Arm device

Arm device adapted to move and position a first basic part (6) relatively to a second basic part (4), comprising at least three arms (1,2,3,7) capable of being extended and shortened in a controlled manner, said arms being free to pivot in attachments (5) on the second basic part, while one attachment on the first basic part is rigid, and one of said arms is torisonally rigid. A third basic part (15) is connected to the first basic part through a joint (16), and at least one auxiliary arm (12,13) is at one end connected to one of the arms (7) through a joint, while the other end of the auxiliary arm is connected to the third basic part (15), and the lengths of the auxilary arm can be varied. Thereby is achieved that the arm device has a large number of degrees of freedom with respect to movement of the third basic part, which holds a tool or a tool holder. Moreover, the tool or the tool holder may be journalled for rotation relatively to the third basic part ( 15).

BACKGROUND OF THE INVENTION 
The present invention relates to an arm device adapted to move and position 
a first basic part relatively to a second basic part, said arm device 
comprising at least three arms capable of being extended and shortened in 
a controlled manner, and the arms are free to pivot in their attachments 
on the second basic part, while one attachment on the first basic part is 
rigid, and one of the arms is torsionally rigid. Such a device is known 
from Norwegian acceptance print No. 148216. As examples of the use of such 
an arm device are mentioned industrial robot, drilling rig for tunnels and 
mines, adjustment device for aerials. 
As further examples of known technique are mentioned: 
U.S. Pat. No. 3,215,391 shows an arm device capable of being used for for 
instance adjustment of the position of an aerial, which, thus, constitutes 
one of the basic parts, while the other end of the arms is fastened to for 
instance a plate or similar, which may be stationary or for instance 
fastened to a vehicle. The arms are rigidly attached in each basic part, 
and are constituted by telescopic arms having universal joints at the 
middle. This permits that one of the basic parts can pivot about two of 
the universal joints relatively to the second basic part, and the pivotal 
movement is controlled by extension or shortening of that arm whose 
universal joint is not situated along the pivot axis. Moreover, it is 
possible to displace the basic parts parallelly to each other, by 
extending and shortening the arms. Thus, the possibilities of moving the 
basic parts mutually are very restricted. 
U.S. Pat. No. 3,374,977 shows a similar arm device, being adapted for 
aerial adjustment. The device comprises four arms being fastened with 
their ends to two basic parts. Said four arms, which can be extended and 
shortened and have universal joints at each end, have attachments at the 
corners of equally large squares, and a fifth arm having a fixed length 
and universal joints at each end is fastened to the basic parts at the 
center of said squares. 
The basic parts can be freely adjusted with respect to mutual direction, 
but the mutual adjustment is restricted, in that the fifth arm maintains a 
fixed distance between the middle portions of the basic parts. At least 
two of those arms that are capable of changing their length must be 
actuated simultaneously. Moreover, the arm device is statically 
indetermined, and is not torsionally rigid, when the arms have equal 
lengths. 
U.S. Pat. No. 3,288,421 also shows an arm device adapted to move a basic 
part relatively to another, and permits both a mutual angular adjustment 
and parallel displacement. The device comprises six arms, and the ends of 
two by two arms are journalled in the same pivot point, whereby the arms 
stand in a zigzag pattern between the basic parts. The device presupposes 
that both of the basic parts have a relatively large area, and the number 
of arms is relatively large. The mutual movement of the basic parts is 
very restricted. 
Said Norwegian acceptance print No. 148216 shows a tool at the free end of 
the arm device. Said tool, which may of course be of a different structure 
than that shown in the print, is rigidly mounted on the first basic part, 
and can consequently only perform movements determined by the movements of 
said basic part. For some applications the possibilities of movement of 
the tool are too restricted. Said basic part, and consequently also the 
tool, are rigidly connected to the end of one arm and can, therefore, only 
perform pivotal movements about the other basic part, about the pivotal 
mounting of said arm on the other basic part, possibly combined with 
movement towards or from the other basic part. In other words the tool 
always follows all the movements of the first basic part. 
SUMMARY OF THE INVENTION 
The object of the present invention is to achieve that the tool may also be 
moved relatively to the first basic part, at least in a tilting movement 
about one pivot axis, possibly about two pivot axes. In accordance with 
the invention this is achieved with an arm device as specified in the 
succeeding claims. 
The invention implies that the third basic part, and consequently also the 
tool, have four or five degrees of freedom with respect to movement. A 
sixth degree of freedom can be achieved in that the third basic part can 
rotate relatively to the arm device. Thereby the tool can be brought to 
any spatial position, within the limits determined by the dimensions of 
the arm device and the possibilities of movement of the arms and the 
auxiliary arms, and the tool can be given any orientation in the space. 
Thus, an arm device has been achieved which theoretically gives unlimited 
possibilities of positioning tools. 
For applications of the arm device in cases where it is essential to 
achieve as exact positioning as possible of the basic parts relatively to 
each other the arm device can be equipped with means for measuring the 
actual length of the arms, i.e. in such a manner that a possible elastic 
extension or shortening of the arms due to the prevailing loads is 
included in the measurement. The measured values can be compared with the 
desired values, and corrections of the arm lengths can be performed. 
The arms may for instance be hydraulic cylinders, and it is possible to use 
programmed control, as for known types of robots. The measured values of 
the arm lengths can be fed to the control system, which continuously 
performs corrections based on the measured values. 
The arm device can be made with only three main arms, of which one must be 
able to transfer a bending moment. The same arm, or one of the others, 
must be able to transfer torque. One arm, therefore, is rigidly connected 
to the first basic part, and the two portions of the arm which can be 
mutually shifted for varying of the length of the arm may be prevented 
from mutual rotation. The arm is fastened to the second basic part in such 
a manner that it can pivot in all planes, but without being able to rotate 
relatively to the second basic part. Alternatively said arm may only be 
adapted to transfer bending movement, and not torque, as the latter is 
transferred through another arm. 
The arms may also be comprised of something else than cylinders and piston 
rods, such as electrically driven arms, for instance according to the 
solenoid principle or by means of a threaded rod which is screwed 
relatively to a sleeve. 
It is no absolute presupposition that the shortening and extension of the 
arms can be controlled within two extreme limits. An arm device according 
to the invention may also be utilized in such a manner that one or more 
arms can merely perform their full stroke, i.e. that the movement cannot 
be stopped in any intermediate position. The arm device may then be used 
for instance for moving items between fixed points, whereby the mutual 
positions of the points are determined by the largest and smallest arm 
lengths.

