GB2207963A

GB2207963A - A gaiter

Info

Publication number: GB2207963A
Application number: GB08817525A
Authority: GB
Inventors: Ronald Philip Pratt
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1987-08-10
Filing date: 1988-07-22
Publication date: 1989-02-15
Also published as: GB8817525D0; GB8718898D0

Abstract

A gaiter 42 is provided for protecting a mechanical arm 22 from contamination, and which avoids problems caused by leakage through end seals 46 of the gaiter. The gaiter includes a low pressure-drop, high efficiency filter 48 which allows the gaiter to breathe, so minimizing the pressure differences between inside and outside the gaiter during movements of the arm. The filter 48 may be of annular shape, surrounding a part of the arm, and connecting two portions 44,50 of the gaiter. <IMAGE>

Description

A GAITER This invention relates to a gaiter for protecting a mechanical arm such as a manipulator slave arm or a robot from contamination.

It is known to enclose the slave arm of a manipulator with a gaiter. If the slave arm is used in a shielded cell in which dust or other contamination exists, then the gaiter prevents such contamination reaching the mechanism of the slave arm. In some designs, a volume of air is trapped inside the gaiter. If the arm changes in length, the air pressure within the gaiter will vary too, and this can cause leakage at the seals at each end of the gaiter and through any defects in the gaiter. Such leakage can transfer contamination to the slave arm mechanism.

According to the present invention there is provided a gaiter for a mechanical arm, the gaiter incorporating a high-efficiency, low pressure-drop, filter unit.

A high efficiency filter is one which filters out 99.99% of particulate matter down to particles of size 0.3 micron in the standard sodium chloride test (BS 3928).

The pressure difference between inside and outside the gaiter is preferably less than 1 kPa (4 inches of water), desirably less than 25 Pa (0.1 inches of water), during movement of the arm, and so the filter unit must be of sufficient volume throughput at the value of pressure difference to allow about half the internal volume of the gaiter to flow in a time of about 4 or 5 seconds.

Desirably the filter unit is of annular shape, and connects two portions of the gaiter. The arm can then be inserted into the gaiter, extending through the middle of the filter unit; to facilitate insertion of the arm, a conically tapered annular guide is provided on the filter unit.

The invention will now be described by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a diagrammatic side view, partly in section of a master/slave manipulator incorporating a gaiter; and Figure 2 shows a sectional view, and to a larger scale, of part of the gaiter of Figure 1.

Referring to Figure 1, a manipulator 10 is shown installed in a shielding wall 12 of a cell 14 with a viewing port 16. The cell 14 is for working with radioactive materials. The manipulator 10 includes a master arm 18, a through tube 20, and a slave arm 22. The master arm 18 comprises a shoulder assembly 24 which pivotally supports a telescopic arm 26, to the other end of which is attached a wrist and hand grip 28. The slave arm 22 has corresponding components: a shoulder assembly 30 which pivotally supports a telescopic arm 32 to the other end of which is attached a wrist 33 and a gripping mechanism 34. Drive means (not shown) such as cables or rotary shafts cause the slave arm 22 to reproduce the movements of the master arm 18, itself moved by an operator.

The through tube 20 locates within a wall liner tube 36 which extends through the wall 12, and is sealed to the liner tube 36 by an O-ring seal 38 near the end remote from the cell 14; the seal 38 allows the through tube 20 to rotate about its longitudinal axis. The bore of the liner tube 36 is stepped outwardly at the end near the cell 14, so that an annular space 40 is defined between the through tube 20 and the liner tube 36.

The slave arm 22 with the exception of the gripping mechanism 34 is enclosed within a hot-side gaiter 42 of polyvinylchloride-coated polyurethane sheet. The gaiter 42 includes an upper portion 44 of tubular form, which at one end has an outwardly operating spring seal 46 which seals against the liner tube 36 within the annular space 40. The other end of the upper portion 44 is sealed to an annular filter assembly 48 whose external diameter is just less than that of the bore of the liner tube 36; a convoluted bellows lower portion 50 is sealed to the other side of the filter assembly 48 and extends down to a seal 52 to the lower end of the slave arm 22 between the wrist 33 and the gripping mechanism 34.

The filter assembly 48 is shown in greater detail in Figure 2, to which reference is now made. The assembly 48 consists of an annular, high-efficiency, low pressure-drop filter unit 54 through the centre of which the telescopic arm 32 (see Figure 1) extends, a lower annular support tray 56, an upper annular support tray 58, and an annular conical guide member 60 with an external flange 62. The upper end of the gaiter portion 50 is sealed between the lower face of the filter unit 54 and the lower support tray 56, while the lower end of the gaiter portion 44 is sealed between the upper support tray 58 and the flange 62, the lower face of the flange 62 sealing against the upper face of the filter unit 54, all the components of the assembly 48 being sealed and held together by polyvinyl adhesive.

The gaiter 42 can be installed, before installation of the manipulator 10, through the wall liner tube 36 and into the cell 14. The slave arm 22, aligned with the through tube 20, can then be inserted through the liner- tube 36 and so into the gaiter 42, the guide member 60 facilitating passage of the lower part of the slave arm 22 through the filter assembly 48. The gripping mechanism 34 is attached to the wrist 33 subsequently.

In operation of the manipulator 10 the slave arm 22 varies in length and orientation, the gaiter 42 accommodates these changes, and its internal volume undergoes corresponding changes. By virtue of the O-ring seal 38, the spring seal 46 and the seal 52, air enters or leaves the gaiter 42 due to these volume changes only through the filter unit 54, and consequently no contamination from the cell 14 reaches the slave arm 22.

The manipulator 10 can move from a position of maximum gaiter volume (ie in-line with the through tube 20 and fully extended) to minimum gaiter volume (ie with the shoulder assembly 30 fully bent and the arm 32 fully retracted) in about 4 seconds. In this time the volume of air within the gaiter 42 must decrease to about half its initial value. For a slave arm 22 which when fully extended is about 2.5 m long, the volume of air which would have to pass through the filter unit 54 would be about 40 litres, so that the volume throughput would be about 10 litres/second. The filter unit provides such a volume throughput for a pressure difference of only about 25 Pa.

This is well below the pressure difference at which the seals 46 and 38 have been found to leak in the absence of the filter assembly 48 - such leakage has been found at a pressure difference of between about 1.5 kPa and 2.5 kPa.

Thus the filter assembly 48 prevents contamination of the slave arm 22 by preventing the seals, in particular the spring seal 46, from being subjected to pressures at which leakage may occur. The pressure difference across the gaiter 42 is maintained at a very low level, also minimising leakage through any defects (cracks or pinholes) which may be present in the gaiter 42.

It will be observed that the filter asembly 48 is at such a location that it does not interfere with the telescopic or other movements of the arm 22.

Claims

1. A gaiter for a mechanical arm, the gaiter incorporating a high-efficiency, low pressure-drop, filter unit.

2. A gaiter as claimed in Claim 1 wherein the filter unit is such that during operation of the arm the pressure drop across the filter unit is less than 1 kPa.

3. A gaiter as claimed in Claim 1 or Claim 2 wherein the filter unit is of annular shape connecting two portions of the gaiter, so that the arm can be inserted through the centre of the filter unit.

4. A gaiter for a mechanical arm substantially as hereinbefore described with reference to, and as shown in, the accompanying drawings.