No step losses: stepper motors in synchronised operation

Speeding up, stopping and speeding up again – the two EMMS-ST series stepper motors move in perfect harmony. Running extremely smoothly and almost completely resonance free, they move up and down on parallel axes. As no steps are lost even in the event of power failures, the new encoder-fitted stepper motors provide optimum operational reliability and are an affordable alternative to synchronous servo motors EMMS-AS – the super performers of the electric drive family.

Up until now it has been possible to achieve an electrical drive solution that gives feedback to the controller, is fully regulated and can be freely positioned using only servo motors – even though these provide significantly more functions than are required for simple handling jobs. Yet particularly in sectors such as the packaging industry low costs are the primary concern, thus calling for simple, inexpensive solutions. The new EMMS-ST stepper motors add to the Festo range of electrical drives and, together with encoders and the matching CMMS-ST controller, form a “Servo Lite” solution. They provide fully regulated movement, optimum operational precision and the ability to control torque, position and power.

Closed loop keeps everything under control
The CMMS-ST controller works on the closed loop principle as a full servo-drive package. By regulating power, torque and position, it keeps the stepper motors well under control. If the motor defined as the master stops due to a fault, the position synchronisation immediately stops the slave motor as well. The stepper motors thus move in fully synchronised fashion. The CMMS-ST can be connected to a CANopen system and be retrofitted to Profibus or DeviceNet. Network filters and brake resistance are fully integrated, and an SD card provides portable parameter storage. Combined with the EMMS-ST stepper motor and Festo axis modules, the CMMS-ST controller is the right solution for price-sensitive applications with a loading range of up to 6.5 Nm.

Optimised operational precision
There is no risk of step loss with “Servo Lite”. Fitted with an integrated absolute encoder, the motor gives permanent positioning feedback to the motor controller. If power is lost and then restored, the encoder provides the position anew. The motor controller compares the actual and specified position across the full number of revolutions travelled in relation to the feedback from the motor and permanently corrects any deviation within the closed loop – thus producing a complete servo system.

Versatile servo motors
If the tasks are too complex for a stepper motor solution, the EMMS-AS servo motor comes into play – for example, for cutting strips whilst in motion. A straight edge can be cut only if the cutting tool is travelling at the same speed as the conveyor. The servo motors of the conveyor and cutting tool are therefore synchronised via their controllers. These servo motors and controllers show their strengths in particular on time-critical handling jobs, such as fitting mass production parts. They move flexibly and dynamically into position, respond quickly and have high acceleration capacity and final speed. These motors score well, even on intricate jobs. Combined with electric spindle drives, they work with extreme accuracy – ideal for assembly work in precision engineering.

Festo provides a suitable electric drive solution for every job. The company’s range of stepper and servo motors, plus the associated controllers cover all requirements. Combined with toothed belt or spindle axes or with servo-pneumatic positioning axes, the range offers everything that users require – from simple, inexpensive drives to intelligent, high-performance solutions for complex tasks.

In perfect harmony: The stepper motors move up and down on parallel axes.

The EMMS-ST stepper motors provide fully regulated movement, high operational precision and control of torque and power – a “Servo Lite” solution.

Stepper motors under control: The CMMS-ST controller works on the closed loop principle as a complete servo drive package.

The super performer of the electric drive family: The EMMS-AS servo motor.

Courtesy of  Festo