Technologies The NASA Space Telerobotics Program

Schilling Hydraulic Manipulator Controller Development

In support of the WP-02 Hardware Testing "Track Task" a heavy lift Schilling hydraulic manipulator system was procured and modified to emulate a sub-set of the capabilities of the Special Purpose Dextrous Manipulator (SPDM). The most significant modification was the replacement of the standard Master-Slave Control System. A Cartesian Space Control System was designed and developed that could position the end-effector based on input from a teleoperator using two three-degree-of-freedom hand controllers (translation and rotation) at a Multi-Purpose Applications Console (MPAC) workstation.

The goals of the project were to achieve a minimal level of capability by mid-year to allow the Track Task Hardware Testing Group to run some preliminary tests and then meet all functional and performance requirements, for SPDM emulation, by the end of the year. These goals and schedules were met with two phases of development.

Phase I: This first phase was to provide general teleoperated control of the manipulator in Cartesian space and to have a simple force moment accommodation (FMA) capability. This required the development of the computer architecture (VME-Bus based Embedded PCs), the low-level servo-valve controller for joint position control, and the higher-level motion controller to perform inverse-kinematics and FMA calculations. Other features included multiple operating frames and a user definable point-of-resolution.

Phase II: The second phase focused on more detailed system enhancements. The FMA algorithm was modified to be more SPDM-like. Computed gravity compen-sation was added to negate the effects of gravity on the FMA. The servo-valve controller was modified to provide tighter control of the manipulator joint positions. A payload data-base was included to allow the operator to modify payload specific parameters in the controller. The ability to record all data that was sensed and computed during a run was included along with a post-processor to help analyze the data. And the ability to interface external devices, such as the gripper and the workstation displays was also added.

All of the Track Task Hardware Testing functional and performance requirements and schedules were met within the year. The system is currently in a phase III which is an enhancement of the MPAC workstation to include SPDM representative display pages and operational procedures.


Point of Contact:
Scott A. Hankins



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Last updated: May 10, 1996