Sliding-mode control of a flexure based mechanism using piezoelectric actuators

The position control of designed 3 PRR flexure based mechanism is examined in this paper. The aims of the work are to eliminate the parasitic motions of the stage, misalignments of the actuators, errors of manufacturing and hysteresis of the system by having a redundant mechanism with the implementation of a sliding mode control and a disturbance observe. x-y motion of the end-effector is measured by using a laser position sensor and the necessary references for the piezoelectric actuators are calculated using the pseudo inverse of the transformation matrix coming from the experimentally determined kinematics of the mechanism. The effect of the observer and closed loop control is presented by comparing the results with open loop control. The system is designed to be redundant to enhance the position control. In order to see the effects of the redundant system firstly the closed loop control for active 2 piezoelectric actuators experiments then for active 3 piezoelectric actuators experiments are presented. As a result, our redundant mechanism tracks the desired trajectory accurately and its workspace is bigger

Tasarlanan düzlemsel paralel esnek bağlantılı mekanizmanın kayan kipli kontrolü

Günümüzde mikro/nano teknolojileri geliştikçe bildiğimiz rijit mekanizmaların yerini esnekliği ayarlanabilir, yeniden yapılandırılabilir yüksek hassasiyetli konum kontrollerine elverişli esnek bağlantılı mekanizma tasarımları öne çıkmıştır. Bu mekanizmalar malzemelerin esnekliğinden yararlanarak yer değişim ve kuvvet transferlerini sürekli, kararlı ve mikron seviyede yapılmasını sağlamaktadır. Bu çalışmada da yeni bir düzlemsel paralel esnek bağlantılı mekanizma tasarlanıp konum kontrolü yapılmıştır. Esnek bağlantılı mekanizma tasarımında göz önünde bulundurulması gereken önemli noktalar sunulmuştur. Hassas konum kontrolü için kayan kipli bozan etken gözlemleyicisi ile kayan kipli konum kontrolü metoduyla hassas konum kontrolü metodu sunulmus¸ deney sonuçları açık çevrim kontrol ve bilinen PID kontrol yöntemleriyle karşılaştırılmıştır. Sonuç olarak önerilen kontrol yöntemi ile mekanizmanın mikron seviyede kontrolü sağlanmıştır

Micro position control of a 3-RRR compliant mechanism

A 3-RRR compliant mechanism is designed to be used as a micro positioning stage. The stage displacements are analyzed by using structural FEA. However the experimental results for the manufactured mechanism are not compatible with the FEA which are mostly accepted as ideal while designing. A position control using Sliding Mode Control with Disturbance Observer is proposed for the reference tracking of the center of the stage. The motion of the center is measured by using a laser position sensor and the necessary references for the piezoelectric actuators are calculated using the pseudo inverse of the transformation matrix coming from the experimentally determined kinematics of the mechanism. Piezoelectric actuator linear models are used for disturbance rejection. Finally, the position control of the mechanism is succeeded although it has big errors in manufacturing, assembly etc

Micro position control of a designed 3-PRR compliant mechanism using experimental models

A new compliant stage based on 3-PRR kinematic structure is designed to be used as a planar micro positioner. The mechanism is actuated by using piezoelectric actuators and center position of the stage is measured using a dual laser position sensor. It's seen that manufactured mechanism has unpredictable motion errors due to manufacturing and assembly faults. Thus, sliding mode control with disturbance observer is chosen to be implemented as position control in x-y axes of the center of the mechanism. Instead of piezoelectric actuator models, experimental models are extracted for each actuation direction in order to be used as nominal plants for the disturbance observer. The position control results are compared with the previous position control using linear piezoelectric actuator models and it's seen that the implemented control methodology is better in terms of errors in x and y axes. Besides, the position errors are lowered down to ±0.06 microns, which is the accuracy of the dual laser position sensor