15
Bucci, David A. (Department: 3682)
Machine element or mechanism
Control lever and linkage systems
Multiple controlling elements for single controlled element
C074S490050, C074S490080, C414S735000, C414S744200, C901S014000, C901S015000
Reexamination Certificate
active
06748819
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a robot such as articulated manipulators and more particularly to a robot having an arm which makes use of a parallel linkage.
There have been well known robots such as manipulators utilizing a four-bar linkage (e.g., parallel linkage) as an articulation mechanism.
FIG. 1
is a side elevation showing a structure of a known robot of this type. The robot shown in
FIG. 1
mainly comprises a bar-like arm member A, a first link
1
, a second link
2
, a third link
3
and a base
6
.
Attached to the distal end of the arm member A is an end effector (not shown) such as a hand for gripping a workpiece or a welder for executing welding work on a workpiece. The part around the distal end of the arm member A is able to pivot about the central axis of the arm member A and flex relative to a longitudinal direction of the arm member A.
At the intermediate section of the arm member A somewhat closer to its proximal end when viewed in the longitudinal direction of the arm member A, one end of the first link
1
is pivotally connected by a pivotal shaft which extends in a direction perpendicular to the longitudinal direction of the arm member A. The other end of the first link
1
, on the other hand, is pivotally supported on a swivel base
61
by a pivotal shaft extending in substantially the same direction as the above pivotal shaft.
The base
6
is composed of the swivel base
61
and a mount
62
. The mount
62
houses a motor, reduction gears and others (not shown) which cause the swivel base
61
to turn in a horizontal direction.
One end of the second link
2
is pivotally connected to the proximal end of the arm member A by a pivotal shaft extending in substantially the same direction as the above pivotal shafts. The link length (i.e., the distance between two pivotal shafts) of the second link
2
is substantially the same as that of the first link
1
, and the other end of the second link
2
is pivotally connected to one end of the third link
3
by a pivotal shaft which extends in substantially the same direction as the above pivotal shafts.
The other end of the third link
3
is pivotally supported on the swivel base
61
so as to be coaxial with the other end of the first link
1
. The link length of the third link
3
is substantially the same as the distance between the position at which the first link
1
is pivotally connected to the arm member A and the position at which the second link
2
is pivotally connected to the arm member A. Thus, the arm member A, the first link
1
, the second link
2
and the third link
3
constitute a parallel linkage.
In the swivel base
61
, a motor for causing pivoting of the first link
1
and a motor for causing pivoting of the third link
3
are opposed to each other (not shown). The rotary shaft of one of the motors is coupled to the pivotal shaft of the first link
1
such that the rotation of the motor is transmitted to the first link
1
, whereas the rotary shaft of the other motor is coupled to the pivotal shaft of the third link
3
such that the rotation of the motor is transmitted to the third link
3
.
The lower part of the second link
2
extends in a direction opposite to the first link
1
and the distal end of the lower part is provided with a balancer weight (weight) W. The balancer weight W is provided in order that it balances the mass of the arm member A, the end effector, a workpiece to be conveyed etc. in the area around the pivotal shaft for supporting the third link
3
on the swivel base
61
, so that the load imposed on the motor for causing pivoting of the third link
3
can be reduced.
A spring unit
7
housing a spring is disposed in parallel with the first link
1
. One end of the spring unit
7
is pivotally connected to the pivotal shaft for connecting the arm member A and the first link
1
, while the other end being pivotally connected to the upper end part of the swivel base
61
. With this arrangement, when the first link
1
inclines with the arm member A moving, the spring unit
7
energizes the arm member A in a direction opposite to the moving direction, thereby reducing the load imposed on the motor for causing pivoting of the first link
1
.
The conventional robot described above, however, presents the problem that, great load torque is imposed on the motor for causing pivoting of the third link
3
for the following reason, particularly where mass capacity is 100 kg or more.
FIG. 2
is a diagrammatic side elevation illustrating a dynamically balanced condition of a conventional robot. As shown in
FIG. 2
, where a force F is downwardly exerted on the distal end of the arm member A and the third link
3
is inclined from a horizontal position in a counter-clockwise direction in the drawing through an angle [h]&thgr;, the arm member A is also inclined from a horizontal position in the same direction through the angle [h]&thgr; so that the magnitude of the component of the force F working in a direction perpendicular to the arm member A is Fcos[h]&thgr;. Therefore, the force F
1
expressed by Formula (1) is imposed on the proximal end of the arm member A.
F
1
=(
L/L
3)
F
cos [
h
]&thgr;(1)
In this equation, L designates the length between the position where the arm member A is pivotally connected to the first link
1
and the distal end of the arm member A; and L
3
designates the length between the position where the arm member A is pivotally connected to the first link
1
and the position where the arm member A is pivotally connected to the second link
2
.
Since the force F
1
is imposed, by way of the second link
2
, on the position where the third link
3
is pivotally connected to the second link
2
and the link length of the third link
3
is L
3
, load torque t having a magnitude represented by F
1
·L
3
(=L·Fcos[h]&thgr;) is imposed on the motor M for causing pivoting of the third link
3
.
Therefore, where the robot carries a massive workpiece, that is, where the robot has a mass capacity of 100 kg or more, the load on the motor M becomes extremely great which gives rise to a need for a large-sized motor.
In addition, in the above case, since great torque is exerted on the pivotal axis which pivotally supports the third link
3
on the base
6
, great stresses are generated in the third link
3
, its pivotal shaft and peripheral members. In order to ensure rigidity high enough to withstand the stresses, the sizes of these members are inevitably increased.
In the conventional robot, not only the capacity of the motor M needs to be increased but also the reduction gears coupled to the rotary shaft of the motor M must have a high reduction ratio. As a result, the conventional robot cannot transport a workpiece at high speed.
Another problem presented by the conventional robot is such that while the load on the motor M can be reduced by providing a balancer weight W which can be balanced against the mass of the arm member A, the end effector, the workpiece to be conveyed and others, the balancer weight W should be large in size where the mass capacity is 100 kg or more so that the mass of the robot
1
itself increases, giving rise to a need for a large-sized motor for causing slue of the swivel base
61
in a horizontal direction.
A robot using the so-called hybrid linkage suffers from the following problems.
FIG. 3
schematically, diagrammatically illustrates a side elevation of a robot using the so-called hybrid linkage. The robot using the hybrid linkage has a parallel linkage composed of four links L
11
to L
14
. Of these links L
11
to L
14
, the laterally extending upper link L
11
is provided with an extension part which extends upwardly from the intermediate section of the link L
11
when viewed in a longitudinal direction. The extension part is bent midway at substantially right angles, and a motor and reduction gears (not shown) are attached to the distal end of the extension part. The rotary shaft of the motor is coupled to the intermediate section of t
Inada Takahiro
Maeguchi Yuji
Takayama Hiroyuki
Bucci David A.
Hansen Colby
Kawasaki Jukogyo Kabushiki Kaisha
Marshall & Gerstein & Borun LLP
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