John Lumkes

High-Fidelity Magnetic Equivalent Circuit Model for an Axisymmetric Electromagnetic Actuator

A computationally inexpensive magnetic equivalent circuit (MEC) improves axisymmetric electromagnet design and modeling tools by accurately capturing fringing and leakage effects. Lumped parameter MEC models are typically less accurate for modeling electromagnetic devices than distributed parameter finite-element models (FEMs). However, MEC models require significantly less computational time to solve than FEMs and therefore lend themselves to applications where solution time is critical, such as in optimization routines, dynamic simulation, or preliminary design. This paper describes how fringing permeances in axisymmetric electromagnetic devices can be derived and then included in a MEC model. Including fringing field effects significantly decreases error in the MEC model, creating a more accurate, or high fidelity, magnetic equivalent circuit (HFMEC). Eighty-nine electromagnets with unique geometries, coil currents, and materials were modeled with MEC, HFMEC, and FEM methods. The axisymmetric HFMEC developed in this work had 67% less average force error and 88% less average flux error compared to traditional MEC results while still being computationally inexpensive to solve.

Model Development and Experimental Analysis of a Virtually Variable Displacement Pump System

Abstract This work presents the modelling and testing of a Virtually Variable Displacement Pump (VVDP). The system used a high speed on/off valve to modulate flow from a fixed displacement pump, directing the flow either to the tank or high pressure supply line of the hydraulic system. A lumped parameter model of the system was developed using sub-models to describe the dynamics of each component in the system. A test setup using currently available components was built to validate the overall system model and study the effects of switching frequency on system efficiency. Once verified, the model was used to simulate and further study the effects of changing the compressible fluid volume and line lengths. Simulation results show that reducing the line lengths and compressible volume improves the average VVDP system efficiency by 14% over a range of switching frequencies and duty cycles while holding other system parameters constant.

Analytical Coupled Modeling and Model Validation of Hydraulic On/Off Valves

The goal of this paper is to describe a method for modeling high speed on/off valves. This model focuses on the nonlinearities of the electromagnetic, fluidic, and mechanical domains, specifically within solenoid driven poppet style valves. By including these nonlinearities, the model accurately predicts valve transition time for different driving voltages and valve strokes. The model also predicts fluid transients such as pressure ripple. Unique attributes of the model are the inclusion of the effect of eddy currents and fringing while still being fully coupled with the fluid and mechanical domains. A prototype was constructed and used to experimentally validate the model. By developing accurate lumped parameter models, valve dynamics can be applied to hydraulic systems to accurately capture their dynamics.

Survey of Three Different Methods of Delivering Engineering Content in Lectures

There has been a rapid increase in the use of technology in university classrooms. Many university classrooms and laboratories include an overhead projection unit, computer, and connections for laptops. More recently, tablet PCs have been investigated as another way to effectively engage students in a classroom environment. This study summarizes the results of student surveys comparing three different lecture delivery methods: using complete PowerPoint slides and handouts, using traditional chalkboard lectures without handouts, and using skeleton PowerPoint slides and handouts. Both PowerPoint lectures were delivered through a Tablet PC with a wireless link to an LCD projector, allowing for instructor mobility. Second year engineering students were asked to evaluate six learning assessment statements and to provide written feedback regarding the strengths and weaknesses for each of the three methods. Using the Tablet PC resulted in the highest overall scores but with much variance between the six survey questions.

Coupled model of a magnetic actuator controlling a hydraulic cylinder and load

Magnetic pressures on nonlinear steel are shown to have lower values than typical hydraulic pressures and, thus, small magnetic actuators are often coupled to hydraulic circuits. A new method of modeling a typical electrical/magnetic/hydraulic/mechanical system is described. Results of electromagnetic finite-element analysis of a magnetic actuator are used in a SPICE circuit that contains the differential equations of a hydraulic valve, hydraulic cylinder, and mechanical load. The coupled model is used to compute typical transient pressures, flows, and motions. Due to fluid flow forces the mass of the controlled arm is shown to have a coupling effect on the armature motion of the magnetic actuator.

Coupled Physics Modelling for Bi-Directional Check Valve System

This paper describes the development of a high speed on/off bi-directional check valve. The design was characterized using coupled-physics modelling tools, and a prototype was constructed and tested in the laboratory. The simulated and experimental results were compared. The high speed on/off bi-directional check valve (BDCV) utilizes positive feedback of flow forces and differential port pressure to quickly open and close the primary poppet. The coupled-physics model incorporates mechanical and fluid domains, which was solved through conducting finite element analysis (FEA) on a 2D planar model. After characterizing the BDCV, the system model was expanded for a single piston pumping system using two BDCVs and the simulation on system full displacement pumping was conducted. The modelling results showed a moderate agreement with measurements, which demonstrated the capability of the coupled physics model to effectively investigate the dynamic performances of a BDCV operating in a digital pump system.

