Why Frameless Motors Are at the Forefront of the Surgical Robotic Revolution

Recent advancements in robotics have greatly enhanced surgical procedures, enabling minimally invasive techniques that offer patients the promise of better outcomes with fewer complications and shorter recovery times. Much of this innovation is driven by advanced motion control systems and constant component miniaturization.

Specifically, surgical robots depend upon precise control of the motion of joint and end-effector appendages during procedures. That means the internal motorized systems must deliver seamless, steady, accurate and responsive motion within compact and lightweight envelopes. While these motion systems can take many different form factors, one that has emerged to support surgical robotics is the frameless motor.

What Is a Frameless Motor?

Frameless motors have become an optimum solution for control axes that demand precise servo-driven movement, including surgical robot end effectors and robotic joints. These motors are stripped down to essential components — the stator and rotor — and forego the traditional frame, bearings, and shafts. This simple construction allows designers to mount frameless motors directly onto the robot joint or end-effector assembly to transmit the needed torque. Their working principle is as follows:

The outer stator is composed of wound copper coils in a circular arrangement, and the inner rotor carries an array of permanent magnets. When the stator is energized, its magnetic field interacts with the rotor’s magnets and causes the motor to rotate. The motor’s torque output can be controlled by altering the current that travels through the stator. Frameless motors can be customized with various options to help achieve the application’s required performance needs.

How Do Frameless Motors Benefit Surgical Robots?

Frameless motors are revolutionizing the field of surgical robotics, offering a variety of benefits that enhance their performance and safety. Their high torque and efficiency ensure smooth and accurate movements, enabling surgeons to perform intricate tasks with unparalleled precision. Thanks to the simple structure and operating principle of frameless motors, they offer intrinsic advantages over conventional motors, such as:

• Space and weight savings. By not including the surrounding frame, these motors have inherently small footprints. They also have fewer parts and do not require power transmission components or integrated bearings. Their compact design allows for precise control and maneuverability within confined spaces. When compared to traditional motors, frameless motors are an attractive choice to reduce a system’s size and weight.

• High torque-to-inertia ratio. Frameless motors exhibit fast response times, requiring less torque to accelerate.

• Stiffness and rigidity. Without the power transmission component and shaft attachments typical of conventional motors, frameless motors provide exceptional torsional stiffness and enhance overall system stability.

• Higher efficiency. Frameless motors do not suffer from friction or eddy currents that occur with their framed counterparts, and their light weight helps lower power consumption and, in turn, produce less heat. In addition, their high torque output relative to their small size results in greater torque density. Frameless motors also do not require transmission components that often present mechanical losses that can otherwise lower efficiency.

• Heat dissipation. The absence of a frame allows the motor to dissipate more heat. This ensures the motor performs longer during demanding surgical procedures.

• Other benefits. Frameless motors have minimal parts and require few accompanying components that may be subjected to wear and tear, which helps reduce maintenance requirements. They also operate quietly — an important consideration in surgical equipment.

Portescap, for example, has decades of experience supporting surgical applications, including capabilities to design and manufacture frameless motors. Typical characteristics include diameters of up to 127 mm, nominal torque of 1,500 mNm, up to 20,000 rpm, and power up to 350W. Taken together, these diameters and performance capabilities make frameless motors appropriate for use in robotic systems ranging from small endoscopic devices to larger orthopedic systems.

Optimization of Frameless Motors to Satisfy a System’s Exact Specifications

Along with these benefits, frameless motors are highly customizable and allow designers to meet their torque, speed, feedback, connectivity, space limitations or other special requirements. The motors can be designed with large inner and outer diameters, allowing to thread cables and tubes through the center of the motor.

Regarding magnet material, rare-earth Neodymium magnets are typically used in frameless motors; however, motor suppliers may provide other magnet materials upon request for special requirements. While the construction and direct mounting characteristics of frameless motors offer inherent motion accuracy, they can also be outfitted with encoders or other feedback devices to further enhance their precision as they respond in real time to the surgeon’s commands. Remember to ask your frameless motor supplier about cooling options.

Whether your frameless motor requires special windings, shafts, connectors, or any other modification, suppliers such as Portescap can support a project with a range of miniature motors, gearheads, feedback devices, and controllers well-suited for stringent medical industry requirements. Leveraging a supplier’s application engineering expertise and collaborative approach enables the development and optimization of frameless motors for your surgical robot system’s exact specifications.

Is a Frameless Motor Right for My Surgical Robot?

Determining whether a frameless motor is right for your application can be tricky. A few critical parameters to start any design include:

• Speed-torque requirements, power needs, and the available physical space for the motion elements.

• The required motion profile of the robotic device, considering the smoothness, responsiveness, and precision of its movements.

• The duty cycle to establish the peak and continuous torque necessary for the application.

• Integration capability to ensure precise motor mounting within the assembly, avoiding misalignments and ensuring proper balance.

In addition, applications requiring high torque output could lead to heating issues, so be sure to discuss an optimum cooling method with your motor supplier.

Careful consideration of these factors is necessary to decide which motion control technology is best suited for your surgical robot.

Weigh Your Considerations with a Miniature Motor Expert

With the never-ending advancement in surgical robotics, it is important to recognize the difficult balance between improving performance, commercial value, integration, and compatibility challenges. Select an experienced and flexible partner to support you with these challenges throughout the entire development process.

Portescap, for example, offers frameless motors that are well-suited for the stringent motion requirements of joints and end effectors used in surgical robots. The company offers both standard and fully customized motion control solutions. Engineers can advise and support surgical robot applications and help explore available options.

This article was written by Antonio Herrera, Global Strategic Marketing – Surgical and Industrial Robotics, Portescap, West Chester, PA. For more information visit here .

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