Design and optimization of compliant mechanical amplifiers

Piezoelectric (PZT) actuators are micro motion generators capable of producing a high displacement resolution and low strain with high force outputs. However, due to their relatively short motion ranges, the functions of PZT actuators become limited or infeasible for many of the above mentioned applications. One technique to overcome the mentioned shortcoming is to integrate a PZT actuator with a mechanical displacement amplifier. Such an amplification mechanism can be based on a compliant mechanical displacement amplifier (CMDA). A CMDA has many advantages such as no friction losses, no need for lubrication, no tolerance, and et al. over conventional rotating pinjoint mechanisms. Hence, the primary goal of a CMDA is to achieve a large output displacement in desired direction(s) for a given input displacement generated by a PZT actuator, and to keep a high positioning resolution at the same time. This thesis describes a complete study on the design, development and optimization of two proposed CMDA’s, one for the use in prostate Magnetic Resonance Elastography (MRE) application, and the other for the use as a planar motion generator mechanism for the application in high precision manipulation systems. The design of the both proposed mechanisms are based on the symmetric five-bar topology which facilitates a high amplification ratio (AR) with maintaining a relatively high natural frequency (NF). The first proposed CMDA was designed and optimized to amplify the generated motion of a PZT actuator in only one direction with keeping the NF as high as possible. On the other hand, the design and optimization of the second proposed CMDA was done to convert the linear motions of the integrated PZT actuators into a XY planar motion with high accuracy and resolution. In this study the comprehensive FEM analysis and simulations of both proposed CMDA designs are provided.

Design and optimization of compliant mechanical amplifiers

Piezoelectric (PZT) actuators are micro motion generators capable of producing a high displacement resolution and low strain with high force outputs. However, due to their relatively short motion ranges, the functions of PZT actuators become limited or infeasible for many of the above mentioned applications. One technique to overcome the mentioned shortcoming is to integrate a PZT actuator with a mechanical displacement amplifier. Such an amplification mechanism can be based on a compliant mechanical displacement amplifier (CMDA). A CMDA has many advantages such as no friction losses, no need for lubrication, no tolerance, and et al. over conventional rotating pinjoint mechanisms. Hence, the primary goal of a CMDA is to achieve a large output displacement in desired direction(s) for a given input displacement generated by a PZT actuator, and to keep a high positioning resolution at the same time. This thesis describes a complete study on the design, development and optimization of two proposed CMDA’s, one for the use in prostate Magnetic Resonance Elastography (MRE) application, and the other for the use as a planar motion generator mechanism for the application in high precision manipulation systems. The design of the both proposed mechanisms are based on the symmetric five-bar topology which facilitates a high amplification ratio (AR) with maintaining a relatively high natural frequency (NF). The first proposed CMDA was designed and optimized to amplify the generated motion of a PZT actuator in only one direction with keeping the NF as high as possible. On the other hand, the design and optimization of the second proposed CMDA was done to convert the linear motions of the integrated PZT actuators into a XY planar motion with high accuracy and resolution. In this study the comprehensive FEM analysis and simulations of both proposed CMDA designs are provided.

The effect of displacement of the esophagus by transoesophageal echocardiography probe in cryoablation of atiral fibrillation

Background Esophageal injury caused by cryoballoon-based PVI is common. Cryoablation guided by transoesophageal echocardiography (TEE) for occlusion of the pulmonary vein (PV) is safe and effective. Objective To investigate the protective effect of mechanical displacement of the esophagus by TEE probe in cryoablation of atiral fibrillation. Methods Fifty patients with paroxysmal AF (PAF) were enrolled in the present study. 25 patients underwent cryoablation without TEE (non-TEE group) and the other 25 underwent with TEE (TEE group) for PV occlusion guidance and displacement of the esophagus. In the TEE group during the procedure, TEE was used to guide the movement of the balloon to achieve PV occlusion. And before freezing, the probe of the TEE was moved to displace the esophagus away from the PV being freezed in order to reduce the risk of cryoinjury. All patients underwent esophagogastroscopy within 2 days of the procedure. The patients were followed up in our center at regularly scheduled visits every 2 months. Results There was no significant difference between the TEE group and non-TEE group in regard to the procedure time. The fluoroscopy time in the TEE group was less compared to the non-TEE group (4.1±3.3 min vs. 16.6±6.9 min, P<0.05), and the amount of contrast agent in the TEE group was less than the non-TEE group (4.7±5.7ml vs. 17.9±3.4 ml, P<0.05). The incidence of esophageal injury was significantly lower in TEE group compared with non-TEE group (0 vs. 20%, P<0.05). At a mean of 14.0 months follow-up, success rates were similar between the TEE group and non-TEE group (80.0% vs. 84.0%, P=0.80). Conclusion Cryoablation of AF with TEE for protecting the esophagus from cryoinjury is safe and effective. Lower risk of esophageal injury can be achieved with the help of TEE probe movement for mechanical displacement of the esophagus during freezing. Funding Acknowledgement Type of funding source: None

Bimetallic ammeter: a novel method of current measurement

An electric current flowing through a bimetallic coil heats it up, and due to thermal expansion, the coil either unwinds or winds depending on the direction of net heat transfer and the specific heat capacities of the metals used. This means that by relating a certain measure of its mechanical displacement with current, the bimetallic coil can be used as an ammeter. Thus, a mathematical model relating the current to the time taken by the bimetallic coil to unwind a fixed displacement was developed and verified through experiments, which show a good agreement between theoretical and experimental values.

Picometer mechanical displacement measurement using heterodyne interferometer with phase-locked loop

In this paper, we show picometer-order mechnical displacmment measurements using a heterodyne interferometer with a phase-locked loop (PLL). A heterodyne light source for the interferometer is implemented with a frequency stabilized HeNe laser and two acousto-optic modulators. A real time phase measurement is performed by the PLL, whose software is programmed in a field-programmable gate array (FPGA). A stiff parallel spring stage combined with a high-voltage piezoelectric actuator is used to generate picometer-order mechanical motion. With the above implementations, mechanical displacement of 10 picometer or less can be measured.