Patent Document

RELATED APPLICATION 
     This application claims the benefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional Application No. 60/135,243, filed May 21, 1999 which has been expired. 
    
    
     ORIGIN OF INVENTION 
     The invention described herein was made in the performance of work under a NASA contract, and is subject to the provisions of Public Law 96-517 (35 U.S.C. § 202) in which the Contractor has elected to retain title. 
    
    
     TECHNICAL FIELD 
     This invention relates to an electrometer, and more particularly to an electrometer having a triboelectric field sensor array to evaluate the electrostatic nature of a region. 
     BACKGROUND 
     During space exploration, there are many hazards that a human may encounter. By collecting as much information as possible about the environment to be explored, the hazards can be reduced. Prior to human exploration, probes and test equipment is sent into the environment to collect data. This data may then be used to enhance the safety of human exploration. 
     One hazard that may exist in space is the build-up of static electricity. For example, an astronaut walking on the surface of a planet such as Mars may produce static electricity. If enough static electricity is developed, problems may occur. To prevent the build-up of static electricity, antistatic materials may be used in the manufacturing of space suits and any other objects that may interface with the environment. However, the behavior of antistatic materials in different environments may be unpredictable. To better predict the behavior of a particular material, it is desirable to have empirical data showing the triboelectric properties of materials in the space environment. 
     SUMMARY 
     The present invention provides an array of triboelectric sensors for testing in a remote environment. The sensors may be mounted in the heel of a robot arm scoop. To determine the triboelectric properties of a planet surface, the robot arm scoop may be rubbed on the soil of the planet and the triboelectrically developed charge measured. By having an array of sensors, different insulating materials may be measured simultaneously. The insulating materials may be selected so their triboelectric properties cover a desired range. By mounting the sensor on a robot arm scoop, the measurements can be obtained during an unmanned mission. 
     One aspect of the invention is a method of determining the triboelectric properties of a material. The method comprises selecting a plurality of insulators and simultaneously rubbing the plurality of insulators against the material. The method then measures the change in electrical charge of the insulators. 
     Another aspect of the invention is an electrometer comprising a sensor array. The sensor array includes a plurality of triboelectronic sensors, each including a plurality of insulators. The insulators are selected based on the triboelectronic properties of each insulators. 
    
    
     DESCRIPTION OF DRAWINGS 
     These and other features and advantages of the invention will become more apparent upon reading the following detailed description and upon reference to the accompanying drawings. 
     FIG. 1 illustrates a robotic arm including a electrometer according to an embodiment of the present invention. 
     FIG. 2 illustrates the heel of the robotic arm scoop of FIG. 1 housing the electrometer according to an embodiment of the present invention. 
     FIG. 3 is a schematic diagram of a circuit model for one sensor of the electrometer according to an embodiment of the present invention. 
     FIG. 4 is a block diagram of the operation of one sensor of the electrometer according to an embodiment of the present invention. 
     FIG. 5 illustrates experimental response curves from the array of sensors in the electrometer according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 illustrates a robot  100  designed to operate in remote environments, including other planets such as Mars. The robot  100  may be operated from a base station on Earth. This allows the collection of data in a remote and hostile environment such as Mars without exposing people to the dangers involved with space travel. Data collected by the robot allows for a better understanding of the hazards related to the human exploration of these remote environments. 
     One hazard that may exist is the electrostatic nature of a remote environment. When a person explores a planet surface such as Mars, there is the possibility that the interaction between the person and the planet surface may cause a build-up of static electricity, which may be harmful to people and equipment. To reduce the build-up of static electricity, the nature of the environment may be tested. 
     Based on the results of these tests, materials that may come in contact with the environment may be selected to reduce the build-up of static electricity. 
     The robot  100  includes a body  102  having legs  120  to provide stability. A moveable arm  105  extends from the robot  100  to provide for data collection. An electrometer  115  is attached to the heel of the arm  105 . A camera  110  may also be attached to the arm  105  to provide a visual guide for the electrometer  115 . The electrometer  115  may be dragged along the surface of the remote environment to collect data. 
     FIG. 2 illustrates the heel  200  of the robotic arm  105  of FIG.  1 . The heel  200  houses the electrometer  115  according to an embodiment of the present invention. The electrometer  115  includes a variety of sensors to collect data. A temperature sensor (not shown) is housed within the electrometer  115 . External sensors include a ion current sensor  205 , an electric field sensor  210 , and a plurality of triboelectric sensors  215 ,  220 ,  225 ,  230 , and  235 . The triboelectric sensors  215 ,  220 ,  225 ,  230 , and  235  collectively form a sensor array. Although five sensors are shown and described, any plurality of sensors may be used without departing from the spirit of the invention. 
     Each of the triboelectric sensors  215 ,  220 ,  225 ,  230 , and  235  consists of a different insulating material. Triboelectrification occurs when two different materials come in contact with each other. When two materials are rubbed together, one of the material becomes positively charged and the other takes on a negative charge. A triboelectic series may be used to predict the behavior of the materials. A sample triboelectric series is included as Table 1. 
     
