Innovative research directions

We present selected research directions that we are currently working on

For years, the global economy has seen an expectation of continuous improvement in safety, efficiency, quality, and economy of work performed with a variety of off-road vehicles. In many cases, these expectations are attempted to be met by increasing the autonomy of working machines and their partial or full automation.

We are no longer surprised by new mines where the process is carried out by machines controlled remotely from the surface. Even in Poland there are already sections of mines where particularly burdensome work is carried out remotely. Someone could point out that these are underground mines, where the working conditions  are particularly inconvenient and dangerous. However, on the American market, for several years there have also been available excavators and loaders completely autonomous for work on the surface. Of course, their use, for economic reasons, is so far limited to uninhabited areas, where there is a problem with access to qualified personnel. Nevertheless, hundreds of excavations for wind farms in the far north have already been successfully performed by fully autonomous machines.

In areas where the availability of qualified personnel is easier, or for unit work, it is now much more economical to apply partial automation. One example is the bucket wheel excavators used in Australian opencast mines. Their operators manually control the scooping phase but the transport of the filled bucket to the load drop location is automatic.

Alternatively, in order to improve the performance of modern manually controlled work machines, various on-board operator assistance systems are being developed. Typically, these systems provide the operator with the information needed at the moment, aiding in the efficient control of the machine and preventing the implementation of dangerous controls that the operator may cause accidentally or due to lack of full knowledge of the current state of the machine or the work process.

Although much has been done in recent years in the areas of automation of work machines, operator assistance systems, and autonomous vehicles, there is still much to be done. Therefore, in the Department of Industrial Machines and Vehicles we continue our research work in the above mentioned fields. In the circle of our interest are the following specific issues:

  • automation of the excavation process with excavator equipment,
  • automation of excavation process with loaders,
  • systems for supporting the process of positioning the manipulators of working machinery,
  • systems for guiding working tools along preset trajectories,
  • systems for automatic weighting of excavated/transported soil, 
  • systems for automatic visual detection in the off-road machine environment,
  • systems of automatic steering of off-road machines with the use of GPS,
  • systems for monitoring rollover and directional stability of working machinery,
  • systems of monitoring loads of working tools during soil excavation,
  • remotely operated vehicles for pipe unblocking,
  • remote-controlled vehicles moving on ropes, e.g. mast lashings, 
  • steerable hydrostatic steering systems for articulated vehicles.

The videos below show several applications developed in the Department on this topic, including an automatically executed portion of the soil excavation cycle.

The phenomenon of mechanical resonance occurs very often in practice and is usually associated with negative effects such as failures resulting from material fatigue due to increased dynamic loads, the occurrence of increased vibration amplitudes of machine elements, catastrophic destruction of bridges, water towers, etc. There are fewer studies on the use of mechanical resonance in practice.

In vibratory drives, resonance is used, among other things, in vibrating conveyors. A very significant increase in the energy efficiency of machines of this type with the use of the resonance phenomenon was found.

The main goal of the project is to study the process of mechanical energy accumulation during resonance and to determine the possibility of its use in applications for driving presses. Until now, flywheels are commonly used to store energy in machines with crank-piston systems and to reduce energy consumption in systems for driving piston machines.

The energy accumulated during mechanical resonance can be used in the drives of presses, punching dies or other impact machines. Commonly, a system consisting of an electric motor driven, energy-accumulating flywheel in eccentric presses or pneumatic or hydraulic drives is used to drive the working tool of impact machines. The main benefit of using resonance is the reduced energy consumption compared to conventional machines. In the solution, the energy supplied by the electric motor or the pneumatic or electric actuator is used only to overcome the losses in the friction nodes of the machine. Inertia forces are balanced by spring forces. During the hitting process of the working tool, the energy accumulated in the resonance block is used. In the above manner, a low-power mechanical energy source is able to stimulate a resonant block to the maximum vibration amplitude, the energy of which is received during the working process of the hammer machine working tool.

