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Designing electropneumatic control unit(EPCU)and motor identification setup of the PneuARMM robot

Belinskis, Rihards (2020) Designing electropneumatic control unit(EPCU)and motor identification setup of the PneuARMM robot.

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Abstract:This Master’s thesis project is about designing the control unit of an pneumatically actuated robot prototype for minimally invasive MRI-guided surgeries (PneuARMM). The robot is built to be used within MRI / CT rooms, which requires non-electrically-conductive actuation. To actuate PneuARMM, pneumatic stepper motors (PneuAct, designed by F.S. Farimani) were used. The PneuAct motors are driven by electropneumatic valves, which are controlled by the electropneumatic control unit (EPCU). The EPCU consists of a master controller and several slaves, where each slave controls one PneuAct motor, thus one degree of freedom of PneuARMM. The ability of a slave is to control: the stepping period Ts, the duty cycle DC and the rotational direction of the motor. Additionally, it can enable speed or position-control modes, and has various types of communication protocols: UART, SPI and even physical on-board command possible. For feedback regarding PneuAct’s rotational direction, speed and position, optic signals are used, which are obtained from custom designed (by F. S. Farimani) optic encoders. The EPCU master controls the slaves using SPI protocol with the use of a joystick (designed by M. Morteza). The joystick enables the user to freely choose a positition to which the slaves manoeuvre PneuARMM by sequentially sending signals to a particular slave to achieve the desired position. Additionally, the master can electrically power any number of slaves, if individual slave’s state is not required to be observed via UART. An additional task is to design a complementary device - motor identification setup - which is used to test an individual PneuAct motor and identify possible malfunction. The motor identification setup can read and regulate input pressure, can read input air-flow and detect motor stalls. The aim of the thesis is to create a fully functioning EPCU inside a housing of pre-defined shape and size. The prototype consists of 1 pneumatic input, 3 pneumatic outputs for PneuACT-I, 4 outputs for PneuACT-II, and an electric input to power the circuit logic. The housing holds a PCB, which contains control logic algorithms programmed on a microcontroller, along with 4 electropneumatic valves to drive a single PneuAct motor. The EPCU master and slave, as well as motor identification setup devices are designed on custommade printed circuit boards (PCBs). To build these PCBs, a microcontroller is selected and used as the central piece of electronic design, around which the schematic is designed. After initial calculations and the prototyping stage on breadboards, the electronic (and PCB) design was done in KiCAD. All software programming of the microcontrollers was done using C programming language, whereas the experiments were automated using Python. The first step of designing the EPCU and motor identification setup was to establish system requirements to understand exactly what is needed. Afterwards the functional design was created to understand the functionality of the devices in terms of inputs and outputs, and, lastly, the technical design addresses all points in great detail. When the design is done, experiments are made to test the system. Throughout the process of designing the EPCU (and the motor identification setup) key ideas of safety, simplicity, determinism and reproducability are reiterated and focused on. This report is intended to be as clear regarding the design, tests and limitations of the EPCU and motor identification setup, as possible.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:44 medicine, 53 electrotechnology
Programme:Systems and Control MSc (60359)
Link to this item:http://purl.utwente.nl/essays/80843
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