General description
This page explains who the instrument works and what maintenance and adjustments have to be done to the instrument.
The robot consists off the linear slides X and Y . On these axis the gripper unit is fitted. This unit picks and places the fibres on the field plate
For more detailed information about the parts used (manufacturer type etc) see the partlist.
X and Y slides: each slide consists off a linear slide with recirculating ballunits. This way a smooth movement with a minimum off play is guaranteed. The motion is provided by a DC servomotor with integrated encoder.The motor is connected through a ball screw with nut. When the instrument is woken, the motor drives the slide through a switch (opto-coupler), this then sets the encoder to 0 step counts. Then the axis can be moved by typing the required step counts. Limit switches are fitted just as a matter of safety to prevent any mechanical damage in case the software limits would fail. It is important that the two axis are orthogonal and that the zeroset switch is properly set up. The orthogonallity was defined when the instrument was build, the zeroset switch can be set up and has to be checked if it's damaged or knocked or replaced.
Gripper unit The original design off the gripper unit was redone by ING staff and a complete new gripper unit was made, with less moving parts thus making the mechanism more reliable.
The gripper unit is fitted onto the X and Y shafts and can be placed on any place on the field plate. The unit consists off the gripper jaws, that grab the fibre on the sharks fin. These jaws can be moved in rotation to align with each fibre on the field plate (theta movement). The whole gripper can be moved in Z to allow to pick and lift a fibre off the field plate to move it .
Theta motion: the gripper jaws can be rotated through 360 degrees. It is fitted in a pair of ball bearings. A DC motor with integrated encoder, drives a worm and worm wheel gear. There's a zeroset (opto-coupler) switch mounted on the back of the gripper jaws. When started the motor drives the flag through the switch which resets the encoder to zero. For more details on alignment see alignment and calibration page
Z-motion: The Z-motion is achieved by a linear slide with a ball screw that is driven by a DC motor with integrated encoder. When the mechanism is initialised the motor drives the flag through the switch and this then resets the encoder to zero. There is a limit switch that prevents the gripper to drive into the hardstop if the home switch would fail. For more details on alignment see alignment and calibration page
Camera system Further there is a Pulnix video camera fitted to the unit. This camera looks through some optics to the fibre end on the prism. When fibres are being placed, light is fed into the fibres from the other side. The camera looks at the light coming out and can recognise and centroid on the fibre this way and put the gripper exactly over the sharks fin. A triplet lens is used to relay the image of the fibre to an accessible point through the jaws and centre of the gripper body. A folding prism with silver coating is used to bend the light through 90 degrees before a magnifying lens projects the final image onto the camera. For more details on alignment see alignment and calibration page
Mobile sky viewing probeThis probe is fitted to the side of the gripper unit. It bolts down on the Y axis off the robot. It is used to acquire the object. There's a known offset between the probe and the centre of the gripper jaws. If there has been done major work on the gripper unit or if there's doubt about the offset this should be recalibrated. See for instructions the alignment and calibration page.
Fixed sky viewing probe This probe sits on a linear slide and can be brought into the field. It is mainly used to do mapping.
For alignment and calibration on the mechanisms above look at the alignment and calibration page.
last updated 12 january 2003 by MVDH