Top motor trends in the continuing evolution of robots
19 November 2020
Robots depend on miniature motors for their motion, so evolution within robotics relies on technological advances in motor design. Dave Beckstoffer of Portescap highlights the key trends in miniature motor development for robots.
The use of robots proliferates in applications which span from surgical suites to the battlefield. While robots become more specialised, a commonality is the corresponding development of miniature motors on which robots depend for their motion. Advances in the development of robots therefore must be matched by advances in the motors which drive them, so let’s look at the key trends in miniature motor technology.
Mobility and footprint
Robot design, particularly for cobots, has to enable mobility and compactness. To effectively match the capability of a human hand, the motors that power them require high power density in a small, lightweight package. A higher power density in a smaller and lighter motor details the advantage of brushless DC motors (BLDC) compared to conventional DC designs. Slotless BLDC motors, combined with efficient planetary gearboxes, achieve this combination and can be integrated into typical robot formats to suit the footprint constraint.
Key capabilities of robots involved in tasks such as manufacturing automation are speed and precision. In a pick and place robotic application, coreless DC motors and disc magnet stepper motors are well suited as a result of their extremely low inertia, enabling repeated and rapid changes in acceleration and deceleration. Similarly, applications requiring dynamic yet smooth control, such as camera systems, benefit from the elimination of cogging or detent torque, making slotless BLDC an excellent motor choice.
The mobility of many robotic applications depends on battery power, which makes energy efficiency a critical factor. Ironless brush DC motors can achieve up to 90% efficiency and are selected where long robotic running time is required. For high torque-low speed applications, it is also key to ensure that the gearbox is efficient and matched to the motor.
Robustness and extended life
A significant advantage of robots is that they can be used in environments and under conditions which humans cannot, or ideally would not, sustain. Surveillance and patrol of industrial pipelines, high voltage electrical networks or even theatres of war mean that robots are put into motion by miniature motors protected against the most arduous conditions to ensure ongoing operation.
Protection against extremes of temperature and pressure are required for robotic applications such as surgical robots undergoing autoclave sterilisation. The robot’s motor depends on a high degree of resilience; setting components within a thermoset epoxy maximises robustness and extends its lifecycle.
Safety and productivity
When it comes to robots, safety and productivity are inextricably linked. Inaccurate control can cause physical harm, whether in a surgical setting or on the factory floor, while machine stoppage as a result of a safety breach can mean damage to product and downtime. Robots will therefore continue to rely on high accuracy feedback devices to ensure their protection and that of the environment around them.
High-resolution encoders enable accurate and fast motor control in applications which demand combinations of control and high speed. On a robotic welding system, high resolution feedback achieved within a robust package is crucial to ensure precise robotic motion.
Autonomy and multi-axis control
A key aspect of robotic development is autonomy and machine learning. An example of this is found in autonomous vehicles and surveillance robotics. LiDAR (light imaging, detection, and ranging) technology captures 3D imagery of the environment for self-guided navigation, scanning at very high refresh rates and with high-resolution feedback for speed and precision of control. LiDAR based mirror systems are increasingly driven by brushless slotless mini motors which combine lower heat dissipation with high efficiency.
Complex robotic applications can require multiple axis control, such as surgical robots, which demand close coordination. To achieve this, sensors equipped with serial interface communication can provide absolute position information with a typical resolution of 14 bits and accuracy in the range of one mechanical degree. An important consideration of multi-axis applications is to minimise footprint. The inherent compactness of miniature motors can be combined with serial interface communication protocols which allow daisy chain encoder connections to reduce wiring.
Customisation of miniature motors in robotic control is a growing trend. Tailored designs ensure specific demands on accuracy, efficiency and footprint are met. Miniature motor manufacturers will be increasingly tasked with assessing the load points of a design to develop highly compact, lightweight motors which balance torque and speed performances perfectly to the application’s needs.
Portescap continues to specialise in the development of miniature motors for robotic applications, along with matched gearbox and encoder technologies for low power, small footprint specifications.
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