4 research outputs found
Design and control of a two-degree-of-freedom lightweight flexible arm
No full textAbstract: "This report describes the design and control of a two-joint, two-link flexible arm. Our purpose has been to build an efficient arm in the sense that most of the energy provided by the motors is spent in doing the task (moving the tip mass) instead of moving the arm structure. In order to achieve that, we designed a flexible arm that has most of its mass concentrated on the tip. We also wanted to decouple radial tip motions from angular tip motions. The special mechanical configuration that fulfills all these specifications is described in Section 2.Section 3 describes the control scheme of this arm. An important problem with controlling it was the large Coulomb friction of the motors. A two-nested-loop multivariable controller has been used. The inner loop controls the position of the motors while the outer loop controls the tip position. The resolved acceleration method is generalized to control this flexible arm. The compliance matrix was used to model the oscillations of the structure, and was included in the decoupling/linearizing term of this controller. Experimental results are given in Section 4, and conclusions are drawn in Section 5.
A new approach to control single-link flexible arms.
No full textAbstract: "This third report describes a new method to control single-link lumped-mass flexible arms in the case of having friction in the joint and changes in the payload. Both linear and nonlinear friction components are overcome by using the very robust control scheme developed in the second report, which is based on two nested feedback loops: an inner one that controls the motor position and an outer one that controls the tip position. In order to compensate for changes in the payload, an adaptive control scheme is used. Two cases are considered when compensating for changes in the tip payload: the arm is a minimum phase system or a non-minimum phase one. Different adaptive control schemes are proposed in each case. In them, compensation for changes in the load is achieved in two steps: first the tip payload is estimated from a very simple procedure proposed here, and then the feedforward and feedback controllers are tuned according to this estimated value. It results in a quite simple control law that can be used for real-time control of flexible arms, and that needs minimal computing effort. Experimental results are shown.
