Assessment of the technical condition of lift guides using a magnetic field

The systems that monitor individual components of machines and devices are under constant development. The ability to detect damages at an early stage allows failures to be prevented, so any uncontrolled downtime can be predicted in a controlled manner. Continuous monitoring of technical condition is an activity that also helps to reduce the losses due to equipment failures. However, not all areas can be monitored continuously. Such areas include lift guides where wear and tear can occur naturally, i.e. through abrasion of the material layer due to interaction with moving guide shoes or after emergency braking. Emergency braking causes local damages to the guide through plastic deformation of its surface resulting from indentation of the knurled roller of the brake. Such places are cleaned mechanically, which results in local reduction of the cross-sectional area. In such a case, it is difficult to continuously assess the technical condition of guides due to the prevailing operating conditions. Therefore, a concept of a head enabling assessment of the technical condition of guides at every stage of their operation has been developed. This article presents the novel concept of a magnetic head used for assessing the technical condition of lift guide rails that are the running track of lifting equipment. The initial tests were performed on the original test setup. The concept of the developed measuring head was verified for correct operation on specially prepared flat bars with holes. The results obtained in the form of laboratory tests proved that the proposed measuring head concept can be applied to the measurements under real conditions.


Introduction
Diagnosis of technical equipment is an important factor affecting its service life. Diagnostics as a tool for assessment of technical condition is used in practically every field of engineering as well as in nonengineering domains. In the article [1], the authors presented the use of short-time Fourier transform (STFT) as a tool for detecting undesired states caused by various mechanical and physical phenomena.
The authors considered the use of STFT to monitor and assess the performance of a hydraulic pump system under various operating conditions. A hydraulic tester was used to measure the pressure and flow changes in the pump and a DAQ card was used to evaluate the qualitative and quantitative changes in the system. In the article [2], the author presented the use of diagnostics in medical industry as a tool for quality assurance. Special emphasis was placed on the investigation of hazards and possible product defects in food processing. The research aspect of this paper focuses on an attempt to transfer diagnostics to the food industry solutions applied mainly in in the automotive industry. The practical aspect of the paper presents an analysis of the causes of defects and risks carried out on the example of the baking industry.
In the conference materials [3], the author presented the use of a diagnostic tool to assess the chemical reaction and the electrical process, closely related to the flow of electric current during the electrochemical grinding process. Processing of this type of material is very difficult not only due to unfavourable physical properties of the material itself, but also due to the very high requirements resulting from the operating conditions of the product. Particular attention was paid to the flow of electric current as a function of changes in the active surface, understood as the geometrical surface through which electric current can flow. The calculation results for this surface and an example of the recorded current waveform shape were presented. Such results were used to build a control system based on maintaining a constant working current density. In the article [4], the authors presented the use of analytical data for tool condition assessment and tool life prediction, which are crucial for the manufacturing process reliability and quality. The authors presented a new mathematical model which is intended to effectively classify the condition of a cutting tool blade in real time. The developed model was verified on the basis of real measurement data from an industrial machine tool. Diagnostics is also used in the machine and device supervision processes. In the publication [5], the author described the properties of the most popular diagnostic systems used for the in-plant conveyor transport system operation. He also presented a new method of computer-aided maintenance of such systems.
The operational reliability of conveyor transport systems is a question of ensuring an appropriate level of readiness of the continuous transport system which, in the case of belt conveyors, depends not only on their functional qualities determined by the construction solutions applied and workmanship, but also significantly on the appropriate level of their use understood, among other things, as the degree of advancement and effectiveness of the methods and industrial diagnostics tools applied. In the publication [6], the authors presented the results of their own research on the application of diagnostics to evaluate the value of measured geometric errors of the FV-580A four-axis CNC vertical machining centre with the FANUC 0IMB numerical control system. The article presents the examples of modern, laser-based diagnostic systems for numerically controlled CNC machine tools: LaserTRACER self-tracking interferometer, LaserTRACER-MT diagnostic device, XL80 laser interferometer with XC80 environmental parameters measuring module and heat sensors with XR20-W calibrator. The authors of article [7] described the application of a diagnostic device of their concept, intended to assess hybrid hoisting ropes used in lifting devices. The construction of the ropes, as compared to traditional steel ropes with a round cross-section, made it possible to reduce the diameter of the driving wheel while maintaining the frictional contact conditions and the required ratio of driving wheel and hoisting rope diameters of at least 40. Despite the advantages mentioned above, an interesting but so far not fully examined research issue is the process of hybrid suspension rope wear and the assessment of technical condition of ropes being the load bearing elements in the applied solutions, especially during long-term operation. The paper presents the possibilities of applying the magnetic method to assess the technical condition of steel cables being the load-bearing element of hybrid belts. The authors presented their solution of a measuring head for magnetic testing of hybrid rope carriers, developed by a team of employees of the Department of Mechanical Engineering and Transport of the University of Science and Technology in Kraków.
