How do position encoders improve gimbal performance?

To rotate a gimbal to a desired orientation both reliably and accurately, precise angle feedback is required. Position encoders are high-precision sensors that measure the angular position of a gimbal's axes (pan, tilt, and roll), providing real-time feedback to a gimbal's control system.

Traditionally, some rotating axes have relied on low-precision sensors like resolvers or potentiometers for angle reporting. Position encoders provide significantly higher measurement accuracy, making them ideal for the most demanding gimbal applications. Encoders are immune to mechanical errors such as backlash and often feature non-contact designs, where the rotating component never touches the stationary part. This eliminates wear and friction which are common issues in mechanical systems.

Factors such as size, weight, measurement performance, and environmental stability are crucial considerations when designing gimbals. Renishaw offers a range of encoder solutions to meet these requirements.

• Optical encoders provide excellent angle measurement performance, with fine resolution, high accuracy and superior repeatability.
• Inductive encoders offer robust metrology performance from a lightweight low-profile package.
• Magnetic encoders deliver reliable angle measurement, even in harsh environments, with the lowest weight and smallest form factor.

This application note explores how encoders are used in common gimbal applications; radar systems, telescopes, camera mounts, and UAV (Unmanned Aerial Vehicle) imaging.

This position feedback is essential for the control system to achieve accurate alignment and positioning of the optical elements, enabling focal length and field-of-view adjustments.

Position encoders are also mounted to the telescope's tilt (right ascension) and pan (declination) axes for tracking and pointing. They continuously measure the telescope's position and movement as it tracks celestial objects across the sky, ensuring accurate pointing and compensation for the Earth's rotation.

Example application

In other camera mount systems, ATOM™ miniature optical incremental encoders were chosen for their compact size, signal stability, and reliability.

Combined with data from an Inertial Measurement Unit (IMU), the feedback from the encoder gives a complete picture of the platform's motion and position relative to Earth. The control system uses this data to drive magnetic voice coil actuators, applying controlled moments and linear forces to the gimbal. This ensures the stabilisation system maintains a precise line of sight with a geographic position critical for imaging and targeting applications.

Inductive rotary encoders, such as Renishaw's ASTRiA™ series, are well suited to these applications, offering robust, lightweight, and compact position feedback with low power consumption.

Example application

In a gimbal application with a UAV camera system, RESOLUTE ETR encoders with RESA rings, 26-bit resolution, and BiSS® C serial communication were selected. The RESOLUTE ETR encoder delivers high-accuracy position feedback down to -40° C, ensuring reliable operation at high altitudes where temperatures are low - a performance independently verified by the customer through rigorous testing. Three RESOLUTE rotary encoders were installed on the pitch, yaw, and roll axes, achieving an accuracy of under 10 arc seconds. Renishaw's absolute encoder system provides the precision required for demanding UAV imaging and targeting tasks.

Position encoders are integral to the functionality and precision of gimbal systems across various applications, including radar systems, optical telescopes, and imaging platforms. By delivering accurate angular position feedback, encoders enable precise control and stabilisation of payloads in gimbal applications, ensuring reliability and high performance in demanding environments.