In order to determine the causes of errors in machine aggregates and to determine the method of its release, the task is to perform

  1. Source localization and error analysis.
  2. Identification of vibrations of a mechanical structure by means of modal analysis and analysis of operating vibrations for main energy sources
  3. FEM modeling of vibration damping elements and comparison of calculation results from experimental tests.
  4. Identifying the main sources of noise is crucial to reducing noise emissions. 
  5. Development of guidelines for the reduction of noise emissions in machines.

Location of noise sources and analysis of noise generation mechanisms.

Identifying the main sources of noise is crucial to reducing noise emissions. The location of noise sources is made by measuring with an acoustic camera. The acoustic camera consists of an optical camera and a microphone matrix with approx. 100 microphones. It allows you to convert the emission of sound to the form of an image. Thanks to the visualization of sound levels in a photo or video, it is possible to quickly locate both stationary and non-stationary noise sources. With the use of an acoustic camera, it is possible to locate both sound sources and the level of emitted sound pressure.

The next step is to identify the vibrations for the main noise sources using modal analysis. After modal analysis, information is obtained about the natural frequencies of the mechanical structure of the machine and the form of these vibrations. An example of the results from the modal analysis is shown in Fig. 4.

Identification of vibrations of the mechanical structure by means of experimental modal analysis and analysis of operating vibrations for the main noise sources.

Modal analyses are carried out to determine the frequency and form of natural vibrations for the vibrating mechanical structure, i.e. to establish the relationship between the forces resulting from inertia and the elastic forces of the mechanical structure. The vibrations will be measured using a 3-axis acceleration sensor and the input was performed using an electrodynamic vibration exciter. The multi-channel measurement system from Spectral Dynamics (STAR Modal) will be used for vibration analysis. In contrast to the modal analysis, the analysis of operating vibrations (ODSA) allows to determine the form of vibrations during the operation of a hydraulic unit. Measurements will be carried out at many measurement points to enable the analysis of the forms of vibrations occurring in the hydraulic unit

After determining the main sources of noise and identifying the vibrations of the elements responsible for noise generation, models describing vibrations using the Finite Element Method (FEM) will be created. Based on the comparison of the measurement results with the calculation results, model parameters such as dynamic stiffness coefficients and damping coefficients for 3-dimensional elastic elements will be verified. The results of the theoretical modal analysis will be compared with the results of the experimental modal analysis. At a later stage, the natural frequencies are shifted so that they do not match the frequencies of the forces driving the vibrations. This method has great potential for reducing the noise level of machines and devices.

A separate issue is the vibration isolation of machines and devices.

Vibration isolation of a vibrating conveyor.

Machines that use vibration in the work process, such as vibrating conveyors, are installed in industrial buildings on floors or ceilings. In such applications, the transmission of vibrations at the place where the devices are installed must be reduced, and the vibrations of the conveyors must be maintained.

Fig. 5 shows the conveyor (1), mounted on the frame (4), which is attached to the ceiling (5) on the first floor of the building. The casing of the conveyor is based on a set of four springs (3). The vibration frequency of the actuator was 25 Hz and resulted from the rotation of two unbalanced masses (2). The rotations of these masses are synchronized with each other through the control system. The vibrations of the floor on which the conveyor was placed were 16 times higher than the permissible values.

Fig. 7 compares the frequency characteristics of the vibration function V for the system without inertial mass and with the inertial mass.

Comparing the two waveforms in Fig. 7, it can be seen that the use of inertial mass clearly lowers the values of the transfer function in the range of higher frequencies, i.e. above 7 Hz. If we take into account that the measured natural frequency of the floor was 25 Hz, it is favorable and in the considered case, the use of ballast mass led to the reduction of vibrations transmitted to the floor below the permissible values. Higher ballast mass leads to lower transfer function values. It should be noted that in many similar situations the self-vibrations of the floor may be in a frequency range similar to the operating frequency of the vibrating devices, then the structure on which they are placed should be stiffened. According to DIN 4024-1, the stiffness of the base on which the vibration isolators should be placed should be at least 10 times greater than the stiffness of the vibration isolation system. If this condition is not met, the effectiveness of the vibration isolation system will be reduced.

