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This paper proposes a technique to control a cable robot in the total absence of a model and its parameters. The cable robot is actuated by three motors whose data, including exact positions, pulley diameters, and nominal cable length, are unknown. We just assume to have a very rough knowledge of lower and upper bounds for the partial derivatives of the relation between the cable lengths and the end-effector space coordinates. A structured-light sensor measures the end-effector position, and the goal is to drive it to a designated point. An algorithm is proposed with guaranteed convergence based on the so-called model-free plant tuning approach. No learning stage is required. Experimental results are reported.

Given a static plant described by a differentiable input-output function, which is completely unknown, but whose Jacobian takes values in a known polytope in the matrix space, we consider the problem of tuning the output (i.e., driving the output to a desired value), by suitably choosing the input. To this aim, we assume to have at our disposal a discrete sequence of trials only, as it happens, for instance, when we iteratively run a software, with new input data at each iteration, in order to achieve the desired output value. In this paper we prove that, if the polytope is robustly non-singular (or has full row rank, in the general non-square case), then a suitable discrete-time tuning law drives the output to the desired point. The computation of the tuning law is based on a convex-optimisation problem to be solved on-line. An application example is proposed to show the effectiveness of the approach.

In an attempt to investigate the relationship between respiratory mechanics and pulmonary hemodynamics, we evaluated pulmonary function in 31 infants with left-to-right shunts and subsequent high pulmonary blood flow, undergoing cardiac surgery. Measurements were performed 1 d before and repeated 10 d and 4–5 wk after correction. The age of the patients ranged from 4 d to 24 mo, body weight from 2.7 to 11.8 kg. Pulmonary artery-pressure, assessed by Doppler echocardiography, was preoperatively elevated in 23 patients (group 1), whereas it was within normal values in eight infants (group 2). Respiratory mechanics were measured using the single-breath occlusion technique in sedated infants. To evaluate specific compliance, functional residual capacity was determined by using an open circuit nitrogen washout technique. A reduced preoperative compliance value (mean with 95 confidence interval) was found in group 1: 34.8 (26.5–43.1) mL. kPa−1. After hemodynamic correction, a progressive significant (p< 0.01) improvement was demonstrated at 10 d and 1 mo with values of 47.5 (39.2–55.8) mL. kPa−1and 56.5 (45.6–67.4) mL. kPa−1, respectively. A similar trend was noted evaluating specific compliance with values of 0.27 (0.24–0.30) kPa−1and 0.44 (0.42–0.46) kPa−1, respectively before and after surgery. Preoperative functional residual capacity value was 130 (100–160) mL. In group 2, normal preoperative compliance values were obtained, without significant changes after surgery. In both groups, resistance was within the normal range both before and after surgical correction, and functional residual capacity did not change either. No correlations were found between compliance and pulmonary artery pressure and pulmonary blood flow values. In conclusion, these results show that infants with left-to-right shunts and pulmonary hypertension present with reduced compliance of the respiratory system that rapidly improves after cardiac surgery.