Instrumentation Of Astm Tools

This paper will focus on a laboratory experience using a chip level pressure sensor that will be presented as both a force gauge and a level meter. The goal is to present sensors to the students with enough information to allow them to see how sensors can be adapted to collect different data parameters Background Laboratory experiments often seem disconnected from the “real world”. Examples of instrumentation used in commercial enterprise are used to stimulate conversation and confidence that the material presented is current. Programmable controllers, CNC simulators, computer interface boards, relays, operational amplifiers, and chip level sensors are components that are used in laboratory experiments to show students both how the systems may be interfaced and to allow them to create the interface. Sensors cover a broad range of measurement needs and can be used for many types of data collection. They are application specific so must be used in multiple experiences to show diversity and how the same device can be structured to take different measurements. This laboratory experiment will use the Motorola MPX5010D pressure sensor to measure water level. The class project will include building a PID controller to regulate the level of a water tank. The 5010 will be the level measurement device. Preparation for this experiment requires that sensors be discussed and during that discussion the 5010 will be presented as it was used in a medical research application. During the case history discussion the student is to consider how to collect the desired information. History of the project will assist the student in understanding how the final device was conceived. A discussion of the problems that were solved and those that were not are given to broaden the scope of the sensor experience. The Application and Case History A technique called ASTM (Augmented Soft Tissue Mobilization) has been developed and is under study at Ball Memorial Hospital . It has been known that mobilization (rubbing tissue in (1) the direction of the muscle or across the muscle) of soft tissue can stimulate the body’s normal healing response . Such problems as chronic tendinitis, carpal tunnel syndrome, and adhesions (2) within the soft tissue can be broken down and restored to full function. The populace has always known that if it hurts, you rub it. Massage therapists have use these techniques for years to make their patients feel better. Physical therapists attempt to assist the body in the healing process. Sometimes the body is so damaged that there is nothing that can be done to assist the patient while still outside the skin. In these cases, surgery may be indicated. The purpose of the ASTM technique is to reduce the requirement for surgery and to return patents to the work force . (3) Page 240.1 Figure 1 ASTM was discovered and testing was started at Ball Memorial Hospital. The discovery was that a dull edge like a reflex hammer handle could be used to rub the tissue with less force than would normally be applied by hand. The movement of tissue by a force per square inch can be accomplished with less exterior force if it is applied over a smaller surface area. The hands and fingers of a therapist may cover several square inches and the tissue that needs to be moved may be deep. Force applied on a blunt edge is able to penetrate to greater depths. Micro trauma at the site of fibrous growth causes an inflammation response which will result in tissue repair if the proper stretching and healing cycles are maintained. Fibrous growth can be broken down and will grow back. The return growth must be controlled and located where it will support the tissue instead of limiting its movement. Pressure applied to soft tissue causes the body to start healing. The amount of pressure, the actual process, the possible limits, and what tissue is repairable is still under test. Part of the needed data is a record of the force used during the procedure. Tools used for ASTM need a handle for the operator and an edge appropriate for the surface to be treated. The tools developed were for both large and small muscle groups. Figure 1 shows a crescent shaped tool that was equipped with strain gauges in full bridge configuration . The tool (4) is 8 inches in length, 1.5 inches wide in the center of the crest, and .25 inch thick. Because the leading edge is beveled at 45 degrees to provide a sharpened surface to engage the tissue, there is no flat surface that is square with the primary force axis. Two elements of a full bridge strain gauge were placed on the beveled 45 degree angle leading edge. The other two elements of that set were placed on the top of the device across the thickness and parallel with the long axis. This set of strain gages would indicate pressure applied to the nose of the tool if the therapist used the outside ends as handles. If the operator flexed the tool by holding it tightly or tried to bend it through its thickness, the gauges on the beveled surface would indicate the presence of pressure on the nose. To remove this signal another full bridge was put on the front and back face of the crescent. This set of gages react to flexing forces and not to pressure of the tool nose on the patient tissue. The two signals were amplified and sent to a computer collection device running LabView software by National Instruments. The AT-MIO 16 analog to digital board was used as an interface. It is a 12 bit 100KS/s 16 channel A/D board that was configured to receive two differential channels of input. The board accuracy is +/1.5 LSB. Strain gauge power and amplification was provided by a DMD 460 from Omega . The (4) flexing force was subtracted from the primary force strain elements in software. Calibration was configured in software so that a zero primary force would be indicated while the tool was flexed. This was a first run and many problems were noted. The connecting cable was long (25 ft) from the tool to the DMD 460 and first stage amplifier. Cable noise and cable flex noise were both present. The tool itself was too narrow. The edge was good for the patient but the therapist’s hands would get tired holding the tool. The tool shape was not something that would fit into a hand and be supportable. The instrumentation required the operator to hold the tool by the outside edges and would not read correctly if a shift in hand position was attempted. 30N of force was a typical maximum applied to muscle bodies in the thigh area and therapists were able to “calibrate their hands” so that a consistent treatment could be given. P ge 240.2