Mobile off-road machines and vehicles such as bucket loaders and single-articulated excavators are prevented from losing their stability by selecting the appropriate work equipment. For loaders, for example, the so-called overturning load is determined. The load capacity of the bucket is then selected so that its weight together with the weight of the load does not exceed the overturning load divided by an appropriate safety factor. The values for the safety factors can be found in the relevant standards. Their purpose is to provide compensation for the dynamic forces occurring during the operation of the work machinery, since the standard overturning loads are static quantities.

If operators of industrial off-road vehicles follow standard guidelines and operate their machines on flat and non-deformable ground, they generally do not have to worry about their machines losing their rollover stability. There are many situations, however, where work must be performed on a sloped or highly deformable ground. In this case, the operator must rely heavily on his own experience and intuition, which may fail sometimes.  

In such situations, devices that monitor the rollover stability of the machine can prove to be indispensable. Simple versions of such systems are limited to informing the operator about the current margin of stability of the vehicle. More advanced systems can also correct the dangerous steering performed by the operator, thus preventing a potential accident.

Although available on the market for many years, roll-over stability monitoring systems continue to develop rapidly. Attempts are being made to replace the static stability measures used so far with the dynamic ones. New systems are also being equipped with artificial intelligence. The aim is to allow the systems to predict in advance how the monitored machine will behave in a given moment, considering the control set by the operator and its actual dynamic state. Thanks to it, future systems will be able to take certain actions in advance in order to prevent accidents.

Employees of the Department of Off-Road Machine and Vehicle Engineering have been participating in research work on rollover stability monitoring systems for many years. We have managed to develop a number of prototypes of such devices. Some of our technical solutions in this field are protected by patents.

Articulated vehicles have high operating efficiency due to, among other things, their high manoeuvrability. Unfortunately, they achieve low velocities at a movement. This is due to the difficulty for the driver to maintain a straight-forward trajectory. Ongoing research is aimed at eliminating the drawback consisting in the spontaneous change of direction by the vehicle. The trajectory changes is due to oscillation in the angles between the front and rear frames of the vehicle. Research covers the operation of the steering system, the drive system, the spacing between the front and rear masses, phenomena at the contact between the tyres and the ground, and others. Work is currently underway on using the braking system to influence the trajectory. The principle of the system is to brake one to three wheels of a vehicle.

The moment of activation, time of operation and value of braking force is selected on the basis of a special algorithm obtained as a result of simulations carried out in MSC Adams and Matlab/Simulink environments. An example of effective elimination of oscillations of angle changes in the steering system is shown below.

The Department of Off-Road Machine and Vehicle Engineering (DORMVE) undertakes the research whose results contribute to solving problems that have to be faced by the modern civilization. Consequently, a lot of the research carried out by DORMVE have already resulted in innovative technical solutions appreciated by the engineering society. 

The excessive energy consumption is one of the problems that modern earthmoving, agricultural and other off-road mobile machines suffer from. Poor energy-efficiency of the machines of this type has to be urgently overcome to reduce the environmental pollution and decrease the costs in the field of agricultural production and civil engineering. According to the most up-to-date trends, the pollution of the urban areas is believed to be reduced by fitting the earthmoving, agricultural and other mobile machines with hybrid or electric drives featuring energy recovery systems. The research conducted by DORMVE generally coincides with those trends, however, according to our findings, much more needs to be done to actually develop a machine that could be claimed as an energy-efficient one. To do so, the undercarriage, the working gear as well as the working process, including the attachment trajectories, need to be optimized. In order to fulfill this need, DORMVE undertakes the research on the following topics.

