Manish Paliwal

Investigation of High-Frequency Squeal in a Disc Brake System Using a Friction Layer-Based Coupling Stiffness:

Abstract This paper presents a two degree of freedom model for disk brake systems that makes use of the concept of a friction layer-based coupling stiffness. This model is then used to investigate noise and vibration, especially high-frequency squeal. It is shown that for automotive brake systems, the friction layer plays a significant role in the performance characteristics. Hence, the coupling stiffness between the brake pad and the rotor is modelled as a combination of the elastic stiffness of the friction layer superimposed on the coupling modal stiffness of the brake-pad combination. The elastic properties of the friction layer are obtained from nano-indentor tests and the contact area is approximated using light microscopy and scanning electron microscopy analysis. The coupling modal stiffnesses are obtained from impact tests and finite element studies. Preliminary results from the model are consistent with the actual high squeal data collected from the field. The main objective of this work is to introduce a new way of modelling the coupling stiffness based on the properties of the friction layer, which has not been extensively studied till now.

An innovative design for an Assistive Arm Orthosis for stroke and muscle dystrophy

Rehabilitation robotics specializes in designing machines, such as exoskeletons, which can be utilized to restore function in patients recovering from physical trauma. The proposed Assistive Rehabilitation Arm Orthosis (A.R.A.O.) is designed to restore function and rehabilitate patients suffering from muscular diseases as well as mild-stroke. Clinical studies have shown that task-based repetitive training can improve motor abilities and enhance functional performance in those recovering from stroke. The proposed design improves on the popular four bar linkage systems used in many modern orthoses by incorporating a dynamic feedback system that actuates elastic elements, allowing users to lift heavier objects, while still remaining portable. The dynamic feedback system incorporates force-sensing resistors in conjunction with a linear actuator to vary the tension in the tension bands. The device not only allows patients to perform day-to-day lifting tasks but also has the potential for use in rehabilitation.

Fused Deposition Modeling BioPrinter

Scaffolds with three-dimensional, customizable architectures will be fabricated and populated with fibroblasts via automated processes of a Fused Deposition Modeling BioPrinter. The success of the design will be dependent on the accuracy of fabrication and adhesion/proliferation of the seeded fibroblasts.

Exo-Leg: An Active Single-Leg External Walking Assist Device

Lower extremity weakness is a serious problem afflicting people all over the world. Until recently, the mobility options for people with this condition have been confining and limit the individual’s functionality. Walking assist devices are presently in development to restore hands-free walking to people with lower extremity weakness. These devices provide the necessary support and power to enable the individual to restore normal ambulation. The proposed design of exoleg, a single leg external walking assist device, addresses the demographic of people with lower extremity weakness. The design includes replication of the gait cycle utilizing mechanical links and user control interface with emphasis on safety. The design couples the actuation of the knee and hip through the use of linkages connected to a single motor. The actuation of the hip is controlled by a 4 bars crank-rocker linkage system while the knee is actuated by corresponding linkages (designed in WORKING MODEL 2D , a commercial simulation software) that generates the knee kinematic profile. The angular profiles of the knee and hip actuations are compared with the actual knee and hip angular trajectories. The frame of the device incorporates a passive ankle stabilization system to compensate for the effects of foot drop. The system utilizes feedback from trigger points from pressure sensors on the foot and goniometers at the hip and knee joints to measure the angulations in gait to keep the device in synchronization with natural ambulation. An on-board microprocessor receives the feedback from the trigger points and sends the actuation signal to the motor. A conceptual design of electrostatic actuator motor is also proposed to keep the device light weight and compact.

Cementless modular total hip arthroplasty: a retrieval analysis

This paper reports the analysis of a modular S-ROM hip implant, which was retrieved at revision, secondary to aseptic loosening approximately after 24-months of implantation. Microscopic analysis confirmed the presence of pitting, fretting corrosion, plastic deformation, and stress induced corrosion cracking. Energy-dispersive x-ray microanalysis of the stem surface revealed the release of metal ions. High resolution inductively coupled plasma mass spectroscopy confirmed elevated titanium ion levels (4.66 ppb) in blood serum. Finite element analysis of the implant showed that the micromotion and stress levels were the maximum at the proximal-lateral region of the taper junction, in congruence with the observation.

