FEATURE LINEAR MOTION
A PRECISE SOLUTION FOR CONTROLLING
through to semiconductor equipment. This, however, demands a high level of motion control precision to optimise the observation of samples. Operating on the same principle as a three-axis gantry over X, Y, and Z axes, positioning accuracy is measured in microns or even nanometres. The X and Y axes control the movement of the optical system to view specific regions of the sample. But, a relatively small error in positioning can lead to imaging artifacts or missed regions in a scan. The Z-axis, responsible for focusing the image, doesn’t demand the same exacting level of precision due to the microscope system’s depth of field and range of positions where the image remains in focus, yet the need for resolution remains important. To achieve this level of precision, premium
AUTOMATED MICROSCOPES A
utomated microscopy is vital to applications in life sciences and across industry – from blood analysers
To optimise the clarity and detail of image
capture, an automated microscope’s motion control architecture must synchronise an XYZ axis system with optimum precision.
Gerard Bush, engineer at INMOCO, explains the key considerations
coordinating the X and Y axes with the commanded position of the Z axis maximises accuracy over the sample movement area. 3D ‘maps’ that chart the effective focal height of the XY plane can pre-compensate the Z axis position command to resolve deviation or drift in sample form.
grade automated microscopes typically integrate linear direct drive brushless DC motors. While the control electronics of a brushless DC set- up optimises precision, a direct drive coupling minimises the challenges of backlash, friction, and mechanical compliance that can disturb smooth and controlled motion. Piezo motors, which expand or contract when electrically stimulated to generate motion, can also be integrated to achieve high levels of precision and virtually silent operation. For more cost-effective designs, rotary brushless DC motors with a ball screw are an alternative, or even stepper motors.
OPTIMISING PRECISION To drive the motor, high-resolution encoders have helped to improve the performance of automated microscopes. Absolute position encoders are preferred for higher precision and can provide multi-turn feedback, recording both the angular position within a turn and the total number of turns. Incremental position encoders, which provide relative position tracking, are also an option where designs have higher cost demands. Digital serial connection schemes like SSI,
BiSS-C, and EnDat, which are protocols for transferring position data from an encoder to a controller, have further helped optimise precision thanks to advantages such as synchronised or bidirectional communication and cyclic data exchange. Alternatively, sin/cos encoders, based on analogue signals that can transfer back to digital, achieve high resolution feedback with smooth signals less affected by electrical noise. To reach the precision require to coordinate the
XY table of the microscope, high performance, low noise current loops, controlling the torque output of the motors, must be combined with a high- speed servo loop. Responsible for precision positioning, a servo loop speed of at least 10 kHz
46 DESIGN SOLUTIONS APRIL 2025
is recommended as even the lowest error in current control can cause positioning disturbances. The controller should also be located as close to the motor as possible to minimise noise in the current sensing circuitry. In terms of trajectory, automated microscopy motion profiles typically include point-to-point XY moves and constant velocity pattern scans with simultaneous image capture by camera. To synchronise stage movement and image capture, hardware-based position capture uses a compare register to signal an image capture when an exact encoder position is achieved. Systems can specify a single capture at one location or a selection of potentially thousands of capture trigger points. Integrating the synchronisation of focus,
SPECIFYING COMPONENTS Integrated chip-based embedded motion control, provided by specialists such as Performance Motion Devices, is recommended to achieve the desired design characteristics that optimise the precision required for automated microscopy applications. PMD’s Magellan IC motion controllers can be combined with PMD ION compact drives, while the PMD Prodigy Motion Control Board offers a complete control package. INMOCO’s engineers can help specify a
complete motion control architecture, including PMD control electronics, as well linear direct drive brushless DC motors, and encoders.
INMOCO
https://inmoco.co.uk
NEW DIRECT DRIVE LINEAR MOTOR LAUNCHED
Kollmorgen Corporation has added to its IC Ironcore DDL motor family, expanding beyond 230 VAC products with a new capability to support 400/480 VAC-powered applications. The new direct drive linear motor delivers a continuous
force range up to 8,211 N and peak force up to 13,448 N. When powered at higher bus voltages, the motor is inherently capable of delivering its rated force at higher speeds, making it ideal for applications like machine tools, semiconductor manufacturing, battery production and industrial automation that require rapid and precise movement of heavy loads. In environments with a 400 or 480 VAC bus voltage, the IC Ironcore DDL may eliminate the
need for a transformer. In addition, with smaller drives, lighter cables and no transformers, machine builders may be able to use a smaller control cabinet with lower cooling requirements, the company explains. A water-cooling option is available that increases continuous force output by up to 40-60%, potentially allowing specification of a smaller-size motor. Another key benefit of the motor is that it enables OEMs to serve global markets without
significantly redesigning their machines for each region. The IC Ironcore DDL motor joins Kollmorgen’s complete lineup of direct drive linear motors, including the ICD Ironcore Low Profile DDL and the IL Ironless DDL.
Kollmorgen
www.kollmorgen.com
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