Design I

The first prototype consisted of a four bar linkage that opened and closed the jaws of a cam cleat. As shown in Figure 1, the design is meant to be motorized to enable a powered gripper for the impaired user. A tie rod was going to be used to to attach a servo motor horn to the input link (L3).

Figure 1: Linkage Mechanism for Design I Prototype

In the design process of this mechanism, it was decided from the requirements that a 100 Newton clamping force on the rope would be enough to fully drive the mechanism to the toggle position. Using this assumption, we could use the mechanical advantage calculation described earlier in the 

Figure 2: Free body diagram of rope force interaction with one half of the cam cleat

Figure 2:The working range of the mechanism where the rope will likely be compressed is shown in red. All plots are made with respect to the angle of L2. Top Left: Relative angular velocities of L3 and L4 if L2 is moving at 1 rad/s.  Top Right: Mechanical Advantage spikes to infinity near the toggle position. Bottom Left: Tie rod force input required on L3 to generate required 100 N output compression force on the rope. Bottom Right: Torque required by the motor

Design II

Even though the torque output required by the motor is higher in the new design, it is still well within the maximum output of the servo motor.