motor that could provide stable drive by using chemically reduced LN stator. This stator has higher electric conductivity and prevents charge build-up at the contact area. As the contact area of the flat-plane slider is larger than that of the slider with projections, the flat-plane slider can drive faster than a slider with projections, however under a higher preload. The advantage of the flat-plane slider is that it does not require silicon micromachining processes.
The research work presented in the thesis is aimed at achieving a compact design which is convenient to use and suitable for commercialization. The necessary restructuring of a SAW linear motor with the guide rail replaced by an additional stator to drive the slider simplifies the operating mechanism. The assembly of the proposed SAW motor is shown in Figure 1.30 where a slider with a uniform array of projections on both the contact surfaces is sandwiched between two identical stators aligned to generate SAWs that drive the slider from top and bottom.
The glass substrates provide support to the piezoelectric stators while supplying preload. In each stator, SAW propagating on the surface of the stator interacts with the slider at the contact points and the frictional force acts on the slider in the direction opposite to the propagation of SAW. By applying simultaneous excitation to two IDTs on one side of the motor, one each from the top and bottom stators, the Rayleigh waves propagates on the
stator surfaces and deliver a frictional force on the surface of the slider at the contact points is represented in Figure 1.31. Since the waves propagate in the same direction on the two stator surfaces facing each other, the elliptical motion of the points on the surfaces of the stators generates frictional forces on the two contact surfaces of the slider which results in driving the slider towards the activated IDTs. The direction of motion of the slider can be changed by switching the excitation to the IDT pair on the respective side of the motor, thus forward or reverse translational motion is possible. The proposed DFD technique SAW linear motor could overcome the limitations mentioned above for the conventional SAW linear motor.
Slider with array of
projections Propagation of SAW Preload
Piezoelectric stator
z x Piezoelectric stator
Motion of slider
Figure 1.31: Schematic diagram of proposed principle of working for the dual friction-drive SAW linear motor.
Figure 1.32: Schematic diagram of dual friction-drive SAW motor with a cylindrical shaft.
The assembly of the proposed SAW motor is shown in Figure 1.32 where a cylindrical shaft is sandwiched between two identical stators aligned to generate SAWs that drive the slider from top and bottom. The glass substrates provide support to the piezoelectric stators while
supplying preload. Each stator has an IDT fabricated on the piezoelectric substrate on either side of the shaft. In each stator, SAW propagating on the surface of the stator interacts with the shaft at the contact points and the frictional force acts on the shaft in the direction opposite to the propagation of SAW. The proposed SAW motor is capable of making both translational and rotational motion in forward and reverses directions.
When electrical excitation is applied in a synchronised way to the one side of the stators each of top and bottom stator, Rayleigh SAW is generated that propagates in the the +X direction in both the stators. Since the two stators are kept facing each other, for the SAW travelling in a +X direction, the particles at the surface of the bottom stator make anticlockwise elliptical motion, and the particles on the surface of the top stator make clockwise elliptical motion as drawn in Figure 1. 33. The preload applied to the shaft generates high frictional force on the cylindrical shaft in –X direction at both the contact
Ft Ft
SAW
SAW
Preload Direction of
Motion of particle
Cylindrical shaft LiNbO3
Piezoelectric substrate
Z X
Figure 1. 33: Schematic diagram of proposed principle for dual-drive SAW motor as a linear motor.
Damping material
Piezoelectric stator
z x
Glass Substrate
Piezoelectric stator Glass Substrate
IDT
Damping material
IDT Spacer
Spacer
Shaft Preload
points and the shaft performsatranslational motion in –X direction. Similarly, if IDTs present at other side are activated instead of present activated IDTs, the shaft will perform atranslational motion in the opposite direction i.e. in the +X direction.
When electrical excitation is applied in a synchronised way to the IDTs present on each of top, and bottom stator disposed of crosswise as shown in Figure 1.32, Rayleigh SAW is generated that propagates in the +X direction in the bottom stator and in –X direction in the top stator. With the above arrangement, for the SAW traveling in +X direction, the particles at the surface of the bottom stator make anticlockwise elliptical motion and for the SAW traveling in –X direction the particles at the surface of the top stator make clockwise elliptical motion as drawn in Figure 1.34. The applied preload generates high frictional force on the shaft in –X direction at both the contact points and the shaft performs a rotational motion in a clockwise direction. Similarly, if IDTs on the other side are activated instead of present activated IDTs, the shaft will perform a rotational motion in the opposite direction i.e. in an anticlockwise direction. Thus the shaft can make a rotational motion in both clockwise and anticlockwise directions. By applying alternate excitations for translational and rotational motions through time multiplexing repeatedly, a simultaneous translational and rotational motion is achieved.