Isotropy analysis of redundant parallel six-axis force sensor

• We propose four structures of parallel six-axis force sensors with redundancy.
• We analyze the mathematic models by isotropy and obtain isotropic configuration.
• We compare the relation among parameters leading to isotropic configuration.
• Two relatively thinner structures are selected by comparison.

The structural model of generalized redundant parallel six-axis force sensor is proposed. Based on the modified Stewart platform, its mathematical model is established with screw theory. The structural models of four typical redundant six-axis force sensors are proposed and their mathematical models are established for the corresponding structures. The isotropy of the four structural models is analyzed. The parameters relation leading to spatially isotropic configuration is conduced and demonstrated by a numerical example. Analytic solutions to the isotropy of the four models are conducted and their valid range of the analytic results leading to isotropic configuration is discussed. The conclusion is drawn that under the condition of force isotropy, two structures with the relatively least thickness are selected when all the legs of different structures are the same.