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Haptics Web>StanfordHaptics > KarlinBlog>PrototypeIINeeds (11 Oct 2004, KarlinBark)
Haptics Web>StanfordHaptics > KarlinBlog>PrototypeIINeeds (11 Oct 2004, KarlinBark)
-- KarlinBark - 11 Oct 2004
Stuff that needs to be accomplished for the next design 1) Introduce adjustable height to the device. We need to keep track of the normal force that is being applied to the subject. -The three main ideas of introducing adjustable height is having the entire motor/pulley system translate vertically, making the lower disc travel up and down, or having a base that can move up or down relative to the disc. We've generated rough ideas on how to do so. 2) A way to measure the amount of pressure on the user's skin (spring, pressure sensor, force balance, etc) -One way to accomplish this is to use a pressure sensor at the tip of the rotational disc, various sensors that can be used are FSR, the thin film that can be glued to sense the pressure, using a silicone based sensor that is traditionally used to measure gas pressure, etc. The idea is to simply be able to read the pressure readings, it's not necessary to control the pressure. -Another way is to use a spring somehow. If we can measure the displacement of the spring relative to the user's arm, then a rough estimate of the normal force can be calculated. This is probably the least robust method and least desireable. 3) Ability to stop device from sliding relative to the table top during testing -When applying a high torque, the device will move...it needs to be stationary during the entire testing process. 4) An improved string tensioning system for the drive unit -Although the method being used currently works, it's not ideal. The string must be re-tensioned often. Will showed me a way to tension the string using a wrap-around method with a screw that pulls the string. James also had a similar idea, using a screw to pull the string tighter. These are the main goals of the next prototype. We need to complete this quickly. In addition to these functional changes, we will be using a different Maxon motor, and will have a new motor shaft-pulley ratio. To save some time, we're going to be working on the controls of the system, using the old prototype. Will has been developing a control method that we will be able to use, that utilizes PIC's to control both angular displacement and current/torque.
Stuff that needs to be accomplished for the next design 1) Introduce adjustable height to the device. We need to keep track of the normal force that is being applied to the subject. -The three main ideas of introducing adjustable height is having the entire motor/pulley system translate vertically, making the lower disc travel up and down, or having a base that can move up or down relative to the disc. We've generated rough ideas on how to do so. 2) A way to measure the amount of pressure on the user's skin (spring, pressure sensor, force balance, etc) -One way to accomplish this is to use a pressure sensor at the tip of the rotational disc, various sensors that can be used are FSR, the thin film that can be glued to sense the pressure, using a silicone based sensor that is traditionally used to measure gas pressure, etc. The idea is to simply be able to read the pressure readings, it's not necessary to control the pressure. -Another way is to use a spring somehow. If we can measure the displacement of the spring relative to the user's arm, then a rough estimate of the normal force can be calculated. This is probably the least robust method and least desireable. 3) Ability to stop device from sliding relative to the table top during testing -When applying a high torque, the device will move...it needs to be stationary during the entire testing process. 4) An improved string tensioning system for the drive unit -Although the method being used currently works, it's not ideal. The string must be re-tensioned often. Will showed me a way to tension the string using a wrap-around method with a screw that pulls the string. James also had a similar idea, using a screw to pull the string tighter. These are the main goals of the next prototype. We need to complete this quickly. In addition to these functional changes, we will be using a different Maxon motor, and will have a new motor shaft-pulley ratio. To save some time, we're going to be working on the controls of the system, using the old prototype. Will has been developing a control method that we will be able to use, that utilizes PIC's to control both angular displacement and current/torque.
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