Andrzej Sobczyk

Bio: Andrzej Sobczyk is an academic researcher from Tadeusz Kościuszko University of Technology. The author has contributed to research in topics: Hydraulic cylinder & Hydraulic machinery. The author has an hindex of 7, co-authored 34 publications receiving 143 citations.

An investigation on secondary force contacts of tooth pairs in conventional harmonic drives with involute toothed gear set

Abstract: Originally fixed and uniform circular pitches of flex spline (FS) teeth of a ‘Strain Wave Gearing’ or ‘Harmonic Drive’ (HD) experience variations in pitch lengths when teeth move on ‘strain wave ge...

Properties of High Pressure Water Hydraulic Components with Modern Coatings

Abstract: Water hydraulics is coming back as an alternative to oil and other not environment friendly working fluids used in a very wide range of fluid drive and control systems. The cost of water resistant materials for components is one of the barriers preventing the wide use of water hydraulics, especially moving parts such as pump pistons, surface of cylinder tubes and rods, poppet and seats, etc. to avoid corrosion. One of the common solutions is to use stainless steel there, where it can cooperate with other nonmetallic material such as plastic or other noncorrosive metallic composite to reduce friction. Thus some of research was directed to elaboration of special coating for covering surfaces in critical regions of water hydraulic components. The paper describes results of pilot research on selected components where such coating were introduced on regular carbon steel parts, same as used for oil hydraulics. First part of the article contents description of coating technology and some characteristics of coating layers. Second quotes selected results of conducted by authors research on coated hydraulic cylinders and poppet valves.

Simulation of Water Hydraulic Control System of Francis Turbine

Abstract: In the modern world continually grows ecological consciousness of societies. We are looking for new and develop the already known methods of energy generation from renewable sources. Designing of simulation models using newest software (i.e. Simulation X) of existing system and on their base building new allow in an easy and fast way to demonstrate their advantages but also find areas that need to be improve. Based on previous experiences and virtual tests [12] finally was managed to create model of Francis turbine control system using water hydraulic elements. This article presents of the system consisting of three connected and interacting subsystems: hydraulic model of the guide apparatus control system, three-dimensional model of guide apparatus and model of water flow through the system of guide apparatus - turbine.Copyright © 2014 by ASME

