Electromobility makes it possible to reduce CO2 emissions and improve the efficiency of a vehicle, and so makes a major contribution to climate protection. The ETH's eXact focus project has set itself the aim of converting a mini-excavator to a direct electric drive. The hydraulic cylinders on the excavator arm are replaced by electric linear drives. Pioneering work is being done for the excavators of the future. Electric drives are efficient, quiet, emission-free, and no environmentally harmful hydraulic oils can leak out. New areas of working, such as in enclosed spaces, are also being enabled.
The use of electric linear drives with ball screw actuators on an excavator arm is a first. There are therefore no empirical values available in respect of the loads acting on the drives.
About the control units: Angle and length
Three actuators are installed on one excavator arm, for the boom, arm, and bucket. Two strain gage rosettes are mounted on each of the thrust tubes, one on the top and one on the bottom. A 6-wire circuit compensates for temperature influences and bending tension. This means that only the relevant axial loads acting directly on the drives are measured. A QuantumX MX410B universal measuring amplifier together with the catman software were used to process the measurement signals.
The installation went smoothly thanks to the detailed guide videos and expert advice from HBM/HBK. The catman software enables the MX410B to connect quickly and easily to the laptop and the strain gages.
Three tests were specified to assess the load on the actuators: A blow on a hard surface to assess peak forces. Scraping the excavator teeth across a hard surface to subject the actuators to strong vibration. The third measurement is a realistic cycle simulating digging in homogeneous ground and moving the excavated material. The strain measurements were supplemented with the data from the motor inverters in order to compare the speed of the actuator with the loads, for example.
The measurement setup reliably delivered satisfactory strain gradients. The catman software makes evaluation easy and clear.
Figure 1 ECR25 with direct electric drive
The three measurements provided important findings for the future design of the linear drives, enabling them to be used permanently on excavators. It was possible to determine which drives require vibration damping, what loads the drives must be able to permanently withstand, and how measures to counter shock impact can be implemented. The strain gradients from scraping on a hard surface are shown by way of example. The vibration in the actuators is clearly seen, and is particularly pronounced in the bucket actuator.
Full Electric Excavator enables zero CO2 and noise emissions. Completly new human-machine interface for the user.
ETH Zurich’s annual focus projects offer students in a team of about eight engineers the unique opportunity to develop a product themselves, from the first draft, through engineering and design, to production and marketing. The necessary knowledge is gathered through self-study, parallel to ongoing courses and through dialog with partners from industry, supervisors and professors.
Andreas Reichmuth, Team Leader Products, SUNCAR, Schlieren/Switzerland
The use of electric linear drives with ball screw actuators on an excavator arm is a first. There are therefore no empirical values available in respect of the loads acting on the drives. The strain gage measurements aim to provide important data in this regard. Questions to be answered include: What is a typical load cycle? How does the actuator behave in response to shock impact or strong vibration? The measurements are intended to provide insights into how the drives can be improved further in order to withstand the loads. This will enable environmentally friendly and efficient operation of construction machinery in future.
The expert advice provided by HBK on site, and its active support to the project throughout the measurement chain, enabled optimal execution, including all tests and measurements, and derivation of the findings. The HBK measurement chain deployed consisted of strain gages, the QuantumX MX410B universal measuring amplifier, and the catman software. This enabled us in the eXact project team to make our contribution to developing the electric construction machinery of the future. We would like to thank HBK most sincerely for its support.
Concluding presentation: Focus Rollout Block III
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
This will bring together HBM, Brüel & Kjær, nCode, ReliaSoft, and Discom brands, helping you innovate faster for a cleaner, healthier, and more productive world.
