A concept of adaptive control system for rail grinding

. Rail grinding with the use of rail grinding trains under railway track conditions provides an increase in the rail lifecycle. A main task of rail grinding is to form a rail transverse profile to reduce the contact loading and wear from rolling stock wheels. At present, providing the accuracy of forming a rail repair profile remains a challenge, which overcoming is hampered by the technological features of rail grinding trains. To solve this problem, the paper proposes a concept of adaptive control system for rail grinding process. This system is intended to work as a part of rail grinding train and provide inspection of the results of operations on rail machining and, if required, adjusting grinding modes. The main objectives of this system are: providing accuracy and quality of rail machining by grinding, optimisation of time consumption within a track possession for rail grinding and developing a database to enhance planning of the rail grinding works. Siberian Transport University and JSC "Remputmash" Kaluga Plant are now implementing the introduced concept of adaptive control for grinding in a collaborative project for the development of a new RGT 2.0 rail grinding train.


Introduction
The rail profile grinding has been actively used in the railway network since the early 80s of the 20th century. [1] It has proven itself to be the only technology that extends the rail lifecycle. [2,3] This technology is implemented using rail grinding trains (RCT) with rotating grinding wheels. Rails are machined by using flat grinding with an abrasive wheel face (Fig. 1). The rail grinding technology eliminates such defects as corrugated wear, mechanical damages, metal crushing and flaking. At the same time the key attention is paid to the formation of rail transverse profile. [4,5] Rail profile periodic adjustment provides the best possible interaction of a wheel with a rail, even distribution of internal stresses along the rail surface and thus extends the rail service life. [6] A rail transverse profile is formed based on repair profile geometric parameters which draws from the rail actual geometry in a certain track section (Fig. 2, a). [7] The repair profile is produced by removal of metal by grinding wheels positioned at different angles relative to the vertical rail axis (Fig. 2, b).
a -diagram of rail flat grinding by a wheel face; b -working equipment of a rail grinding train. a -superimposition of actual (1) and repair (2) rail profiles (an example); b -a diagram of arranging grinding wheels at different angles. When profile grinding, a quality parameter for the executed work is the accuracy of a given rail repair profile after grinding. Due to the nature of rail grinding by rail grinding trains, it is difficult to achieve the required rail profile accuracy. This results in the need to carry out additional RGT adjustment passes and, as a consequence, additional costs. Thus, the issue of providing the accuracy for repair profile formation is relevant today.

Problem statement
When developing the technological process of rail grinding, based on the geometric parameters of actual and repair profiles, grinding modes are assigned for each grinding wheel positioned at a certain tilt angle to provide a given metal removal. In other words, the accuracy of rail profile formation depends on the accuracy of a given metal removal. An analysis of papers devoted to different aspects of theory and practical applications of the rail grinding technology has revealed that apart from the similarity in rail grinding and machine grinding schemes, there are fundamental differences introducing significant changes into the rail machining and influencing on the accuracy of rail transverse profile formation. [8][9][10] Firstly, rail grinding is provided by the 'abrasive wheel -machined surface' kinematic circuit closing (Fig. 3). Each single grinding wheel is pressed against the railhead by a pneumatic cylinder via a drive motor attached to the retainer plate. Parallelogram suspension axles are fixed to the end plate of a grinding cart unit. This design guarantees a constant perpendicularity of the axis of wheel rotation relative to the rail's longitudinal axis. At the same time, the grinding wheel pressing force against the rail is determined by pressure in the pneumatic cylinder, which is automatically regulated depending on the current load in the drive motor windings.
1 -abrasive wheel; 2 -drive motor; 3 -retainer plate; 4 -parallelogram suspension; 5 -pneumatic cylinder; 6 -block plate; 7 -axle. Secondly, the cutting conditions for each single working wheel are significantly different depending on the wheel head tilt angle (Fig. 4). For instance, one wheel covers a larger area when machining the running surface than in case of machining the railhead working roundness. In other words, different railhead areas have different grinding track widths and these areas are subject to different specific loads per single grit. b1, b2 -grinding track width; b1>b2; 1 -grinding track; 2 -rail running surface machining; 3 -rail working roundness machining Thirdly, significant differences in the abrasive tool work introduce significant changes in the physical and mechanical properties of rails. The properties along the railhead crosssection change significantly during operation en route. First of all, there is a dramatic change in hardness (Fig. 5). An increase in hardness in certain areas of the rail head results in tighter grinding wheel conditions. The above features of rail grinding with the use of RGT indicate that it is impossible to implement accurately the assign cutting depth t, since metal removal is formed in most spontaneously, depending on a number of factors, and is likely to differ from the given value. All this leads not only to differences in performance and unequal wear of grinding wheels, but also to different accuracy of rail surface formation. [11] To eliminate this drawback, it is necessary that cutting depth t be not only an assignable parameter, but also a controllable one [12]. The solution of this problem is hampered by the lack of scientific and theoretical basis for inspecting and adjusting metal removal during RGT grinding under railway track conditions. [13] Thus, the research task introduced in this article is to develop a system to assign, support and inspect metal removal during rail grinding in order to increase the accuracy of rail repair profile formation in situ the machining process.

