Detailed Description
At the heart of the AMC102 is an Atmel Atmega128 processor running at 12MHz, which
enables the controller to execute tasks whilst simultaneously accepting commands and
returning status data via its RS422 serial port. Possible baud rates are 19200, 28800, and
57600. A second RS422 port is provided for a time synchronisation signal, which can be
provided by a GPS engine.
In normal operation, a command and control computer will be connected to the RS422 port.
This computer will issue commands to the AMC102, and receive back status information,
such as servo positions and velocities, in near real-time. The operator is able to set servo
parameters such as limit positions, and maximum speeds; these values being stored in non-
volatile memory. Stored values may be read back or altered at any time.
Velocity Profiles
Acceleration and deceleration terms may be programmed into the AMC102 to establish
limiting values in the event of a step input. This can be important in order not to over-stress
gearboxes and other servo components. In the event of an emergency stop, the deceleration
profile is ignored.
Axis Brakes and Limits
By default, all axis brakes are applied even when power is not supplied to the unit. When
command by the host computer, the brakes will be released. At this point, the AMC102
dynamically maintains the current position (or will move to a new requested position) aided
by feedback information provided by the position and velocity encoders. However, when a
request is made by the host to apply axis brakes, they are not immediately applied. Instead,
the controller slows each axis to zero velocity independently at the maximum allowable
deceleration rate defined for each axis. When all axes have stopped moving (zero velocity)
the brakes are applied. In this way, the gearbox and servo motor lifetimes are not
compromised due to excess dynamics.
The user may specify a set of 'soft' limits which define the minimum and maximum possible
positions for each axis. It is not possible to command an axis to exceed these limits in normal
operation. However, if a fault should occur in the system and an axis moves past any of
these points then a secondary set of hardware limit switches are activated which prevent any
damage to the system. Uniquely, the AMC102 is able to automatically recover an axis in this
condition by driving out of the limit in a controlled fashion without regard to the position and
velocity encoder readings (which may themselves have been the cause of the problem). The
user simply requests that the brakes be released for the axis in limit and the controller card
does the recovery automatically.
Table Tracking
The host computer may send a table of axis positions (equally spaced in time) to the
controller store for later use. The controller automatically calculates a velocity profile from the
position table data supplied. The host computer then instructs the controller to move to the
start of a table track pass and then issues a run command with a time offset relative to the
next 1PPS reference pulse. When the exact number of milliseconds after this 1PPS pulse have
occurred, the table track mode will commence and all tracking will be performed completely
automatically – all time aligned to the supplied 1PPS pulse stream. Position and velocity
feedback are of course always available to the host to show progress during the table track
run. The host computer can at any time abort the run simply by applying the brakes,
requesting a manual move to a new position or by requesting an emergency stop.
AMC102-031111 Two-axis precision servo controller module
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