We consider the control of Port-Controlled Hamiltonian (PCH) systems, which are a generalization of Euler-Lagrange Systems. A new matching equation for PCH systems is developed so that interconnection damping assignment passivity-based control (IDA-PBC) can be extended to the regulation of some underactuated PCH systems whosekinetic energy must be modified. A simple underactuated mechanical system (the inertial wheel pendulum) is used to demonstrate the effectiveness of the proposed method.

This paper investigates the kinematics and stiffness of an isotropic three-legged manipulator having six degrees of freedom. Rotary motors at the base rotate the tool by using the extensible legs as drive shafts. The manipulator has the positional stiffness of a parallel manipulator and the rotational stiffness of a serial manipulator. Low inertia results from having only three legs and having three motors fixed at the base. The inverse kinematics are obtained in closed form. Singularities are characterized for the case of concentric u-joints at the tool. These singularities yield the constraint singularities of a related 3-universal-prismatic-universal translational manipulator.

This paper investigates a symmetrical configuration of a known 3-UPU manipulator having three extensible legs and 3 translational degrees of freedom. The kinematics are expressed with respect to a frame that in aligned with the three legs when they are mutually orthogonal. The resulting kinematic equations are symmetric with respect to the three tool coordinates. It is shown that the manipulator stiffness is much greater with the prismatic joints actuated than with the revolute joints actuated. Design enhancements are described for increasing the degrees of freedom to 4 or 6 and for fixing the motors to the stationary base.

We propose an algorithm for evaluating the quality of JPEG compressed images, called the psychovisually-based image quality evaluator (PIQE), which measures the severity of artifacts produced by JPEG compression. The PIQE evaluates the image quality using two psychovisually-based fidelity criteria: blockiness and similarity. The blockiness is an index that measures the patterned square artifact created as a by-product of the lossy DCT-based compression technique used by JPEG and MPEG. The similarity measures the perceivable detail remaining after compression. The blockiness and similarity are combined into a single PIQE index used to assess quality. The PIQE model is tuned by using subjective assessment results of five subjects on six sets of images. The results show that the PIQE model is most accurate in the compression range for which JPEG is most effective.

Iterative learning control (ILC) improves the accuracy of a system that repeatedly tracks a reference trajectory. If certain convergence conditions are satisfied, the tracking error tends toward some ultimate error signal as the number of iterations grows. We show that for any causal LTI ILC, there exists a feedback control that, achieves an error arbitrarily close to the ultimate ILC error (in a single iteration). This feedback control requires no knowledge of the plant and can be constructed from the ILC parameters alone. This result is obtained even if the ILC algorithm itself includes feedback. Two cases are considered, corresponding to whether or not a certain transfer function matrix is singular. The nonsingular case is investigated for MIMO systems and it is proved that feedback control achieves the ultimate ILC error exactly. For the singular case, it is proved that feedback control can make the tracking error arbitrarily small in the SISO case. The results of this study suggest that ILC provides no benefit over conventional feedback control, even when no plant knowledge is available.