Microcontrollers for Mechanical Engineers: From Assembly Language to Controller Implementation

This paper describes the evolution of a graduate and advanced undergraduate mechanical engineering course on microcontrollers and electromechanical control systems. The course begins with developing an understanding of the architecture of the microcontroller, and low-level programming in assembly language. It then proceeds to working with various functions of the microcontroller, including serial communications, interrupts, analog to digital conversion, and digital to analog conversion. Finally, the students learn how to characterize first and second order systems, and develop and implement their own controllers for a variety of electromechanical systems. The course takes the uncommon approach of teaching assembly language programming to mechanical engineering students, with the students using assembly language programming for approximately half of the course and the remainder using the C programming language. The authors believe that this approach helps students develop a better understanding of the architecture of the microcontroller and low-level routines found in embedded control applications. The course provides a bridge between traditional mechatronics courses that focus on electronics and interfacing, and lab-based control courses that use turnkey data acquisition systems and graphical programming tools such as Simulink or LabVIEW. The course has existed for over two decades, using a variety of microprocessor and microcontroller platforms. After evaluating numerous alternatives, the course was recently updated to use a 32-bit ARM Cortex-M3 microcontroller evaluation board from STMicroelectronics paired with custom interfacing circuitry. This platform was chosen not only for more modern microcontroller technology, but also for the availability of free development tools and very inexpensive evaluation boards. This allows the students to write and test their programs outside of scheduled lab times, along with the ability to cost-effectively utilize microcontrollers in future projects

Motion Control of Robotic Arm with Command Shaping Method

In the manufacturing industry, lots of rapid point-to-point motion is required while the residual vibration is unfavorable. Residual vibrations caused by flexible elements are limiting the performance of mechanical system, especially when the system needs to make rapid point-to-point motion. As proved in earlier studies, avoiding natural frequencies of the mechanical system reduces the residual vibrations. This work is based on a non-linear, two-link flexible jointed robot with configuration dependent resonance. Command shaping method consisting different combinations of base functions and weighting factors are compared in this work. The compatibility of command shaping with classical feedback control structure allows a computationally effective method for real time implementation. By measuring the acceleration after the input stops, the residual vibration is analyzed. The best case would be the one with the least peak-to-peak residual acceleration and reasonable peak acceleration during the motion. Experimental results show that the residual vibrations can be reduced considerably after the implementation of command shaping method. As verified in this work, command shaping method is a practical way to control motion with flexible elements without exciting the system’s natural frequencies and demanding significantly more computation capability

Model-Independent Control of a Flexible-Joint Robot Manipulator

Flexibility at the joint of a manipulator is an intrinsic property. Even "rigid-joint" robots, i

DIAGNOSTICS-ORIENTED MODEL FOR AUTOMOTIVE SCR-ASC

This paper presents a diagnostics-oriented aging model for combined Selective Catalytic Reduction (SCR) and Ammonia Slip Catalyst (ASC) system, along with a model-based on-board diagnostic (OBD) method applied to both test-cell data and on-road data from commercial trucks. The key challenge with model development was unavailability of NOx and NH3 measurements between SCR and ASC. Since it would have been very difficult to calibrate both SCR and ASC dynamics without any measurements between SCR and ASC, therefore ASC was modeled using static look-up tables to determine ASC’s NH3 conversion efficiency and its selectivity to NOx and N2O as a function of temperature and flow rate. The traditional three-state single-cell ordinary differential equation (ODE) model was used for SCR. Hot Federal Test Procedure (hFTP) was used to calibrate the model. Cold FTP (cFTP) and Ramped Mode Cycle (RMC) were used for validation. Results show that the SCR-ASC model can capture the aging signatures in tailpipe NOx, NH3, and N2O reasonably well for cFTP, hFTP, and RMC cycles in the testcell data. After slight re-calibration and combining with a simple model for commercial NOx sensor’s cross-sensitivity to NH3, the model works reasonably well for on-road data from commercial trucks. A model-based on-board diagnostic (OBD) method has been presented with enable conditions designed to detect operating conditions suitable for detecting aging signatures, while minimizing false positives and false negatives. The OBD method is applied to both test-cell and real-world truck data with commercial NOx sensors. Results on test-cell data demonstrate the challenges of robust SCR monitoring even on the limited data set used in this work. The model-based enable conditions are shown to be robust but extremely restrictive as the OBD gets enabled at very few points in the test-cell data. Application on truck data showed that the proposed OBD method can be implemented on commercial trucks with limited sensors. In the truck data, the enable conditions were satisfied on many more points than the test-cell data. Results on truck data show encouraging trends between relative degradation level and the number of miles on four trucks. In future work, these trends will be validated using more data from commercial trucks with known aging levels

The Educational Impact of Modular, Open-ended Controller Design Projects*

In the fall of 2001 we implemented the first of a series of new controller design projects in ou

THE EDUCATIONAL IMPACT OF A GANTRY CRANE PROJECT IN AN UNDERGRADUATE CONTROLS CLASS

In the fall of 2001 we implemented a new controller design project in our Junior/Senior level controls class in Mechanical Engineering at Purdue University. The old project, which involved the identification and control of a “black box”, failed to challenge and motivate students. Our new project is the design of a controller for the point-to-point motion of a gantry crane system. Student teams modeled the gantry crane and developed a controller to meet several performance specifications. The designs were implemented in Simulink with MATLAB’s Real-Time Workshop. A competition served to further motivate the students. In the end we were very impressed with the great effort the students gave and the quality of their designs. Each group presented their design and most students stayed and asked questions for several hours