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Sterilizable Encoders and BLDC Motors Drive Surgical Hand Tool Advances

September 27, 2021

Sterilizable Encoders and BLDC Motors Drive Surgical Hand Tool Advances


 As handheld surgical tools gain wider adoption, there’s a growing demand for smaller, lightweight devices that can offer more capability and precise motion profiles. When it comes to brushless DC motors (BLDC) commonly used in handheld surgical tools, magnetic encoders provide the high-resolution feedback that makes high-performance drive systems possible, and they offer many benefits. However, not all encoder/feedback technologies are the same.  Here are some situations that call for an encoder as part of a drive system:

Angular position control. A position control system, which is used to precisely rotate the output shaft of a motor from one angle to another, requires tight control and knowledge of the rotor shaft position. Applications involving robotic actuation or fine-tuned tightening control are well-suited for this type of motion profile.

 Velocity control. Within velocity control systems, encoders not only provide shaft position information, they also determine speed and acceleration. Because encoders provide velocity feedback, a control system can achieve a target motion profile.

 Torque control. Typically, accurate field-oriented-control (FOC) systems provide smooth torque over a wide speed range. These control systems require high-fidelity position feedback, and an encoder is the typical solution.

 Safety. Tools requiring safety features for shutdown routines or to protect an operator from a blade or bit can also benefit from the absolute shaft position information an encoder can provide.

 Integration Challenges and Benefits.  An integrated magnetic encoder can often meet the feedback requirements for a drive while remaining within the motor’s maximum outer diameter, sealing all sensing components internal to the motor body and minimizing the axial length growth.

A Hall-effect-based magnetic encoder requires a radially magnetized di-pole magnet attached to the shaft that will be sensed. In a BLDC motor, this is typically the main rotor or output shaft. When positioned parallel to the magnet, an array of Hall-effect sensors on the encoder can detect the angle of this di-pole as it rotates and translates the information into either incremental or absolute position information as required by the application.

 Portescap offers encoders in a small leadless form factor for easy integration into motors. They feature an axially in-line design, with a small, simple sensing magnet that allows motors as small as 0.5 inch in diameter to internally locate the encoder and sensing magnet. The contactless encoders have no optical wheel that can be prone to damage or obfuscation, and the electronics can be sealed and protected against the autoclave environment. These encoders allow designers to achieve both incremental and absolute operation.

 With a proven, integrated BLDC motor and encoder, surgical hand tools can become sophisticated electrical drive systems capable of satisfying the most demanding motion control requirements while also withstanding the rigors inside of an autoclave.

 For more information about BLDC motor and sterilizable encoder integration, visit our encoders page.