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Transducer

IP.com Disclosure Number: IPCOM000093480D
Original Publication Date: 1967-Oct-01
Included in the Prior Art Database: 2005-Mar-06
Document File: 3 page(s) / 44K

Publishing Venue

IBM

Related People

Dym, H: AUTHOR

Abstract

This transducer provides analog outputs representing the X and Y coordinates of the position of a writing stylus. This device can be used for the entry of transmission of graphical or handwriting information. The mechanism has the capability of being made so the force required for operation is so small that it is almost imperceptible. This, together with the lack of a bulky or restrictive linkage, can provide operation with a feel approaching that of a free stylus.

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Transducer

This transducer provides analog outputs representing the X and Y coordinates of the position of a writing stylus. This device can be used for the entry of transmission of graphical or handwriting information. The mechanism has the capability of being made so the force required for operation is so small that it is almost imperceptible. This, together with the lack of a bulky or restrictive linkage, can provide operation with a feel approaching that of a free stylus.

With this transducer, connection to the writing implement is made by a single nonrigid member. The position of the stylus is determined by connecting to it a fine spring or an elastic fiber which has its other end fixed. If the spring remains in tension over the entire writing area and the spring parameters are known, then the angle and force manifested by the spring at the fixed end determine the position of the stylus. By measuring the components of the spring's force, the coordinates of the position are obtained. This is effected by the use of strain gauges 10 and 12 arranged at the fixed end of spring 14 so that only the desired force component is coupled to each gauge 10 and 12 as in drawing 1. The component forces are exactly proportional to the position coordinates if the force applied by spring 14 is linearly proportional to its total length. The latter is the length from the fixed end to the tip of the writing stylus.

The proportionality relationship required for a perfectly linear transducer can be obtained by using a proper, zero or negative length, extension spring. That is a spring with an initial rest length L(i) and an initial tension F(i) that meet the relationship F(i) = kL(i). If F(i) > kL(i) additional lengthening above L(i) equal to L(n) is necessary. This can be done by connecting the spring to the pivot with the proper length of wire. This also allows for compensation of the space between the pen tip and the end of the spring.

To minimize position error caused by pen angle, the spring is attached to the pen near the writing point. This is effected by having a small arm fixed to a rotatable collar, with a ring or hook for attaching the spring at the end near the writing point. This allows the spring to maintain the proper orientation as the pen is rotated and tilted. The angle through which the spring can rotate about the fixed end is not limited to a 90 degree quadrant as shown in drawing 1. If the strain gauge level arms are arranged to sense force in both directions, then the transducer is capable of providing position output over a full 360 degrees.

The magnitude of the force applied by the spring to the strain gauge sensors can be increased or decreased by appropriate connection through a level arm. In this way, the spring choice can be guided by human factor considerations without regard for the sensors.

The proportionality of the force components at the fixed end of the spring to the position coordinates at the free end holds for t...