Tests of new methods of manufacturing elements for water hydraulics

Abstract: The article presents a review of modern methods of producing hydraulic components that can work with water as a working medium. The presented technology of coating and production of plastic elements is an alternative to the currently used stainless steel construction. Large-scale testing of cylinders and valves made in coating technology has been carried out. Innovative methods for designing pumps made of plastic have been developed, and were confirmed by laboratory tests. Introduction Research conducted on the use of water as a working medium not only in power hydraulics, but also in other branches of industry (fire extinguishing, refrigeration, etc.) confirm the existence of problems with its use [1, 2, 3]. However, the advantages far outweigh its disadvantages. That is why it is so important to use water hydraulics in natural environment friendly applications [4]. Especially if their price will not be a big obstacle. Currently, the cost of components made of stainless steel 3 ÷ 4 times exceeds the price of standard oil hydraulic elements [5, 6]. The first solution to its reduction is the technology of chemical-physical coatings integrating the Diamond Like Carbon coating technology (DLC) Coating with innovative technology with self-lubricating properties of the Columnar Nanostructured Coating (CNC). The research of these coatings was one of the topics of the EU project called "Novel high-pressure water hydraulic equipment for application in the mining and mining sector" with the working name “Hydrocoat”. Tests were carried out in the fluid power laboratory which currently is a part of the Laboratory of Techno-Climatic Research and Heavy-Duty Machines at the Cracow University of Technology. The second method is the use of plastics. The research of hydraulic pumps and other elements made of plastic bodies is carried out by the Fluid Power Research Group at the Wrocław University of Science and Technology. Materials The parts produced for oil hydraulics were specially treated. The metal-contacting parts were covered with special patented protective layers. This technology is treated as a solution enabling an adaptation of the already existing valves and cylinders to work in a water hydraulic system. These layers are the following: the Diamond Like Carbon (DLC) and Columnar Nanostructured Coating (CNC) with self-lubricating properties. Their use contributes to the lowering of the friction force and also provides a layer protecting steel from corrosion [2, 7]. In addition, using the experience gained Terotechnology 2017 Materials Research Forum LLC Materials Research Proceedings 5 (2018) 200-205 doi: http://dx.doi.org/10.21741/9781945291814-35 201 in the research of water hydraulic systems, the seals were replaced in the tested cylinders. The new seals were made of materials that could cooperate with water, such as: ULTRALEN 90 and KEFLOY 22 [1]. In turn, the use of plastics in the construction of pumps brings design, technological, operational and economic benefits such as reduction of mass, simplification of construction, self-sealing ability, improvement of tribological properties between cooperating elements, increase of resistance to contaminants in the working fluid, increase of the ability to damp vibrations and reduce noise [8]. And above all, pumps made of plastics can work with various working fluids, such as hydraulic oils, water, emulsions, nanofluids and chemical fluids [2, 9]. As a plastics easily available on the market, cheap and easy to process polyoxymethylene POM was chosen [10]. Cylinder tests The aim of the research was to confirm the effectiveness of the developed cover technologies. The Polish Standard PN 72 / M 73202 concerning tests of oil hydraulic cylinders was used during the tests of a water hydraulic cylinder. No standards have yet been developed for testing elements using water as a working fluid. According to it, external leak tests and internal leak tests were conducted, the friction force, volumetric efficiency, hydraulic mechanical efficiency and total efficiency were determined [11]. Tests with a static pressure load did not show measurable external or internal leaks. Therefore, the determination of hydraulic mechanical efficiency was reduced to determine the equivalent, total efficiency of the cylinder as a function of piston velocity and working pressure. A special stand was designed for the tests, where in the welded frame of C profiles, cylinders connected with a trolley were mounted. The wheels of a trolley were run along the inner surface of the frame. One of the cylinders was used for the drive, while the other was used to generate the load. The displacement of the piston L, the pressure on the piston side pa1 and the pressure on the rod side pa2 of the cylinder were measured. During efficiency tests, the temperature of the water in the hydraulic system was T = + 40 °C. They were repeated, for comparison, for other values of temperature. To determine the impact of pressure on the total efficiency, tests were carried out at the piston velocity of v = 0,2 m/s and the working pressure pZ changing from the minimum to the nominal value. To determine the influence of velocity on the total efficiency of the cylinder, tests were carried out at the nominal load pressure and the speed changing from 0,05 to 0,2 m/s. Figure 1 shows three dimensional characteristics of the determined total cylinder η efficiency for the extension and retraction depending on the velocity of the v piston and the theoretical F force. The force was calculated as a product of pressure and surface area on the piston side of the cylinder during extension and on the rod side of the cylinder during retraction. Fig. 1. Characteristics of the total cylinder efficiency during extension and retracting [7] Terotechnology 2017 Materials Research Forum LLC Materials Research Proceedings 5 (2018) 200-205 doi: http://dx.doi.org/10.21741/9781945291814-35 202 Valves tests The problem of a proper design of the gap between the movable elements of the spool directional control valve is particularly difficult when water is used as a working medium [12]. The low value of its viscosity coefficient causes the increase of leakages and a friction force. For these reasons, a directional control valve was constructed of four two-way ON/OFF valves. They were chosen because they are durable and relatively uncomplicated. Four separate ON/OFF valves were covered with a CNC coating and mounted in a specially designed aluminium block (Fig. 2). To control the coils of these valves, a programmable electronic module was designed and made. It enabled an independent activation and deactivation of each ON/OFF valve. That is why the distributor could work in any configuration of ways. Tests of the directional control valve consisted of functional tests in a hydraulic system with a cylinder and determination of flow characteristics for individual way of valve (Fig. 3) [13]. Fig. 2. View of a four way, three position manifold body with four ON/OFF valves [13]. Fig. 3. Flow characteristics for roads P A (red graph, negative values Q), P B (red graph, positive values Q), A T (blue graph, positive values Q), B T (blue graph, negative values Q) Pump tests The tests of pumps and rotary motors with the use of covers did not bring the expected results. The exact analysis of the problem revealed that the use of coatings presents difficulties in keeping the strength and clearances between the elements. Therefore, it was considered reasonable to make such an element from scratch, ideally, from an easily accessible and easily machinable material such as plastics [14, 15]. It was assumed that the general shape of a pump body should be formed as a prism with a square base. By removing the material from this general shape and applying the principles of global and local modification, the final shape of the pump body was obtained (Fig. 4). In addition, using the generally known methods of designing hydraulic machines and systems and the Finite Element Method (FEM), the author's methodology for shaping the bodies of hydraulic machines from plastics was developed [14]. Terotechnology 2017 Materials Research Forum LLC Materials Research Proceedings 5 (2018) 200-205 doi: http://dx.doi.org/10.21741/9781945291814-35 203 Fig. 4. View of a gerotor pump with a body made of plastics The assembled gerotor pump with a plastic body has been subjected to experimental research on a test stand in order to determine its basic hydraulic characteristics. The test stand enabled the measurement of hydraulic parameters, such as flow and pressure at the inlet and outlet of the pump, and measurements of mechanical parameters, such as torque and rotational speed. Signals from measuring instruments were sent to the computer using a laboratory signal amplifier. The CatmanEasy computer program was used to archive and analyze the measurements on the computer. The tested pump was driven by a DC electric motor with the power of 30 kW and the maximum speed of n = 3000 rpm. A throttle valve was used to load the pump. To protect the pump and electric motor from overload, an overflow valve was used. Fig. 5. The characteristics of volumetric and total efficiency, depending on the output pressure ηv, η = f (pout), for different rotational speeds n = 500 ÷ 1000 rpm Figure 5 shows that the pump was working in the range of working pressure of p = 0 20 bar and rotational speed of n = 500 1000 rpm. The ηv volumetric efficiency varied in the range of ηv = 89 70%, and the total η efficiency varied in the range of η = 73 50%. The relatively low efficiency prevented further loading of the pump, which could lead to its seizure. Figure 4 shows that the volumetric ηv and total η efficiency decreases with the increase of the p output pressure and the n rotational speed. This is explained by the fact that as the p pressure and n rotational speed increase, Terotechnology 2017 Materials Research Forum LLC Materi

