90° Pneumatic Actuator Technical Guide

Precision rotation mechanisms and control systems

1. Mechanical Design Fundamentals

Rack-and-Pinion Mechanism

The actuator contains a piston (rack) that converts linear air pressure into rotational motion via meshed pinions on the output shaft. The rack's straight-line movement drives the pinion to rotate exactly 90°, with the gear ratio ensuring consistent angular displacement.

Example: 50mm stroke rack with 50mm diameter pinion achieves precise 90° rotation.

Scotch Yoke Design

A yoke attached to the piston converts linear motion to rotation via a sliding pin on the output shaft. The yoke's geometry is machined to constrain rotation to 90°, using stops or mechanical limits to prevent over-travel.

2. Pneumatic Control Systems

Solenoid Valve Precision

5/2-way solenoid valves direct air to either side of the piston, initiating extension/retraction. By controlling air pressure and flow (via needle valves), the actuator's speed and acceleration are regulated to avoid overshoot.

Example: Limiting airflow to 100 L/min ensures smooth 90° rotation in 150ms.

Pressure Regulation

Consistent air pressure (6 bar standard) is critical for repeatable torque. Pressure regulators maintain stable force, preventing rotational inconsistencies caused by supply fluctuations (±2% variation).

3. Mechanical Limit Stops

Internal Stops

Machined metal stops within the actuator housing physically restrict the output shaft to 90°. Adjustable in some models via shims or set screws (±1° precision).

Example: 0.5mm shim reduces rotation from 90.5° to 90°.

External Stops

In high-precision applications, external mechanical stops (bolted brackets) supplement internal limits, providing rigid positioning. Common in valves requiring tight shutoff.

4. Position Feedback Systems

Limit Switches

Magnetic or mechanical switches mounted on the actuator detect when the shaft reaches 0° and 90°, sending electrical signals to the control system.

Analog Positioners

Devices like 4-20mA positioners continuously monitor shaft angle via potentiometers or Hall effect sensors, allowing closed-loop control (±0.5° precision).