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Motion Control for Medical Devices


Today, motion control has moved well beyond its traditional uses in manufacturing. Medical devices, automotive, robotics and personal tools like smartphones and tablets have all benefited from motion control subsystems with lower cost, lower power, and smaller footprints and packaging due to better miniaturization. The key to harnessing the complexity of the electronics and embedded software for motion control is understanding and managing the accuracy and precision needed for the positioning, rate of movement and force measurements. These key system level needs will drive many of the system requirements and sensor specifications

Here are three examples of motion control projects we’ve done that demanded high accuracy and/or precision.

Bone Drill

We developed a special bone drill that allows a surgeon to see and control precise real-time depth sensing measurements on a touch screen display. Using internal sensor technology, special lighting and auto-stop motion control, the bone drill monitors drill bit tip location and depth. It is accurate to at least a quarter of a millimeter. It stops the drill automatically when it passes out of the bone before it can damage delicate soft tissue. The drill has a distance sensor and a force sensor for very accurate measurements. Some very complicated algorithms use information to accurately determine when it breaks through the bone and then stops the drill before it tears up the other tissue. This type of drill ultimately means less surgical time and better outcomes for the patient.

Motion Control in a Rehabilitation Device

Voler developed this rehabilitation device for a startup who needed it designed and developed at a fairly low cost but to still be FDA compliant. We achieved this by combining off-the-shelf modules that had a low development cost with custom electronic components that gave the design the flexibility it required. The result was a device that enabled an innovative treatment for rehabilitating stroke patients that facilitated complex exercise to improve a patient’s grasp and their ability to move their wrists and ankles.

When moving a person’s hand, the machine first determines their range of motion. Going beyond that range of motion can be very painful, or cause injury. Making those measurements, they’re not highly precise. If you’re off by one degree, it doesn’t matter. But if the motion is not very smooth and accurate, it’s a very serious problem. This uses absolute measurements to control the movement.

Complex Motion Control Software in Surgical Table

You would probably be surprised at how much software would be needed to enable the complex motions that the latest surgical tables need to execute depending upon the patient, the operation, and the physician’s needs. We recently developed motion control software for a new surgical table that had to support 6 axes of unique but coordinated movement. The table supports spine surgeries so it needs to hinge in the middle, but there couldn’t be any metal in the middle. In effect, the two separate pieces are independently controlled by motors. We had to develop and code algorithms that would predict the position of both halves of the table and not allow them to drift closer or farther apart than a tight tolerance or the table would literally tear itself apart. The design was complicated by the need to control six separate motors, three on each half of the table, and to coordinate their movements to facilitate a surgical procedure. Because of the multiple motors, the accuracy and precision measurements were very complicated.

Accuracy vs. Precision

Accuracy and precision for the positioning, rate of movement and force measurements are critical for many motion control systems. Accuracy includes several factors. One is, the resolution of your measurement. Another is the noise that’s in the system, that will determine how precise or repeatable you can get. Other very important factors in both precision and accuracy are temperature drift, linearity, and offset. Both of these are factors in precision and accuracy. The difference between precision and accuracy is that accuracy refers to position compared to a standard, such as the standard for one meter. To be accurate, it is necessary to calibrate to a standard. For more information on the impact of these see https://www.volersystems.com/blog/design-tips/122-data-acquisition-basics

About Voler Systems

We understand motion control systems. We specialize in electronics and software, and in particular we are good at interfaces for sensors of all types, including cameras, as well as motion control, wireless and medical devices. We see an increasing trend toward combining sensors and wireless so that measurements and observations can be made remotely without requiring a cable.

We provide full-service R&D consulting from concept and design to production of devices for human use and instruments. Our multidisciplinary team knows the regulatory process and procedures and delivers high-quality products on time and on budget.

Voler Systems can design to the strict requirements for federal and European design that include:

  • IEC60601 – medical device requirements
  • IEC62304 – medical device software
  • FDA 21CFR 820.30 Quality System Regulation – Design control
  • ISO 13485:2003 quality management systems – Quality System Regulations
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