Browse Prior Art Database

Flexible Pressure Safety Switch

IP.com Disclosure Number: IPCOM000116000D
Original Publication Date: 1995-Jul-01
Included in the Prior Art Database: 2005-Mar-30
Document File: 2 page(s) / 73K

Publishing Venue

IBM

Related People

Murray, JC: AUTHOR

Abstract

Described is the use of a flexible pressure-activated switch. The switch was required to satisfy safety requirements for equipment in use in manufacturing operations. This switch, presently in use as a close proximity safety switch on hydraulic lifts, is a combination of inexpensive "off the shelf" parts.

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Flexible Pressure Safety Switch

      Described is the use of a flexible pressure-activated switch.
The switch was required to satisfy safety requirements for equipment
in use in manufacturing operations.  This switch, presently in use as
a close proximity safety switch on hydraulic lifts, is a combination
of inexpensive "off the shelf" parts.

      A computer systems manufacturing process utilizes pit mounted
hydraulic lifts to position frames for manufacturing operations.
These lifts consist of circular platforms approximately 1.5 meters in
diameter connected to the end of a vertical hydraulic ram.  The pump
and ram are mounted in a pit to allow the platform a range of motion
from flush with the flooring to 1.6 meters above the floor.

      As these lifts are used in assembly stations that require
operators to complete operations while standing near the lift, there
is a significant safety concern when loaded lifts are lowered.  As a
loaded lift nears the "home" position of flush with the flooring, the
underside edge of its platform passes below the floor level -
potentially shearing anything extending across the edge of the pit,
like an operators foot.

      For rectangular platforms, there exist mechanical pressure
switches that can be wired into a safety circuit to reverse the
motion of the lift if an object is sensed in below the platform
during lowering.  Unfortunately, these switches are not flexible such
that they offer the same function in a circular pattern, nor can they
be connected in a segmented approximation of a circle without gaps.
We were unable to find any "off the shelf" switch that satisfied our
requirements.

      The solution was extremely simple and effective.  A 1.5 meter
length of thin wall PVC tubing was plugged at one end and cemented to
the underside of the circular lift platform as near to the outside
edge as possible.  The open end of the tubing was spliced to a length
of 1/4-inch flexible...