Browsing by Author "Ristevski, Stefan"
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Item Open Access A self-adjusting and modular supervisory control algorithm for planar dexterous manipulation(Elsevier, 2023-04) Ristevski, Stefan; Çakmakçı, MelihMany applications require precise handling and manipulation of delicate objects. In some cases, the object must be transported to a new location following a strict travel path including time-related constraints. This paper presents a self-adjusting modular control algorithm for dexterous manipulation of planar objects using multiple manipulators with precise path and timing deliveries. The popular caging approach is simple, and usually effective when manipulating objects with multiple devices but can fail following complex paths with orientation adjustments under time-critical tracking requirements. The proposed approach exploits the dynamics of the object in real-time using tracking control and allocates the force that needs to be applied by each manipulator based on their current position around the object to maximize their capability to push in the direction of the contact angle. The new algorithm is self-adjusting and modular; It can adjust its force allocation according to configuration changes during operation, and manipulators execute the same algorithm regardless of their number. The advantages of the new approach are successfully demonstrated both with simulations and testbed experiments, including orientation tracking, which is not typically featured with the caging approach. Conditions to check when the new algorithm is most effective are also analyzed. The closed-loop stability and performance of the new algorithm are also studied and necessary conditions are identified.Item Open Access An extremum seeking estimator design and its application to monitoring unbalanced mass dynamics(IEEE, 2020) Çakmakçı, Melih; Ristevski, StefanWhen sensor information of a controlled-system output is not available, estimators can be used. Estimators are algorithms that take the available sensor data from the system and estimate the necessary data to be used by the feedback controller. Typically, estimation is done by running a model of the plant inside the controller and formulating an output error minimization mechanism to calculate the unknown dynamics and parameters. In this paper, a new estimation mechanism based on extremum seeking is presented. The method utilizes the idea of minimization of a non-linear error function of written in a specific structure, which may be suitable for systems with periodic dynamics such as systems with unbalanced masses. An estimation adjustment algorithm can be built based on the error between the model outputs and the actual sensor data. This adjustment algorithm drives the error between the model and the actual plant output to zero, while the feedback controller uses the information from the model. This proposed method is then applied to a mobile robotic system to improve its locomotion. Our initial results showed promising improvements up to five times more displacement with the same command on a testbed environment with challenges in eluding high-order dynamics and digital effects at high-frequency input.Item Open Access Mechanical and controller design of a modular mechatronic device - mechacell(Bilkent University, 2015-08) Ristevski, StefanSince ancient times people have been building tools to aid them in their life. Robots evolved from being purely mechanical to mechatronic, from immobile to mobile and became smaller in scale. As the technology in building robots matured researchers, began working to build robotic systems that cooperate similar to the ones in nature. Ability of ants to accomplish tasks beyond the capability of a single ant intrigued scientists in robotics society to mimic that feature of ants and develop simple modules that alone cannot accomplish much, but together can complete complex assignments. Our motivation is to develop a miniaturizable mechatronic module{MechaCell. Mechanical design focuses on a novel locomotion system having a mechanism that converts vibrations into translational motion. Two independent controllers, one for steering and one for translational speed control are designed such that MechaCell can follow a complex path and group of MechaCells can guide an object to follow a complex path. Simulation results from the model of the MechaCell developed in SimMechanics are presented. Experimental setup comprising of a Bluetooth enabled PC, a platform, an overhead camera and four MechaCells is set up and simulation results are experimentally veri ed. Possible application of coordinated object manipulation is in manufacturing systems that have limited xture capabilities and desired precision in sub{centimeter levels.Item Open Access Mechanical design and position control of a modular mechatronic device (MechaCell)(IEEE, 2015) Ristevski, Stefan; Çakmakçı, MelihManufacturing techniques have advanced exponentially in recent years, providing means for production of smaller and more powerful electronics, which makes it compelling to design small and more powerful robots. Our work focuses on a mechanical design and position control of a modular mechatronic device called MechaCell. Mechacells are designed as modular semi-autonomous devices which can be used alone or part of a pack. In this paper our main focus is on the mechanical design of the Mechacell, especially the locomotion system which uses forces produced by a rotating unbalance that moves in a spherical domain for steering of the Mechacell. As part of the supervisory algorithm an overhead HD camera is used for position tracking of the Mechacell; the data is then sent to the Mechacells through a wireless connection. A proportional integral derivative controller is used as a base controller; then a friction compensation algorithm is added, based on the mathematical model of the Mechacell's locomotion system. Steering and locomotion controller of the Mechacell is validated using a complex motion profile in the developed testbed.Item Open Access Planar motion controller design for a modular mechatronic device with heading compensation(Elsevier, 2019) Ristevski, Stefan; Çakmakçı, MelihMechaCells are designed as closed, scalable and modular semi-autonomous devices that can be used alone or part of a pack. In this paper, we discuss a locomotion system that uses the reaction force produced by a rotating unbalance that moves in a spherical domain with a steering mechanism. In order to produce the precise motion capability, a multi-loop controller is developed. This controller uses a friction compensation algorithm based on the mathematical model of the locomotion system. To improve the accuracy of tracking, conventional LuGre friction estimation model is extended for rapid directional changes of the MechaCell during planar motion. The linear and rotational acceleration of the device is also included in controller calculations since it affects the locomotion force generated by the unbalanced mass. The resulting control system is validated both with simulations and experiments and the effectiveness of the extended model and the controller is verified. Our results show significant improvement when a detailed friction compensation observer is used in the controller that includes the effect of sudden steering changes for precise path following.