New advances in motor technology still enhance machine applications
its sizeand the application in questionthe wrong motor can lead to excessive energy consumptioncompromised reliabilitynoise and vibration problemsand the machine’s speed or cycle time can be adversely affected. "Most machines incorporate one or more electric motors, the choice of which can make a...
two-quadrant controllers are available to accompany each unitand customers can select from a number of different motor flange mounting options. A customisable range of Parvalux gearboxes is also offeredincluding the new G and LS worm-wheel units.Most machines incorporate one or more electric motorsthe choice of which can make a significant difference to the finished machine. Depending on the type of motorits sizeand the application in questionthe wrong motor can lead to excessive energy consumptioncompromised reliabilitynoise and vibration problemsand the machine’s speed or cycle time can be adversely affected.Motor technology is relatively matureespecially when compared with the rapid developments still underway in electronic control productsbut there are still significant advances being made in all types of motors for machineryincluding three-phase synchronousasynchronous ac inductionservo and stepper types. In this article we will review some of the latest motors that offer notable features and benefits.B&R has recently launched the 8KS family of three-phase synchronous motors with high power densities and compact outer dimensions (Fig.1). This has been possible through the use of liquid cooling and is said to create new opportunities for the design of machines where space is at a premium.Integrated water cooling eliminates the need for energy-consuming and noisy fanssaves spacereduces emissions and lowers costs. Furthermorethe motor’s operating life can benefit enormously because the motor parts â“ other than the bearings â“ are wear-free.8KS series motors are available in four sizes with a rated speed of 1100â“2200rpm and a maximum speed of 4500â“10000rpm. The rated torque is between 8.3 and 605Nm. B&R says the motors can be controlled with its Acopos or Acoposmulti servo drives.In some applications machine builders would ideally like the efficiency of simple induction motors with the precision of servo motors. Rockwell Automation has sought to address this need by launching the Allen-Bradley High-Power Kinetix (HPK) series motors (Fig.2). Suitable for applications such as material handling or web converting where high power capacities are requiredthe motors are said to deliver servo motor precision and performance but with the power ratings and purchase prices normally associated with induction motors.150 horsepower servo motorDavid Hansenthe product manager at Rockwell Automationcommented: "We have never offered a servo motor with power ranges over 30horsepowerbut the HPK motor extends the normal power range of a traditional servo motor up to 150horsepower. This allows machine builders to increase acceleration and improve the positioningprecision and overall system throughputin some cases by as much as 25percent."Rockwell Automation has achieved this high performance by optimising the electrical winding design of the HPK series motors to mimic the speed/torque curve of a conventional permanent-magnet servo motor. The HPK motors therefore deliver a peak torque that is twice the continuous torque available at base speeds. Furthermorethe motors are equipped with single- or multi-turnhigh-resolution absolute feedback devices that eliminate the need for time-consuming homing routinesimprove velocity regulationand expand the system’s inertia-matching capacity. Rockwell Automation believes this capability is new to induction motor technologymaking HPK series motors the first of their kind to offer positioningacceleration and productivity capabilities that are comparable to traditional permanent-magnet servo motors.Parvalux has recently entered the market for dc brushless motors and controllers with products that benefit from high build qualitya two-year warranty and very competitive pricing. Justin Levinethe managing director of Parvaluxexplains why the market for dc brushless motors is growing faster than the markets for conventional dc brushed motors and ac induction motors: "It seems that the convenience of having no brushes to wear out combined with good speed holding is attractive to designers; for examplea 0.18kW ac motor with a variable-speed drive is the staple diet of many builders of simple machinespoweringsaya conveyor on a checkweigher. For about 50percent of the price you get a dc brushless motor that is almost 25percent smaller and offers a more dynamic performance. Of courseeach application needs to be selected according to its specific design merits. HoweverI can understand why dc brushless is taking off so fast."The latest release from Parvalux is a customisable 86mm motor designated the PBL86 (Fig.3). This square-framed unit is available in lengths of 91118 or 145mmoffering continuous rated power outputs of 220346 and 440W at a nominal speed of 3000rpm. Windings allow speeds of up to 4000rpm to be achieved with a 48Vdc bus as standardalthough a 24V version of the 91mm motor is also available. Matched Many motion control manufacturers today offer integrated motor-drive or motor-controller units. One such company is JVLwhich specialises in integrated servo and stepper motors. The latest development from JVL is IP65 sealing for its large MAC800 integrated servo motor that has a nominal power rating of 750W (Fig.4). This makes the MAC800 suitable for applications in more demanding environments such as those commonly encountered in the food processing industries.IP65 protection has been achieved by replacing the built-in fan with large fins. In additionan IP67 Rulon bush provides a watertight seal on the shaft bearing. This seal has very low friction and requires no lubrication. Because the IP65 motors are likely to be used in wet environmentsboth the flange and shaft are made of stainless steel.Direct-drive motorsIf space on a machine is at a premiumunits such as the recently launched small frame cartridge DDR direct-drive motors from Danaher Motion can be attractive. The new models with 108137 and 188mm flanges can be connected directly to the load to eliminate intermediate mechanical elements such as gearboxescouplings and belts. They therefore combine the advantages of direct-drive motors â“ including compactnessconstant high torqueimpressive dynamic responseaccuracyand low maintenance and wear â“ with the ease of mounting of enclosed motors. This enables smaller machines to be built more quickly and it saves the costs associated with specifyingsourcingpurchasing and installing intermediate power transmission elements.MoreoverDanaher Motion claims that eliminating the intermediate components helps the DDR direct-drive motors to achieve up to 50 times greater accuracy than conventional drive-motor combinations. The motors also offer improved dynamicsas the moment of inertia is significantly loweras well as higher speeds that lead to faster cycle times. There is virtually no limitation in terms of the motor-to-load inertia torque ratiohence there is no need for gearing between the motor and load. A final benefit of the cartridge DDR motors is that they produce up to 20dB less noise than conventional motors with power transmission systems.Stepper motors are extremely versatile and often used in machinery applications. Usually two- and four-phase designs are specifiedbut Astrosyn International Technology has introduced an advanced three-phase stepper motor with driver (Fig.5). The three-phase layout makes the motor very quietsmooth and accuratewith a step angle of 1.2 degrees compared with the usual 1.8degrees. Packaged in a Nema size 24 housingthe three-phase stepper motor has six inputs instead of the four or eight found on two-and four-phase stepper motors.A complementary P306 driver operates with a direct current input of 18-45Vproducing an output current of 3.0â“5.8A per phase. Eight microstepping resolutions can be selected.Typical applications for the three-phase motorwhere the smooth running and low noise and vibration will be beneficialinclude the control of laser beams in laser engraving machinesscanning control in medical instrumentsand the movement of stage lighting in theatres.
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