Pneumatic Gripper

Overview

A pneumatic parallel-jaw gripper is the workhorse of factory automation. Two Gripper Jaws move in unison toward a common centerline, clamping workpieces with controlled force. The Left Cylinder and Right Cylinder drive the jaws via a Wedge Force Amplifier, an ingenious wedge pair that converts linear thrust into lateral clamping force with 2.5–4× mechanical advantage. The Control Valve switches pressurized air to open or close, while Open Position Sensor and Closed Position Sensor tell the robot controller jaw position.

How it works

Pressurized air (typically 5–6 bar) enters the Port Block. When the Control Valve's solenoid is energized, the Valve Spool shifts, routing pressure to the head-end ports of both cylinders. The Piston Head in each Left Cylinder and Right Cylinder pushes the Piston Rod outward, extending both rods simultaneously.

Each rod is connected to a Left Wedge (or right). The wedges are inclined at 10–20° and push apart as the rods retract; this spreading motion forces the Gripper Jaws inward toward the part. The wedge angle provides mechanical advantage: a 500 N cylinder force becomes 1500–2000 N jaw clamping force. The part is squeezed between the Jaw Liners, replaceable rubber or cork facing that protects delicate surfaces.

When the solenoid is de-energized, the Valve Spring returns the spool to neutral, bleeding both work ports to exhaust. The Return Springs push back, driving the wedges apart and the jaws open. Compressed return springs on the Piston Rod accelerate the jaws to their open position. The Open Position Sensor switch detects this, signaling the robot "jaws open; ready to pick."

Force adjustment and feedback

The Force Adjustment assembly is a pilot relief valve mounted in the pressure line. As the jaws clamp the part, pressure rises. When it reaches the setpoint (adjustable via the Relief Knob), the relief poppet cracks open and bleeds excess pressure to exhaust. This soft-limit prevents damage to fragile parts. For instance, a delicate plastic component might be gripped at 1 bar (100 N total clamping), while a steel forging requires 4 bar (500 N).

The Closed Position Sensor detects when the jaws have closed on the part (no further motion). This "close confirmation" tells the controller that a part is truly present and secure before the arm moves. Absence of this signal triggers an alarm: part missed.

Sizing and selection

Parallel-jaw grippers are sized by stroke (open distance), grip range (min/max part width), and required force. A 50 mm stroke, 0–40 mm grip range, 250 N gripper handles small plastic components. A 100 mm stroke, 0–80 mm range, 1000 N unit grips larger stamped parts or castings. Some designs include compliant jaw pads that absorb impact and accommodate slight part size variation.

Most industrial robots support parallel-jaw grippers via standard tool interfaces (ISO 13849 pneumatic connectors), making gripper swap-out routine during product changeovers.