Common Misconceptions About Robotic Grippers
When sizing your gripper, the two most important factors are force and torque. Gripper force requirements depend on the jaw’s style, along with the part’s weight from gravity and acceleration. Jaw torque, the other critical sizing factor, has two sources: the torque generated by the gripper on itself, and the torque generated by the part’s acceleration and weight.
Before sizing your gripper based on these two parameters, it’s important to dispel some common misconceptions about these robotic components. Here’s a quick rundown of what they are:
Only One Jaw Supplies Gripper Force
When selecting robotic grippers, engineers tend to consider the force both grippers apply to the part. However, this value only tells half the story.
The first misconception is this idea that a part experiences the combined forces from both jaws. In other words, 10 pounds of force per jaw applies 20 pounds of force to a part. In reality, however, the part only experiences 10 pounds of force. Why? The force provided by one jaw must counteract the force provided by the other.
Torque, Not Slide Efficiency, Is Important for Sizing
Charts that display jaw length versus force indicate a gripper’s slide efficiency, or the amount of actual force provided by the gripper versus the theoretical force provided by the pneumatic or electrical system.
In most cases, however, efficiency has little to do with sizing the gripper because the slide is equally efficient in both directions. If the part pushes back on the jaw due to weight or acceleration, the slide will be just as efficient in transmitting the part’s force to the gripper as it is in transmitting the gripper’s force to the part.
Slide efficiency typically only matters when the jaws provide a friction grip — i.e., when the jaws squeeze a part to hold it in place. Slide efficiency charts provide only a rough measurement of a slide’s torque capability, so while these charts are helpful, it’s better to ask your gripper manufacturer for torque specifications for jaw pitch yaw and roll.
To learn more about these and other common gripper misconceptions, check out our e-book.