Reconstruction of Hydrostatic Drive and Control System Dedicated for Small Mobile Platform

Abstract: The paper presents modification of drive and control system for specially developed small size multipurpose mobile platform which has been built based on existing vehicle undercarriage. For such redesigned object new concept of hydrostatic drive and control system is proposed. The control system consists of selected hydraulic components and controllers which were chosen from Sauer-Danfoss PLUS+1 package which is the system dedicated for mobile hydraulic control systems application. The hydraulic system has been equipped with extra valves, enabling to obtain of assumed functions.Copyright © 2014 by ASME

Modeling and Offset-Free Model Predictive Control of a Hydraulic Mini Excavator

Abstract: During the virtual development and experimental testing of advanced construction machinery, automation approaches for automated task execution can prove very valuable In this paper, modeling and automation approaches for a hydraulic mini excavator are developed In particular, a physical model for detailed system analysis and a simplified Hammerstein model for controller tuning are developed and validated with measurement data from the mini excavator For attitude estimation of the excavator, inertial measurement units and extended Kalman filters are used in a sensor fusion framework The control concept for automation is based on a virtual driver consisting of a state machine for task coordination as well as offset-free model predictive controllers (MPCs) for decentralized and robust tracking control of all motion axes The constrained MPC optimization problems are solved in real time by means of the accelerated proximal gradient method Experimental results from the mini excavator prove the developed control approach to be valuable for virtual development and automated testing during the commissioning of hydraulic machinery Note to Practitioners —In this paper, a hydraulic mini excavator is considered for demonstrating the benefits of automation with regard to the development of advanced mobile machinery A detailed physical model and a simplified model are introduced for virtual analysis and comissioning of the excavator This allows for detailed system analysis even at an early development stage Then, a framework for automated testing of the real prototype is introduced This concept is based on attitude estimation filters, a state machine, and model predictive controllers and closely resembles the human driver in its behavior, but allows for reproducible testing results and therefore reduces commissioning efforts and development costs Particular attention is paid to the robustness of the control concept, since the coupling of the hydraulic axes and digging forces lead to disturbances that need to be compensated A simple, yet efficient and real-time capable algorithm is provided for numerical optimization Experimental results show that the developed methods can contribute to the automation of hydraulic machinery, and that the introduced framework can easily be extended in order to automate other types of machinery with simple hydraulics

Load sharing by tooth pairs in involute toothed harmonic drive with conventional wave generator cam

Abstract: A harmonic drive is a two gear epicyclic drive with a gear set of circular ring gear (RG), a flex rimmed external toothed gear (FG) and an oval cam. FG, with oval cam inside, takes non-circular gear shape encounters improper teeth mating with RG, having only two teeth difference. Consequently, interferences occur at several tooth pairs even at no load. These are inherent and obvious. Overcoming such interferences and further with applied load estimation of load sharing by tooth pairs poses a complex problem. In solving it, first, tooth stiffness of internal gear and external gear are derived in the present investigation. A method of estimating the load shared by the multiple tooth pairs in contact is proposed. The load distribution pattern in proportion to the tooth deformation is considered. Load shared by contacting tooth pairs is estimated and stresses in FG cup are found out using FEM. Finally, such results are compared with experimental results, which have good agreement.

