Encoder Sensors for Surgical Robots

Encoder sensors are a requirement in sophisticated medical equipment, where it is necessary to have precise control over machine movements, rotations, and positioning.

With Celera Motion's MicroE encoders, customers were able to develop a wide variety of medical solutions using their encoder sensors. This article briefs about the projects in robotic surgery, radiation therapy, and cataract surgery that Celera Motion has been a part of.

Surgical Robotic Arm

The Challenge

Precision rotary axis control in the lowest profile form factor for several sequential robot arm joints was required by the customer. Considerable additional requirements included minimal signal cabling to ensure that the overall arm size is kept as small as possible and that minimal movement at start-up reports absolute position.

The Solution

A series of custom-sized PCB-based encoder modules with FPGA control and BiSS communication interfaces were developed by Celera Motion. Each of these modules includes two standard ChipEncoder™ readheads and a Micro Motion Absolute™ (MMA) rotary grating disk.

A standard 40-micron pitch incremental counting track, in combination with a reference track where each index is uniquely spaced, was used by MMA grating technology. Just a slight movement at start-up makes it possible to detect multiple index marks, and the measured spacing is compared to a lookup table in firmware so as to establish the absolute position.

The Benefit

In order to ensure improved rotational accuracy, the output of the two encoders is averaged and the absolute position at start-up was then determined with minimal axial rotation.

A BiSS serial communication protocol is used to connect each successive robot joint in a daisy-chain arrangement, rather than having dedicated bus cables for each axis, which along with the small size of the ChipEncoder helps to reduce the overall size of each individual joint.

High robot responsiveness to the operator’s commands is ensured by high-speed serial communication (32 MHz clock, 1 µsec update rate).

Radiation Therapy

The Challenge

Radiotherapy cancer treatments can be carried out more efficiently with high speed, high-resolution beam collimation. It is imperative to shape the beam so that more focused treatment of tumors can be delivered at destinations within the body.

The customer achieved the requisite beam shaping by making use of a new system that is capable of highly precise motion of seven parallel axes in a space that is merely 1.5" wide. This solution required the addition of a linear motor and two encoders per for safety and redundancy.

The Solution

Beginning with the customer’s payload and move profile, Celera Motion developed a set of custom Javelin™ Series linear motor assemblies that fit seven axes in the customer’s compact 1.5" housing.

Celera Motion worked in parallel with the customer to design a custom linear scale and interface card that allowed the customer to acquire position data from two sets of seven ChipEncoder™Series encoders out of one connector and cable. Each of the axes was designed using a fully redundant feedback system.

The Benefit

The close association between the Celera Motion team and the customer resulted in a complete, highly integrated motion and beam collimation mechatronic assembly.

The resulting design was highly optimized for size and weight, which reduced the payload to be carried by the rest of the system and also helped to reduce the size of the doctor manipulated end, thus improving the overall comfort of the patients during the procedure.

After integrating and testing the entire assembly, Celera Motion delivered it to the customer ready to install in their new radiation therapy system.

Laser Cataract Surgery

The Challenge

The most commonly performed surgical procedure in the world is cataract surgery. Femtosecond laser-assisted technology has been introduced by recent advancements as a possible way to enhance clinical outcomes, safety and accuracy.

The customer was in need of a reliable, small and field-proven optical encoder to implement this latest technology; this encoder should have adequate resolution and accuracy to focus the 3-micron spot size in precisely the right location.

The Solution

Celera Motion worked extensively with the customer to help narrow down their need and ultimately selected the Celera Motions’s Mercury 1500 Series encoder and small linear glass scales. Mercury Model M1500H is an RS-422 compatible with a miniature 5x2 micro-connector.

It has become the ideal choice for the compact working area in the customer’s new laser surgery system, thanks to its small sensor size and wide alignment tolerances which are among the best in the industry.

The Benefit

After receiving its FDA approval, the customer's new laser surgery system has become one of the most widely used solutions for laser cataract surgery on the market today, offering new levels of safety and accuracy and delivering excellent patient results.

This information has been sourced, reviewed and adapted from materials provided by Celera Motion.

For more information on this source, please visit Celera Motion


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