Decentralised EtherCAT motion system offers machine cost benefits

10th September 2018
Posted By : Alex Lynn
Decentralised EtherCAT motion system offers machine cost benefits

The Suspension Parameter Measurement Machine (SPMM) from AB Dynamics, is used by global vehicle manufacturers, vehicle standards test houses and tier-one component suppliers for the measurement of kinematics and compliance (K&C) testing as part of progressive R&D and for production quality control. 

With the ability to dynamically simulate braking, accelerating and cornering scenarios under highly repeatable test conditions, the SPMM provides the capability to obtain precise measurements of vehicle body and component deflections on the 19-axis motion controlled machine. AB Dynamics’ SPMM delivers a complete and faithful simulation of on-road vehicle behaviour through a comprehensive range of upgrades and options including Vision Systems, Moment of Inertia (MIMS) and Centre of Gravity (C of G) measurement capability.

Heason Technology is a long-term support and supply partner for motion control components specified by Bradford on Avon based AB Dynamics. Recently, for a next-generation SPMM, Heason supplied AKD-N series EtherCAT-enabled decentralised servo drives from its distribution partner Kollmorgen that has reduced control cabinet hardware, cabling, and build time and cost, whilst facilitating measurement accuracy and improved performance.

The moving body platform of AB Dynamics’ SPMM 5000 features a central table which is precisely motion controlled via electric servo actuators in six degrees of freedom. This enables a combination of roll, pitch, bounce and yaw motion that can be applied to the vehicle body during K&C and MIMS testing.

The design geometry of the machine ensures that the ground plane (which replicates the road) is fixed during cornering and braking simulations. A wheel station for two or four wheels, mounted on the moving platform, includes additional motion axes that generate X, Y and Delta forces to each wheel. In combination with high accuracy multi-component piezoelectric load cell assemblies below each wheel, the SPMM 5000 derives extremely high precision measurement of the forces, displacements and wheel moments with wheel position measurement for X, Y, Z, steer, camber and spin motion of the wheel centre.

All of the motion axes on the machine (up to 18 for the four wheel version) include Heason supplied AKD-N EtherCAT enabled decentralised servo drives. In addition, the Delta axes include Heason developed servo actuators based around TwinSpin precision gear reducers from Spinea, also a distribution partner for the West-Sussex based motion specialist. 

This gear reduction solution integrates heavy-duty radial-axial bearings with a trochoidal gear reduction system into a single compact unit that removes the need for separate load support bearings or mechanics. In addition, a single AKD-N servo drive with EtherCAT is directly coupled to and provides simulation of the vehicle’s steering system.

The SPMM 5000’s measurement systems and algorithms provide suspension engineers with an essential aid to the thorough understanding of a vehicles performance in terms of ride, steering and handling.

Previous SPMM machine designs have also typically used up to 19 motion axes, however with centralised (cabinet-installed) motion control, the need to house high-power servo drives and power supplies centrally necessitated large air-conditioned control cabinets with the requisite motor power + feedback cable management systems installed over long runs across the large area of the machine, which has nominal dimensions in the region of 7.5x4.5x2.5m. 

With continuous machine power requirements up to 15kVA, the associated commissioning, inventory and component cost burden for the centralised design concept combines for a significant proportion of its overall build cost. These costs have been significantly reduced thanks to the AKD-N decentralised motion control system now used on the new SPMM 5000. 

With each AKD-N servo drive located and connected close to its motor, and with DC power daisy-chained around the machine to each drive, significant savings in installation time and cost has led to faster assembly production and site commissioning times.

Simplified wiring and cable management means AB Dynamics’ modular machine design requires less hardware, spares inventory, and field upgrades, for example two to four wheel set-ups are more easily achieved. The new SPMM 5000, without the need for a large control cabinet, also requires a smaller footprint which is an important factor for production test area installation.

Kollmorgen’s AKD-N also has a single hybrid cable connection for motor power and its Hiperface DSL enabled absolute encoder feedback (from a wide range of feedback options). Furthermore, the single cable philosophy extends to the servo drive power and fieldbus where an 11mm diameter hybrid cable is used for the DC-bus and EtherCAT connection. It is also possible to run Safe Torque Off (STO) safety through this single cable. These factors combine for even less machine wiring than decentralised drives that require separate drive power and fieldbus connections as well as separate motor power and encoder cabling.

As a decentralised system, Kollmorgen’s AKD-N series servo drives suit AB Dynamics’ range of system configuration and measurement options it offers the SPMM 5000. A single AKD-C power supply may be used for up to 16 AKD-N drives and may also be machine mounted for convenience. Individual AKD-N drives cover a power range up to 4kW and may be combined with centralised AKD series EtherCAT drives where even higher powers are required.

Kollmorgen’s AKD-N series decentralised drives have a proven record not just for lower machine complexity but also for the high-speed synchronisation offered by the EtherCAT industry standard fieldbus. The real time deterministic fieldbus system with low communication jitter is particularly suited to automation applications requiring short data update times. 

The freely scalable plug-and-play solution allows additional motion axes, sensors or machine I/O to be readily added to ensure the highest degree of design freedom for machine building. Commissioning and servo tuning is fast and straightforward with the graphical-based Kollmorgen Workbench. 

The AKD-N decentralised drives used for the SPMM perform in concert with AB Dynamics’ own EtherCAT master-based hardware and software system. Complex kinematics algorithms generate a series of motor current (torque) demands to each individual axis in real time and in close synchronisation with all the sensor measurement data.

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