Analysis of High Frequency Squeal in a Disc-Brake System Using a Stick-Slip Friction Model

This paper presents a two degree of freedom (2-DOF) stick-slip friction model for studying the effect of contact stiffness on the stability of the system. It is shown that the stability is not only a function of non-linear variation in the friction force provide by stick-slip but also depends on the variation in stiffness of contact due to the formation of friction layers on the surface of the rotor and the brake pad. Parametric studies have been presented to show the effect of variation in coefficient of friction and contact stiffness on the system stability.Copyright

Ceramic on-Ceramic Hip Implants: Analysis of Friction Induced Squeal

Ceramic-on-Ceramic (CoC) bearings are an ideal choice for a total hip replacement because of the ceramic bearings’ longer wear life than Metal-on-Metal or Metal-on-Polyethylene bearings. Friction-induced squeaking has been reported in 1–10% of patients who have a ceramic-on-ceramic total hip replacement, which is a subject of annoyance. Many mechanisms have been proposed to address the squeaking phenomena in CoC hip replacements, but there is no consensus among researchers on the root cause behind the squeaking of hip implants. The goal of this study was to investigate the possible factors attributing to the hip squeak, and understand the underlying phenomenon based on the coupling stiffness of the bearing surface. Boundary conditions for the CoC hip bearing to produce audible noise were also identified. An explanted Stryker Trident CoC hip bearing that had been removed due to squeaking was analyzed visually and by computer simulation. Grey marks on the femoral head of the implant showed material transfer of titanium alloy onto the alumina head. Using modal analysis, the natural frequencies of all the components of the implant were determined. Random vibration analysis was conducted to identify the ideal boundary conditions for the CoC hip bearing.The results from the modal analysis and calculated stiffness and damping coefficients were used in the mathematical two degree-of-freedom (DOF) model to calculate the velocity and position of the two masses in the system. State-Space plots of the parametric analysis were used to evaluate the stability of the system. Mathematical Analysis involved the investigation of the role of the frictional stick-slip phenomenon of the metal shell and ceramic liner on squeal. The size of the limit cycle provides an indication of the degree of severity of a noisy condition.With only metallic shell affixed to the acetabulum constrained, the modal natural frequency was 3600 Hz which was very close to the free vibration results of the bearing. The Power Spectral Densities displayed the audible frequencies at 11.4 kHz. The limit cycle plots show that a variation in coupling contact stiffness has an influence on the behavior/stability of the system. The study underscored the relevance of material transfer on the bearing surface using the mathematical analysis by varying the coupling stiffness of the bearing surface. In addition, random vibration analysis in conjunction with the parametric analysis identified the ideal boundary condition to produce the squeal frequencies as observed by others.Copyright

uGrip II: A Novel Functional Hybrid Prosthetic Hand Design

Current prosthetic devices frequently offer limited function at high costs. This proof-of-concept design proposes a hybrid trans-radial prosthesis that uses gross body movements to control multiple degrees of freedom. The novel actuation system uses signals transduced from shoulder articulations to control pneumatic actuators, which power the hand.

Failure of Three Cementless Modular Total Hip Arthroplasty Prostheses: A Retrieval Analysis

The reasons leading to the in vivo failure of three titanium alloy modular implants in cementless total hip arthroplasty were investigated. The implantation period ranged from 18 months to over three years. Two were fractured in vivo and the other was retrieved secondary to aseptic loosening after 18 months in service. Macroscopic examination showed close topographical similarities between the two fractured implants. Dark elliptical striations on the fractured site indicated the occurrence of low cycle fatigue. Light Microscopy and Scanning Electron Microscopy confirmed the presence of fretting, pitting, plastic deformation, and stress-induced corrosion cracking. In two of the three implants, EDS confirmed metal ion traces in the tissue around the implant. However, nothing unusual was found in the third unfractured implant. Taper performance is influenced by metallurgy, the load carried and the effect of the local microenvironment. Methods to reduce the impact of these factors may reduce the incidence of taper related failure.Copyright

Analysis of a retrieved squeaking ceramic-on-ceramic hip arthroplasty bearing

Ceramic-on-ceramic bearings in total hip replacements have shown superior wear performance compared to other material couples. However, 1–10% of patients have reported squeaking with the use of ceramic-on-ceramic bearings. A ceramic-on-ceramic bearing was retrieved from a patient after 4.5 years in service secondary to squeaking. The explant was analyzed to investigate the possible factors attributing to the hip squeak utilizing acoustic analysis, visual inspection, modal analysis, random vibration analysis, and mathematical modeling. Random vibration analysis of the parts of the implant showed that boundary conditions along the metallic shell play an important role in squeal occurrence. The implant also showed the evidence of material transfer. Using the results of modal analysis, a 2-degree of freedom friction model demonstrated the influence of third body material transfer on the stability of the system to be an important factor in squeaking. The mathematical parametric analysis showed that a larger mass creates more instability, and hence more noise and vibration. Increased stiffness of the shell proved to stabilize the system for most loading conditions. Limit-cycle plots showed a definite change in the system behavior but stability was maintained through a significant increase in contact stiffness.