1.3.1 Spring-Direct-Pressing Type Damper [101]
The structure of the adaptive damper composed of ER fluids and piezoelectric ceramics is shown in figure 4. There are holes in the piston and the electrode fixtures, through which the ER fluid filling the damper cavity flows freely. Piezoelectric ceramics are fixed beneath the pressing plate. A sealing rubber is looped onto the pressing plate so that the ER fluid cannot exude into the chamber containing the ceramics. The piston and the pressing plate are connected by a stiff spring. A set of concentric electrodes is fixed onto the piston rod by the electrode fixtures. These electrodes are connected to the output electrodes of the piezoelectric ceramics.
Figure 4. Spring-direct-pressing type damper.
The working process of this damper is as follows: when the piston moves up and down, it compresses or releases the spring. At the same time, the stimulated piezoelectric ceramics produces a high voltage and hence an electric field between the electrodes. Thus, the ER fluid flowing between these electrodes is solidified. As a result, the system damping increases and the vibration is suppressed.
1.3.2 Wedge-Push Type Damper [102]
Figure 5. Wedge-push type damper.
The wedge-push type ER damper has a wedge pad fixed on one end of the piston rod.
The ceramics are placed in a box that has a rotary wrench. As the wrench rotates, the piezoelectric ceramics are compressed by a bias axle, which rotates with the wrench. The voltage output produced by the ceramics is conducted by electric wires to concentric electrodes that are fixed inside the cylinder. The whole structure of the damper is shown in figure 5. The working process of the damper is as follows: when the piston and the wedge pad move up and down, the wedge pad rotates or releases the wrenches. In this way, the piezoelectric ceramics generate a voltage output that is conducted to the concentric electrodes. At the same time, the ER fluid flowing through the electrodes is solidified and its flow is restricted. The damping inside the cylinder increases and the movement of the piston is suppressed.
We fabricate a wedge-push type damper and conduct a test to demonstrate the vibration suppression effect of the damper. The geometry of the outer cylinder of the wedge-push type damper is ij52 × 100 mm. The height of the electrodes is 60 mm. The diameter of the inner electrode is 40 mm. The gap between the inner and outer electrodes is 1.5 mm. The thickness of the outer cylinder is 3 mm.
1.3.3 Vibration Suppression Properties
The ER fluid used in the damper is a suspension of rare earth doped TiO2 particles in silicone oil [103]. The volume content of particles in the ER fluid is set to 27% in this experiment.
The yield stress of the suspension is over 4kPa under a DC electric field of 2.5kV/mm.
Figure 6. Schematic diagram of the experiment.
The experimental connection diagram is shown as Fig.6. To test the vibration suppression effect of the damper, a vibration stimulator (JZ5-5) providing driving force is perpendicularly erected and its driving rod is connected with an accelerator sensor and then the wedge-push ER damper that waits to be tested. The damper bottom is fixed on the ground. The vibrations provided by the stimulator are applied on the damper. The accelerator sensor conveys detected signals to an electric charge amplifier (DHF-9) and a signal analyzer (CF350). Test results are printed from a printer.
The output power of the stimulator is set at 75%. Fig. 7(a) and Fig. 7(b) are curves of accelerator amplitude vs. frequency. The former is the result of the condition where the ceramics’ voltage output is absent, while the later is the result of the other condition where the ceramics’ output is present. Similarly, setting the output power of the stimulator at 50%, disconnecting or connecting the ceramics’ voltage respectively, we get Fig. 8(a) and Fig. 8(b) accordingly. In these figures the ordinate of plot is the magnitude of electric signal measured by accelerator sensor in scale of milli-volt.
Figure 7. The accelerator amplitude spectrum on frequency domain under 75% driving power: (a) the voltage output of piezoceramic is absent and (b) the voltage is present.
Comparing Fig. 7(a) and Fig. 7(b), it can be seen that the envelope of accelerator magnitude spectrum in Fig. 7(b) is lower than in Fig. 7(a). It infers that after connected the voltage output of piezoceramics the accelerator magnitude decreased. Furthermore, according to the relationship of displacement amplitude and accelerator amplitude, Ad Aa / Z2, it implies that the displacement amplitude decreases too. In addition, the frequency of maximal accelerator amplitude moves toward the direction of high frequency from 57.3Hz in Fig. 7(a) where the piezoceramics voltage is absent to 64.7Hz in Fig. 7(b) where the piezoceramics voltage is present. It is shown that because of the stimulation of electric field generated from
the piezoceramics, the ER fluid in damper solidifies and its yield stress increases; so the damping force of the damper increases and the vibration of damper piston is suppressed.
Figure 8. The accelerator amplitude spectrum on frequency domain under 50% driving power, (a) the voltage output of piezoceramic is absent and (b) the voltage is present.
In Fig. 8(a) and Fig. 8(b) the output power of stimulator decreased. It still can be seen that the envelope in Fig. 8(b) got lower than Fig. 8(a), but the degree of decrease is light.
However the motion of frequency of maximal accelerator amplitude is still obvious, moving from 56.6Hz in Fig. 8(a) to 65.7Hz in Fig. 8(b) where the voltage is present. This is due to the ER effect, which makes the damping force of damper increase and the vibration of damper suppressed.
The curves in Fig. 7 and Fig. 8 are serrated but smooth ones. This probably is induced by the non-linear factors in the damper system, such as the friction between the wedge piston and the wrench of ceramic box, the non-linearity of the wrenching force vs. the displacement of vibration, and the swash of ER fluid in damper. But from a viewpoint of whole the decrease of the envelope of curves and the motion of maximal amplitude of accelerator toward high frequency are both obvious.