In the publication [9], the authors presented a new approach to the classification of energy efficiency of lifts based on a heuristic estimator, using the parameters of energy characteristics of the lift installation recorded during a weekly operation cycle as a diagnostic tool. Due to the fact that energy performance evaluation by the commonly used methods involves many variables and complex nonlinear relationships, an expert model was developed using a fuzzy logic approach. The basic objectives are defined together with the energy characteristics and operational parameters of the lift installation in the running and standby modes. The estimator is based on the operational efficiency of the equipment for each lift mode, and membership functions (model input and output) are defined. In the article [10], the authors presented the proposals for a monitoring system based on cloud-based databases. The monitoring system concerns the main components responsible for the safety of passenger lifts. The IOP Publishing doi:10.1088/1742-6596/2130/1/012003 3 described system was successfully tested on several devices which were connected to a common base. In the publication [11], the authors described an intelligent remote monitoring system for lifts which is known as Eleview. Apart from supporting live or recorded video transmission over the Internet, it also provides intelligent monitoring and web-based monitoring. Intelligent monitoring analyses the movements of people in a lift to detect unusual or criminal activities. As the live video data transmission over the Internet can cause packet loss and quality degradation, the Eleview system implements an adaptive transmission and recovery mechanism to improve the quality of real-time video transmission. In the publication [12], the author presented a monitoring system for passenger lifts based on Big Data which he used for an early warning of possible equipment failure. In the publication [13], the authors described the operation of a system monitoring the lift guides in a plane perpendicular to the movement direction of the cabin and the counterweight. The described system was based on image processing of the guides to prevent wear of their surfaces. The images of guide surfaces are recorded by four digital cameras mounted in the lift cabin. The image processing methods are applied to the images recorded by the cameras to detect damage or wear of the guide surfaces. In the article [14], the authors described the influence of vibration arising during the ride of high-speed lifts on the comfort level of the travelling passengers. In order to assess the effect of vibration on the comfort of travellers, the authors developed a model of a high-speed lift and then analysed the effect of travel speed, the guide deviation from the vertical and the dynamic parameters associated with the rolling of guide shoes along the guides. The lifts moving at speeds of 5 m/s, 7 m/s, 8 m/s and 10 m/s were tested.
The publication [15] presents the application of a monitoring system to evaluate the vibration level and aerodynamic load changes of a high-speed lift. The authors presented a three-dimensional computational model of airflow coupling vibration in the shaft based on the Lagrange-Euler method and the finite volume method. Then, the authors evaluated the aerodynamic load and horizontal vibration acceleration of the cabin for different speed conditions using unidirectional and bidirectional numerical simulation methods of airflow coupling to influence the vibration response of the cabin. In the publication [16], the authors described the effect of non-linear contact between the guide shoe and the guide on the counterweight guide vibration. The results showed that the contact and separation between guide shoes and guides can be simulated using a numerical model. The efficient computational method proposed by the authors can be used for quantitative analysis of the lift vibration response. In the article [17], the authors presented a monitoring system in the form of an active control strategy for damping of horizontal lift vibration based on linear matrix inequalities. The 6-stage horizontal vibration model was used for the analysis. The authors proposed to monitor an effective vibration damping system on the adopted vibration model.
