Comau C3G Plus, Operation And Maintenance Manual, Page: 173 / 266

CALIBRATION
This paragraph describes the calibration and Turn-set procedures that can be carried out using the controller
and examines the subject of calibration in detail.
The basic concepts, the terminology used and the internal mechanisms for handling axis position information
are given below.
TERMINOLOGY
·
AXIS POSITIONAL VALUE: the axis positional value contains all the information necessary to determine
the exact position of an axis in space; it is handled by the control unit using information contained in 32
bits.
·
FLASH EPROM: is a memory used to save the characteristic information about the robot associated
with the controller, the calibration constant values and the length of the levers and other parameters for
use of the emergency terminal without the optional RPT module.
·
RPT module: the RPT (Resolver Position Tracker) module is an optional microprocessor device housed
at the base of the robot. Its main functions are:
- counting resolver revolutions for eight axes;
- containing the specifications of the robot to which it is associated, the calibration constants, the length
of the levers and other parameters for the emergency terminal;
This module makes the robot ABSOLUTE, as the data stored in it are retained even in the case of a power
failure. If this module is not operative when the controller is turned on, the revolution count cannot be re-
called.
The C3G controller handles a system without RPT. At system restart, the controller checks that the values
read from the resolver are the same as those read before switching off (either with a warm/cold restart or af-
ter a power failure). If the values correspond, the machine is considered calibrated. If they do not corre-
spond, a Turn_set procedure will be necessary.
Note that no check is performed on the resolver turn numbers. For this reason, the user is advised to put the
arm in the DRIVE OFF state before switching the system off.
·
RECONSTRUCTION OF THE AXIS POSITIONAL VALUE: when the controller is turned on, the system
software reconstructs the axes positional values among the various initialisations.
The system software verifies this value checking that the difference between the reconstructed position
and the position before switching off is below a threshold. If the threshold is exceeded, the controller dis-
plays the 59411 SAX: motion after switchoff error and the operator is responsible for checking that the
physical position of the robot corresponds to the new value.
·
CALIBRATION POSITION: the calibration position is the value that the positional value of the axis must
have. The calibration position is a “joint type” reference position in the robot working space.
·
CALIBRATION CONSTANTS (or calibration error): a calibration constant is the difference between the
data read by the resolver and the theoretical position that the resolver should have in that particular ro-
bot position. In fact, as positioning of the resolver in relation to the robot joint is random, the real position
of the resolver must be corrected according to the theoretical position required for the joint. The calibra-
tion constant is contained inside the resolver revolution. It is described in the variable $CAL_DATA and
can be read using the command CAV (Configure, Arm, View_cal).
·
NUMBER OF RESOLVER REVOLUTIONS: the number of revolutions is pre-set by the calibration oper-
ation.
·
SYSTEM CALIBRATION: the purpose of this calibration procedure is to establish the position of the
axes of a robot comparing this to an ideal robot. This makes it possible to interchange robots of the
same type (if explicitly allowed) and assures universal applicability of the programmes they use.
C3G
Plus
MAIN OPERATIONS FOR SYSTEM USE
00/1097 5-13
CALIBRATION