DS-NOV23-PG38_Layout 1 17/11/2023 12:10 Page 1
FEATURE LINEAR MOTION
BETWEEN STEPPER AND SERVO DRIVE
BRIDGING THE GAP
Whether to use a stepper or a servo drive can be a difficult decision for machine builders. The development of a new range of low voltage
servo drives, however, means machine builders can access the best of both worlds, as Josh Roberts, Electric Drives expert at Festo explains
he high dynamics and controllability of servo control loops can be useful in many automation applications, but there can be other times where the pulse, lock and stay characteristics of a stepper are the better choice. For machine builders, whether to use a stepper or a servo drive can therefore be a difficult decision. Festo, however, has developed a new range of low voltage servo drives to help. Called the CMMT-ST, this new servo drive
T
range has been developed by industrial automation specialists at Festo. The new extra low voltage servo drive
is capable of open or closed loop positioning, effectively bridging the gap between stepper and servo drives. It also comes with free software for ease of programming, making it easy for the user to tailor the drive to the application needs and reap the benefits of both control formats.
ADVANTAGES The new servo drives have been termed ‘extra-low’ voltage because they work at 24 or 48VDC. This new generation of controllers has a raft of new features setting them apart from previous Festo devices and from the competition. For example, the CMMT-ST has a microcontroller which is three times more powerful than previous models. This creates performance user advantages such as multi-protocol fieldbus compatibility, field weakening, energy management, auto-tuning and U/f open loop control. It also features an integrated web server, which is an advanced feature for a low-cost device. This enables the easy transfer of data to and from the servo drive for fast, simple set-up, diagnostics and file transfers. Within the servo drive is the capability to
communicate instantly to more than 75% of major fieldbus systems (including PROFINET, EtherCAT, EtherNet IP and Modbus), either through simple DIP switch settings, software set-up or auto- recognition. This means no changes to electrical designs, cabinet layout or wiring
when swapping between control architectures, which is time- consuming and expensive for special purpose machine builders adapting to end- user specifications. It also means less stocked or service parts and less parts for installers and service technicians to become familiar with. While field
weakening sounds counterintuitive for a user benefit, it enables the
connected motors
to achieve higher maximum speeds or torques.
For example, at low torques the maximum speed increases from 1,600 to 2,300 rpm – an increase of 44%. This
presents the opportunity to select a smaller, lower cost motor to perform the same task. In addition, the CMMT-ST drops below the
power class (300 W nominal) of the Festo standard range of servo drives but shares the same control integration and function blocks. This means significant cost reductions can be achieved by combining the two types of drives within one system.
38 DESIGN SOLUTIONS NOVEMBER 2023 Josh Roberts
ROBUST DESIGN Mechanically the CMMT-ST very efficiently packages advanced electronics within a robust enclosure with good EMC protection. An earthing fin shields the encoder feedback cabling, protecting the drive within ‘noisy’ environments on industrial machinery. Connectivity for braking resistors enables efficient energy management, soaking up the energy spikes and increasing the drive’s peak performance characteristics. A further energy saving option is to use the DC link, sharing energy peaks between different drives within a system. For a compact drive which is only 144mm high, 88mm deep and 27mm wide, it can manage an impressive nominal current of 8A and up to 20A peak for limited durations (three sec. max.) for maximum acceleration or de- acceleration peaks within a positioning cycle.
BIG SAVINGS! With a list price of under £500 and free programming software, this new generation of low voltage servo drives has the potential to deliver big savings for both machine builders and users. Free to access Electric Motion Sizing software also enables you to select the right motor/drive combination by simply inputting your key parameters. Within seconds the optimal solution is proposed, with or without mechanical axis, using Festo or third party guides or a totally rotary application. The software identifies possible options, standard or extra-low voltage, prioritised by cost, handily showing the servo drive and motor workloads to enable you to make an informed choice. The ease with which the drives can be
combined proves particularly advantageous in applications where the drives are currently over-specified to combat the compatibility and control issues usually associated with mixing drives within a single control system.
Festo
www.festo.com/cmmt-st
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