Investigating Force Control Strategies for a Servo Actuator
Author
Jørgensen, Kristian Øeby
Term
7. term
Education
Publication year
2018
Submitted on
2018-01-18
Pages
71
Abstract
Dette projekt undersøger, hvordan man kan designe en kraftregulator til et servoaktuatorsystem med en asymmetrisk cylinder (forskellige stempelarealer på de to sider) og en symmetrisk proportionalventil (samme flow i begge retninger). Vi opstiller en ikke-lineær model af systemet og validerer den ved at sammenligne simulationer med målinger på det faktiske anlæg. Med lineær reguleringsteori udformes en PI-regulator, der giver tilfredsstillende kraftsporing for en sinusformet kraftreference. For at forbedre styringen udvides løsningen med en ventilkompensator. Den bedste estimering af flow fås, når kompensationen baseres på trykket i ét kammer frem for i begge kamre. Fejlen blev reduceret, når kompensatoren blev anvendt. Ved sænket tilførselstryk kunne der opnås tilsvarende opførsel med kompensator, mens fejlen steg uden kompensator. Kompensatoren kan styres enten af ventilsignalet eller af kraftreferencen, forudsat at ventilens dynamik er tilstrækkelig hurtig. Endelig opnås tilsvarende kraftsporing med en ventil, der er matchet til cylinderen; trykgradienterne i kamrene bliver mere jævne, og der kræves et lavere tilførselstryk.
This thesis examines how to design a force controller for a servo actuator system with an asymmetric cylinder (different piston areas on the two sides) and a symmetrical proportional valve (the same flow in both directions). We derive a nonlinear model of the system and validate it by comparing simulations with measurements from the real setup. Using linear control theory, we design a PI controller that provides satisfactory force tracking for a sinusoidal force reference. To improve performance, we add a valve compensator. The most accurate flow estimation is achieved when the compensator uses pressure from one chamber rather than both. The error decreased when the compensator was applied. When the supply pressure was reduced, similar behavior was maintained with the compensator, whereas the error increased without it. The compensator can be driven by either the valve command or the force reference, provided the valve dynamics are sufficiently fast. Comparable force tracking is achieved with a valve matched to the cylinder; the chamber pressure gradients are smoother, and a lower supply pressure is required.
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