Motion systems project file – September 2012

Micromech Systems provides a comprehensive motion service ranging from just simple modifications to motors, to bespoke multi axis control systems including full installation, commissioning and after sales service.

Year:  2011 to 2012

Industry or Research faculty: Industry

Customer: Aerodynamic Test Equipment Ltd

Location: Heathfield, East Sussex, UK.

Application: 28-Tonne XYZ Gantry for automotive aerodynamic testing

In automotive acoustic wind tunnel testing it is required to move an assortment of test probes around the vehicle periphery whilst collecting data during the wind–force test.

Low level pressure and acoustic tests are performed to check design aerodynamics. It is therefore imperative that the XYZ gantry carrying the probe has a specific degree of mechanical stiffness and to avoid any parasitic vibrations which would distort the gathered test data.

The mechanical structures for the XYZ assembly are designed and FEA qualified to ensure the desired figure of stiffness would be achieved prior to manufacture.               The main design work was undertaken by ATE’s design engineers and the computer modelled FEA verification was covered by one of ATE’s partners who have successfully designed two former lower mass systems (15 tonne) which have now been in service for some years.

The new design required the following axis travel ranges:

Y-axis: Twin units at each end of main beam element 15metres across the tunnel width

X axis: Single unit: 20metres along wind tunnel length

Z-axis: Vertical to carry 1tonne probe assembly 5.3metres carried along X-axis.

The complete 28Tonne assembly is hung from the wind tunnel roof structure on two parallel heavy-duty linear bearing rails.

Scope of overall contract To propose the motion control positioning actuators and associated servo drive components for managing the load masses specified in accordance with the client’s motion control specification as follows:
All axes 320mm per second max speed.
Positioning resolution 10microns linear.
Absolute Encoder feedback and holding brakes on all four axes.
Special disc brake mechanism on vertical axis.
Site visits during initial build.

Description of equipment and services supplied

Linear actuators:

Y-axes: Twin Parker Hannifin HPLA180 Belt Drive units. 10KN thrust force total. 14.4metres travel.

X-axis: Single Parker Hannifin HPLA 180 Belt Drive Unit with 5KN thrust force.19.8metres travel.

Z-axis: Thomson Linear Non-bearing guided enclosed ball-screw actuator with 20mm pitch screw type WV12D20. Special Disc Brake unit designed by Micromech Systems Ltd.

Reduction Gearheads:

Y-axes: Stober planetary P812 ratio 100:1 800Nm nominal output torque rating.

X-Axis: Stober planetary P712 ratio 49:1 400Nm nominal output torque rating.

Z-Axis: Wittenstein high efficiency servo RT angle worm drive.VDT63 ratio 4:1

Brushless Servo Motors:

Parker Hannifin SMHA 142 15 Nm and 19Nm at 4500 and 5600 rpm with resolver feedback and a holding brake.

Absolute Encoders:

TR Electronic Controls type CE65 8192, counts by 4096 turns fitted to the rear shaft extension of each servomotor.

Servo Drive Power Package:

Parker Hannifin Compax M and S Systems powered from 400V AC were used to drive the motors.

Three Compax M servos with common DC BUS were employed for the main horizontal axes X and Y.

A stand-alone Compax S Servo Drive was employed for the vertical servo axis due to it’s associated electronics mounted remotely within the main traverser beam structure.

Motion Controller Card:

Labview package with multi axis motion capability
Deva Electronics SSI, absolute encoder interface.

Position Control Software: (Devised by ATE)

Bespoke software package dedicated to application task and linked with motion command requirements for accurate positioning capability.

Merits of solution provided

As this was the heaviest mass ever handled by the HPLA actuator system it was important to have a very straightforward ‘proving’ base.

Each of the twin Y-axis linear units were supplied split into two equal length sections so that a shorter belted drive unit could be assembled on just half of the eventual unit length. This was arranged so that it would fit comfortably into the test platform floor space whilst being pre-assembled and tested in the UK.

The 19.8metre long X-axis positioner was supplied in three sections due to limitations in aluminium profile length capacity.

It was possible to run the servomotors just from the resolver feedback for initial functional trials and drive tuning. The absolute encoder references were then introduced once the main control programme was loaded and running via the Deva Electronics multi-axis card.

On the vertical axis it was necessary to employ a special disc brake unit which could stop any further screw rotation in case of a drive coupling failure. The vertical load mass was estimated at 800kgs and the top speed specified at 320mm per sec. It was necessary to be able to stop a downward moving load running on the 20mm pitch screw within 50mm to avoid very expensive damage to the probe assembly and the wind tunnel floor.

Importantly most major elements of the drive system can be replaced very quickly for service and breakdown requirements.

Partners in collaboration on the contract

Parker Hannifin: Belt drive actuators and servo equipment

Thomson Linear: Vertical screw drive unit

TR Controls: Absolute encoders

Stober: Large planetary gearheads

Wittenstein: Vertical axis servo worm unit

Tiptree Precision Engineers: Disc brake manufacture

Micromech Systems builds motion control systems to customer’s specifications, ranging from simple single-axis applications to complex multi-axis systems. We will design, build test, and produce application software, install and commission providing a cost-effective trouble-free solution to your Motion Control problems. Whether the application is a machine upgrade or a new project, Micromech Systems have the answer.

Octobers project: Laser wave-plate synchronisation unit