A. A. Abouelsoud

Robust Regulator for Flexible-Joint Robots Using Integrator Backstepping

A robust regulator for flexible-joint robots is proposed, which yields constant torque disturbance rejection acting on the links. The design uses the integrator backstepping technique [4,5] to cancel nonlinearities and disturbance not in the range space of the control. Stability of the closed loop system is shown using iterative Liapunov functions.

An adaptive observer for robots with persistent excitation

An adaptive state observer for rigid link manipulators is proposed. The proposed adaptive state observer is based on parametrizing the robot dynamic model via the estimated state and parameters, thus yielding a nominal model plus two perturbation terms, one is linear and the other is quadratic in the state and parameter estimation errors. The update law for the adaptive observer is derived using the MKY lemma (Narendra and Annaswamy 1989). Stability of the origin of the overall error system is shown using the Gronwall-Belmann lemma (Khalil 1992) and a converse Lyapunov theorem (Khalil 1992). The proposed adaptive observer is tested through simulations

Linear state feedback regulator for rigid link manipulators

A new generic representation of the gravity vector in the rigid link robot dynamic model is proposed. We use this representation to design a linear state feedback regulator and show that the closed loop nonlinear system is globally asymptotically stable and exponentially stable in any closed ball. We exploit the fact that the gravity vector is the gradient of the potential function. We also consider robustness of the linear state feedback regulator to parameter uncertainty.

Output regulation for flexible-joint manipulators using partial state measurement

A linear-state feedback regulator for flexible-joint manipulators is proposed. The link-position vector (in the joint space) is regulated to a given desired position using partial state measurement. The actuator-position vector is regulated to a certain equilibrium point related to the link-desired position. This work uses our earlier result [1] which puts the gravity vector of the robot dynamic model in a new specific form. The fact that the spring matrix representing joint flexibility is of high order of magnitude [3–5] is exploited to prove the global asymptotic stability of the origin of the closed loop system.

Error Source Identification in Measuring Soft Tissue Stiffness and Self Compensating This Error Using Three Probes Configuration

One of the biggest challenges for measuring soft tissue stiffness using tactile sensors is to have an output independent of the contact conditions. Although the approach of using two springs with different stiffness is used, the output of sensor is usually unstable because of the soft tissue surface irregularity. This irregularity creates an inclination angle between the sensor tips and the tissue. By scanning some real organs of a chicken using laser microscope, it is found that the angle value does not exceed 3 degrees. A modification on the original sensor is proposed to compensate that error. A finite element analysis for the two sensors is carried out to compare their behavior. The error of the original approach is about 55% and 103% with an inclination angle 3 degrees on the left and right direction, respectively. However, the modified sensor output is stable up to 8 degrees with an error not exceeding 4%. Furthermore, it could differentiate between different soft tissues stiffness within the specified range.