Design considerations for ferrofluid pressure bearing pads

The novel contribution of this research is insight into the influence of different parameters in the magnet configurations on the load and stiffness of a ferrofluid pressure bearing. It is shown that magnets with a small cross-section magnetized alternatively up and downwards combine a high load capacity and moderate stiffness while being low on material cost and complexity. The configuration where magnets are placed alternatively in left and right direction magnetized inter spaced with iron yields the highest load capacity and stiffness, albeit at the cost of weight and complexity. It is shown that an increase in the number of magnets is beneficial for the stiffness in both magnetization configurations, as is an increase in remanent flux density of the magnet. A metal bottom plate made of iron reduces the necessary height of the magnet in the up-down magnetization configuration. The model was validated using a bearing pad arranged in the up-down configuration. The force-displacement curve of this pad was measured in a load frame, using the APG 513 ​A ferrofluid from Ferrotec. A load capacity of 1.75 ​N/cm2 was achieved, this exceeds previous pressure bearing implementations and performs comparable or better than implementations of single seal ferrofluid pocket bearings. These results show that the ferrofluid pressure bearing is a passive alternative in motion systems where the designer otherwise would have needed to use an active bearing

A contactless capacitive angular-position sensor

This paper presents an absolute capacitive angular-position sensor with a contactless rotor. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor, and a microcontroller. The electrically floating rotor can be either conductive or dielectric. For the dielectric material, we chose plastic, and for the conductive rotor, we chose aluminum. The sensing element has a redundant structure, which reduces mechanical nonidealities. The signal processor has a multicapacitance input and a single output, which is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. Theoretical analysis, supported by experimental results, show that the sensitivity to mechanical nonidealities of the sensing element is higher in the case of a conductive rotor. The resolution of the capacitive angular-position sensor over the full range (360/spl deg/) was better than 1". The measured nonlinearity was /spl plusmn/ 100" and /spl plusmn/ 300" for the dielectric and the conductive rotor, respectively.Peer Reviewe

A contactless capacitive angular-position sensor

This paper presents an absolute capacitive angular-position sensor with a contactless rotor. The sensor is mainly composed of three parts: the capacitive sensing element, a signal processor, and a microcontroller. The electrically floating rotor can be either conductive or dielectric. For the dielectric material, we chose plastic, and for the conductive rotor, we chose aluminum. The sensing element has a redundant structure, which reduces mechanical nonidealities. The signal processor has a multicapacitance input and a single output, which is a period-modulated square-wave voltage. The microcontroller acquires output data from the processor and sends them to a PC, which calculates the rotor position. Theoretical analysis, supported by experimental results, show that the sensitivity to mechanical nonidealities of the sensing element is higher in the case of a conductive rotor. The resolution of the capacitive angular-position sensor over the full range (360/spl deg/) was better than 1". The measured nonlinearity was /spl plusmn/ 100" and /spl plusmn/ 300" for the dielectric and the conductive rotor, respectively.Peer Reviewe

Frequency stabilized three mode HeNe laser using nonlinear optical phenomena

Accurate and traceable length metrology is employed by laser frequency stabilization. This paper describes a laser frequency stabilzation technique as a secondary standard with a fractional frequency stability of 5.2×10?10 with 2 mW of power, suitable for practical applications. The feedback stabilization is driven by an intrinsic mixed mode signal, caused by nonlinear optical phenomena with adjacent modes. The mixed mode signals are described theoretically and experimentally verified.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

Simple heterodyne laser interferometer with subnanometer periodic errors

We describe a simple heterodyne laser interferometer that has subnanometer periodic errors and is applicable to industrial fields. Two spatially separated beams can reduce the periodic errors, and the use of a right-angle prism makes the optical configuration much simpler than previous interferometers. Moreover, the optical resolution can be enhanced by a factor of 2, because the phase change direction is opposite between reference and measurement signals. Experiments have demonstrated the periodic errors are less than 0.15 nm owing to the frequency mixing of the optical source. The improvements for reducing the frequency mixing of the optical system are also discussed.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin

High resolution heterodyne interferometer without detectable periodic nonlinearity

A high resolution heterodyne laser interferometer without periodic nonlinearity for linear displacement measurements is described. It uses two spatially separated beams with an offset frequency and an interferometer configuration which has no mixed states to prevent polarization mixing. In this research, a simple interferometer configuration for both retroreflector and plane mirror targets which are both applicable to industrial applications was developed. Experimental results show there is no detectable periodic nonlinearity for both of the retro-reflector interferometer and plane mirror interferometer to the noise level of 20 pm. Additionally, the optical configuration has the benefit of doubling the measurement resolution when compared to its respective traditional counterparts. Because of non-symmetry in the plane mirror interferometer, a differential plane mirror interferometer to reduce the thermal error is also discussed.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin