Results
The ESTOMAD methodology is being developed and tested, using a number of benchmark cases. On this page you can find a selection of the project results that have achieved on these cases:
Badminton robot
One of the benchmark cases is a badmintonrobot. FMTC constructed this badmintonrobot to demonstrate its mechatronic competences (Fig. 1).
Fig. 1: Badminton demonstrator. A movie of the badminton robot in action can be found here.
A visual system with two high-definition black and white cameras is used to localize the fast moving shuttle. The robot itself consists of one linear motor and two rotational motors. The robot was designed in 2009 following a standard engineering approach, that is, without taking into account energy consumption considerations. In the ESTOMAD project, this high dynamic motion system is being modeled and analyzed with respect to energy consumption to identify the main sources of energy loss and find ways of reduce losses. Fig. 2 shows the electric drive configuration of the robot.
Fig. 2: Electrical drive configuration of the badminton robot.
The energetic behavior of the linear motion has been modeled in Matlab/Simulink and AMESim (see Fig. 3) and the model parameters were obtained from suppliers or experimentally identified on the robot.
Fig. 3: AMESim model of the badminton robot's linear axis.
The badmintonrobot is typically performing point-to-point motions. Analysis of the energetic behavior of the badmintonrobot for these operating scenarios using this model revealed that more than half of the provided energy is lost in copper losses in the windings of the motor (see Fig. 4 and Fig. 5).
Fig. 4: Energy loss components during a standard movement of the linear motor (E_grid indicates the total energy consumed, while E_cu indicates the copper losses).
Fig. 5: Energy loss components during a standard movement of the linear motor (E_cu indicates the copper losses).
These copper losses can be lowered by lowering the acceleration of the badmintonrobot. Analysis using the AMESim model showed that a reduction of 32% of energy losses can be realized for an increase of response time of 14% only. These findings were experimentally verified, giving an even higher return (35% reduction of energy for 11% increase of response time). More details on this analysis can be found in this paper.
Bearing frictional power loss models
In ESTOMAD, a methodology has been developed to verify and update the different loss models to make them suitable for accurate estimation of frictional power loss. On this page you can find a brief description of the developed methodology applied to the analysis of a needle roller bearing.
Recent decades have witnessed growing global energy concerns. In industry, higher energy efficiency helps to save non-renewable energy, reducing production costs, thereby making finished goods cheaper. Every machine or equipment is designed with several bearings. Although bearings are known as anti-friction elements, a typical bearing power loss of over 100W is quite common and as such, bearings are often key contributors to the overall system frictional power loss.
One approach to increase the energy efficiency of the overall system is hence to reduce the power loss in key machine components such as bearings. This can be achieved by accurate estimation of the losses followed by improved design. Estimation of the bearing frictional power loss can be achieved relatively quickly by considering advanced bearing power loss models, instead of time consuming and costly measurements.
In literature, a number of state-of-the-art models for bearing loss prediction are available. The most commonly know ones are the Palmgen and SKF® models. Within ESTOMAD, a methodology has been developed to verify and update these models to make them suitable for accurate estimation of bearing friction power loss.
The methodology is briefly described below:
- Conduct experiments to obtain the bearing frictional power loss information using a dedicated set-up
- Asses the existing state-of-the-art bearing frictional power loss models by a correlation study between data obtained by simulations using models and those obtained by experiments
- Update the model parameters using a model updating technique to make the models more suitable for the bearing under investigation
- Validate the developed model with different test cases to check its robustness
This methodology is verified for the needle roller bearing as an application case. Some key results are shared below:
Fig. 6 (a) shows the bearing test setup. It consists of an AC motor, which rotates the test bearing via a coupling with an electro motor. The test bearing is placed on an experimental head supported on a hydrostatic bearing. The experimental head is located between two support bearings. A radial load is applied to the test bearing, acting through the hydrostatic bearing. Fig. 6 (b) shows the obtained power loss (W) in function of speed (rpm) for different constant loading conditions between 1-8 kN.
Fig. 6: (a) Test Setup [Courtesy EC Engineering], (b) Experimental results.
Fig. 7 (a) shows that there is a quite big difference between the measurement results (dotted surfaces) and the simulation results (coloured surface) using a bearing frictional power loss model with initial, catalogue parameters. In this case the Palmgren model is shown. The model is then updated, based on a non linear least square surface fitting technique to make it more suitable for the considered bearing. A data set is used of constant load and constant speed measurements. The results with the updated model are shown in fig. 7 (b). Very similar results are obtained when updating the SKF® model (see figure 8).
Fig. 7: Correlation between experimental results and results obtained by simulations using (a) Initial model (b) Updated model.
Fig. 8: Frictional power loss for standard cylindrical roller bearing estimated by updated (a) Palmgren and (b) SKF® models.
To validate the updated Palmgren and SKF® models and to check their robustness, the models are compared with a second set of experimental results with a varying speed profile (while the models themselves were updated with measurements at constant speed levels) as shown in Fig. 9 (a). Fig. 9 (b) shows that a good correlation is achieved between the simulation results using the updated models and the measurements.
Fig. 9: (a) Correlation between experimental results (varying speed profile) and results obtained by updated models (b) Varying speed profile.
The updated models can be used for energy efficiency analysis of systems and sub-systems such as drive trains and gearboxes. Also, the developed methodology is applicable for other bearing types/components.
More details on this research can be found in following papers:
- Shoaib Iqbal, Jan Croes, Farid Al-Bender, Bert Pluymers, Wim Desmet; Frictional power loss in solid grease needle roller bearing, LS-11-0048-RA-TT, under review for publication in Journal of Lubrication Science, © John Wiley & Sons, Ltd., Online ISSN: 1557-6833, July 2011.
- Shoaib Iqbal, Farid Al-Bender, Jan Croes, Bert Pluymers, Wim Desmet; Palmgren and SKF models with updated parameters for a solid grease lubricated needle roller bearing, under internal review.