NavBot 4 "Arm Logic Robot" Updated 12/11/14 Article 4: Caliper Style Gripper in Action - 1
 Here you will find a photo sequence of an actual autonomous run of the Navbot 4 moving a foam block around from one end of the Arena to the other. At the end, Ive posted the actual movie so you can see the caliper gripper in action.
 The robot starts in the center of the arena, the green block on the left is the target, the bin on the right is the destination. This block could also be any thing in the household that needs to be moved about daily, such as pet food, plants, cleaning supplies or errant socks.
 The robot drives to the block, and stops exactly one inch from it using sonar.
 The gripper arm lowers, and the caliper gripper itself opens wide.
 The caliper closes on the block and if the robot senses it in its grip, it continues.
 Lifting the block to the transport position.
 Backing up away from the start position.
 The robot rotates 180 degrees, and travels toward the storage bin.
 Heading toward the bin
 Using sonar once again, the robot sets its distance from the bin and centers itself.
 Lowering the arm into the bin
 Grippers opened, block delivered!
 Arm and gripper put in stowed position.
 Backing up
 Leaving back to the center start position. The entire procedure takes a few minutes.
 Movie 1
 This is a movie I made with my Sony cam, which can record tiny .mpg clips for use on the web. Turn your volume up to hear the robots sounds....

 Conclusions on this type of gripper.

The caliper type gripper works fine for payloads you can pull right up to with the robot, but because the gripper is on the end of a fixed length arm, the distance between target and grip must be fairly precise. Also, without running the motor constantly on the grip, the motor tends to get loose when the processor stops sending the servo pulses and it cannot hold on very tight. Thus the foam blocks. Ideally, each servo should have its own controller to keep the pulses running and keep the arm and gripper set for a specific pressure.

Additional articles in this series:

1. Descriptive components and math of a one armed system

2. More images and videos of the one armed robot in action

3. Caliper Gripper final mechanical details (here)