Disk Mis-Load Sensing with Passive Gripper

Disk Mis-Load Sensing with Passive Gripper

      A reliable means was required to prevent costly, time-consuming
jamming of the system caused by misloaded disks falling from position
during the sputter process of hard disk manufacture.  By meeting this
requirement, the design for Disk Misload Sensing with Passive Gripper
disclosed herein represents a significant improvement over previous
practice.

      In preparation for the sputter process, a robotic arm loads
disks into openings in a pallet that carries them in an upright
position during processing.  As shown in Fig. 1A, a properly loaded
disk 1 is centered in a tapered groove 2 that holds it in place in
the pallet 3.  The depth of the groove is between 300 and 500um.  A
misloaded disk 4 rides on the edge of the groove and can fall out of
the pallet from vibration or other forces encountered in the sputter
process (Fig. 1B).

      When this occurs, the system becomes jammed and the following
steps must be performed before operation can resume:
  o  Shut system down
  o  Bleed down vacuum
  o  Let system cool to ambient temperature
  o  Clear and remove jammed disk
  o  Restore vacuum
  o  Reheat and circulate system
  o  Test for:
     Contamination
     Temperature profile
     Target spitting.

      Since this recovery sequence extends over several work shifts,
the resulting cost from loss of production is extremely high, placing
a great premium on reliable means of detecting disks misloads.
Formerly, a sensor 5 (Fig. 2) located in the gripper box 6 was used
to sense the disk after loading to ensure that it had not fallen from
the pallet during loading.  Since the pallets are subject to
vibration as well as to warping from heat distortion, a misloaded
disk 4 (Fig. 1B)...