Browse Prior Art Database

Method of Aligning Library Accessor to Reference Datum

IP.com Disclosure Number: IPCOM000109300D
Original Publication Date: 1992-Aug-01
Included in the Prior Art Database: 2005-Mar-23
Document File: 6 page(s) / 278K

Publishing Venue

IBM

Related People

Chang, P: AUTHOR [+4]

Abstract

In any library, the robotic picker or accessor mechanism must be aligned to a reference datum so that the cartridges in the library may be reliably serviced to and from the I/O devices. Such alignment can be facilitated by use of an instrumented test plate held by the robotic accessor solely for the purpose of this alignment.

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Method of Aligning Library Accessor to Reference Datum

       In any library, the robotic picker or accessor mechanism
must be aligned to a reference datum so that the cartridges in the
library may be reliably serviced to and from the I/O devices.  Such
alignment can be facilitated by use of an instrumented test plate
held by the robotic accessor solely for the purpose of this
alignment.

      This article describes (a) such a test plate with three
displacement sensors and (b) accompanying vector algebra to correct
small angular misalignments between the sensored test plate and the
reference datum.  The end result of this alignment process is that
the test plate is parallel to the reference datum and that the
cartridge gripper mechanism is perpendicular to that datum.

      These three displacement sensors 10 are located on the test
plate by the following coordinates: (X1, Y1, Z1), (X2, Y2, Z2), (X3,
Y3, Z3).  These three sensors are coaxial.  However, they need not be
arranged in a right triangle pattern.  Currently, it is preferred
that these three sensors be spread in the outline of an equilateral
triangle 20, as shown in Fig. 1.  This test plate is mounted to block
21.  Block 21 is mounted to the robotic accessor via holes 22.

      It is preferred that each sensor telescopes.  Once the first
sensor makes contact with the reference datum 30, the robot can
continue to press the test plate towards the datum without distorting
the test plate.  The best way to do this is to have each of the
three sensors spring-loaded in a tube, similar to an LVDT (Linear
Variable Differential Transformer).

      The distance each sensor is away from the reference datum when
the first sensor makes contact is D1, D2, and D3.  Although the
distance of the first sensor to make contact with the reference datum
will be zero, we use variables for all three distances so that we do
not need to derive three different cases, one for each sensor to
first make contact.

      We now define a reference coordinate system 40.  The vertical
axis will be "Z" and the axis normal to the reference datum will be
"Y".  By the right hand rule, this makes "X" the axis pointing down
the rails away from the reference datum and towards the cartridges 50
and their storage slots 51 (Fig. 2).

      When the first sensor makes contact, the robot will continue to
push the test plate against the reference datum until all three
sensors make contact.  During this phase, the robot will be measuring
the "Y" displacement to make each subsequent sensor seat against the
reference datum, as Y is the axis normal to the surface of the
reference datum.  An alternative embodiment would utilize rigidly
mounted inductance or capacitance probe sensors and the analog output
from the two sensors not in contact would be used to electronically
measure the remaining separation distances.

      Either with the telescoping contact sensors or alternately with
t...