Stepping up to the mark

A medical optical specialist has used advanced miniature motor technology to help develop a headset that lets clinicians more effectively carry out microscopic inspections.

The Varioscope headset, developed by Austrian group Life Optics, uses miniature stepper motors to control magnification and focus for each eye, giving surgeons and dentists a clear 3D view in situations where conventional stereoscopic microscopes or magnifying glasses would be impractical to use.

The increasing sophistication of surgery and dentistry, for example in keyhole procedures, has added to the need for clinical teams to work with the body at a microscopic level while moving, placing extra demands on their skills and strain on their eyes.

According to the development team, stationary microscopes are generally cumbersome and difficult to use in complex micro-medical situations, while magnifying glasses require a fixed distance to be kept from the object under examination. Both also offer a limited field of vision.

In the case of Life Optics’ system, the autofocus functionality — similar to a standard camcorder’s — infinitely variable zoom functions and parallax control all require complex mechanics when used in a portable, head-mounted microscope.

To develop the device, the Austrian company worked with Precistep, a specialist in micro-stepper motors and part of the Faulhaber group of precision engineering companies.

Unlike DC motors, the micro-stepper motors move on per pulse at a step angle dictated by their specific design. This means that the number of digital pulses output always corresponds to a defined rotation and as a result additional linear or angular position sensors are not needed, making the overall drive smaller and lighter.

The Varioscope requires two motors for each eye, with a diameter of 10mm for the focus setting and 8mm for the zoom. In the case of the focus drive, operation is virtually continuous as it must compensate for each movement of the wearer’s head.

There were particular challenges of accuracy of positioning when developing a vision system the size of the Varioscope. Precistep addressed the potential problem of inaccuracies in the system caused by ‘play’ in the mechanics by using a spindle with micro-toothing. With a pitch of 0.2mm and operating in conjunction with the built-in motors, it enables a resolution of 10 microns. Focus and zoom are set backlash free and without jolts at high-resolution, requiring the spindle shafts to be given an additional fine polish — a process usually only undertaken in the design of precision watches. When used in conjunction with a special lubricant, this considerably reduces the level of friction and, as a consequence, the initial breakaway torque. Pre-tensioning on the precision ball bearings by disk springs enables zero-backlash movement at torques of up to 1N.

According to Faulhaber — the range of which is distributed in the UK by Electro Mechanical Systems (EMS) — the Varioscope is a good example of the many positioning applications, even highly dynamic ones, for which stepper motors are practical. The development team said the units can accelerate up to 1,200rpm in one step without overshooting. One of the key elements of their operation is the use of high-quality NdFeB magnets with superior temperature resistance. The motors are said to provide continuous problem-free operation at a 70°C housing temperature for several days. During that period the coil could in practice reach a temperature of 120°C and the magnet 100°C without compromising service life or performance, it is claimed.

Other advantages of the motors include the ability to perform to maximum precision if out of service for a long period (performance verified after seven years of non-operation) and a 3V operating voltage.

The project partners say the end result of the application allows complex procedures to be carried out more effectively and reduces eye strain for clinicians.

The basic Varioscope version lets users move freely around a working distance of 300 to 600mm. The foot-operated zoom enables infinitely variable magnification from 3.6 to 7.2 and field of vision is 30 to 144mm. The M5 version offers an extendable modular optical system. Changeable oculars extend the magnification range while integrated lighting deals with shadows.

what’snew

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Wittenstein has enhanced its alpha V-Drive servo worm gear to feature optimised hollow-flank teeth, a move claimed to achieve accuracy and low backlash, 50 per cent more torque and 97 per cent efficiencies. The V-Drive gearbox comes in two versions, V-Drive+ and V-Drive economy. The former replaces the classic version of the V-Drive and is said to have continuously high positioning accuracy and low backlash of less than 3arc/min. V-drive+ is available in three output options: VDH (hollow shaft), VDS (smooth/keyed/involute shaft) and VDT (flange). www.wittenstein.co.uk

»Driving out disturbances

Danfoss Drives said its VLT Low Harmonic Drive actively imposes currents into the grid to eliminate harmonic disturbances, restoring the sine wave of the grid current. The company said that rather than simply reducing or masking current distortion, the drive attacks it at source by performing real-time analysis and imposing currents as required. The drive features a modular design, ensuring that most elements are produced at cost-effective scale. The drives do not increase winding stress and have no impact on bearing life. www.danfoss.com

»New Tolomatic SmartActuator

Motion Control Products has launched a new generation of integrated SmartActuator from Tolomatic. The ICR rod-style series of compact ‘all-in-one’ electric linear actuators (servomotor, drive, controller and actuator integrated into a single unit) simplifies linear motion control for industrial applications. According to the company, the SmartActuator provides continuous operation industrial duty cycle motion control, needing only a DC power source and motion inputs from the host PLC, at a lower cost than other systems. www.motioncontrolproducts.co.uk

»Cutting control

Parker Hannifin has developed a hydraulic saw motor that automatically maintains an optimum cutting speed of 40m/s and achieves 35 per cent faster cutting. The F11-iP motor also eliminates over-revving and uses a hyper-fast hydraulic control circuit to maintain optimum chain speed throughout the log. This constant speed is automatically adjusted to match timber quality and lets the chain work at maximum efficiency, with all available power going to the log. The motor uses Parker’s Intelligent Power technology to reduce damage to motors, chains and hydraulic systems. www.parker.com/uk

»Torqueing off

ABB has unveiled its ACS850 drive module, featuring onboard safe torque-off, a removable memory bock, a user interface with assistant wizards, a built-in energy-saving calculator and modular hardware and software. The module also includes an advanced adaptation of ABB’s Direct Torque Control (DTC) motor-control platform. ABB’s industrial drive modules are designed for industrial machinery and applications such as extruders, cranes and mixers, handling and converting in the range 1.5 to 600hp at 480V AC. The ACS850 is targeted at OEMs, panel builders and system integrators. www.abb.co.uk

»Allowing access

Castell has launched its Salus access interlock, which allows safe, easy access to industrial machinery and electrical equipment. The company said the system is based on a high-integrity locking mechanism and features benefits that include quick close and release, stainless steel construction and increased tolerance for misaligned doors. www.castell.com

design essentials

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