The strain wave gearing

Abstract: Ein erster und ein zweiter ausen verzahnter Verzahnungsbereich (7, 9) eines Verformungswellgetriebes (1) werden durch einen Wellgenerator (10) in eine elliptische Form verbogen, um in ein erstes bzw. in ein zweites innen verzahntes Zahnrad (2, 4) einzugreifen. Der erste und der zweite ausen verzahnte Verzahnungsbereich (7, 9) werden so verbogen, dass sie elliptische Formen haben, deren Phasen um eine Rotationszentralachse (1a) um 90° gegeneinander verdreht sind. Zwischen dem ersten und dem zweiten ausen verzahnten Verzahnungsbereich (7, 9) ist ein ausen verzahntes Kopplungsverzahnungsbereich (8) ausgebildet, der eine kreisformige Querschnittsform behalt, die sich nicht verbiegt. Der ausen verzahnte Kopplungsverzahnungsbereich (8) wird so auf eingreifende Art und Weise mit einem innen verzahnten Kopplungszahnrad (3) gekoppelt gehalten. Das Verformungswellgetriebe (1) hat eine hohe Eingriffssteifigkeit und ist in der Lage, ein groses Drehmoment zu ubertragen.

Distribution Performance Analysis and Experimental Research on the Port Plate Pairs of Low Speed High Torque Seawater Hydraulic Motor

Abstract: The current research of seawater hydraulic motor mainly focused on piston motor and vane motor, but seldom regarded low speed high torque seawater hydraulic motor. Low speed high torque seawater hydraulic motor as a kind of energy conversion device and actuator plays an important role in seawater hydraulic transmission system. However, the physical and chemical properties of seawater, such as low viscosity, high causticity and poor lubrication, result in numerous problems. In this paper, the flow distribution characteristics of port plate pairs for the seawater hydraulic motor are investigated, and the leakage flow and power loss models of port plate pairs are established. Numerical simulations are carried out to examine the effects of water film, inlet pressure and rotating speed on the pressure distribution and leakage flow. And the friction and wear tests of port plate pairs are also carried out. Moreover, the test system of the seawater hydraulic motor is constructed and the performance of prototype with no-load or loading is conducted. The results indicate that the clearance of port plate pairs and inlet pressure have a significant effect on distribution characteristics, but the effect of rotating speed is not very obvious. The experimental results show that the minimum error rate can be maintained within 0.3% by the proposed flow model and the counter materials of 316L against carbon-fiber-reinforced polyetheretherketone (CFRPEEK) are suitable for the port plate pairs of seawater hydraulic motor. Finally, based on the seawater hydraulic experiment platform, the volumetric efficiency of no-load and loading are obtained that the maximum can achieve 94.71% and 90.14%, respectively. This research work may improve the flow distribution performance, lubrication and the friction and wear properties, enhance energy converting efficiency of port plate pair and provide theoretical and technical support for the design of high-performance water hydraulic components.

A method for detection and quantification of meshing characteristics of harmonic drive gears using computer vision

Abstract: A lack of accurate description of the meshing characteristics and the corresponding frictional mechanism of the harmonic drive gear has limited progress toward modeling the hysteresis stiffness. This paper presents a method for detection and quantification of the meshing characteristics of the harmonic drive gear based on computer vision. First, an experimental set-up that integrates a high speed camera system with a lighting system is developed, and the image processing is adopted to extract and polish the tooth profiles of the meshed teeth pairs in each acquired video sequence. Next, a physical-mathematical model is established to determine the relative positions of the selected tooth pair in the process of the gear engagement, and the combined standard uncertainty is utilized to evaluate the accuracy of the calculated kinematics parameters. Last, the kinematics analysis of the gear engagement under the ultra-low speed condition is performed with our method and previous method, and the influence of the input rotational speed on the results is examined. The results validate the effectiveness of our method, and indicate that the conventional method is not available in the future friction analysis. It is also shown that the engaging-in phase is approximately a uniform motion process, the engaging-out phase is a variable motion process, and these characteristics remain unchanged with the variation of the input rotational speed. Our method affords the ability to understand the frictional mechanism on the meshed contact surfaces of the harmonic drive gear, and also allows for the dynamic monitoring of the meshing properties.