  • Reducing the resistance arising from the interaction between different types of attachments (working tools) and the ground. In this research we focus mainly on optimizing the trajectories of the attachments and tools involved in excavation and loading of loose materials, or cutting the rocks. 
  • Maximizing the tractive performance of tracked and wheeled vehicles. Our comprehensive research in that field concentrates on determining the design of track plates and grousers which improves the traction force transmitted in the contact patch with the ground. Furthermore, we define the conditions of interaction between the tracks or wheels and the ground where the tractive force reaches its maximum.
  • Minimizing the energy consumption of tracked undercarriages, especially the rubber-tracked ones. The main objective of the theoretical and experimental studies in this field is to distinguish a balanced combination of the layout, design features, dimensions, operating parameters and materials implemented in tracked undercarriages. The optimization process allows for a number of criterions including minimizing the resistance arising from soil compaction, turning resistance and the phenomena classified as the internal motion resistance, such as bending resistance of the tracks, rolling resistance of road wheels as well as the energy losses attributed to the vibrations induced on the tracked running gear. 
  • Optimizing the wheeled vehicles, especially the articulated-body ones, in terms of minimizing the resistance arising from soil compaction and turning resistance.

Research on granular materials is an important part of many industries and science, such as mining, civil engineering, geology, Logistics, pharmacy and others. Due to non-homogenous structure and stochastic properties of these materials, for decades soil tests have been based on experiments. With a rapid development of fast computers, it became possible to shift some of the tests from the laboratory to a virtual environment. Today it is possible thanks to the Discrete Element Method. Unfortunately, despite developments of this method for over 30 years, current simulation models are based on relationships describing quasi-static loads in soils.

The research on soils in our department is focused on better understanding the phenomena that occur during dynamic loading of soil masses, especially during interaction of soil with earth-moving machinery. Such information may help to better predict off-road vehicle performance, digging or loading resistance in cohesive soils or soil behavior during rapid or impulse loads such as earth-quakes or explosions. The information may also be an aid during the design process of silos of mixers.

One of the main uses of DEM in our department is to help describe the phenomena that occur under wheels and tracks. With its better understanding it will be possible to better predict traction and tractive forces, rut depth and subject of vehicle mobility. Furthermore it will lead to optimization of the undercarriages, especially in terms of increasing drawbar pull and decreasing motion resistance.

Below a simple simulation of a lunar rover wheel on loose soil, as a part of research on the influence of the shape and size of lugs on vehicle performance is presented.

The second video shows an exemplary simulation of hopper discharge of crushed quartz is shown. Thanks to similar simulations, it is possible to determine optimum geometry of the hopper, especially the hopper angle depending on the discharged material, as well as estimation of discharge speed depending on the hopper dimensions and auxiliary devices.

Profile ground testing is a comprehensive method of vehicle testing that supplements rig and diagnostic testing. This research is carried out in the direction of determining a set of parameters relevant to the determination of technical, operational and reliability characteristics, in which the influence of actual operating conditions is taken into account. Their implementation requires, among other things, building a model of the vehicle operating conditions (e.g. road profiles, driving speed distribution), decomposition of the vehicle into assemblies and subassemblies with their appropriate grouping and determination of detailed functional and reliability requirements, construction of measurement systems and conducting experimental tests, analysis of collected results and assessment of correct operation of subassemblies and vehicle assemblies.

Work completed to date has included:

  • selection of road test sections for modeling the operating conditions of special high mobility wheeled vehicles,
  • evaluation of ride comfort of special high mobility wheeled vehicles,
  • modeling and determination of travel speed distributions to assumed road types,
  • development of a parameter to characterize the effect of operating conditions on the durability of selected vehicle components,
  • evaluation of the durability of parabolic springs and torsion bars in a special 4×4 wheeled vehicle (Gross Vehicle Weight – 16 tons),
  • evaluation of the risk of kinematic incompatibility in the drive system of a special 4×4 wheeled vehicle (DMC – 16 tons).

In a profile ground tests it is important to correctly select the travel speed for the adopted road test sections, Figure 1 shows an example of the travel speed distribution on a selected test section from one of the studies.

The instantaneous value of the drive shaft ratio as a function of shaft rotation φ can provide a measure of kinematic incompatibility in the vehicle drive system. This fact was used in one of the tests conducted in the Department, as shown in Figure 6.