ergonomic arm support


Requested Project

Arm support with swivel base to assist consumer with severe physical disability to make functional movements with arm (e.g. to activate switches.  Russ Schuchmann has volunteered for this project.

Design Notes

Project Status:  These designs replace ergonomic arm rests destroyed in the floods of 2008 in Cedar Rapids, Iowa.

The designs destroyed in the flood were constructed of chrome-moly steel tubing with mitered and brazed joints between the arms and the bearing housings at the end of each arm.  This design was very labor intensive, particularly in the mitering and brazing steps.  So, goals in this re-design were to simplify construction and also to reduce material cost.

Design Description:  The egrorest arm support shown in Figures 1 and 2 consists of a cradle to support the wrist to elbow area of the consumer?s arm, in turn supported by articulating arms attached by a clamp to the edge of a table or work surface.  All of the joints in the support arms allow rotary motion so a wide area can be traversed by the support cradle.

The cradle shown in these figures  is sawed from 4? plastic plumbing pipe and the edges are smoothed and contoured to eliminate sharp edges.  The cradle is mounted to a large washer by four #6-32 flat-head screws.  This washer is bent to conform to the contour of cradle.  It is brazed to a ?? OD, 3/8? ID steel tube that slips into a nylon bearing in the outermost support arm. Small adjustments in the height of the cradle can be made by adding plastic washers or spacers on the supporting tube that slips into the outer arm bearing.  The cradle design is the same for both versions of the ergonomic arm rest that are described here.

Version A of the arm support is constructed of ?? plastic pluming pipe and is shown in Figure 1.  ?T? fittings  are bonded to each end of the plumbing pipe arms to form the end bearings.  Short pieces of ?? plastic plumbing pipe are bonded into the vertical ends of the T fittings to form the bearing surface for the pins that connect the arms to their associated member.  As the plastic plumbing pipe is slightly smaller than ? ? ID, it is reamed with a ?? straight reamer to provide a close tolerance fit to the pins or metal tubing that connects the articulating joints.  

The first set of arms that were formed by this method lacked rigidity when tested.  The arm support would sag an undesirable amount when weight was applied to the cradle.  To remedy this, prior to bonding the arms to the end T fittings, the arms were reamed out to ?? ID and a ?? OD metal tube was inserted in each arm.  This measure provided a suitable amount of stiffness.

The inner arm is connected to the mounting bracket with a ? inch shoulder bolt. The joint between the two arms is made by connecting the holes on the end of each arm with ?? chrome-moly tubing secured by a 5/16? carriage bolt.  This tubing is chrome-moly aircraft tubing which has a good surface finish and tight tolerance on diameter.  A nylon spacer is used between the arms to provide clearance and smooth operation.  

The mounting pin for the arm rest cradle slips into the outer joint of the outer arm.  A spacer is used between the arm and the armrest bracket to provide height adjustment and promote smoother operation.


The clamp is bent up from steel mending strap material, 1? wide and about 3/16? thick.  It consists of two members brazed together.  The lower section of the clamp is tapped for a 7/16? clamp bolt.  The bolt itself is machined from a 7/16? carriage bolt where the head of the bolt is machined to the shape of a ball.  The brass clamp shoe is machined to accept this ball and the edge of the brass cup is rolled over into a depression between the ball and the remainder of the bolt to secure it to the bolt.

Version B of the arm support represents an effort to further reduce the labor and complexity of the ergorest arm support.  The inner arm is fabricated from 1? PVC plumbing pipe as shown in Figure 2.  The bearing surfaces for the articulating joints at each end of the arm consist of the pipe material itself.  To have good dimensional control of the bearing holes they are bored undersize and reamed with a ?? straight reamer.  

The outer articulating arm is fabricated from ?? PVC plumbing pipe.  This material is stiff enough that it does not require reinforcing with steel tubing as in the version A.

The joint between the two arms is made by connecting the holes on the end of each arm with ?? chrome-moly tubing secured by a 5/16? carriage bolt.  A nylon spacer is used between the arms to provide clearance and smooth operation.  

The mounting pin for the arm rest cradle slips into the outer hole of the outer arm.  Again a spacer is used between the arm and the armrest bracket to provide height adjustment and promote smoother operation.

Figure 2 also shows the clamp that secures the arm rest to a work surface and provides the suspension bearing for the support arms.  This clamp has a large mouth that will accommodate thick work surfaces or work surfaces with edge support.  The bracket which contains the clamping screw and the surface that is clamped to a work surface is fabricated from mending braces ?" thick and about 1 ?? wide.  A ?? toggle bolt is used for the clamp screw, a ball is machined on the clamping end which receives a brass shoe which applies the clamping pressure.  The brass shoe is rolled over the ball edge to keep it attached.

A second bracket of lighter material is bolted to the clamp bracket to provide an attachment point for the support arms.  This bracket contains a ? inch rod, one end of which is machined to seat in a ?? hole in the lower end of the bracket.  The rod is fitted with a shaft collar bearing against the upper end of the bracket to hold it in place.  The rod then extends beyond the upper surface of the clamp about 1 ?? to provide a mounting point for the inner arm of the wrist support.  Some adjustment of the working height of the arm over the work surface can be done by using shims between the bracket and the arm.  Additional coarse height adjustment can be made by moving the arm support bracket to a second set of bolt holes that are provided in the bracket.

One each of versions A and B have been provided to Options of Linn County for their use.

RCRV designer is Russell Schuchmann, and was requested by Options of Linn County, Wayne Clayton. The project was begun Dec 30, 2008 and completed Aug 5, 2009.


Additional Information:

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Figures

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