GB2347883A

GB2347883A - Tripod manipulator

Info

Publication number: GB2347883A
Application number: GB9906250A
Authority: GB
Inventors: Neil Trevor Smith
Original assignee: Individual
Current assignee: Individual
Priority date: 1999-03-19
Filing date: 1999-03-19
Publication date: 2000-09-20
Also published as: GB9906250D0

Abstract

A mechanism which is capable of moving or measuring in 3 dimensions comprising 3 articulated legs A, B and C arranged in a tripod formation so that they each attach to individual swivel bases D and join through swivel joints to a common head assembly E at the apex. By altering the angle of articulation of each leg, the head assembly can be moved and controlled in space in three dimensions. The system resembles a tripod thus providing a high degree of triangulation stiffness. Because each of the joints lies either in the horizontal or vertical plane, the head assembly is constrained from tilting.

Description

Artripod This invention relates to a machine configuration which can control movement and positioning in three linear dimensions.

Machines which are able to move and position in three linear dimensions usually make use of three sets of slideways, each of which constrains movement to a single linear axis. On each slideway is mounted a moving carriage which gives movement to either a tool or work piece. At least one slideway must be mounted on the moving carriage of another slideway. This construction requires high manufacturing accuracn and usually involves heavy moving carriages. These in turn lead to high costs and poor dynamic performance at high speeds.

Alternative machine configurations exist which utilise limbs with rotary joints or extending legs in place of slideways. However these machines generally have low rigidity and are therefore most suited to applications such as robotics and measuring systems where applied forces are low.

The Artripod machine configuration allows movements to be made in three axes, without the use of slideways, yet with greater rigidity than alternative ! imb tvpe structures.

The machine configuration consists of a set of three articulated legs arranged in a tripod formation so that they each attach a common head assembly at the apex. Each leg contains three horizontal hinges: The lower hinge is mounted to a vertical swivel joint with a fixed axis. The upper hinge is mounted to the movable common head assembly via another vertical swivel joint. The central hinge allows the distance between the upper and lower hinges to be altered thus allowing the head assembly to be moved and controlled in space in three dimensions.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawing in which: Figure 1 shows a plan view of the machine ; Figure 2 shows a section through the machine ; Referring to the drawings the machine is made up of three legs (A, B and C), each of which has three parallel hinged joints which all lie in the horizontal plane.

Each lower hinge is joined to individual base swivel mechanisms D, whose axes are vertical and which are fixed in space.

Each upper hinge is attached to individual upper swivel mechanisms E, whose axes are vertical but which can move in space.

The upper swivel mechanisms pivot around a common head assembly F.

Control devices (motors, brakes, measuring devices, etc.) G are connected to the central horizontal hinged joint of each leg.

By controlling the angle of articulation of the central hinged joints the positioning of the head assembly can be completely controlled in three dimensions. The vertical swivel joints and the hinged joints at the top and bottom of each articulated leg do not need to be separately controlled as their angles are automatically defined by the articulation angle of the central hinged joints in each of the three legs.

The upper swivel joint mav be omitted from one of the leg assemblies so that the upper hinged joint attaches directly to the head assembly. This will allow the leg to absorb torsion forces which might be applied externally. In this case the upper swivel joints of the other two legs may be arranged so that thev do not pivot on a common axis.

The head assembly is constrained from tilting due to the horizontal and vertical orientation of the each of the joints. However, parallelogram linkages H, as shown in figure 3, may be added to the leg assemblies to further constrain the head from being tilted by externally applied forces.

The specific application shown in figures I & 2 is for a machine tool. In this case geared motors are used to control the articulation angle of each of the central hinged leg joints. A cutting tool is suspended from the head assembly and this is moved around a stationary work piece mounted to a work table and bed. In this case the working area is bounded by lines I.

The machine tool application shown is for illustration purposes only, as the Artripod machine configuration may be applied wherever 3 dimensional movement and positioning needs to be controlled.

Claims

CLAIMS 1 A machine configuration which consists of a set of three articulated legs arranged in a tripod formation so that they each attach a common head assembly at the apex. Each leg contains three horizontal hinges: The lower hinge is mounted to a vertical swivel joint with a fixed axis. The upper hinge is mounted to the movable common head assembly via another vertical swivel joint. The central hinge allows the distance between the upper and lower hinges to be altered thus allowing the head assembly to be moved and controlled in space in three dimensions.
2 A machine as claimed in Claim I wherein one upper leg does not swivel around the head assembly and which can therefore constrain rotation of the head assembly.
3 A machine as claimed in Claim 2 above wherein the two swivel mounted upper legs do not swivel on a common axis.
4 A machine as claimed in anv preceding claim wherein passive control devices (brakes, measuring devices etc.) are provided on the central horizontally hinged joints on each leg
5 A machine as claimed in any preceding claim wherein active control devices (motors, actuators, etc. j are provided on the central horizontally hinged joints on each leg.
6 A machine as claimed in anv preceding claim wherein parallelogram type linkages are provided on at least one articulated leg to further constrain the head from tilting.
7 A machine as described in any preceding claim in which the complete machine is inverted or reoriented so that he hinged joints do not lie in the horizontal plane.
8 A machine capable of moving or measuring in 3 dimensions substantially as described herein with reference to Figures 1, 2 & 3 of the accompanying drawings.