Intrument Tables HSM-901

The spring balanced table with an ingenious inner life
Haag-Streit  produces  not  only  ophthalmic  instruments  but  also the necessary  instrument  tables. The  term “spring  balanced  table” originates  from  the  fact  that  the weight of the table board and instrument is always completely compensated at every height by a suitable spring mechanism. This allows a comfortable height adjustment with very little effort.
The solution presented here is purely mechanical (without electrical equipment, hydraulics, pneumatics), needs  no  external  energy, and  is  maintenance free. The  height  of  the  table  is  adjusted  to  suit  the  patient’s  height  by operating a lever on a readily accessible place (releasing the brake) and  at  the  same  time  adjusting  the  height  of  the  spring  balanced table by hand.
The first ideas concerning this instrument table go back to the early 1960s. It took several more years before in 1966 the final form was found. The well thought out design of the spring balanced table is based  on  the  theoretical  idea  of  a  “continuous  compensation  of strength for optional positions.” Hans Papritz had already claimed a patent  for  the  design  in  1966. After  some  clarifications  regarding other  patents, which, however, could  not  meet  the  conditions  of complete  compensation, the  German  patent  was  finally  issued  in 1976.
The  solution  is  based  on  the  principle  shown  in  the  sketch. The weight G, which acts vertically on a lever, is compensated by a spring, independent of the angle of the lever. When the manually operated lever is released, it remains at rest so that there is balance in anyposition. In the functioning principle described, the weight moves on a circular path around pivot C. The weight moves laterally with respect to the pivot of the lever whereas point A of the spring suspension is fixed. The  practical  function  of  the  spring  balanced  table  requires  thereverse of this principle, which means that the weight (table boardwith instrument) is adjustable only in a vertical position. The lateral movement  described  in  the  functioning  principle  (description  of  acircular  path)  is  accommodated  by  the  parallelogram  arm  (x)  onthe left. This is horizontally movable and supported below by a ball bearing (y). Moreover, the parallelogram solution allows the attachment of additional  springs  to  compensate  the  weight  of  different  instruments. The fine balance of the spring power comes from a height-adjustable slide with the suspension points of several compensation springs. The clever and well thought out, purely mechanical solution has led to a reliable and continually desired product for many years.