Date of Award
Doctor of Philosophy (PhD)
Agricultural and Biological Engineering
Committee Member 1
Committee Member 2
John H. Lumkes Jr.
Committee Member 3
Kartik B. Ariyur
Mobile hydraulic machines are affected by numerous undesired dynamics, mainly discontinuous motion and vibrations. Over the years, many methods have been developed to limit the extent of those undesired dynamics and improve controllability and safety of operation of the machine. However, in most of the cases, today's methods do not significantly differ from those developed in a time when electronic controllers were slower and less reliable than they are today.
This dissertation addresses this aspect and presents a unique control method designed to be applicable to all mobile hydraulic machines controlled by proportional directional valves. In particular, the proposed control method is targeted to hydraulic machines such as those used in the field including construction (wheel loaders, excavators, and backhoes, etc.), load handling (cranes, reach-stackers, and aerial lift, etc.), agriculture (harvesters, etc.), forestry, and aerospace.
For these applications the proposed control method is designed to achieve the following goals:
A. Improvement of the machine dynamics by reducing mechanical vibrations of mechanical arms, load, as well as operator seat;
B. Reduction of the energy dissipation introduced by current vibration damping methods;
C. Reduction of system slowdowns introduced by current vibration damping methods.
Goal A is generally intended for all machines; goal B refers to those applications in which the damping is introduced by means of energy losses on the main hydraulic transmission line; goal C is related to those applications in which the vibration attenuation is introduced by slowing down the main transmission line dynamics.
Two case studies are discussed in this work:
1. Hydraulic crane: the focus is on the vibrations of the mechanical arms and load (goals A and B).
2. Wheel loader: the focus is on the vibrations of the driver's seat and bucket (goals A and C).
The controller structure is basically unvaried for different machines. However, what differs in each application are the controller parameters, whose adaptation and tuning method represent the main innovations of this work.
The proposed controller structure is organized so that the control parameters are adapted with respect to the instantaneous operating point which is identified by means of feedback sensors. The Gain Scheduling technique is used to implement the controller whose set of parameters are function of the specific identified operating point.
The optimal set of control parameters for each operating point is determined through the non-model-based controller tuning. The technique determines the optimal set of controller parameters through the optimization of the experimental machine dynamics. The optimization is based on an innovative application of the Extremum Seeking algorithm. The optimal controller parameters are then indexed into the Gain Scheduler.
The proposed method does not require the modification of the standard valve controlled machine layout since it only needs for the addition of feedback sensors. The feedback signals are used by the control unit to modify the electric currents to the proportional directional valves and cancel the undesired dynamics of the machine by controlling the actuator motion. In order for the proposed method to be effective, the proportional valve bandwidth must be significantly higher than the frequency of the undesired dynamics. This condition, which is typically true for heavy machineries, is further investigated in the research.
The research mostly focuses on the use of pressure feedback. In fact, although the use of position, velocity, or acceleration sensors on the vibrating bodies of the machine would provide a more straightforward measurement of the vibration, they are extremely rare on mobile hydraulic machines where mechanical and environmental stress harm their integrity. A comparison between pressure feedback and acceleration feedback alternatives of the proposed method is investigated with the aim to outline the conditions making one alternative preferable over the other one (for those applications were both alternatives are technically viable in terms of sensors and wiring reliability).
A mid-sized hydraulic crane (case study 1) was instrumented at Maha Fluid Power Research Center to study the effectiveness of the proposed control method, its stability and its experimental validation. Up to 30% vibration damping and 40% energy savings were observed for a specific cycle over the standard vibration damping method for this application. The proposed control method was also applied to a wheel loader (case study 2), and up to 70% vibrations attenuation on the bucket and 30% on the driver's cab were found in simulations. These results also served to demonstrate the applicability of the control method to different hydraulic machines.
Improved system response and a straightforward controller parameters tuning methodology are the features which give to the proposed method the potential to become a widespread technology for fluid power machines. The proposed method also has potential for improving several current vibration damping methods in terms of energy efficiency as well as simplification of both the hydraulic system layout and tuning process.
Cristofori, Davide, "Advanced Control Strategies for Mobile Hydraulic Applications" (2013). Open Access Dissertations. 169.