The guidance systems in the lifting equipment are constantly being developed mainly due to the increasingly faster operating speeds of lifts. In the article [18], the authors presented their own research on the use of a vibration absorbing insert in the guide bracket as a method to reduce vibration and noise in high-rise buildings. On the basis of the result of vibration-absorbing insert operation, the authors estimated that the vibration and noise levels were reduced by about 65.49% on the cabin side and by about 90.05% on the counterweight side. The article [19] deals with the quantification of uncertainty in a lift system subjected to lateral vibration induced by guide bumps with and without a feedback control system. A mathematical model of the lift system was derived and a stochastic model for the rail profile irregularities was constructed. This uncertainty model describes the guide profile as a random field, which is represented using the Karhunen-Loève expansion. The polynomial chaos is used to calculate the propagation of uncertainty through the stochastic model, in order to evaluate the disturbance rejection and robustness properties of the closed system.
In the articles [20,21], the authors address the research with the application of a magnetic method in wire rope diagnostics. The article [20] compares the functional features of mine hoist ropes determined by organoleptic, strength and magnetic tests. The article [21] describes the authors' experience in assessing the technical condition of ropes used in the building structures.

Description of tests
The use of diagnostics for the assessment of technical facilities for their technical condition is still being developed in various branches of technology. Such a need has also arisen in the field of material handling equipment related to the vertical transport of people and goods. Various parameters are monitored, as shown in the graphical representation in Figure 1. Due to the fact that currently there are no available design solutions for the heads intended for the diagnostics of lift guide rails, the authors' own concept of a measuring head was developed, the main purpose of which would be the diagnostics of the technical condition of guide rails the exemplary crosssection of which is shown in Figure 2. The guide rail system consists of two T-shaped guide rails positioned opposite one another. The working surfaces (marked red in Figure 2) are the surfaces exposed to the interaction of the components (a knurled roller) of the brake under unfavourable operating conditions. The guide rails are manufactured as T-shaped steel profiles using the drawing or rolling process with grinding of the "S" working surface. The material from which the E235B guide rails are manufactured according to ISO 630:1995 has the following physical and mechanical properties:  Figure 3 shows the guide rail with the surface formed after contact with the harder knurled roller that is an element of the brake. Figure 3. View with plastic damage on the guide rail working surface [8].
Such a surface is levelled using mechanical methods that result in a reduction of the cross-sectional area at the point of contact between the roller and the guide rail. For both assessment and monitoring of the technical condition of guide rails, the authors developed a device (a magnetic head) the operation of which is based on the stray magnetic field analysis. Due to the commenced process of patenting the head, its technical description at the date of preparation of this publication has been omitted.
The initial method of verifying the developed head concept with the measurement method was based on the measurements of a flat bar in which a damage was modelled in the form of a 1 mm diameter hole that had been drilled (see Figure 4). In order to determine the possibility of damage detection depending on its depth, the position of the hole in relation to the surface was gradually increased, resulting in 7 samples.  For the purpose of validating the measurement, 7 samples were prepared in which a hole was located at the following distances: 1 mm, 2 mm, 3 mm, 5 mm, 7 mm, 11 mm and 13 mm.
The influence of the sensor distance from the surface of the tested element was also verified. In this case, the tests involved moving the sensor away from the surface of the flat bar using spacers. The orientation of the magnetic coil remained unchanged during all the tests, which allowed the measurements to be carried out under constant conditions with a repeated value of the magnetic field, the same material and the same modelled defect. For the samples prepared in this way, it was examined how the signal changes as the sensor is moved away from the surface of the flat bar, and also as the distance between the hole and its surface increases. Figures 5, 6, 7      After performing the tests with a flat bar, the initial measurements were taken using a section of the actual lift guide rail. Due to the complexity of the issue, the initial stage of testing consisted in verifying the correct identification of damage of the guide rail surface. To this end, the initial reading tests were carried out on the guide rails on the surfaces of which the mechanical scratches were made, as shown in Figure 9. The prepared guide rail was used to take preliminary readings recorded by means of an initial prototype of the diagnostic system. The measurement methodology consisted in applying the magnetic system to the guide rail surface and manually moving it along the guide rail. In the location where the guide rail surface was intact, the voltage signal being a function of a change in stray magnetic field around the tested component (X and Z components, Figure 10) was maintained at a constant level of about -700 mV for the X axis and 560 mV for the Z axis. In the location where the modelled damage occurred for both X and Z components (about 35 mm in Figure 10) there is a clear change in the shape and amplitude of the voltage signal resulting from the damage (Figure 9). The Y axis signal was omitted because it did not carry any significant information from the diagnostic point of view.