DESCRIPTION OF PREFERRED EMBODIMENTS 
The arm device shown comprises three arms 1,2,3 provided mainly in the 
corner edges of a pyramid. These three arms are fastened with one end to 
each basic part 4,6 through ball joints or universal joints 5, and each 
arm can be extended and shortened. Moreover, the arm device comprises a 
fourth arm 7. The arm 7 is fastened to the basic part 4 through a 
universal joint 5, while the other end of the arm 7 is rigidly connected 
with the basic part 6. In addition the arm 7 can transfer torque. This is 
indicated in that the rod portion of the arm is splined, whereby the 
splines are guided in corresponding recesses in the cylinder portion. The 
arm 7 is not connected to any system for forced variation of the length, 
because the length of the arm alone is adapted to the length variations of 
the other arms 1,2 and 3. 
Moreover, the arm device may be equipped with not shown means for 
indicating the actual length of the arms 1,2 and 3. 
The arm 7 will transfer both bending moments and torque. The arms 1,2 and 3 
are only able to be exposed to tension and pressure, and measuring or 
indicating of the actual arm length, therefore, gives an unambiguous 
expression of the position of the tool relatively to the basic part 4 or 
of the relative position of the two basic parts 4 and 6. 
The arm being capable of transferring torque may have the function of 
preventing mutual rotation of the basic parts, but may also be used to 
cause a controlled mutual rotation of the basic parts. Such rotation is 
possible due to the joints at each end of the other arms, and mutual 
rotation of the basic parts can be performed to such an extent (rotation 
angle) that the arms are obstructed by each other. Thus, the rotation 
angle can be very large. During such rotation the basic parts will, 
provided that the lengths of the arms which have joints are held constant, 
approach each other progressively on both sides of a normal position where 
the distance between the basic parts is at a maximum. If the rotation 
starts when the arms are somewhat shortened the distance between the basic 
parts can be held constant during the rotation, by gradually extending the 
arms. The arm causing the rotation will take the necessary length at any 
moment. 
There are several possibilities of transferring the torque necessary for 
such rotation. A servomotor may for instance be provided in one of the 
basic parts, in order to rotate the end of the arm being capable of 
transferring torque relatively to the respective basic part. The mutual 
rotation may also take place in the arm proper, in that means are provided 
for controlled mutual rotation of two arm portions. 
In the embodiment shown such rotation as mentioned above can be carried out 
for instance in that the thick portion of the arm 7 contains a servomotor 
which can rotate the thin portion of the arm relatively to the thick 
portion, so that the basic part 6 rotates relatively to the basic part 4. 
The rotation angle will be limited by mutual contact between the arms 1, 2 
and 3. 
The above described arm device corresponds to the arm device appearing from 
Norwegian acceptance print No. 148216. 
In the example shown there are, between the arm 7 and a third basic part 
15, provided auxiliary arms 12 and 13. The third basic part 15, being 
merely shown diagrammatically in the form of a cylinder, is fastened to 
the basic part 6 by means of a joint 16, being a hinge or a ball joint or 
universal joint, and in the example the auxiliary arms 12 and 13 are 
fastened through supports 8,9 and 10,11 to the arm 7 and the third basic 
part 15, respectively. The auxiliary arms 12 and 13 are telescopic and are 
connected to the supports 8,9,10 and 11 through joints, and the lengths of 
the auxiliary arms can be adjusted. It will be appreciated that all the 
supports 8,9,10 and 11 will follow the movements of the arm 7 as long as 
the auxiliary arms 12 and 13 have constant lengths. Thereby the movements 
of the third basic part 15 are determined merely by the arms 1,2,3 and 7. 
In addition extension and shortening of the arms 12 and 13 cause tilting 
movement of the third basic part about the joint 16. 
The third basic part, and hence the tool, has five degrees of freedom for 
movement. A sixth degree of freedom can be achieved in that the tool 14 
can rotate relatively to the third basic part 15, which is shown 
diagrammatically as a short cylinder, while the tool 14 is shown 
diagrammatically as an elongate, thinner cylinder. 
In the embodiment shown the arm 7 is inverted relatively to the arms 1,2 
and 3. This is merely due to practical reasons when the arms are 
constituted by cylinders having pistons and piston rods. The provision of 
the cylinders of the arms 1,2 and 3 nearest to the basic part 4 implies 
that the mass of the moving parts is small and that the cylinders take up 
space where most space is available. The arm 7 has its cylinder nearest to 
the third basic part 15 because it is most appropriate to mount the 
supports 8 and 9 on a cylinder rather than mounting them on a 
substantially thinner piston rod. 
The invention can be materialized with only one auxiliary arm, provided 
that the joint 16 is a hinge joint having only one pivot axis. This, 
however, reduces the number of degrees of freedom. 
Under all circumstances the joint 16 must be capable of transferring 
torque, because the third basic part 15 must not be able to pivot freely 
relatively to the first basic part 6.