An array of triboelectric sensors is used for testing the electrostatic properties of 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

Buehler, Martin C.

Gompf, Raymond

NASA Technical Reports Server

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US006518765Bl 
(12) United States Patent (io) Patent No.: US 6,518,765 B1 
Gompf et al. (45) Date of Patent: Feb. 11,2003 
(54) MULTI-SENSOR ELECTROMETER 
(75) Inventors: Raymond Gompf, Merritt Island, FL 
(US); Martin C. Buehler, La Canada, 
CA (US) 
(73) Assignee: California Institute of Technology, 
Pasadena, CA (US) 
Subject to any disclaimer, the term of this 
patent is extended or adjusted under 35 
U.S.C. 154(b) by 0 days. 
( * ) Notice: 
(21) Appl. No.: 09/575,828 
(22) Filed: May 18, 2000 
Related U.S. Application Data 
(60) Provisional application No. 601135,243, filed on May 21, 
1999. 
(51) Int. C1.7 ................................................ GOlR 27/26 
(52) U.S. C1. ........................................ 324/454; 3241452 
(58) Field of Search ................................. 3241454, 458, 
3241449, 457, 452; 4301137.13, 20, 121 
(56) References Cited 
U.S. PATENT DOCUMENTS 
2,618,552 A * 1111952 Wise et al. ................. 4301121 
2,934,649 A * 411960 Walkup ...................... 2501649 
3,873,356 A * 311975 Queener et al. ....... 4301137.13 
3,907,559 A * 911975 Goffe .......................... 430120 
3,922,382 A * 1111975 Kukla et al. ........... 4301137.13 
4,256,402 A * 311981 Nishikawa ................... 399158 
5,341,103 A * 811994 Dasgupta et al. ........... 3241452 
5,608,326 A * 311997 Mucci et al. ............... 3241452 
* cited by examiner 
Primary Examinerxhristine Oda 
Assistant Examiner-Vincent Q. Nguyen 
(74) Attorney, Agent, or F i r m C i s h  & Richardson P.C. 
(57) ABSTRACT 
An array of triboelectric sensors is used for testing the 
electrostatic properties of a remote environment. The sen- 
sors 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. 
6 Claims, 4 Drawing Sheets 
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US 6,518,765 B3 
1 
MULTI-SENSOR ELECTROMETER 
RELATED APPLICATION 
This application claims the benefit of priority under 35 
U.S.C. 5 119(e) of U.S. Provisional Application No. 601135, 
243, filed May 21, 1999 which has been expired. 
ORIGIN OF INVENTION 
The invention described herein was made in the perfor- 
mance of work under a NASA contract, and is subject to the 
provisions of Public Law 96-517 (35 U.S.C. 5 202) in which 
the Contractor has elected to retain title. 
TECHNICAL FIELD 
This invention relates to an electrometer, and more par- 
ticularly 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 mate- 
rials 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 mate- 
rials 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 mb- 
bing 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 com- 
prising 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 triboelec- 
tronic 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. 
2 
FIG. 1 illustrates a robotic arm including a electrometer 
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 embodi- 
ment of the present invention. 
according to an embodiment of the present invention. 
10 
DETAILED DESCRIPTION 
20 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 
30 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 
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. Acamera 110 may also 
be attached to the arm 105 to provide a visual guide for the 
4s 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 tempera- 
ture 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. Triboelectri- 
fication 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 
65 takes on a negative charge. Atriboelectic series may be used 
to predict the behavior of the materials. A sample triboelec- 
tric series is included as Table 1. 
2s 
3s electricity, the nature of the environment may be tested. 
40 
so 
5s 
60 
US 6,518,765 B3 
3 
TABLE 1 
MHERIAL CHARGE 
Air 
Human Hands 
Glass 
Mica 
Human Hair 
Nylon 
Wool 
Lead 
Aluminum 
Paper 
Cotton 
Steel 
Wood 
Hard Rubber 
Nickel & Copper 
Brass & Silver 
Gold & Platinum 
Acetate Rayon 
Polyester 
Polyurethane 
Polypropylene 
PVC 
Silicon 
Teflon 
Positive 
Neutral 
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 prac- 
tical 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. Asecond 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. 
S 
10 
1s 
20 
2s 
30 
3s 
40 
4s 
so 
5s 
60 
65 
4 
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 con- 
structed 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 elec- 
trometer 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 insu- 
lator. 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 spe- 
cific forms without departing from its spirit or essential 
characteristics. 
What is claimed is: 
1. A method of determining the triboelectric properties of 
a material comprising: 
selecting a plurality of insulators; 
simultaneously rubbing the plurality of insulators against 
the material; 
measuring a change in a magnitude and polarity of an 
electrical charge on each of a plurality of the insulators 
over time; and 
determining a triboelectric property of the material in 
response to results from said measuring. 
2. The method of claim 1, further comprising lifting the 
3. The method of claim 1, wherein the change in electrical 
4. The method of claim 3, further comprising discharging 
5 .  The method of claim 4, wherein the capacitor is 
6. The method of claim 5,  wherein the switch is a 
plurality of insulators from the material. 
charge is stored in a capacitor. 
the capacitor prior to the rubbing step. 
discharged using a switch. 
low-leakage solid state switch. 
* * * * *  


Multi-sensor electrometer

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