Introduction

In an early startup venture (prior to any investor funding), I designed grippers to be mounted on a Dobot CR3 collaborative robot for extremely low-budget tech demonstrations. Simulation videos were hard to sell, so physical demonstrations were required. The grippers were used to showcase the accuracy of the software team's computer vision algorithms as well as the advantage of compliant parts to compensate for any inaccuracies. Various fingertip designs and textures were tested to explore picking reliability.

Design

The gripper used a double rack and pinion mechanism driven by a single servo motor. Each fingertip was attached to one rack, so the rotation of the pinion would cause them to move in opposite directions.

Types

There were many iterations of the parallel gripper, and different fingertips were adopted for different applications. The initial design used the most basic rigid fingertips, which could grasp reasonably well if the target was square and hard. For softer objects, a compliant material was needed such as rubber.

Among those designs was a vacuum gripper, which was very reliable for picking up solid flat objects such as boxes. However, it was not able to maintain a vacuum seal on dusty surface and very compliant materials such as plastic wrap.

Challenges

Due to the lack of force control in the gripper, compliant materials were more favourable. The natural springiness applied a non-damaging amount of gripping force while maintaining pressure on the objects. This is particularly important when picking objects that vary in size and geometry, as the gripper can't know when the object has been picked.