24 n MOTION CONTROL April 2026 www.drivesncontrols.com Motion matters: designing a motion control system The basic task of any motion control system is to manage the movement of a load. However, for many applications, the crucial element is to achieve this with precision and reliability. Motion control is needed across a diverse range of sectors, from manufacturing to health care, but with compact systems, typically generating less than 1kW of power, the need for precision is at its highest. The smaller the scale, the higher the level of accuracy, stability, and fine control that’s required – think of manoeuvring a robotic arm during a complex procedure, compared to controlling a crane at a port. Within this realm, we’re talking about applications such as surgical tools that need to operate with micrometre precision inside the human body, or extremely lightweight devices, such as those involved in aerospace or space exploration. Ideal motor designs for these compact motion systems include brushed and brushless (BLDC) DC motors, preferred because of their small size and relatively high torque generation. Open-loop control While a motor, or motors, do the actual work, controlling their motion is vital. The most basic principle is open-loop control, where the motor moves at a certain acceleration, speed, deceleration and position, based on the commands it is given, and without checking if it has achieved the desired result. Open-loop control is used for applications that are inherently stable, meaning the system’s response is usually known because interference is limited, or varying conditions will not affect the system’s operation. This could involve applications such as fans for cooling electronic devices, where the airflow requirements are approximate and precise levels are not critical, or conveyors with generally constant loads, where the torque requirement does not vary significantly and maintaining approximate speed is sufficient. In an open-loop system, the motor operates on the applied voltage, with no feedback to verify how fast or how far it has moved, relying instead on predictable loads and mechanical devices to stop the motion. To achieve this, a compact DC motor can operate directly from the voltage supply, sized accordingly and with current limits. For open-loop applications using a BLDC motor – which may be selected to achieve higher speeds or torque levels, or longer service lives – the design always needs a controller to enable electronic commutation, the switching of the phases to make the motor spin. Closed-loop control To optimise precision and accuracy, closedloop control techniques are needed. Closing the loop means monitoring the output variable using sensors to provide feedback data. This information is then used by the control device to modulate motion continually according to parameters such as torque, speed and acceleration. A motor controller is needed to manage these parameters, acting on information provided by a sensor such as an encoder, which detects movement of the motor shaft or another moving part of the motion system. The encoder uses sensors that generate electrical signals, which the controller interprets to determine angle, direction and speed. Ultimately, the control of an application is always rooted in torque control, which is necessary to set mass into motion and manage acceleration and deceleration, including tasks such as lifting, lowering or holding objects in tension. Consequently, Compact motion control systems are essential to applications ranging from surgical robots to drones. While their design is based on the laws of motion, perfecting it is an iterative process. Motion engineering expertise is key to fast and effective development. maxon engineer Ronak Samani discusses the process of designing motion control systems. When designing motion control systems it is important to ensure that any design issues are identified and resolved early in the process
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