32 n MACHINE-BUILDING April 2025 www.drivesncontrols.com How to specify motion controls for gantry applications Gantries are used across a range of machine automation applications, from 3D printing to CNC machine tools. They move tools or platforms through three-dimensional space with a high degree of precision – whether controlling a pipette on a liquid-handling system, or a suction cup on a pick-and-place application. Because precision is essential, the gantry’s motion control system is critical. Gantries operate to pre-programmed proles, and rely on a motion controllers to coordinate their three axes of travel (X, Y and Z). Each axis typically involves a motor with a sensor for position feedback, controlled locally by a drive. Choosing a gantry’s motor control technology depends on the levels of torque and precision required by the application. For larger machines, AC servomotors are often used, with rotary motion being converted into linear motion by belts, pulleys or leadscrews. For smaller machines – typically those requiring power ratings up to around 500W – brushless DC (BLDC) motors are increasingly used to optimise control precision. Linear BLDC designs can also be used. This technology also enables high-speed operation, maximising the throughput of pick-and-place applications, for example, and accelerating and decelerating rapidly without losing position. For smaller applications, stepper motors are an alternative, ensuring repeatable accuracy by providing discrete steps of motion. Traditional DC motors can also be applied if cost is critical. For applications such as laser cutting or 3D printing, where precision is essential, the control system must support smooth, accurate motion. Crucial to achieving this are the motion proles for each axis, including acceleration and deceleration ramps, which are commanded by drives. A typical requirement for gantry control is an S-curve prole, which adds stability as well as reducing mechanical stress. Shaped like the letter, S-curves usually involve seven speed prole segments to achieve smooth acceleration and deceleration. The initial motion phase includes gradual acceleration up to a set rate, where a constant speed is maintained, before decelerating gradually. These controlled changes in speed reduce jerks, oscillations and sudden stops, enhancing motion smoothness. Feedforward Another important technique is acceleration feedforward. If it is left unmanaged, inertia can result in delays or position errors, causing oscillations or overshoot that can impact accuracy and smoothness of motion. Acceleration feedforward mitigates this by improving the system’s response. To achieve this, the drive sends an additional command to the motor based on the expected acceleration, and this input enables the motor to achieve the desired acceleration from the outset. As a result, this technique reduces lag and ensures that end-eectors reach their target positions accurately and smoothly. Motion error detection is also important to ensure accuracy by identifying, in real time, unwanted deviations in the motion path or prole, and enabling corrective action. Vibration, for example, can cause motion path deviation sucient to impact precision. A suitable intelligent drive, combined with a feedback device that monitors deviation, can correct the error. When specifying gantry control systems, wider considerations must also be taken into account, such as reliability requirements, thermal management, and demands placed on the system. Fundamental design considerations such as power supplies, form factors and installation, are also important, especially for machines that use embedded electronics. As a result of the complexities involved when developing 3D gantry systems, it’s often useful to talk to a specialist. Dedicated motion engineers can specify the most suitable system for an application. Engaging early with a motion experts can not only save time during development, but also help to optimise the ultimate performance of the application. n Gantries are a vital component for a variety of machine applications, from 3D printing to CNC machine tools. Gerard Bush, engineer at motion specialist Inmoco, discusses how to specify motion systems for gantry applications. Gantry control involves the management of a mechanism that moves along X, Y and Z axes
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