Conference Paper

A Low-cost Compliant 7-DOF Robotic Manipulator

Dept. of Comput. Sci., Stanford Univ., Stanford, CA, USA
DOI: 10.1109/ICRA.2011.5980332 Conference: IEEE International Conference on Robotics and Automation, ICRA 2011, Shanghai, China, 9-13 May 2011
Source: IEEE Xplore


We present the design of a new low-cost series elastic robotic arm. The arm is unique in that it achieves reasonable performance for the envisioned tasks (backlash-free, sub-3mm repeatability, moves at 1.5m/s, 2kg payload) but with a significantly lower parts cost than comparable manipulators. The paper explores the design decisions and tradeoffs made in achieving this combination of price and performance. A new, human-safe design is also described: the arm uses stepper motors with a series-elastic transmission for the proximal four degrees of freedom (DOF), and non-series-elastic robotics servos for the distal three DOF. Tradeoffs of the design are discussed, especially in the areas of human safety and control bandwidth. The arm is used to demonstrate pancake cooking (pouring batter, flipping pancakes), using the intrinsic compliance of the arm to aid in interaction with objects.

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    • "Werkmeister et al. [61] and Baser et al. [62] studied the capstan drive stiffness and slip error respectively. A capstan cable drive is used, for example, in the WAM TM Arm from Barret Technology R , in an anthropomorphic dexterous hand [63], in a low-cost compliant 7-DOF robotic manipulator [64], and in a five degree-of freedom haptic arm exoskeleton [65]. By controlling the force on the cable, a capstan can also be used as an active locking device. "
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    • "There is also another serial robot designed for small surgeries (Seibold et al., 2004) that employs fixed motors. Quigley et al. (2011) used fixed motors and wires to drive their low cost manipulator. Commercial manipulator has used a novel cabling transmission system to reach zero backlashes with low friction and low inertia (Townsend and Guertin, 1999). "
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    • "The location of the object relative to the tool frame can then be easily found from the sensor-based object pose estimate. However, for lower cost [1], [2] and non rigid robot arms, or for arms using tendons in the drive system (such as the Barrett WAM arm used in the experiments of Section V), the tool or palm frame location can not be well estimated from a forward kinematic model, as large deviations in end effector position are experienced when manipulating heavier objects. The errors in tool or palm frame can also be highly task dependent. "
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    ABSTRACT: This paper develops an estimation framework for sensor-guided manipulation of a rigid object via a robot arm. Using an unscented Kalman Filter (UKF), the method combines dense range information (from stereo cameras and 3D ranging sensors) as well as visual appearance features and silhouettes of the object and manipulator to track both an object-fixed frame location as well as a manipulator tool or palm frame location. If available, tactile data is also incorporated. By using these different imaging sensors and different imaging properties, we can leverage the advantages of each sensor and each feature type to realize more accurate and robust object and reference frame tracking. The method is demonstrated using the DARPA ARM-S system, consisting of a Barrett™WAM manipulator.
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