Adjustable stand for optical observation instruments

Claim 1

An adjustable stand having a stand base, a stand column and a support arm for supporting an operation microscope or the like observation instrument, said arm comprising a four-bar linkage establishing a parallelogram wherein (a) a first vertical bar is mounted to said column, (b) a second vertical bar is adapted to support the instrument, and (c) two vertically spaced parallel elongate bars have upper and lower pivoted connections to said vertical bars, spring-anchor means on said first vertical bar and including means for continuously adjustably positioning the same within a limited range of elevations between the elevations of elongate-bar connection thereto, and prestressed spring means connecting said spring-anchor means to said second vertical bar at one to the exclusion of the other of the points of elongate-bar connection to said second vertical bar, whereby said spring means may be essentially fully contained within the geometrical volume generally defined by and between said elongate bars; whereby for a limited range of elongate-bar angular elevation, said spring means may apply a counterbalancing elevational moment to said linkage, such counterbalancing moment varying as a function of elevation angle; and further whereby, within a limited range of weight of an observation instrument mounted to said second vertical bar, an observation instrument of given weight may be counterbalanced by selectively varied adjustment in the elevational position of said spring-anchor means, said spring-anchor means being adjustably displaceable on said first vertical bar along a straight line which forms an angle of 18° to 24° with the line connecting the upper and lower pivoted connections of said elongate bars to said first vertical bar, whereby adjustment of said spring-anchor means effects a change in moment-arm offset with accompanying relatively small change in spring force.