This thesis adds to the knowledge base of constant-force mechanisms (CFMs). It begins by reviewing past work done in the area of CFMs and then develops new nondimensionalized parameters that are used to simplify the calculations required to design a CFM. Comparison techniques are then developed that utilize these non-dimensionalized parameters to compare mechanisms based on stiffnesses, percent constant-force, actual lengths, normal displacements, and feasible design orientations. These comparison techniques are then combined with optimization to define new mechanisms with improved performance and range of capabilities. This thesis also outlines a design process, methods to identify mechanisms that are suitable for a given design problem, and relationships and trends between variables. The thesis concludes by discussing the adaptation of CFMs for use in electrical contacts and presenting the results of a design case study which successfully developed a constant-force electrical contact (CFEC).

Wearable Health Devices (WHDs) are an emerging technology that enables continuous monitoring of vital signs during daily life. Issues with constant and consistent data acquisition have been found while WHD technology has developed. The force of the measurement area and movement of the sensors are key mechanical issues that need to be solved for WHDs to become a viable way to continuously monitor health conditions. This work explores Constant-Force Mechanisms (CFMs) as a solution to problems the current WHD industry faces. Additionally, the relationship between force provided from the mechanism, sensor pressure on the wrist, patient comfort, and sensor readings quality are explored and analyzed. Design requirements for a constant-force wristband were narrowed down to seven critical requirements (mechanism size vs. allowable travel, ability to be used on a curved surface, works well with existing clasps, ease of assembly, direction of travel, material, and force generation). These key requirements need to be considered for a WHD with an integrated CFM to be designed successfully. Two main concepts (buckling beams and tape springs) were prototyped and evaluated against the seven key requirements. The design and testing of a wrist worn sensing band used to gather relationship data among band tension, sensor pressure, patient comfort, and pulsatile signal quality is also presented. Human subject testing (IRB2020-268) was performed on a wristband with an integrated CFM and the wrist worn sensing band that were developed. The band with an integrated CFM compared pressure on the wrist for both a band with and without an integrated CFM for eight different movement activities. On average the band with the integrated CFM had a lower coefficient of variation for all except one of the activities. The data collected from the wrist worn sensing band shows that tension varies linearly with pressure, and that the pressure vs. tension slope increases with increasing wrist width. There also exists a linear relationship between tension and patient pain/comfort, but pressure does not show an effect on the patient discomfort or pain experienced. Signal quality when measured in the range of of 0-4 N and 0-20 kPa does not have a direct correlation to either tension or pressure.

Constant-force mechanisms are mechanical devices that provide a near-constant output force over a prescribed deflection range. This thesis develops various optimization-based methods for designing robust constant-force mechanisms. The configuration of the mechanisms that are the focus of this research comprises a cam and a compliant spring fixed at one end while making contact with the cam at the other end. This configuration has proven to be an innovative solution in several applications because of its simplicity in manufacturing and operation. In this work, several methods are introduced to design these mechanisms, and reduce the sensitivity of these mechanisms to manufacturing uncertainties and frictional effects. The mechanism's sensitivity to these factors is critical in small scale applications where manufacturing variations can be large relative to overall dimensions, and frictional forces can be large relative to the output force. The methods in this work are demonstrated on a small scale electrical contact on the order of millimeters in size. The method identifies a design whose output force is 98.20% constant over its operational deflection range. When this design is analyzed using a Monte Carlo simulation the standard deviation in constant force performance is 0.76%. When compared to a benchmark design from earlier research, this represents a 34% increase in constant-force performance, and a reduction from 1.68% in the standard deviation of performance. When this new optimal design is evaluated to reduce frictional effects a design is identifed that shows a 36% reduction in frictional energy loss while giving up, however, 18.63% in constant force.

