1.4 The Second Generation Product: Self-Coupled ER Damper
1.4.1 Configuration of the Self-Coupled ER Damper [106]
Figure 9 is the cutaway view of a manufactured self-coupled ER damper. Three aspects of modification for structure design have been adopted in the second-generation damper compared with the first one.
(1). The number, arrangement style and electrically connecting style of piezoelectric ceramics are modified in the second-generation damper. See table 1. (a) Three piezoelectric ceramics, instead of two, are employed in the second-generation damper and the arrangement style of piezo-ceramics is adjusted into triangularity. This triangular style guarantees a better stability of the damper applied under load. (b) The electrically connecting style of piezo- ceramics is changed from in-parallel to in-series. In this way the total voltage output is boosted and then the stimulation for ER fluid is more manifest.
Figure 9. The cutaway view of the manufactured self-coupled ER damper.
TABLE 1. Comparison for piezoelectric ceramics between two generation dampers Number Arrangement style (top view) Connecting style First generation Damper 2
In parallel
Second-generation Damper 3 In series
Figure 10. Comparison for the load application mode between (a) the first generation damper and (b) the second-generation damper.
(2). The load application model is modified as shown in figure 10. The piezo-ceramics are positioned upper the damping cavity (see figure 9) instead of the reverse order in the first
generation damper [104]. The modified structure allows that the acting force of external load is transmitted on piezoelectric ceramics efficiently. So the working sensitivity of the whole system is improved.
(3). In figure 9, the hole-channels are added to the electrodes of concentric cylinder, and connect with the damping cavity and the gap of cylinder electrodes. Since the yield stress of ER fluid is not high enough in present, the design of structure can substantially improve the load-bearing ability of the system.
Table.2 lists some quantitative comparing data between the two generation dampers.
Modifications mentioned above make the new generation damper to excel in structure stability, working sensitivity and load-bearing ability.
Table 2. Comparison for stability, sensitivity and load-bearing ability between two generation dampers
The first generation damper The second-generation damper 1(a) Stability Wedge piston easily sliding
out laterally;
Piezo-ceramics arranged in parallel
Piston in direct-push type moving coaxially;
Piezo-ceramics arranged in triangle
1(b) Voltage output Only 2kV or so Over 5kV 2 Working sensitivity Friction between wedge face
and wrench of piezo-ceramic box;
Load application mode:
load-ER-piezoceramics
No friction face in direct-push type damper;
Load application mode:
load-piezoceramics-ER
3 Load-bearing ability 600N 5kN
A self-coupled ER damper has been manufactured. The photographs of the damper are shown in Figure 11. The damper is divided into five parts, driving-force-applied (including piston and piston rod), piezoelectric power supply (including spring, pressing-spring plate and piezoelectric ceramics), damping part (including inner and outer damping cylinders, ER fluid), electric connecting part (wires and insulating plate) and packing or encapsulating part (e.g. fasteners) [106].
Figure 11. Photographs for (a) the facade and (b) the components of the manufactured self-coupled ER damper.
The working process of the ER damper can be explained as following. When the driving force applies on the piston rod and makes the rod moving up and down, the pressing-spring plate moves with the rod too. A pressure is applied on the piezoelectric ceramics via the spring and the insulating plate. An output voltage is generated from the piezoelectric ceramics under the pressure. The output voltage is connected on the inner and outer electrodes. The ER fluid filled between the electrodes is induced and its viscosity increases quickly. Propelled by the moving piston, the ER fluid flows through the hole-channels in the bottom of the damping cavity and comes back through the hole-channels in the upper of the damping cavity. Since the viscosity of ER fluid increases drastically, a damping force acts back on the piston and then the vibration suppression is achieved. The presented damper is composed of electrorheological fluid and piezoelectric ceramics. It not only can be self-energized without an external power source but also generates the voltage magnitude according to the strength of external excitation. The stronger the external excitation is, the higher the pressure acting on piezo-ceramics and the voltage generated from piezo-ceramics is. Hence a more effective solidification occurs in ER fluid. As a result, the damper exhibits a more effective vibration suppression effect. In this meaning, the damper possesses a feature of adaptive control.