       
         
               
               
               
             
           
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 MATERIAL 
                 CHARGE 
               
               
                   
                   
               
             
             
               
                   
                 Air 
                 Positive 
               
               
                   
                 Human Hands 
               
               
                   
                 Glass 
               
               
                   
                 Mica 
               
               
                   
                 Human Hair 
               
               
                   
                 Nylon 
               
               
                   
                 Wool 
               
               
                   
                 Lead 
               
               
                   
                 Aluminum 
               
               
                   
                 Paper 
               
               
                   
                 Cotton 
                 Neutral 
               
               
                   
                 Steel 
               
               
                   
                 Wood 
               
               
                   
                 Hard Rubber 
               
               
                   
                 Nickel &amp; Copper 
               
               
                   
                 Brass &amp; Silver 
               
               
                   
                 Gold &amp; Platinum 
               
               
                   
                 Acetate Rayon 
               
               
                   
                 Polyester 
               
               
                   
                 Polyurethane 
               
               
                   
                 Polypropylene 
               
               
                   
                 PVC 
               
               
                   
                 Silicon 
               
               
                   
                 Teflon 
                 Negative 
               
               
                   
                   
               
             
          
         
       
     
     Of course, the materials listed in Table 1 are just a sample of the thousands of materials available. Each triboelectric sensor  215 ,  220 ,  225 ,  230 , and  235  includes one of the materials. Materials may be selected along the triboelectic series to provide data that may be extrapolated to all materials. In the case of space exploration, materials practical for use in devices such as gloves, visors, boots, and habitat materials may be selected. 
     FIG. 3 is a schematic diagram of a circuit model for one sensor of a triboelectonic electrometer  300  according to an embodiment of the present invention. The triboelectonic electrometer  300  includes capacitors  305 ,  310 , and  315 , a resistor  320 , and a switch  325 . A first terminal of the capacitor  315  is connected to a first terminal of the resistor  320  and a first terminal of the capacitor  310 . A second terminal of the capacitor  315  and a second terminal of the resistor  320  are connected to ground. The second terminal of the capacitor  310  is connected to the first terminal of the capacitor  305 , to a first terminal of a switch  325 , and to an operational amplifier. A second terminal of the capacitor  305  and a second terminal of the switch  325  are connected to ground. 
     The triboelectonic electrometer  300  is similar to the design of a traditional electrometer. In the triboelectonic electrometer  300 , the switch  325  is typically a low-leakage solid state switch and is used to remove voltage from the capacitor  305 . The capacitor  310  may be replaced by an insulator that is adapted to be rubbed against the test material to determine the potential build-up of charge. The resistor  320  functions as a discharge mechanism for the capacitor  310 . 
     FIG. 4 is a block diagram of the operation of one sensor of the electrometer according to an embodiment of the present invention. At position  400 , the sensor is in contact with the test soil  405  just prior to being rubbed against the test soil  405 . The switch  325  has discharged the capacitor  305  and the insulator  410  includes a charge based on the material selected for the insulator. The sensor is then rubbed against the test soil  405  and the insulator  410  and the test soil  405  experience triboelectrification. The insulator  410  then changes polarity depending on the material of the insulator  410 . 
     At position  405 , the sensor has just been lifted from the test soil  405  and the polarity of the insulator  410  has been changed due to triboelectrification. The change in polarity of the insulator  410  causes a charge in the capacitor  305 . The charge in the capacitor  305  is measured over time to determine the triboelectric properties of the test soil  405 . Of course, the electrometer  115  is simultaneously using a plurality of sensors. 
     In an experimental test, the electrometer  115  was constructed using insulators of ABS, polycarbonate, linen filled phenolic, Rulon-J, and Teflon. The sensor array was then rubbed against wool felt at room temperature to obtain a triboelectric response. FIG. 5 illustrates experimental response curves  500  from the array of sensors in the electrometer according to the experimental setup. The curve  505  shows the response of the sensor having ABS as an insulator. The curve  510  shows the response of the sensor having polycarbonate as an insulator. The curve  515  shows the response of sensor having linen filled phenolic as an insulator. The curve  520  shows the response of the sensor having Rulon-J as an insulator. The curve  525  shows the response of the sensor having Teflon as an insulator. 
     The response at approximately 0.2 seconds is during the rubbing process. After secession of rubbing, the curves show a small loss of charge which indicates that these insulators have good insulating properties. In addition, the response show both positive, zero, and negative behavior. The zero behavior may be used to identify an important anti-static material. The voltage at the output of the amplifier had a gain of four with respect to the input. 
     By using the sensor array, a variety of insulating materials may be simultaneously tested to determine the triboelectric response of each material. By using the sensor array, a detailed picture of the static response of the test material may be obtained. This allows for the selection of materials to reduce the static electricity. 
     Numerous variations and modifications of the invention will become readily apparent to those skilled in the art. Accordingly, the invention may be embodied in other specific forms without departing from its spirit or essential characteristics.

Technology Category: g