Integrated stepper motors

Paul Boughton

A hot topic in engineering magazines around five or six years ago was integrated ac induction motors and inverter drives. These were easier – and cheaper – to install than separate motors and invertersand some products enabled machine builders and OEMs to implement ‘distributed intelligence’.

Today integrated ac induction motors and inverters are commonplacebut a new type of integrated motor and drive is starting to be introduced by a number of manufacturers.

Design engineers working with productsmachines or systems that incorporate stepper motors are now being offered integrated stepper motorswherein the stepper drive and motor are combined as a single unit. These relatively specialist products are available through many of the major channels.

It appears that the sudden expansion in the number of integrated stepper motors on the market is being driven partly by market demand and partly by technological developments. Demand for reliablecompact stepper motors in factory automation and OEM applications can be better met by using components that avoid some of the pitfalls of separately configured units; at the same timeusers can take advantage of steadily advancing standards of design and improvements in manufacturing techniques. Integrated units are also more cost-effective and use less space overall than separate units.

One reason why integrated stepper motors – and also integrated servo motors – have been so popular is that the benefits are simple and easy to understandjudging from the feedback manufacturers have received from their distributors. Many stepper motor applications do not require high torque or high speedso less powerful drives can be used. Being able to switch currents of 2–3A or less at modest voltages – typically 24 to 48volts – provides ample torque for many applications.

“Installation is more expensive for non-integrated units” says Klaus Kramer of JVL in Denmark. “If a system was going to use a stepper motorand the motor was going to be built as an ordinary systemyou would need additional cabling between the motor and the controllerwhich adds the cost of cable and the labour cost for the installation. Plusin an industrial environment there is always electrical noise that can interfere with signals going to and from the motor. This problem is avoided when everything is encapsulated in a metal housing.”

Saving cabling

“Eliminating the cable between the motor and the drive is probably one of the most important benefits” agrees Dick Tecca of USA-based IMSwhich distributes products worldwide through a variety of channels. “That cable is the largest source of electrical noise; when a designer is putting together a control systemif he uses integrated stepper motors he does not have to worry about that. It can also eliminate anywhere from 2–5m of cable in the machineso there are also savings in terms of material and labour cost when it comes to construction. And you also save panel space in the machine that would be needed to mount the driver or to mount the driver in the controller.”

“For cost-effective solutionsyou eliminate as many parts as you can” says Leo Brennan of USA-based AMCIwhich distributes through Allan-BradleyGE Industrial Systems and Schneider-Modicon. “An integrated drive on the back of the motor reduces cabling costs and connectors. Many applications have a 24Vdc supply availableso often another power supply is not needed and there is less need for panel space. There are many cost benefits for such an integrated designwhich came from a market demand for low-costsimplestepper motors in motion systems at a time when the necessary technology was available to make it happen.”

Saving space means saving money for the customer; and avoiding the problems brought about by electrical interference means that systems are more reliable. It is generally accepted that when using integrated unitsmaintenance becomes simpler because discrete integrated units can be replaced as a whole; there is no longer any need to dismount and reinstall sensitive cabling between the controller and the stepper motor. Lifetime cost using integrated stepper motor units should be much lower than when using separate components connected by cabling.

“Swapping out a motor as well as the electronics might be considered a disadvantage” says Tecca. “But motors do not cost very much. I have not really heard of this being a problembut if I try to think of disadvantagesthat is one I can think of. Alsoof courseif an integrated drive is buried deep in a machine it might be difficult to get to. You do not have access to the drive as you would on a control panelbut the integrated stepper motors have been really quite reliable.”

Restricted choice

Integrated stepper motors areby their naturelimited to applications where they will provide the required torque and speed in the space available. As automation is introduced for more and more applicationsso the potential market size increases. Howeverintegrated units are manufactured only in fixed sizes with clearly defined performance characteristicsso designers must choose from what is available in order to satisfy their requirements.

Projects where updated controls are being retro-fitted into existing spaces may sometimes encounter problems when trying to use these cost-effective components because of their physical shape or sizebut this problem is unlikely to occur with new systems. Apart from these physical constraintswhich may well be overcome as new products reach the marketintegrated stepper motors are being used in almost all industry sectors on a wide range of applications.

“It seems to be quite natural to use our type of motor in packaginglabelling and printing applicationsfor example” says JVL’s Kramer. “We can deliver the power and the torque needed to operate pick-and-place robots in industries like semiconductor manufacture and food – or anywhere that uses hi-tech machinery and where space is at a premium.”

“Multi-axis applications would be the main places where integrated stepper motors are used” says IMS’s Tecca. “In this type of application the benefits of not having to run cables between drives and motors and the saving in panel space become even more significant. Single-axis applications do not benefits quite so muchbut the minute you have a machine with many axes to operatethe benefits really multiply. This would mean that they are mainly used by OEM manufacturers and in factory automation. You really get the benefits in multi-axis applications where a designer needs something that is small.”

AMCI offers the SMD23 integrated stepper motor and drive packagebased on a Nema23 motorwhich is intended to save customers timemoneyand frustration. The SMD23 is approximately half the cost of a conventional stepper motor and driver configuration. Unlike separate stepper motors and stepper drives that are built independentlyusing components and skills unique to each assembly processthe SMD23 uses powerful processors to reduce manufacturing time. Customers also save time by not having to researchspecifypurchaseand install two separate components.

AMCI has designed the SMD23 to boost a system's efficiency and performance by dynamically matching the Nema 23 stepper motor to powerful integrated drive circuitry (Fig.3). Besides achieving maximum torquespeedand range variablesthe SMD23’s self-regulating current flow eliminates the risk of driver-to-motor overload. Integrated circuitry also minimises costly set-up times by omitting the drive-to-motor cabling.

The SMD23 is a PC programmable suitable for applications across a variety of industriesincluding packagingsemiconductorsautomotivefood processingpharmaceuticals and scientific.

Integrated stepper motorslike integrated ac induction motors before themare a common-sense application of existing technology to solve some of the practical problems often encountered by automaton designers. The selection available is increasing year by yearand incremental improvements to underlying technologies are incorporated as they become available in the mainstream. For the greater number of applicationsthe drive and motor can be combined in the same physical unit that is compactreliableeasy to installunaffected by electrical noisesimple to maintain and good value.

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