Motors and Drives
Fig. 1. New Scale has developed compact custom positioners comprising two rotary piezo motors in a two-stage theta-phi configuration.
4 Miniature motors and micro- motors can be extremely versatile, and their cost today makes them very attractive for both miniaturisation and for enhancing products by adding new functionality. Jon Severn takes a look at what the latest evolutions of these products can offer design engineers.
4 Les moteurs miniatures et les micromoteurs peuvent être extrêmement polyvalents. Leurs coûts sont maintenant particulièrement intéressants pour la miniaturisation et ils permettent d’ajouter de nouvelles fonctionnalités. Jon Severn explique les avantages que les évolutions les plus récentes apportent aux ingénieurs concepteurs.
4 Miniatur- und Mikromotoren können äußerst vielseitig sein. Ihre Kosten machen sie außerdem sehr attraktiv sowohl für die Miniaturisierung als auch die Verbesserung von Produkten durch zusätzliche Funktionalität. Jon Severn untersucht, was die neuesten Versionen dieser Produkte Konstrukteuren zu bieten haben.
Motors drive the move to miniaturisation
M
iniature motors and micro-motors are more widely used today thanks to two trends: product miniaturisation and the desire to incorporate more functionality.
For example, if your mobile telephone has a ‘silent’ ring mode in which it vibrates, the chances are that the vibration will be generated by means of a small electric motor with an offset load on the shaft. Today’s miniature motors and micro-motors are, relatively speaking, more powerful than their predecessors, plus they offer good reliability and they are becoming increasingly cost-effective. For a simple vibration motor that just starts
and stops, there is no need for great sophistication. However, for other applications - perhaps, for example, in medical devices - it will be necessary to monitor and control the speed, position and maybe even torque. A gearbox may also be required to reduce the output speed. For this type of application, designers can select miniature motors that are equipped with inline gearboxes and encoders, plus it will be necessary to specify a compatible controller, which could even offer true servo control. Clearly it is impossible to generalise when
it comes to miniature and micro-motors, as the ideal product for one application will seldom be perfect for another application. Indeed, it is not unusual for original equipment manufacturers to work with motor suppliers on custom designs. This present article, therefore, will review a selection of the products available, highlighting some recent
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developments in this interesting field. Starting at the small end of the scale, Namiki
Precision Jewel has developed a 1.5mm diameter micro geared motor that it claims to be the smallest diameter electromagnetic motor in the world. Typical applications are expected to be in fields such as advanced medical equipment (catheters and endoscopes) and micro-robots. Despite its small size, the motor is said to offer high torque and a long operating life. Three gearhead ratios have been used, namely 40:1 (in two stages), 254:1 (in three stages) and 1609:1 (in four stages), with lengths of 9.4, 10.0 and 10.5mm, respectively. All operate form a nominal 3 V DC and have no-load output speeds of 3800, 600 and 95rpm, and stall torques of 100, 450 and 2070 µNm, respectively. 1.5mm motors are extreme; even Namiki
normally restricts itself to motor diameters of 2 to 4mm for use in industries such as medical equipment, analytical instruments, physics and chemicals. Namiki also offers micro servo gearmotors; these brushless DC units are 12mm in diameter and the motor element is 22mm long, but customers can specify inline gearheads with one to four stages to give reduction ratios of 4.00:1 to 428.69:1. The same gearmotors are also equipped with a 128 pulse-per-revolution, TTL-compatible encoder, and suitable servo drives are available from Namiki.
Piezo-electric motors
While Namiki is focused on electromagnetic motors, New Scale uses piezo-electric technologies.
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