2009

Magnetic Rotary Encoders Aid Remote Control Vehicle

AB Precision (ABP) prefers to call its Guardian a vehicle (as in MROV - Miniature Remotely Operated Vehicle) rather than a robot. Names aside, the UK-based engineering company’s quadtracked, articulated creation is characterized by dexterity and maneuverability. Its network of ten Renishaw non-contact encoders provide absolute positional feedback to a CPU.

altOn a remote control, at a safe distance from whatever hazard is being dealt with, the operator is able to see alive, rotating graphical representation. When viewed alongside images from four on-board video cameras, Guardian can be operated out of sight and in constricted spaces.

“The vehicle has several moveable parts,” said ABP’s Explosive Ordnance Disposal (EOD) project manager Cindy Barfoot, “including the base, which is a turntable. You can also raise, lower, extend, and retract the main arm, pan and tilt, plus tilt the camera and the onboard weapon, both of which can move independently.” Guardian can climb stairs; reach under or inside vehicles or stand over 2.6 meters high on ‘tip-toe’. It has bi-directional audio capability, traction control, and is sufficiently narrow to move down aircraft and train aisles. A remote control with four video feeds enables Guardian to be used out of sight in confined areas.

The on-board Renishaw rotary encoders detect the positions of all articulated components of the arm and track mechanisms, with the data being sent via a continuous telemetry stream back to the base station control. ABP’s proprietary software prevents further movement if two parts of the vehicle are about to collide.

Renishaw non-contact encoders provide positional feedback. Guardian’s spatial awareness is as advanced as an electro mechanical device can be. The arm carries a various tools, including water jets and x-ray.

Spatial Awareness

“Angular position sensing on the vehicle is achieved using a Renishaw AM512 magnetic sensor,” said Nigel Peter, project engineer for Guardian who is responsible for specifying Renishaw components. We also use RMB20 high-speed rotary magnetic encoders in modular format, which makes them very easy to integrate.”

All of the Renishaw encoders are physically small enough to use where space is at a premium and, at the same time are robust, simple, and reliable; important considerations for a vehicle designed for use in hostile and corrosive environments. “They are also very easy to interface to our data collection PICs,” said Peter, “and because they are non-contact, they provide seamless feedback through 360° of movement.

The AM512 sensors are mounted directly to our controller PCBs, so no wiring is required, reducing cost and increasing reliability.” The result is a remote, ‘intelligent’ limb with full vision, able to carry and use various tools, depending upon the application. In bomb disposal situations, it’s armed with a disruptor- referred to as a weapon - which can fire a jet of very high-pressure water to neutralize a device.

Peter added, “The water jet is used to disable the circuitry controlling an explosive device and renders it safe but without destroying the forensic evidence. We can mount up to four different disruptors or other weapons on a single vehicle. In nuclear, biological or chemical applications, these disruptors can be replaced withhandling devices or sensors.”

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