Simulation Based Design and Optimization of Digital Pump/Motors

Current state of the art variable displacement pump/motors have high efficiencies when operating at high displacements. However, as the displacement of the pump/motor is reduced, the efficiency significantly decreases. Digital pump/motors aim to increase the efficiency and range of operation of the fluid power system by minimizing leakages, friction losses and compressibility losses. It is based on the concept of actively controlling high speed on/off valves connected to each piston cylinder displacement chamber. This work involves the development of a coupled dynamic model of a digital hydraulic pump/motor that is crucial for understanding the design tradeoffs and operating characteristics of the digital pump/motor. This simulation model can be used to characterize and predict the efficiency, define the dynamic response and flow requirements of on/off valves required to provide significant improvements in efficiency and dynamic response over traditional pump/motors, and perform design optimization studies. The model can analyze different operating strategies (flow limiting and flow diverting) and characterize the effects on pump/motor efficiency and flow ripple. The simulation analysis shows that the sequential flow limiting strategy yields the lowest power loss in both pumping and motoring and that small variances in the valve response would cause a significant loss of power.Copyright

Comparative Study Of Position Control with 2-Way and 3-Way on/off Electrohydraulic Valves

Abstract A comparative study of system-level performance is given for on/off valve control of a hydraulic cylinder. A dynamic model was created and simulated to develop and evaluate innovative control strategies specific to the use of on/off valves. Cylinder position control was investigated using a configuration consisting of two 3-way on/off valves and a configuration with four 2-way on/off valves. Controllers were developed to minimize the influence of on/off valve performance on the cylinder position responses. All controllers and valve configurations were experimentally tested and compared with the simulation results. A sensitivity analysis was performed by varying the supply pressure and external load applied to the cylinder. It was determined that successful performance to sine wave and step inputs can be achieved with the control theories presented and that the four 2-way on/off valve configuration provides superior position performance.

The Impact of Peak-and-Hold and Reverse Current Driving Strategies on the Dynamic Performance of Commercial Cartridge Valves

High speed valves have an important role in many existing fluid power systems and are an enabler for many proposed digital hydraulic systems. One method commonly used to improve the dynamic performance of on-off valves involves modifying the electrical input signal to the solenoids to reduce the inductive lag and eddy current decay. This research examined two commercially available direct actuated and pilot-stage actuated cartridge poppet valves and the role of peak-and-hold voltage and reverse current input profiles on opening and closing switching times. A test stand was built to characterize the performance of these valves. The valves were placed between two high frequency pressure transducers and the pressure differential across the valves was recorded, allowing the calculation of transition and delay time. The peak and reverse voltage duration was tested over a range of zero to ten milliseconds and an optimum response was found at a peak duration of six to eight milliseconds. Peak voltages ranged from 50 to 55 volts, followed by a holding voltage of 12 volts. Reverse current profiles were used to turn off the valves with a maximum peak current of three amps. The reverse current was used to increase the decay rate of eddy currents thus improving the turning off performance of the valves. Commercial valves that had a range of 33 to 55 millisecond turn-on response without input signal modification; these same valves had response times reduced to a range of seven to nine milliseconds after applying the peak and hold method. The turn-off time was reduced from 130 milliseconds to a range of 16 to 50 milliseconds after adding reverse current inputs. This improvement in valve performance can lead to siginificant energy savings due to reduction of transition losses and can widen the useful application of the valves.© 2014 ASME

Global Design Teams: Case Studies of Student and Community Impact

The rising globalization trends of international competition and the changing societal, professional, and global landscapes for engineering graduates, call for action towards integrated learning strategies to prepare engineers to address grand challenges. This paper describes a global service-learning experience, the Global Design Team (GDT), which provides students with high-impact, multi-disciplinary, collaborative experience. GDT provides real-world, full-cycle design experiences, that raise global awareness amongst team members, faculty, and partners. This experience strives for positive, sustainable interaction with stakeholder communities through the application of technical skills and competencies of students to address specific needs within the partner community. The goal is positive, mutual benefit with partner communities. The paper presents the GDT curricular model and assessment results of design experiences occurring in 2010 in Cameroon, Kenya, and Palestine, and preliminary results from design experiences occurring in 2011 in Cameroon, Colombia, Lebanon, Palestine, and Jordan. Results show that the Global Design Team experience positively impacts the measured attributes of global competence in engineering students, and also provides a positive impact on partner communities and organizations.