Seals and apparatus including seals

• US 5,029,401 A
• Filed: 12/22/1989
• Issued: 07/09/1991
• Est. Priority Date: 02/08/1989
• Status: Expired due to Fees

• Current Assignee: Smiths Industries Public Limited Company
• Original Assignee: Smiths Industries Public Limited Company
• Inventors: Masom, Ronald A.
• Primary Examiner(s): Cuchlinski, Jr., William A.
• Assistant Examiner(s): Cummings, Scott
• Application Number:
  US07/454,823
• Time in Patent Office: 564 Days
• Field of Search: 33/703, 33/705, 33/706, 33/707, 33/708, 74/18, 74/18.2, 267/64.13, 267/64.14, 267/64.19, 267/64.23, 267/64.27, 267/122, 277/3, 277/200, 277/212 FB, 403/50
• US Class Current: 33/705
• CPC Class Codes: F16J 15/52 by means of sealing bellows or diaphragms connection of valves to inflatable elastic bodies B60C29/00

Abstract

A seal for a linear displacement optical transducer has a tubular flexible bellows which is joined at one end to a movable carriage supporting an optically encoded track and which is movable along a cylinder supporting an optical read head. The bellows extends within the cylinder and has its other end sealed to an open end of the cylinder. A compensation chamber is sealed to the outside of the cylinder to enclose a major part of the length of the bellows and forms a sliding seal with a push-rod extending from a carriage. The bellows encloses a first volume of the dry inert gas within the cylinder to one side of the bellows and a second, similar volume of gas on the other side of the bellows and in the compensation chamber. Displacement of the carriage causes only a small change in pressure across the bellows which is accommodated by flexure. The compensation chamber isolates the bellows from atmospheric pressure change and ensures that temperature change affects both volume equally, minimizing pressure difference across the bellows.

Claims

1. Apparatus comprising:

a first member;

a second member, said second member having a closed end and an open end, said first member being displaceable along said second member; and

a seal between said first and second members, said seal comprising;

a flexible tubular bellows member;

means sealing said bellows member with the open end of said second member;

means sealing said bellows member with the first member, such that the first member extends within the bellows member and such that the bellows member extends entirely within the second member and encloses a first volume of fluid within the second member externally of the bellows member;

a compensating chamber;

a sliding seal between the compensating chamber and said first member; and

means sealing said compensating chamber with said second member such that the compensating chamber extends around the outside of the second member along a major part of the bellows member and encloses a second volume of fluid a part of which is external of the second member and the remainder of which is internal of the bellows member, and such that displacement of the first member along the second member causes only a small change in pressure across the bellows member which is accommodated by flexure of the bellows member.

2. Apparatus according to claim 1, wherein the fluid is a dry, inert gas.

3. Apparatus according to claim 1, wherein one of the first and second members carries an optically encoded track, wherein the other of the first and second members carries an optical read head, and wherein the optical head is arranged to read said track.

4. A linear displacement transducer comprising:

carriage means, said carriage means having an encoded track along its length;

a cylinder, said cylinder having a closed end, an open end, and a read head, said read head being arranged to read the said track and to provide an output in accordance with the position of the carriage;

a seal between the carriage and the cylinder to prevent contamination of the encoded track, said seal comprising;

a flexible tubular bellows;

means sealing the bellows with the open end of the cylinder;

means sealing the bellows with the carriage such that a part of the carriage extends within the bellows and such that the bellows extends entirely within the cylinder and such that the bellows encloses a first volume of gas within the cylinder externally of the bellows;

a compensating chamber;

means sealing said compensating chamber with the cylinder; and

a sliding seal between the compensating chamber and the carriage, the compensating chamber enclosing a second volume of fluid a part of which is internal of the bellows member, such that displacement of the carriage along the cylinder causes only small changes in pressure across the bellows which are accommodated by flexure of the bellows.

5. A transducer according to claim 4, wherein the encoded track is optically encoded, and wherein the read head is an optical read head.