Date: 27 July 2015
In one of the laboratories of VSL in Delft an installation for very precise measurement of the mass of gas cylinders has recently been put into operation. VSL and Mijnsbergen developped a handling system - the heart of this plant - in close cooperation. VSL is the National Metrology Institute of the Netherlands (formerly NMi) and is a leading international knowledge institute in the field of metrology.
Nothing as complex as measuring weights in the nano range. The customers of VSL entrust these challenges to the specialists in Delft. Because there are always external influences, such as temperature, the calibration of the measuring system is always the basis of accurate measurement. The latest assignment for VSL concerns weighing gas cylinders with a mass of up to 20 kg. Not easy to put place manually on a weighing scale. And in addition, to reducing external influences to a minimum, a robot carries out the handling of the gas cylinders.
The weighing system is always calibrated first with calibrated masses. In the system is a depot with these calibrated masses, which are placed on the weighing system by the handling system. In addition, the same handling system picks up the cylinders and place them on the scale. The gas cylinders are in a depot on the opposite side, with the weighing system in between.
In order to fit the system in the small space of the laboratory, this had to be compact. Due to the size of the depot and the diversity of the cylinder sizes, the range in the X and Z directions has become one meter. During some brainstorming sessions between VSL and Mijnsbergen a rigid cartesian robot solution was soon put forward. As a basis an X-axis of 1000 mm, containing a vertical Z-axis of 1000 mm. On the carriage of the Z-axis placed a rotary drive is placed that can rotate gripper in three positions, i.e. the picking positions of the calibrated masses and at 180 degrees thereof the picking positions of the gas cylinders. In between, at 90 degrees the place position at the measuring system. A Y-axis with a range of 300 mm is placed on the rotatory drive, which thereby rotates and as a telescope the gripper moves to the pick and place positions.
Realizing a stiff construction within a compact space was mechanically the biggest challenge. The solution to this was the HSB linear units from the Delta series. These linear units consist of aluminum profiles with integrated ball screw and double ball screw rail guide. Good for tilting moments up to 8500 Nm. Each linear axis is equipped with a mounted Stöber servo motor. As actuator for the rotational movement the Stöber KS series right-angle planetary drive is used. Thanks to the robust bearing no additional support bearing is necessary, so that the rotational movement between Z and Y-axis is very compact and easily constructed.
The measuring and control system of VSL has been developed with Labview. Besides the mechanical challenge it is always the challenge how the robot is controlled from the central control system. The center within the solution of Mijnsbergen is often, as well as in this application, the motion control system of Trio Motion Technology. Through the standard functionality with OCX commands in this motion controller it is pretty easy to let the central control system of VSL communicate with Labview. The applied Trio MC464 controller then controls the SD6 Stober servo drives via EtherCAT. Resulting in a flexible full digital solution with a minimum of cabling.
Good cooperation between the control specialist at VSL and Mijnsbergen led to a rapid implementation and operation of the system.
A major reason that VSL chose for Mijnsbergen, is that we are able to provide a complete system, by integrating components from various suppliers from the delivery programm into a system. From compact linear axes, servo systems up to the motion controller. But the most important reason might be the collaboration between VSL and Mijnsbergen, where VSL provide their specialism and the specialists at Mijnsbergen engineer the mechanical idea, calculation and eventually come to the selection of components. The colleagues of the project department subsequently take care that everything that is theoretically conceived will also be realized in practice. A fine piece of work between VLS and Mijnsbergen.
We supply slewing ring bearings, oscillating mountings, tensioner devices from stock and we also have spiral bevel gearboxes, servo gears and electromechanical actuators in our delivery program.
In addition we also select and offer the right components and systems for motion control solutions, such as servo gear motors, linear servo actuators and complete XYZ cartesian systems.
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