We report the control and simulation of a planar cable-driven parallel robot with four cables. The application of the robot is to fully control the lower limb, shank, for gait rehabilitation. The main challenge in control of the cable-driven parallel robot is to avoid negative cable tensions during dynamic motions. For this purpose a redundant robot with capability to exert a general wrench on the target limb with only positive cable tensions for all the poses of the limb near to the trajectory in the gait cycle is used. It is explained that the proposed robot can control both rotational and translational degree of freedom of the shank without slack cable conditions in the gait cycle. Then the dynamic model and control of the robot is proposed with a strategy to choose the forces of cables in order to avoid the negative tension. Examples of simulation are presented to demonstrate the capability of the robot in efficiently tracking the trajectory.