RESUMEN
A cascade control structure for the simultaneous position and stiffness control of antagonistic tendon-driven variable stiffness actuators (VSAs) implemented in a laboratory setup is presented in the paper. Cascade control has the ability to accelerate, additionally stabilize, and reduce oscillations, which are all extremely important in systems such as a tendon-driven compliant actuators with elastic transmission. Inner-loop controllers are closed in terms of motor positions, and outer-loop controllers in terms of actuator position and estimated stiffness. The dominant dynamics of the system (position and stiffness), composed of the mechanical part and inner loops, are identified by a closed-loop auto-regressive with exogenous input (ARX) model. The outer-loop controllers are tuned on the basis of experimentally identified transfer functions of the system in several nominal operating points for different stiffness values. After the system is identified, a controller bank is generated in which a pair of actuator position and stiffness controllers correspond to a nominal operating point and covers the area surrounding the nominal point for which it is designed. The controllers used are integral-proportional differential (I-PD) and integral-proportional (I-P) controllers, which are a variation of the PID and PI controllers with dislocated proportional and derivative gains from a direct to feedback branch that result to no overshoot for even fast reference changes (i.e., step signal), which is essential for preventing tendon slackening (meeting the pulling constraint). Analytical formulas for controller tuning based on only one parameter, λ, are also presented. Since position and stiffness loops are decoupled, it is possible to change λ for both loops independently and adjust their performance separately according to the needs. Also, the controller structure secures the smooth response without overshooting step reference or step disturbance signal, which make practical implementation possible. After all the controllers were designed, the cascade control structure for simultaneous position and stiffness control was successfully evaluated in a laboratory setup. Thus, the presented control approach is simple to implement, but with a performance that ensures a pulling constraint for tendon-driven actuators as a foundation for bioinspired antagonistic VSAs.
RESUMEN
PURPOSE: The aim of this study was to analyze outcomes of breast conserving surgery (BCS) after neoadjuvant treatment (NAT) in comparison to radical mastectomy (RM) after NAT in terms of disease-free survival (DFS), overall survival (OS) and patients' satisfaction with the esthetic outcomes of surgery. METHODS: This prospective study was conducted at the National Cancer Research Center of Serbia, Belgrade, from January 1st 2011 to December 31st 2015, on breast carcinoma patients receiving NAT. Treatment outcome was assessed by MDAPI (MD Anderson Prognostic Index). Female patients (n=52) with satisfactory clinical response to NAT and MDAPI scores 0 or 1 were included into the treatment group (NAT-BCS group). The control group (NAT-RM group) consisted of patients (n=52) with poorer clinical response and MDAPI scores 2 to 4. On check-ups, local or distant relapses were noted and both groups were asked to value their satisfaction with the esthetic outcomes of surgery using the Likert scale. RESULTS: OS was 100% in both groups. DFS was 96.1% in NAT-BCS group and 100% in NAT-RM group. Local recurrences were observed in two patients from the age group ≥60 years, with initial disease stage IIIA and "clear" resection margins on frozen section study. Patients in the NAT-BCS group were more satisfied with the esthetic outcome of surgery than the control group. CONCLUSIONS: BCS after NAT provides good esthetic outcome and is oncologically safe if adequate clinical response is achieved after NAT and if established criteria for patient selection are followed.
