This chapter includes the design procedure for the vibration absorber system made up of SMA springs. The vibration absorber is consisting of a mass M on which we mounted a bracelet which is made up of four mass-spring-damper systems as shown in fig. two vertical and two horizontal.
This system would follow the principles of inertia to counterbalance the forces of a tremor. Let’s assume, throughout a tremor the hand will moves in X and Y direction and also sometime it will rotate between X and Y direction. In this case inertia will take effort to retain the bracelet in its earlier position. This will perform like a force dragging in the opposite direction to the tremor. Because of this force hand will tried to regain its original position. …show more content…
But they knew that the bracelet masses required to be a ten percent of the arm weight. So for a sake of design purpose, they decided to use a 150-pound male subject as our imaginary patient. From the literature review they found that the arm weight of a male human was 2.26% of the body weight. This indicates that our test object would have an arm weight of 3.36 pounds, and therefore, the bracelet needed 0.336 pounds in each of the X and Y-axis directions. This weight would be equally divided between either side of the bracelet to keep it balanced. A weight of 0.168 pounds in steel was going to be large and bulky. It was going to be too large to be workable. On the other hand, a lead mass would be smaller than steel it was still too large to work. So they decided that we required the thickest material that we could get. This search led them to tungsten. Tungsten is extremely thick, hard, and expensive. Since the device was intended for medical patients so they decided that the device has to be a good quality of life, then expensive was not a …show more content…
In ordered to get a proper mass-spring-damper system we should know the frequency of a tremor. From the literature review we knew that for Parkinson’s disease frequency was lies between 3 to 7 Hz. So we decided to go with a 3 Hz frequency. Using this information and weight of bracelet mass we can easily calculate the spring constant value. After we had the spring constant, we calculated rest of the spring parameters based on spring constant like wire diameter, free length, mean coil dia. etc. After that we searched for the actual SMA compression spring which match our requirements. But unfortunately we didn’t get the spring that we wanted because the compression springs are not available they can be made by custom orders only and it will cost a lot. So we decided to ordered the SMA wire of required wire diameter and we would make a spring in house. Before we started making the spring we searched how we can make a spring in house, we found that using lathe machine we can made the spring. For that we had to run the lathe machine at a very low speed but we had a problem over here because the SMA wire is too thin to wound on lathe machine than the normal steel wire so we can’t make a spring on lathe machine. Then we got a Martindale spring winder machine which is a manual operated device and very easy to handle. Before we start making springs we have to select a desired size arbor and its matching bushing. After that
This system would follow the principles of inertia to counterbalance the forces of a tremor. Let’s assume, throughout a tremor the hand will moves in X and Y direction and also sometime it will rotate between X and Y direction. In this case inertia will take effort to retain the bracelet in its earlier position. This will perform like a force dragging in the opposite direction to the tremor. Because of this force hand will tried to regain its original position. …show more content…
But they knew that the bracelet masses required to be a ten percent of the arm weight. So for a sake of design purpose, they decided to use a 150-pound male subject as our imaginary patient. From the literature review they found that the arm weight of a male human was 2.26% of the body weight. This indicates that our test object would have an arm weight of 3.36 pounds, and therefore, the bracelet needed 0.336 pounds in each of the X and Y-axis directions. This weight would be equally divided between either side of the bracelet to keep it balanced. A weight of 0.168 pounds in steel was going to be large and bulky. It was going to be too large to be workable. On the other hand, a lead mass would be smaller than steel it was still too large to work. So they decided that we required the thickest material that we could get. This search led them to tungsten. Tungsten is extremely thick, hard, and expensive. Since the device was intended for medical patients so they decided that the device has to be a good quality of life, then expensive was not a …show more content…
In ordered to get a proper mass-spring-damper system we should know the frequency of a tremor. From the literature review we knew that for Parkinson’s disease frequency was lies between 3 to 7 Hz. So we decided to go with a 3 Hz frequency. Using this information and weight of bracelet mass we can easily calculate the spring constant value. After we had the spring constant, we calculated rest of the spring parameters based on spring constant like wire diameter, free length, mean coil dia. etc. After that we searched for the actual SMA compression spring which match our requirements. But unfortunately we didn’t get the spring that we wanted because the compression springs are not available they can be made by custom orders only and it will cost a lot. So we decided to ordered the SMA wire of required wire diameter and we would make a spring in house. Before we started making the spring we searched how we can make a spring in house, we found that using lathe machine we can made the spring. For that we had to run the lathe machine at a very low speed but we had a problem over here because the SMA wire is too thin to wound on lathe machine than the normal steel wire so we can’t make a spring on lathe machine. Then we got a Martindale spring winder machine which is a manual operated device and very easy to handle. Before we start making springs we have to select a desired size arbor and its matching bushing. After that