Encoder Sensors in Medical Devices – Surgical Robots, Radiation Therapy and Precise Lasers

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Encoder sensors are a necessity in advanced medical equipment, where precise control over machine movements, rotations and positioning is required.

Celera Motion's MicroE encoders have helped their customers develop a wide range of medical solutions using their encoder sensors. Read on to find out more about the projects in robotic surgery, radiation therapy and cataract surgery that Celera Motion have been involved in.

Surgical Robotic Arm

The Challenge

The customer required precision rotary axis control in the lowest profile form factor for multiple sequential robot arm joints.

Significant additional requirements included minimal signal cabling to keep the overall arm size as small as possible and minimal movement at start-up to report absolute position.

The Solution

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

A standard 40 micron pitch incremental counting track, combined with a reference track where each index is uniquely spaced was employed by MMA grating technology. Just a small movement at start-up helps to detect multiple index marks, and the measured spacing is compared to a lookup table in firmware in order to determine the absolute position.

The Benefit

To ensure improved rotational accuracy, the output of the two encoders is averaged and this is followed by determining the absolute position at start-up with minimal axial rotation.

Using a BiSS serial communication protocol, each successive robot joint can be connected in a daisy-chain arrangement, instead of having dedicated bus cables for each axis, which together with the small size of the ChipEncoder helps to decrease the overall size of each individual joint.

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

Radiation Therapy

The Challenge

Radiotherapy cancer treatments can be delivered in a more effective manner with high resolution, high speed beam collimation. It is important to shape the beam to help deliver more focused treatment of tumors at destinations within the body.

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

The Solution

Starting 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 very small 1.5" housing.

Celera Motion worked in parallel with the customer to develop a custom linear scale and interface card that enabled the customer to obtain position data from two sets of seven ChipEncoder™Series encoders out of a single connector and cable. A fully redundant feedback system was used to design each of the axes.

The Benefit

A complete, highly integrated motion and beam collimation mechatronic assembly was produced through the close collaboration between the Celera Motion team and the customer.

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

Celera Motion integrated and tested the entire assembly and then delivered it to the customer ready to install in their new radiation therapy system.

Laser Cataract Surgery

The Challenge

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

The customer required a reliable, small, and field proven optical encoder to implement this new technology; this encoder should have sufficient accuracy and resolution to focus the 3-micron spot size in exactly the right location.

The Solution

Celera Motion worked extensively with the customer to help narrow down their requirements and eventually selected the MicroE 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 perfect choice for the compact working area in the customer’s new laser surgery system, due to its industry leading small sensor size and wide alignment tolerances.

The Benefit

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

Celera Motion

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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