A mathematical dynamic model is derived for the compliant constant-force mechanism, based on the pseudo-rigid-body model simplification of the device. The compliant constant-force mechanism is a slider mechanism incorporating large-deflection beams, which outputs near-constant-force across the range of its designed deflection. The equation of motion is successfully validated with empirical data from five separate mechanisms, comprising two configurations of compliant constant-force mechanism. The dynamic model is cast in generalized form to represent all possible configurations of compliant constant-force mechanism. Deriving the dynamic equation from the pseudo-rigid-body model is useful because every configuration is represented by the same model, so a separate treatment is not required for each configuration. An unexpected dynamic trait of the constant-force mechanism is discovered: there exists a range of frequencies for which the output force of the mechanism accords nearer to constant-force than does the output force at static levels.

Linjett Segelbåtar konstruerar och producerar högkvalitativa  segelbåtar på Rosättravarvet. Detta arbete syftar till att presentera en bättre mekanisk lösning till den nedgångslucka som Linjett har idag. Förbättringen består i att sänka produktionskostnaderna, underlätta montering och service men framförallt öka livslängden på mekanismen. Nedgångsluckan är den vertikala ”dörr” som skiljer utsidan från insidan på en segelbåt. I Linjett’s befintliga lösning så skjuts luckan ned i en balja under durken och försvinner undan på ett väldigt smidigt sätt. Tack vare en gasfjäder görs den annars ganska tunga luckan viktlös och kan lämnas halvöppen vilket kan vara väldigt praktiskt, det är en typ av funktion som den nya lösningen måste bibehålla. Arbetet har följt en generisk utvecklingsprocess. Koncept från en idégenerering har ställts mot varandra med hjälp av en pughmatris och en multiomröstning. Det vinnande konceptet har sedan förbättrats i en iterativ process för att uppfylla målen i så hög utsträckning som möjligt. Under vidareutvecklingen har fokus legat på att minimera antal komponenter genom DFA (Design For Assembley). För att motivera lösningen har monteringsscheman ställts upp och kompletterats med en självkostnadskalkyl. Dessa detaljstuderas och utvärderas för att agera beslutsunderlag till Linjett. Den presenterade lösningen använder konstantkraftsfjädrar för att bära upp luckans vikt. Dessa fjädrar ger lång livslängd i dessa utsatta miljöer och har ett förhållandevis lågt inköpspris. / Linjett Segelbåtar constructs and produces high quality sailing yachts at Rosättravarvet. This rapport aims to enhance the mechanical solution of the companionway door that Linjett is using. The enhancement consists in lowering production costs, simplify the mounting and service but most important, raise the lifetime of the mechanism. The companionway door is what separates the outside from the inside on a sailing yacht. Linjett has a special solution were the companionway door slides in under the cockpit floor and disappears in a clever way. Thanks to a gas spring the otherwise heavy door becomes weightless and can be left at any desired height which can come in handy. This is one of the function that the new solution must maintain. The work has followed a generic developmentprocess. Concepts from a brainstormingsession have been evaluated and compared in a pughmatris and a multivote. The winning concept has then been improved in a iterative process to fulfill the goals in the best way possible. During the enhancement of the concept there has been a strive to minimize the number of components throughout DFA (Deisgn for Assembley) To motivate the solution a mounting schedule was produced which in turn were complemented by a cost price calculation. These were studied in detail and evaluated to create a basis for decision making to Linjett. The presented solution uses constant force springs to carry the weight of the companionway door. Springs of these type provide long lifetime in these harsh conditions and is reasonably priced.

Diploma thesis is focused on mechanical properties testing by small punch test and comparison of these properties with mechanical properties obtained by conventional tensile test. Steels P92 and AISI 316L in a shape of discs were tested. There were determined values of mechanical properties, namely yield stress, and ultimate tensile stress, obtained by the small punch test – constant deflection rate in this thesis. Values of initial stress and residual stress were evaluated from relaxation small punch test. Mechanical properties obtained by small punch test – constant deflection rate, and small punch test – relaxation, respectively, are compared with mechanical properties obtained by conventional tensile test, and relaxation tensile test, respectively. There were proposed own empirical relationships for restatement of mechanical properties obtained by small punch test to mechanical properties obtained by conventional tensile test in the thesis. Relatively small agreement of results obtained by small punch test, and conventional tensile test was demonstrated by a comparison. Application of own empirical relationships resulted in better agreement. Very good agreement of results of small punch test – relaxation, and relaxation tensile test was shown by their comparison.