MagnaTran 7.1 User’s Manual
Operation
MN-003-1600-00
Theory of Operation
Brooks Automation
Revision 2.2
6-13
Motion Control
The design and operation of the MagnaTran 7 robot uses a minimum of moving parts
to ensure minimal maintenance requirements. The T1 and T2 drives are concentri-
cally mounted to the drive shafts in the vacuum environment eliminating the need for
rotary seals. Since there are no mechanical or electrical connections to the T1 and T2
drive shafts, unlimited rotation of the arms is allowed. The optional Z Axis Drive is
coupled to the T1/T2 drive assembly.
The MagnaTran 7 Robot uses three digitally encoded servo systems (T1-Axis Encoder,
T2-Axis Encoder and Z-Axis Encoder) which are controlled by the DSP microproces-
sor on the Personality PCB, to govern the motion of the robot’s arm(s). The servo sys-
tems for the T1 and T2 drives utilize directly mounted disk encoders in each drive
unit.
Position monitoring circuits in all three servo loops signal an out-of-tolerance motion
profile, disabling the servos and setting a latched fault condition. This error is usually
caused by physical obstruction of the arm motion of greater than 4° and will stop the
servos and report a hard tracking error. Small bumps to the robot will cause it to settle
back into position without excessive vibration or overshoot.
The MagnaTran 7 robot uses the Brooks patented “Time Optimal Trajectory™”
motion control algorithms to determine all robot motion. The speed of the robot is
determined by “wafer tracking” as described below.
Speed
The MagnaTran 7 is a servo controlled robot where the maximum speeds are deter-
mined by a combination of torque limit, maximum acceleration limits, and jerk limits
(3rd time derivative of distance). These limits are factory set in the firmware.
To ensure optimal performance and efficient motion sequences, the actual arm
motions occur at three different speeds. Additionally, when the system references
itself during a Home sequence, the motion is a special slow Homing Speed to insure
maximum positional accuracy.
•
The slowest speed (usually somewhat faster than Homing speed), the “with
wafer” or Low Speed, is used for wafer transfer motions.
•
The Medium Speed is used for motions that occur when the active arm is
empty and the inactive arm is occupied (dual arms only).
•
The fastest speed, the “without wafer” or High Speed, is used for motions that
occur when no wafer is on the End Effector.
