More motion developments, last 20 years
Electronic motion and motor control has advanced in a series of evolutionary steps as most technologies tend to do. The process moves from concepts to prototypes to products with improvements and refinements added as new methods or tools emerge. Application experience also serves as a good teacher. Various motor and motion control developments were covered in the main article "Electronic motion control, then and now," appearing in Control Engineering’s 60th anniversary issue, September 2014. Newer developments over the last 20 years are discussed in this online extension (2 of 4) of the main article.
Variable-speed drives (VSDs) have benefitted from evolution. Early ac drives offered only open-loop (V/Hz) control, but modern VSD design can also incorporate vector control variants (such as sensorless vector and closed-loop flux vector) and servo control into the same unit, selectable by software. The resulting ability to control permanent magnet (PM) synchronous or brushless dc motors as well as ac induction motors has widened the applications for these drives.
An early example of this approach was Control Techniques Ltd.’s Unidrive, "universal" ac drive, incorporating this capability when introduced in 1995 (Ref. 32; references are provided in a separate article, linked below). Unidrive M is the product line’s latest version introduced in 2013. The top range model of the Unidrive M family (M800) integrates a machine controller within the drive and uses the CoDeSys programming environment with IEC 61131‐3 programming languages. Ethernet TCP/IP is used to synchronize machine axes and for communications over a plant network. Control Techniques is an Emerson Industrial Automation company. All references cited appear in online extension 4 (Ref. 4).
Another multimode drive offering is MoviDrive from SEW-Eurodrive, dubbed a single-axis "servo inverter" by the manufacturer. MoviDrive comes in two power ranges and supply voltages: 1.5-37 kW at 200-240 V ac and 0.55-160 kW at 380-500 V ac input.
Still other motor topologies could be incorporated into one VSD design, but may not be economically justified. Depending on different strategic objectives for product introductions, not all drives manufacturers opt for a universal drive approach.
Electronic integration has helped motion control components to continue to shrink in size. Prime examples are board-level servo controllers and amplifiers and ultra-small ac VSDs (or so-called microdrives.)
The recent 4-axis servo drive addition (AMP-43540) from Galil Motion Control is packaged inside one of the company’s 4-axis motion controllers (DMC-4040 or -4143) to save cost, space, and wiring compared to an external drives arrangement. Four transconductance PWM amplifiers provide sinusoidal commutation for driving brushless servo motors. The drive has automatic initialization for commutation and requires no Hall effect sensors (Ref. 33). Switching frequency is 33 kHz. The combination controller and drive package measures 8.1 x 7.3 x 1.7-in. (206 x 185 x 43 mm)-as shown in the Figure 1 photo (right). An 8-axis version is shown at the left.
A related miniature amplifier available 20 years earlier indicates the progress made possible by electronic integration. A photo in online extension 3 (Ref. 3) shows the counterpoint.
Microdrives deliver a lower-cost solution with reduced drive functionality for appropriate applications. Still, some models on the market come with quite remarkable features (Ref. 34). The power range of microdrives was always subject to interpretation, but at one time 4 kW was an arbitrary limit. This is being exceeded as examples indicate below.
In the 1990s serious competition persisted among drives manufacturers as to what the smallest physical size of a VSD could be (Ref. 35). Some models rated up to 0.75 kW were small enough to fit the palm of a hand (Figure 2 photo) or a technician’s coverall pocket. That was good publicity but not a practical mounting location.
A sampling of today’s ac microdrives includes the following.
- Automation Direct GS2 Series has ½-3 hp (0.37-2.2 kW) ratings at 230 V ac input, 3-phase (3-ph). Other series models have higher input voltages and power up to 10 hp; also ¼-2 hp at 110 V (1-ph input).
- ABB ACS150 offers 0.37-4 kW output with 200-480 V supply options (3-ph) and 200-240 V supply (1-ph). A smaller ACS model (1-ph input) is available as well as three larger ACS models up to 30 kW rating, which are still classified as "micro drives" by ABB.
- Rockwell Automation PowerFlex 4M offers 0.2-7.5 kW output at 240 V input. Models with lower and higher power/voltage ratings are available.
Approximate dimensions for the above drives are about 7 by 4 by 5.5 in. (height x width x depth).
For some motion applications, especially at lower power requirements, chip-based control becomes an option. Chip-level controllers offer smaller physical size and less system cost (wiring, power usage, etc.) versus a motion board approach (Ref. 36). However, implementation requires an amplifier card, host computer, and software tools. User expertise is also helpful.
Off-the-shelf chips with onboard motion processor reduce the software tasks compared to direct purchase from chip manufacturers. Motion chips provide numerous functions, including network connectivity, and are available from various companies for a specific or multiple motor topologies. Two examples follow; several other motion silicon suppliers and products are discussed in Ref. 37.
Performance Motion Devices Inc. (PMD) offers the Magellan MC58000 Series motion processor chips for controlling brush dc, brushless dc, microstepping, and pulse/direction motors in 1, 2, 3, and 4-axis versions. Motor type and number of axes are software selectable. Various profiling modes, such as S-curve and velocity contouring, are user selectable, along with several advanced servo-loop compensation features.
The cSpin single-chip digital motion controller from STMicroelectronics is intended for 2-phase stepper motors operating under microstep control. One chip does all calculation, control, and interfacing functions without the need for added motor-control software. cSpin provides on-chip gate-driver circuitry for the motor’s power stage and includes a resonance avoidance function.
Integration of safety and motion control functions in production machinery and automation systems is a relatively new development. The initiative seeks to combine the two functions in one system, where separate safety and motion systems were used in the past. The payoff is simpler machine operations and cost savings.
Not every presumed "emergency" requires full shutdown of a machine system. Yet, conventional safety systems impose complete removal of power regardless of the risk level involved. Unavoidable loss of productivity is the result. The newer approach is based on comprehensive risk and reliability assessment of the machine system, which is then associated with the degree of machine shutdown needed to prevent harm or injury. When deemed appropriate, this allows safe access to machines with the main power left on. The benefit is easier setups and troubleshooting and a quicker return to production (Ref. 38).
The movement to "safe motion" or "drive-based machine safety" or other similar titles is growing among motion control technology companies. Product examples that embed safe motion features include IndraDrive Mi from Bosch Rexroth; Kinetix 5500 servo drive from Rockwell Automation; Lexium 32 servo drive from Schneider Electric; and Sinamics S120 modular drive system from Siemens.
Technology associations are likewise onboard for the safe motion approach. For example, ODVA has recently announced that "services for safe motion applications" will be part of the next edition of its CIP Safety specification. When conformance testing for these services is added to CIP Safety, users will be able to deploy networked motion control systems using EtherNet/IP and Sercos III in applications requiring safe motion functions, according to ODVA (Ref. 39). Typical functions include safe torque off and safety limited positions (Ref. 38).
ODVA is an international association that promotes interoperable information and communication technologies in industrial automation. CIP Safety is one of the specifications under ODVA’s trademarked Common Industrial Protocol (CIP), billed as one media-independent platform shared by a variety of networking technologies.
The next decade ahead for motion control looks just as exciting as the previous one.
– Frank J. Bartos, PE, is a Control Engineering contributing content specialist. Reach him at firstname.lastname@example.org
See four related motor and motion control articles at bottom, including references.