where x d {\displaystyle {\boldsymbol {x}}_{\mathrm {d} }} denotes the desired task-space position, K x {\displaystyle {\boldsymbol {K}}_{\mathrm {x} }} and D x {\displaystyle {\boldsymbol {D}}_{\mathrm {x} }} are the task-space stiffness and damping matrices, and Λ ^ {\displaystyle {\hat {\boldsymbol {\Lambda }}}} , μ ^ {\displaystyle {\hat {\boldsymbol {\mu }}}} , γ ^ {\displaystyle {\hat {\boldsymbol {\gamma }}}} , and η ^ {\displaystyle {\hat {\boldsymbol {\eta }}}} are the internal model of the corresponding mechanical terms.