Hodge E. Jenkins

Design of a robust controller for a grinding system

Grinding is a process that is often used in the manufacture of precision components. Variations in position, velocity, and force trajectories can affect part quality by changing part surface finish, geometry, and process material removal rate. Thus, controlling the position, velocity, and force is critical to achieving a high quality product from the grinding process. In designing a compensator for a robust force controlled grinding system, several constraints must be considered. It is critical that the normal grinding force is decoupled from the tangential feed velocity of the system. Therefore, two separate control loops are designed; a standard feed velocity loop and a force loop. Besides decoupling the force and velocity, a variety of other system performance specifications must be achieved. To aid in the design of the control loops, several parametric plots are used to visualize the effects of various control parameters on the closed-loop system dynamics as well as the coupling of the two loops.

Adaptive pole-zero cancellation in grinding force control

Describes the development of an adaptive force controller for the grinding process. Using a real-time grinding model an adaptive pole-zero cancellation technique is developed and implemented to reduce the grinding process variation. Real-time model parameter estimation and controller designs are implemented to achieve higher bandwidth control capability than is presently available in machine tool controllers. The results of this research have culminated in a stable adaptive force controller for grinding, and have demonstrated the potential for increasing productivity. The implementation of this adaptive pole-zero cancellation in force controlled grinding provides a superior surface following capability for fine finishing, as compared to fixed gain controllers.

Preparing engineering students for working in teams through senior design projects

This paper explores teaming and its cultivation in senior capstone design projects to better prepare students for occupational interaction with other professionals, clients, and management to solve complex or open-ended problems. Teaming is deemed an important skill for engineers, by organizations employing engineers and other professionals. In the global marketplace organizations that value and capitalize on these skills can be more agile and competitive. The impact of current and future trends on teaming, including outsourcing and globalization, are discussed in terms of non-technical skills required for practicing engineers and the preparation of new engineers. Parallels between senior design projects and actual industry projects are drawn to highlight the key personal interaction skills and tools required for success. Examples of successful student teams and professional teams are presented for discussion. Measurements of project and teaming success by industry and professional organizations are presented. Topics include: traditional, global and virtual team structures emphasizing the nontechnical aspects necessary for modern teams including, team communication, diversity and cultural aspects, problem resolution, and other elements necessary for project success.

Dynamic Stiffness Implications for a Multiaxis Grinding System

Operating a machine tool, such as a grinder, so that the spindle speed is at a system natural fre quency may be useful, since the dynamic stiffness is lower at that frequency and thus may be more tolerant to force variations. It is hoped that a result of this type of operation may produce a better quality surface. In this research, the dynamic stiffness of a three-axis grinding system is experimentally determined. Grind ing experiments are then conducted to determine the effects of dynamic stiffness on surface finish in terms of the surface profile characteristics. Displacements induced by grinding wheels typically exhibit a once- per-revolution effect. Thus, the first experimental grinding wheel speed (in terms of revolutions per second) is selected by examining the empirical dynamic stiffness data and choosing a resonant frequency (cycles per second) in the range of achievable grinding wheel speeds (revolutions per second). For comparison, a grinding run is performed using a higher grinding wheel speed, where the system dynamic stiffness at the cor responding frequency is larger. Additionally, simulations are performed for estimated grinding displacement time-histories based on wheel speed. Simulated results support the preliminary experimental data, which indicate smoother surfaces result when grinding with rotational speeds corresponding to a natural frequency.

Determination of a Dynamic Grinding Model

In precision abrasive machining, it is important to control process variables such as the material removal rate, normal force and power input, as these factors influence surface finish, dimensional precision, and material damage. In this research, a linear grinding process model, with enhancements over past models, is developed relating normal force to material removal rates. Two experimental procedures for the determination of the grinding models parameters are presented. Simulations are performed to validate the grinding model. The determined model is found to be a valid representation of the grinding process that should prove useful in adaptive control with real-time parameter estimation.