Results
Based on the defined task, the concept of Adaptive Control System (ACS) of rail grinding by rail grinding trains was developed. The ACS is intended for operation as a part of RGT and providing inspection of the results of rail machining operations and, if required, adjusting grinding modes. The main objectives of ACS development are: providing the accuracy and quality of rail grinding machining, optimisation of time consumption within a track possession for rail grinding, and development of a database to enhance rail grinding work planning.
When implementing the ACS, the object of automation is the technological process of rail grinding, carried out on a rail grinding train, which includes: 1. Obtaining input data for designing the technological processes of rail grinding. 2. Designing the technological processes of rail grinding and generating assignments for rail grinding and work equipment control.
3. RGT work equipment control. 4. Inspecting the implementation of operations in the technological process of rail grinding.
5. Adaptive adjustment of machining modes during rail grinding. 6. Adjustment of the assignment for further grinding passes. Fig. 6 illustrates the ACS structure and interactions of its subsystems. The ACS includes: 1. The Control Unit (Subsystem) (hereinafter -CU) is intended for determining geometric parameters of transverse and longitudinal profiles of rails, as well as assessment of rail defects on the running surface and in the subsurface layer. The CU comprises an internal rail defect assessment tool (hereinafter referred to as DT) and an automated measuring tool (hereinafter referred to as MT).
The DT is intended to assess the presence of cracks in the railhead surface layers by the eddy current method. In addition, the DT helps to determine the defect occurrence depth to estimate the minimum required metal removal when designing a rail repair profile.
The MT comprises two measuring systems installed at the rail grinding train edges, which provide data on grinding results in situ the rail machining process. When grinding, the measuring system positioned on the last wagon in the direction of RGT travel inspects the metal removal of the rail profile being formed (Fig. 7). 2. The Data Processing Unit (subsystem) (hereinafter referred to as DP), intended for designing technological processes of rail grinding, the analysis of their correct implementation and development of recommendations for their adjustment. The DP contains the following application software: a) Software for the calculation of geometric parameters of rail repair transverse profiles (hereinafter referred to as the "Calculation" Software). The "Calculation" Software functions are as follows:  Obtaining actual rail profile geometry data from the MT;  Receiving rail wave wear data from the MT or the Unified Corporate Automated System of Infrastructure Management (UC ASIM) via the "Integration" Software;  Receiving data on the presence and magnitude of defects on the rail running surface and in the surface layer (pittings, shelling, cracks) from the UC ASIM via the "Integration" Software or by means of ACS measuring instruments;  Receiving data on operational and structural parameters of the railway track from the UC ASIM via the "Integration" Software or manual input using track unit data;  Calculation of the geometric parameters of repair rail transverse profiles taking into account their actual condition, structural and operational parameters of the railway track separately for each rail;  Transferring data on geometric parameters of the actual and repair rail profile into the "Project" Software. b) Software for the design of single technological processes for rail grinding (hereinafter referred to as the "Project" Software). The "Project" Software functions are as follows:  Receiving the geometric data of the actual and repair rail profile from the "Calculation" Software;  Receiving data on the serviceability of RGT work equipment from the CS;  Calculation of the required metal removal from the rail head to form the design rail repair profile for each rail;  Calculation of the required transverse tilt angles of the wheel heads for each RGT pass;  Assignment of grinding modes to each wheel head;  Formation of the geometry of potential rail profiles after each pass;  Determining the number of RGT passes required to form the design rail repair profile;  Generating an assignment for rail grinding works along a railway track section;  Transferring the assignment for rail grinding into the CS;  Transferring geometric parameters of the potential rail profiles after each pass into the "Analysis" Software. c) Software to analyse and inspect the correct performance of rail grinding technological processes (hereinafter referred to as the "Analysis" Software). The composition of the "Analysis" Software functions is as follows:  Receiving an assignment for rail section grinding from the "Project" Software;  Obtaining the geometric parameters of potential rail profiles after each pass from the "Project" Software;  Receiving actual rail profile geometry data during a pass from the CS;  Comparison of the actual rail profile after a pass with the designed (potential) profile;  Determining the actual metal removal for each wheel head;  Identifying the wheel heads which deviate from the designed metal removal values;  Generating recommendations for changing the grinding modes (if required) during the machining process for each wheel head;  Transferring grinding mode changes on the wheel heads into the CS;  Analysis of completion the assignment (in terms of profile and defects) after the last pass and taking a decision on additional passes;  Transferring grinding results into the UC ASIM via the "Integration" Software. d) Software for measurement data processing and integration (hereinafter referred to as the "Integration" Software) with the Unified Corporate Automated System of Infrastructure Management of JSC "Russian Railways" (hereinafter referred to as the UC ASIM). The composition of the "Integration" Software functions is as follows:  Receiving actual rail profile geometry data from the UC ASIM and transferring them into the "Analysis" Software;  Receiving rail wave wear data from the UC ASIM and transferring them into the "Analysis" Software;  Receiving data on the presence and magnitude of defects on the rail running surface and surface layer (pittings, shelling, cracks) from the UC ASIM and transferring them into the "Analysis" Software;  Receiving data on operational and structural parameters of the railway track from the UC ASIM and transferring them into the "Analysis" Software;  Receiving rail grinding data from the "Analysis" Software and transferring them into the UC ASIM. 3. The subsystem for RGT working equipment control intended for lifting/lowering a grinding cart, controlling the operation of drive motors, arranging the transverse tilt angles of wheel heads and controlling the grinding wheel pressing force against the rail. This subsystem is a part of the RGT control system (hereinafter referred to as CS).
