Modelling and Control of Stepper Motors for High Accuracy PDF
Preview Modelling and Control of Stepper Motors for High Accuracy
Departamento de automa´tica, ingenier´ıa electro´nica e informa´tica industrial Escuela Te´cnica Superior de Ingenieros Industriales Centro de Electro´nica Industrial Modelling and Control of Stepper Motors for High Accuracy Positioning Systems Used in Radioactive Environments Autor: Ricardo Picatoste Ruilope Ingeniero en Autom´atica y Electr´onica Industrial por la Universidad Polit´ecnica de Madrid Directores: Jesu´s A´ngel Oliver Ram´ırez Doctor Ingeniero Industrial por la Universidad Polit´ecnica de Madrid Alessandro Masi Doctor en Ingenier´ıa de Control e Informa´tica por la Universit`a degli Studi di Napoli Federico II 2014 Tribunal Tribunal nombrado por el Mgfco. y Excmo. Sr. Rector de la Universidad Polit´ecnica de Madrid, el d´ıa de de 2014. Presidente: Prof. Jos´e Antonio Cobos M´arquez, Universidad Polit´ecnica de Madrid Vocales: Dr. Mark Butcher, CERN Prof. Marco Storace, Universidad de G´enova Prof. Antonio L´azaro, Universidad Carlos III de Madrid Secretario: Prof. Pedro Alou Cervera, Universidad Polit´ecnica de Madrid Suplentes: Pablo Zumel Vaquero, Universidad Carlos III de Madrid Prof. Jesu´s Acero Acero, Universidad de Zaragoza Realizado el acto de lectura y defensa de la Tesis el d´ıa de de 2014 en la Escuela T´ecnica Superior de Ingenieros Industriales de la Universi- dad Polit´ecnica de Madrid. Calificacio´n: EL PRESIDENTE LOS VOCALES EL SECRETARIO A la t´ıa Mari “A la aceitera ...” i Acknowledgements (Agradecimientos) I would like to express my deepest appreciation to my CERN supervisor, Alessan- dro Masi, who gave me the opportunity which allowed this thesis to become a reality. Thanks for the support and encouragement to never stop, no matter how hard things could be. Equally important has been my supervision and guidance from my university. For all the support and wise counselling, specially in spite of the difficulties that ´ the distance imposes, I want to thank my thesis director, Jesu´s Angel Oliver. Thanks to my working colleagues, in special to Mark, for the help and support all along this work. Thanks to all the students with whom I was so lucky to work. Thecollaborationwithyouhasbeenfundamental. Alsoanimportantthanksgoes to my international friends, whom has been like a family in this distant land. Para mis agradecimientos personales comenzar´e utilizando una cita de mi escritor favorito, Antoine de Saint-Exup`ery: “No es la distancia la que sirve para medir la lejan´ıa”. Y empiezo con ella porque las circunstancias me han llevado a estar lejos de la mayor´ıa, es por eso que quiero agradecer el esfuerzo que hab´eis hecho para que la distancia no nos aleje. Empiezo dando las gracias a mi familia, la cual ha m´as que demostrado que siempreestara´ah´ıparam´ı,apoya´ndomeyd´andomecarin˜o. ¡Esperoquetengamos la oportunidad de celebrar muchas ma´s Picatostadas! Y no s´olo mi familia m´as cercana. A todos mis t´ıos y primos, y a la abuela, muchas gracias por seguir siendo una familia tan especial y de la que me siento tan orgulloso de ser parte. Me gustar´ıa tambi´en agradecer todas las personas que han pasado por mi vida durante este tiempo, y que ahora siguen cerca o dispersos por el mundo. Los primeros como siempre son los Pichos. Aunque la distancia ha puesto las cosas dif´ıciles, seguiremos dando guerra. A mi familia en Suiza, englobada en Ola k ase. Cada vez esta´ ma´s repartidos por el mundo, ¡pero nunca parando de crecer! Lo hemos pasado muy bien juntos, y que siga siendo as´ı. A mis compan˜eros de IAEI y la EUITI. Con vosotros cada vez que podemos reunirnos, parece que nos dijimos adi´os ayer mismo. A mis amigos del INTA, esas grandes personas que te encuentras en el camino y que a veces tienes la suerte de poder conservar. Para el final como no, dejo lo m´as importante. Gracias a Isa por ser mi compan˜era en este viaje. En esta especie de odisea que es la vida y por haber so- brevivido, el uno apoyado sobre el otro, a todas las tormentas. Por estar conmigo y ser mi familia, pareja y amiga. Gracias por ese futuro que ya compartimos y que empieza hoy. ii Abstract Hybrid Stepper Motors are widely used in open-loop position applications. They are the choice of actuation for the collimators in the Large Hadron Collider, the largest particle accelerator at CERN. In this case the positioning requirements and the highly radioactive operating