Increasing Student Interest and Understanding in a First Mechanics Course Through Software Modules

Increasing student understanding of engineering mechanics, interest, and readiness for engineering practice are significant concerns of engineering faculty. As a part of an attempt to address these concerns, engineering application software was integrated into a first engineering mechanics course at the sophomore level, Statics and Mechanics of Materials. The course software component is part of an educational initiative across the Mercer University School of Engineering to infuse a common software thread within the curriculum, especially relating to mechanics and design areas. Two course modules using solid modeling and finite element analysis software were included via laboratory sessions and assignments emphasizing visualization and relationships between design and analysis. Descriptions of the modules and their learning objectives as well as results of student surveys taken after each module are presented and discussed.Copyright

Development of a cascaded controller for temperature and core growth rate in vapour-phase axial deposition

Abstract A cascaded feedback control strategy for an industrial vapour-phase axial deposition (VAD) process is investigated in this paper. VAD is a widely used process in the creation of high-purity glass for optical fibre. In previous work a soot tip surface temperature controller was developed for the VAD process to reduce the effects of core soot temperature variation on deposition geometry, leading to a more stable process. However, it is desired to regulate both the core soot and clad soot such that they deposit at the same axial rate to provide a more uniform product. This paper presents the development of a cascaded controller strategy and process model to couple and regulate the surface temperature and deposition rates of core and clad soot. Simulation studies demonstrate a potential improvement in the uniformity of the core and clad soot geometry over the soot product length.

Precision Grasping With Variable Compliance Using Force Sensing Resistors

The ability to precisely control the applied force and deformation of a grasped object is the focus of this paper. A simple mechanical end effector system with parallel grippers was developed to study compliance effects in precision grasping. A servo gripper was instrumented with force and position sensors, associated circuitry, hardware, and visual indicators; moreover, the sensors and servo motor were connected to a microcontroller that interfaced with a laptop computer. A closed-loop position control system was embedded within a force control system. Springs of varying, known stiffness were grasped to characterize and calibrate the force control system. Compliance effects of the servo gripper were observed and measured while grasping these springs under several discrete control conditions. Experimental data were compared to reduced order theoretical models for validation. A control scheme was successfully developed to precisely grasp and hold objects of varying size, shape, stiffness, and orientation, using the real-time data to establish correction factors for compliance and sensor drift. It was demonstrated that these effects can be minimized by modifying the motor control signals using the presented force and position feedback scheme.Copyright

Design and Control of Capstan-Pulley Draw System for Optical Fiber Manufacturing

Optical fiber for data communication is manufactured by the draw process, which involves heating and pulling high purity glass cylinders to diameters of 125 μm. The diameter of the glass fiber and its light-guide core must remain constant to create a product capable of transmitting high-bandwidth optical data. The draw capstan design has a significant impact on the optical fiber quality. As the draw speed is used to control the fiber diameter, the ability of the draw capstan to follow velocity commands directly affects the resulting fiber diameter. To improve the control of the optical fiber diameter, the design of the overall system was revisited. A lumped-parameter model of the capstan drive was developed. It accounts for disturbances in the draw process that arise from sources such as the variation in the diameter of the input glass cylinder and the draw tension control, affecting the glass temperature and viscosity. The selection of the motor and the design of the speed controller in the optical fiber draw capstan pulley system were studied. Simulation studies over a range of parameters demonstrate that speed regulation, necessary to manufacture optical fiber within allowable diameter tolerances, can be achieved in the presence of estimated process disturbances without motor current saturation. The model predictions suggest that an effective draw capstan system can be synthesized and controlled. This case study has broad applications for the design of practical engineering systems that include control, electrical, and mechanical subsystems, typical in modern manufacturing. The paper highlights the use of mechanical and electrical modeling, system identification, and control design as necessary parts of product and process improvement.© 2008 ASME

Control Approach for Mitigating Off-Axis Position Variation in Vapor-Phase Axial Deposition

VAD (vapor-phase axial deposition) is a widely used glass soot fabrication process for the creation of high purity optical glass fiber. It is critical for low signal loss and manufacturing productivity that the core and clad geometry remain constant. Variation (off-axis) of the deposition torch position relative to the deposited core soot tip can cause an appreciable change in the deposition rate and the resulting glass soot cylinder core and clad diameters. This paper presents deposition torch position control schemes to effectively eliminate the soot growth rate variation caused by the mechanical, off-axis (horizontal) positioning errors. Two control approaches are compared for their effectiveness on the resulting geometry of the deposited glass soot cylinder. A direct approach, clad diameter control, requires the addition of a non-contact sensor to feedback the measured clad diameter. The second approach, pull speed control, uses the change in the axial growth rate of the core soot as feedback. Using a previously determined empirical model of the soot deposition process, a suitable system model was implemented to simulate the VAD deposition and the resulting soot cylinder diameters. The system response to mechanical positioning errors was evaluated using the two control approaches as well as open-loop. Uniformity of soot clad diameter was used as an evaluation metric for comparison. Simulation results indicated significant diameter regulation improvement obtained by both control methods. However, since diameter measurement lagged the pull speed change, pull speed control was more effective when comparing maximum, minimum, and range of core and clad soot diameters over the deposited soot length. The control approach presented here might be extended to other situations such as machining.