Motion Control
To enable robotic arms to operate as closely together as possible, you instead need to minimize the axial length. | Kollmorgen appropriate gear set. No matter what ratio is required, this application calls for strain wave technology, also known as “harmonic” gearing. Strain wave gearing provides three indispensable advantages: 1. It enables the most compact axial integration within the joint. 2. It offers relatively high gear ratios— typically ranging from a gear reduction of 30:1 to 320:1—to accelerate/decelerate loads smoothly and position them precisely.
3. It operates with zero backlash to minimize any unwanted movement that could potentially affect the precision of the procedure or induce unnecessary trauma. Match the motor to the gearing and thermal requirements Having specified the appropriate gear technology and ratio, you can select a motor based on the gear ratio, the speed at which the arm must run, and the mass it needs to hold. Thermal rise when operating at typical or maximum load can also be an important consideration, as excessive heat in the tight confines of the joint can damage gearing lubricant, encoder electronics and other components in close proximity. A motor that can deliver full performance at a lower thermal rise is desirable.
Take advantage of the D2L rule As part of your motor specification process, you can further reduce axial length through an often-overlooked principle of motor design referred to as the D2L rule. In robotic joint design, the diameter of the motor is typically of minor concern. To enable robotic arms to operate as closely together as possible, you instead need to minimize the axial length. The D2L rule allows you to trade off a larger diameter for a significantly reduced axial length. Here’s how it works. In the frameless motors used in robotic joints, torque increases or decreases in direct proportion to changes in motor length, but as the square of changes in the moment arm of the motor. In other words, under the D2L rule, doubling the moment arm—and thereby approximately doubling the overall diameter—produces a fourfold increase in torque. Or, more relevant to surgical robot design, doubling the moment arm allows you to reduce the stack height by a factor of four while maintaining the same torque. This is a huge advantage when your design priority is to achieve the most compact axial length. For next-generation surgical robot performance, choose next-generation motors specially designed for robotic applications. This will help you accelerate your development time and deliver surgical robots that allow doctors to operate instruments as close together and as close to parallel as possible. Better tools mean better healthcare— and a healthier surgical robotics business. RR
According to surgeons, the ideal angle of approach for the camera and instruments into the incision site is as parallel and close together as possible. | Kollmorgen 56
November 2022
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