The robotic mechanism may be used to position a tissue retractor assembly relative to body tissue. Once the tissue retractor assembly has been positioned relative to the body tissue by the robotic mechanism, the robotic mechanism effects operation of the tissue retractor assembly from a contracted condition to an expanded condition to move body tissue. This movement of body tissue may advantageously create a space for the performance of a surgical procedure by the robotic mechanism. Embodiments may facilitate the insertion of one or more surgical instruments through a cannula to a working space created by expansion of a balloon or bladder from the contracted condition to the expanded condition. As the bladder or balloon expands, portions of body tissue are deflected under the influence of force applied to the body tissue by the bladder or balloon.
