The Department on Civil and Structural Engineering at Sheffield University is a world authority on soil dynamics. Its research group continues to explore how soil behaves under different stress conditions and for this purpose has developed a non-intrusive modelling technique using transparent soil. Central to this work is a test rig, whose design and construction has brought together the expertise of the linear motion company, HepcoMotion, and SmartDrive, specialists in motion control.
Transparent soil is a combination of silicon and oil which behaves like soil under pressure. It was developed by Sheffield University to enable dynamic tests results to be demonstrated and evaluated visually.
A typical test involves a tray of transparent soil being placed in the upper section of the rig beneath which resides a power class 4 laser. The rig pushes boring devices into the soil, the laser provides the means of measuring the distortion and a digital camera held in the vertical plane captures images.
Dennis Murphy, Managing Director of SmartDrive explains: “SmartDrive and HepcoMotion visited Sheffield University together to discuss the basic principles of the system. We then created CAD drawings and, following a little fine tuning, we cut the metal and made a perfect system first time round!”
An important element of the system was its ability to provide up to 3kN or down force, so it was essential that the construction should be robust. The resultant rig therefore comprises two geared pairs of HepcoMotion SBD 30-100 Sealed Belt Drives that perform the X and Y motion with a geared PSD80 lead screw delivering the huge 3kN of down force.
The rigidity of the HepcoMotion SBD makes it well suited for this test rig. It is compact and exceptionally clean, incorporating a flush, metal cover strip. This runs the entire length of the high-strength aluminium beam which houses the linear guide and belt, preventing any ingress of dirt or debris into the system. The requirement for Z-axis movement in this application called for a product that can accommodate enhanced linear force and higher gearing. The PSD80 screw driven linear actuator is suited for this duty and is available in a wide range of screw pitches.
This actuator features HepcoMotion’s high-performance Herculane wheel technology that provides a combination of load capacity, speed and low friction that exceeds that of other similar sized units.
All axes on the Sheffield University test rig are engineered to accommodate the reflected stresses, in particular those exerted on the supporting MCS aluminium frame profile also supplied by HepcoMotion. They are driven from the SmartDrive multi-axis SA46 intelligent stepper motor drive system with gears and motors carefully selected to ensure the required speeds and torques are achieved.
Comprehensive visual front-end
As the University had no software programming capability in house, SmartDrive was also asked to provide a simple but comprehensive visual front-end that would allow any user to control and report on the motion as well as measure the stresses.
This rig is reported to be performing well and is seen as an important development in laboratory scale physical modelling. Its compact nature also allows it to be easily transported across the world to demonstrate Sheffield University’s expertise at the leading edge of soil dynamics.
To learn more about linear motion products from HepcoMotion, please visit the website at www.hepcomotion.com.