 |
 |
Canadarm
Courtesy of MDRobotics
|
|
CanadarmCourtesy of MDRobotics
Since its maiden voyage aboard U.S. Space Shuttle Columbia in 1981, the Shuttle Remote Manipulator System (SRMS), known as Canadarm, has demonstrated its reliability, usefulness, and versatility and has provided strong, yet precise and delicate handling of its payloads.
Canadarm was designed, developed and built by Spar Robotics operation, now MD Robotics, under contract to the National Research Council of Canada. The first arm was Canada's contribution to NASA's Space Shuttle Program. Subsequently, NASA ordered four additional units which have resulted in over $600 million in export sales for Canada.
Canadarm has performed flawlessly on more than 50 missions; placing satellites into their proper orbit and retrieving malfunctioning ones for repair. Perhaps its most notable mission was the repair of the Hubble Space Telescope. Canadarm was used as a mobile work platform for astronauts during numerous space walks required to repair the faulty telescope. Canadarm played a critical role retrieving the satellite, placing it in the cargo bay for repairs, and then re-deploying it.
Unplanned exercises for Canadarm have included knocking a block of ice from a clogged waste-water vent that might have endangered the shuttle upon re-entry, pushing a faulty antenna into place, and successfully activating a satellite that failed to go into proper orbit.
In December, 1998 Canadarm played a critical role in the first assembly mission of the International Space Station, mating the U.S. Unity Node to the Russian-built Zarya. The SRMS will continue to play a vital role in the assembly of the space station.
The Shuttle Remote Manipulator System consists of a shoulder, elbow and wrist joint separated by an upper and lower arm boom. The shoulder joint has two degrees of freedom, the elbow joint has one degree of freedom, and the wrist joint has up to three degrees of freedom.
At a total weight of approximately 905 lbs., the Canadarm has recently been upgraded to maneuver payloads of up to 266,000 kgs. (in the weightlessness of space). Canadarm uses an end effector with a specially designed grapple fixture to capture payloads & place them in orbit.
The SRMS is a remotely controlled six degree-of-freedom payload handling device comprised of the following component sub-systems:
Each subassembly component of the SRMS i.e. the shoulder, elbow or wrist is made up of a basic element called a joint one-degree-of-freedom or JOD. The JOD's are simply motor driven gearboxes that allow the basic structure of the arm to articulate much like the human arm. There are two JOD's in the shoulder joint which allow the whole arm to pitch (up and down motion) and yaw (side to side motion). One in the elbow joint to allow the lower arm to pitch and three in the wrist joint to allow the tip of the arm to pitch, yaw and roll (rotating motion). SRMS is much more articulate than even the human arm and can therefore accomplish very complex manoeuvres. The JOD motors are equipped with their own brakes and joint motor speed control. Each JOD also incorporates a device called an encoder, which accurately measures joint angles. Thus each joint is capable of moving independently at different speeds and in different directions with respect to any or all the other JOD's.
Linking the shoulder, elbow and wrist joints are the upper and lower arm booms. These booms are constructed of graphite-epoxy. The upper arm boom is approximately 5 m. long by 33 cm. in diameter comprising of 16 plies of graphite-epoxy (each ply is .013 cm thick) for a total weight of just under 23 kg. The lower arm boom is approximately 5.8 m. long by 33 cm. in diameter comprising of 11 plies of graphite-epoxy for a total weight of just over 22.7 kg. Each boom is protected with a Kevlar bumper (the same material used in bulletproof vests) to preclude the possibility of dents or scratches on the carbon composite.
Just as the arm booms linked the shoulder, elbow and wrist joints mechanically, the wiring harness (electrical cabling) accomplishes the same thing only electrically. The wiring harness provides electrical power to all the joints and the End Effector (mechanical hand) as well as data and feed back information from each of the joints. This link continues from the SRMS in the payload bay and continues on into cabin of the space shuttle where astronauts control the actions of the arm remotely.
The End Effector or mechanical hand of the SRMS allows the arm to capture stationary or free flying payloads by providing a large capture envelope (a cylinder20.3 cm. in diameter by 10 cm. deep) and a mechanism/structure capable of soft docking and rigidizing. This action is accomplished by a two stage mechanism in the End Effector which closes three cables (like a snare) around a grapple probe (knobbed pin) bolted onto the payload and then draws it into the device until close contact is established and a load of approximately 499 kg. is imparted to the grapple probe. The forces developed by the End Effector on the payload through the grapple probe will allow for manoeuvring of the payload without separation from the remainder of the SRMS to the positional accuracy's previously stated.
The SRMS has two CCTV's, one at the elbow joint and one at the wrist joint. The CCTV units are used to aid the astronauts in the positioning of the arm for payload capture/retrieval or payload by capture/deployment.
The movement of the SRMS is controlled by the space shuttles general-purpose computer (GPC). The hand controllers used by the astronauts tell the computer what the astronauts would like the arm to do. Built in software examines what the astronauts commanded inputs are and calculates which joints to move, what direction to move them in, how fast to move them and what angle to move to. As the computer issues the commands to each of the joints it also looks at what is happening to each joint every 80 milliseconds. Any changes inputted by the astronauts to the initial trajectory commanded are re-examined and recalculated by the GPC and updated commands are then sent out to each of the joints. The SRMS control system is continuously monitoring its “health” every 80 milliseconds and should a failure occur the GPC will automatically apply the brakes to all joints and notify the astronaut of a failure condition. The control system also provides a continuous display of joint rates and speeds, which are displayed on monitors located on the flight deck in the orbiter. As with any control system, the GPC can be over-rided and the joints can be operated individually from the flight deck by the astronaut.
The SRMS is covered over its entire length with a multi-layer insulation thermal blanket system, which provides passive thermal control. This material consists of alternate layers of godized Kapton, Dacron scrim cloth and a Beta cloth outer covering. In extreme cold conditions, thermostatically controlled electric heaters (resistance elements) attached to critical mechanical and electronic hardware can be powered on to maintain a stable operating temperature.
| Length | 15.2m |
| Diameter | 38cm |
| Weight on Earth | 410Kg |
| Speed of Movement | -unloaded 60 cm/sec. -loaded 6 cm/sec. |
| Upper & Lower Arm Boom | Carbon Composite Material |
| Wrist Joint | Three degrees of movement (pitch/yaw/roll) |
| Elbow Joint | One degree of movement (pitch) |
| Shoulder Joint | Two degrees of movement (pitch/yaw) |
| Translational Hand Controller | Right, up, down forward, and backward movement of the arm |
| Rotational Hand Controller | Controls the pitch, roll, and yaw of the arm |
