Passive und aktive sekundäre Maßnahmen zur Reduzierung der Hand-Arm-Schwingungsbelastung
(Passive and active mechanical systems for reducing hand-arm vibration emission)
Gillmeister, F.
If no primary method of vibration reduction is practible, vibration isolation handles represent a suitable possibility of reducing the hand-arm vibration caused by hand-held tools. Due to the wide range of possible variation, e.g. the spring stiffness, the damping rate or the geometrie, vibration isolation systems can be adapted only in consideration of the vibration characteristics of the respective machine. For this purpose a universal test rig was built.
To simulate the different vibration isolation handles on the test rig in combination with various hand held tools, an electromagnetic shaker was used. The vibration characteristics of the tools were generated by several signal generators. Using this rig, it was guaranteed that the power input for the vibration isolation system was constant for all different handles. The measurement of the weighted acceleration was only performed in z-direction on the inside of the handle in the middle of the palm. The power of the shaker was sufficient to produce a range of the weighted acceleration values comparable to real machines.
The investigation was divided into two seperate sections. First, the mechanical models of the different vibration isolation handles were simulated on a PC in combination with the machine excitation data and the mechanical impedance of the hand-arm system. Second, the systems were reproduced on the test rig and measured.
The test included the following vibration isolation handles:
- a simple isolation system with spring and damper,
- an isolation system with spring, damper and absorber mass,
- an isolation system with spring, damper and a specially coupled "integrated" absorber mass and
- three differently controlled hydraulic actuators
The choice of the actuator was based on the requirements for the vibration displacement, the acceleration forces, the accuracy and the control rate. The most important working range of the actuator was defined to be the lower frequencies. The first actuator system was simply tuned to the impact frequency. The second actuator system had an analog PID-controller, the third a PC based fuzzy controller.
The results of the PC-simulation and the measurements on the test rig showed a good correspondence. It was possible to reduce the vibration emission at the handle down to 20-30% of the original values for the impact drill and the angle grinder. The passive isolation handles on the rotary hammer and the pavement breaker were more effective, when an absorber mass was attached. In particular, the coupled integrated absorber mass had a good effect. But none of these passive isolation systems archieved a reduction effect of more than approximatly 60%.
The actuator reduced the weighted acclereration down to 20% for the rotary hammer and down to 10% for the low frequency pavement breaker (impact frequency 14 Hz) of the original values.
Passive vibration reduction today is still possible. Simple passive systems archieve a good effectivity for a lot of tools. For the lower frequency machines, a controlled actuator is able to reduce the vibration emission with good results. With the development of simpler sensors, low cost controllers and actuators, new ways of vibration isolation systems will be possible.
Published as
Dissertation, Universität Dortmund, Vulkan Verlag, Essen, 1999, ISBN 3-8027-8706-4