4. Devices and communication lines for the exchange of information and commands between the different devices and subsystems of the AСS developed, as well as between the AСS and related systems.
The ACS operation, according to the block diagram (Fig. 6), is as follows. Before the work starts in a given railway track section, it is necessary to determine the geometric parameters of the rail repair transverse profile required for the section to be machined. For this purpose, the RGT makes a measuring pass and measures the actual rail condition parameters with the help of MT and DT. Based on these measurements, the coordinates of points describing the actual rail transverse profile in a given coordinate system and data on rail wave wear with coordinates of the wave beginning and end and its height are transferred from the MT to the "Calculation" Software. Data on the presence and magnitude of defects on the rail surface and in the surface layer (pittings, shelling, cracks) are transferred from the MT into the "Calculation" Software. In addition, the "Calculation" Software calculates the operational and structural parameters of the railway track (line, section, track category, rail type, straight/curved track (curve radius), density and tonnage run-in). All these parameters can be obtained from the UC ASIM via the "Integration" Software (if these data are available in the system) without a measuring pass, prior to entering the line. The ACS also provides for manual input of rail parameters and track features supplied by a track unit (TU) based on the results of measurements by manual monitoring tools.
Based on the data received, the "Calculation" Software calculates the geometric parameters of the rail repair transverse profile taking into account their actual condition, structural and operational parameters of the railway track separately for each rail. The calculation data in a form of coordinates of points describing the actual rail transverse profile and the rail repair profile in a given coordinate system are transferred into the "Project" Software to design the technological process of rail grinding. To develop the technology, the data on serviceability of the RGT working equipment is additionally transferred from the CS into the "Project" Software. The "Project" Software calculates the required metal removal from the railhead to form a design rail repair profile for each rail, determines the transverse tilt angles of grinding wheels for each RGT pass and assigns the grinding modes for each wheel head. The required number of RGT passes is determined to form the designed repair profile of rails. For functional inspection of the technology implementation, the geometric parameters of intermediate, potential rail profiles are also formed in the "Project" Software after each RGT pass. The results of the technological process design are transferred to the RGT CS in a form of assignment for grinding of rails along the railway section. At the same time, the geometric parameters of potential rail profiles after each pass are transferred from the "Project" Software to the "Analysis" Software for further adaptive adjustments during execution of works.
The grinding programmes received from the "Project" Software are used to start the wheel grinding system under the CS control. During the rail grinding process, the accuracy of rail grinding operations is analysed and monitored. For this purpose, the CS is used to measure the post-processed rail profile during the grinding process right after rail machining, and the actual metal removal for each wheel head is determined. The data on the geometry of the actual rail profile after the pass is transferred from the MT into the "Analysis" Software. The "Analysis" Software identifies the wheel heads which deviate from the designed metal removal values and compares the actual rail profile after the pass with the designed (potential) one. Based on the analysis, recommendations on changing grinding modes (if required) during the machining process for each wheel head are developed and sent into the CS. The CS makes adjustments to the operating modes of wheel heads. After the last pass, the "Analysis" Software makes a final evaluation of the repair profile formation accuracy and completeness of surface defect removal. If necessary, a decision might be taken for additional passes. The results of rail grinding on a given rail section are transferred into the UC ASIM via the "Integration" Software.

Conclusion
The proposed Adaptive Control System for rail grinding with the use of rail grinding trains provides the following: 1. To execute functional inspection of rail grinding technological process implementation and form the repair profile of rails with the given accuracy by the timely adjustment of grinding modes and providing the given metal removal. 2. To reduce the time of preparatory and final works along the line by automating the technological processes of rail grinding design and eliminating the RGT reference measurement pass. 3. To develop an actual base of true rail condition on a railway track section by integrating the Adaptive Control System for rail grinding with the Unified Corporate Automated System of Infrastructure Management of JSC "Russian Railways" to enhance rail grinding work planning. Siberian Transport University and JSC "Remputmash" Kaluga Plant are now implementing the introduced concept of adaptive control for grinding in a collaborative project for the development of a new RGT 2.0 rail grinding train.