Experimental studies
In addition to the services presented below, we also encourage you to get familiar with the research base of our laboratory
Normal wheel / track reaction tests
Identification of the weight distribution of the vehicle on individual wheels by measuring the normal responses of the wheels enables verification of the vehicle parameters related to the load distribution in the cargo space, exceeding the permissible load capacity, etc.
The Department’s overrun scales with a measuring range of up to 200 kN, allow for carrying out, under operating conditions (without the use of additional lifting devices, e.g., gantries), identification of the distribution of vehicle wheel loads, its weight or mass, axle loads and determination of the center location of gravity (Fig. 1). A large measuring range of scales and additional equipment allow for unconventional tests of the interaction of the drive systems of industrial vehicles with the ground (Fig. 2).
Pulling / thrust force tests for industrial vehicles
We have the equipment and knowledge to carry out efficient measurements of pulling and/or thrust forces for various types of mobile industrial machines. We have a wide range of force sensors with measuring ranges from 100 N to 1000 kN. For recording the measured forces we use measuring amplifiers of the well-known company Hottinger Baldwin Messtechnik GmbH. In case of the need to test large machines, we expect cooperation in finding a place to carry out tests, as we currently do not have our own testing ground.
For small industrial vehicles with a gross vehicle weight of up to 2 tons, we are able to precisely determine the thrust force per individual running wheel. For this purpose, the test vehicle is placed on a specially designed measuring platform. The device allows to sum up the instantaneous measured tangential reactions (thrust force) when the machine tool is pushing against a pile with shredded material or a vertical retaining plate.
Experimental modal analysis
The purpose of Experimental Modal Analysis (EMA) is to determine the natural frequencies, damping coefficient values, and vibration forms corresponding to these frequencies.
The primary quantity measured during experimental modal analysis is the Frequency Response Function (FRF).
The FRF function is a frequency characteristic that describes the relationship between the excitation force F(f) and the vibration acceleration X(f) as a response signal. The method of its determination on real objects is shown in Fig. 2.
Fig. 1 shows a schematic of the measurement system for performing experimental modal analysis. The excitation of vibrations of the tested structure is usually performed with the use of an electrodynamic vibration exciter or a modal hammer, which are equipped with a force sensor.
In addition to the FRF function, the coherence function (COH) is measured during modal analysis to check the quality of the measurements made. This is a function whose values range from 0 to 1. If the values of the coherence function in the intervals where natural frequencies occur are close to 1, it means that the system response (measured acceleration) is strongly dependent on the excitation and the measurement is correct. In the opposite case, when the values of the coherence function are lower than 0.5 then the relationship between the system response and the forcing is less and the interference occurring during the measurement can have a significant effect on the result.
The connection between the vibration inductor and the structure under test is realized by a thin rod, as shown in Fig. 2.
As a result of modal analysis, information about the frequencies and forms of natural vibration is obtained. Fig. 3 shows the results of modal analysis for a hydraulic power unit.
Based on such results it is possible to determine how the structure vibrates and what amplitudes occur for individual areas of the structure. This is because at certain natural frequencies the vibrations of individual elements of the structure occur (local resonance), e.g. the fan cover of an electric motor.
Location of noise sources
Construction machines produce high levels of external noise. The noise from construction equipment is very often not a threat to the operators of the machines – because the noise in the cabins is usually reduced to standard conditions – but the noise outside the machines very often exceeds the standard values and threatens people in the surrounding area. Effective reduction of machine noise is only possible if it is determined which are the dominant sources of the noise. Hence, locating the main sources of noise is a key issue in establishing methods for reducing machine noise. The following section describes an example of such a study.
A universal wheel machine MECALAC 12 was used for the research. Its diagram is presented in fig. 1. The main sources of noise from the hydraulic system are the hydraulic pumps and motors. In the discussed machine there are 3 pumps and 2 hydraulic motors. The vibration and noise they generate affect the overall noise level of the machine.
An acoustic camera was used to locate the noise sources (fig. 2). It allows the conversion of sound emission into image form. By visualizing sound levels on a photo or video, it is possible to quickly locate noise sources. Using an acoustic camera, both the sound source and the noise level generated by it can be determined.