environment are unique. The latter forces both the use of long cables to connect the motors to the drives which act as transmission lines and also prevents the use of standard position sensors. How- ever, reliable and precise operation of the collimators is critical for the machine, requiring the prevention of step loss in the motors and maintenance to be foreseen in case of mechanical degradation. In order to make the above possible, an approach is proposed for the appli- cation of an Extended Kalman Filter to a sensorless stepper motor drive, when the motor is separated from its drive by long cables. When the long cables and high frequency pulse width modulated control voltage signals are used together, the electrical signals differ greatly between the motor and drive-side of the cable. Since in the considered case only drive-side data is available, it is therefore nec- essary to estimate the motor-side signals. Modelling the entire cable and motor system in an Extended Kalman Filter is too computationally intensive for stan- dard embedded real-time platforms. It is, in consequence, proposed to divide the problem into an Extended Kalman Filter, based only on the motor model, and separated motor-side signal estimators, the combination of which is less demand- ing computationally. The effectiveness of this approach is shown in simulation. Then its validity is experimentally demonstrated via implementation in a DSP based drive. A testbench to test its performance when driving an axis of a Large Hadron Collider collimator is presented along with the results achieved. It is shown that the proposed method is capable of achieving position and load torque estimates which allow step loss to be detected and mechanical degradation to be evaluated without the need for physical sensors. iii iv These estimation algorithms often require a precise model of the motor, but the standard electrical model used for hybrid stepper motors is limited when currents, which are high enough to produce saturation of the magnetic circuit, are present. New model extensions are proposed in order to have a more precise model of the motor independently of the current level, whilst maintaining a low computational cost. It is shown that a significant improvement in the model fit is achieved with these extensions, and their computational performance is compared to study the cost of model improvement versus computation cost. The applicability of the proposed model extensions is demonstrated via their use in an Extended Kalman Filter running in real-time for closed-loop current control and mechanical state estimation. An additional problem arises from the use of stepper motors. The mechanics of the collimators can wear due to the abrupt motion and torque profiles that are applied by them when used in the standard way, i.e. stepping in open-loop. Closed-loop position control, more specifically Field Oriented Control, would al- lowsmootherprofiles,morerespectfultothemechanics,tobeappliedbutrequires position feedback. As mentioned already, the use of sensors in radioactive envi- ronments is very limited for reliability reasons. Sensorless control is a known option but when the speed is very low or zero, as is the case most of the time for the motors used in the LHC collimator, the loss of observability prevents its use. In order to allow the use of position sensors without reducing the long term reli- ability of the whole system, the possibility to switch from closed to open loop is proposed and validated, allowing the use of closed-loop control when the position sensors function correctly and open-loop when there is a sensor failure. A different approach to deal with the switched drive working with long cables is also presented. Switched mode stepper motor drives tend to have poor perfor- mance or even fail completely when the motor is fed through a long cable due to the high oscillations in the drive-side current. The design of a stepper motor output filter which solves this problem is thus proposed. A two stage filter, one devoted to dealing with the differential mode and the other with the common mode, is designed and validated experimentally. With this filter the drive perfor- mance is greatly improved, achieving a positioning repeatability even better than with the drive working without a long cable, the radiated emissions are reduced and the overvoltages at the motor terminals are eliminated.
Description:The list of books you might like