The camera consists of a microphone array, a video camera built into the array, and image and signal processing modules. The device is operated with software installed on a computer.
The measurements were made in an open area to avoid interference from the reflection of acoustic waves from the surrounding elements. The measurement was performed at a distance of 5m and 10m. The machine was tested during no-load operation at 1700 rpm and 2150 rpm, and while digging soil with debris at variable engine speed. Additionally, measurements were made with the engine cover open.
Figures 3 and 4 show photos of the right side of the machine taken from a distance of 5m during no-load operation for two speeds: 1700 rpm and the maximum 2150 rpm. The maximum sound level is about 83.5 dB for 2150 rpm.
Research indicates that construction machinery can generate relatively high levels of external noise. They pose a threat to people in their surrounding areas. These machines also often operate inside residential areas or in areas with heavy pedestrian traffic. There is a need to develop methods to reduce external noise emitted by construction and mining machinery. Further research will be conducted for other work machines, including mining machines, to identify the main sources of noise and to develop noise reduction methods, e.g., by designing better sound-insulating enclosures, using acoustic silencers, and other noise reduction methods.
Optimization and automation of excavation and loading systems
The excavation of ground is a very energy-consuming and often very complicated process that requires a lot of experience and concentration from the machine operator. It is therefore reasonable to look for solutions that would enable optimization of the mining or loading process (for example by guiding the tool along the optimal trajectory in terms of energy efficiency). For more than 40 years, the Department has been carrying out research related to the optimisation of the excavation process, with considerable knowledge of, for example, different strategies for filling the bucket of a loader. Thanks to this knowledge and experience, it is possible to determine the optimal execution of the mining process for different classes of working machines.
However, the implementation of the optimum mining strategy requires a repeatable, motion-stable guidance of the tool, which is difficult to achieve even by an experienced operator. Therefore, the Department undertakes research on the automation of machine operation, especially in the aspect of guiding the tool in the excavated material. Thanks to automation of mining or loading it is possible to achieve the optimal process in terms of energy consumption and tool wear.
Strain gauge load measurements
During machine operations a load is changing in a support structure. Knowledge of how the load is changing allows for machine cross section optimization and gives a possibility for more efficient drive selection. It reduces production costs. It can lead to power demand reduction which is more and more important for customers.
For many years the Department gained experience in prototyping measurement devices for controlling machines operation. Measurement devices could be implemented in prototypes machines and already built machines where no commercial sensor could be implemented because of for example sensor size or machine vibration. As an example a pin in a machine joint can be replaced to measure all force and torque components. Controlling parameters of work gives a possibility for easier automatic controlling and process optimisation.
Measurements of vibrations, pressure, flow, temperatures
Parameters such as pressure and flow are essential information for the study and subsequent characterization and optimization of the hydraulic systems of industrial machines. Temperature and vibration parameters of machine components are, in turn, basic means of determining their technical condition.
The Department has the knowledge and equipment necessary to determine e.g. the frequency of tool vibrations, destructive pressures, which can significantly shorten the life of a machine or cause a required service action. Measurements of such parameters as temperature and flow allow to control their influence on the quality of the product or the efficiency of the production process by, e.g. obtaining correct mixed proportions.
Measurements of the kinematic and dynamic properties of vehicles
Identification of kinematic and dynamic properties of work machines and vehicles is carried out to verify the assumptions made at the object design stage. Such tests are conducted under rig test and proving ground test conditions. The basic values determined during such tests include acceleration and braking distances, run-out distances, maintenance of the assumed traffic speed, acceleration and deceleration achieved. Variable loads arising while the vehicle is moving or the machine is working can lead to temporary kinematic incompatibilities affecting the dynamic state of the object, and ultimately its durability.
The Department conducts research focused on modeling of operating conditions of working machines and vehicles and registration of selected kinematic and dynamic loads. In our research we use, among others, measuring device from Peiseler GmBH (so called fifth wheel) (fig.1-2), acceleration sensors from PCB, devices for recording wheel rotations (fig.3), relative displacement sensors from Micro-Epsilon (fig.4) and mobile recorders from HBM (fig.5).
