Electricity: electrical systems and devices – Safety and protection of systems and devices – Impedance insertion
Reexamination Certificate
2002-04-25
2004-10-05
Ngo, Hung V. (Department: 2831)
Electricity: electrical systems and devices
Safety and protection of systems and devices
Impedance insertion
C361S200000, C174S051000
Reexamination Certificate
active
06801418
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to the general art of electrical systems and devices, and to the particular field of discharging or preventing accumulation of electric charges.
BACKGROUND OF THE INVENTION
The problem of electrostatic discharge (ESD) is well known. From merely receiving a mild shock after crossing a room and touching a metal object, to sending a shock into electronic equipment, nearly everyone has experienced an ESD problem at some time.
While static electricity is extremely complex, several overall theories are generally accepted with regard to the action of ESD. Static electricity charges on a person or object are generally like charges. As such, as static electricity charges build up on a person or object, these charges tend to migrate as far apart from each other as possible as determined by the geometry of the person of object. Thus, for example, it is common for static electricity charges to migrate to a person's fingertips. For this reason, when that person reaches out to touch an electrically conductive object, a spark will jump when the gap between that person's fingertips and the object based upon the potential difference between the fingertips and the object. This discharge is very rapid and can be quite violent. If the electrically conductive object is sensitive electronic equipment, that equipment may be damaged either from the magnitude of the discharge and/or from the speed of the discharge. At the least, the charge could cause the equipment to execute an error. A sufficient number of such discharges may eventually damage the equipment.
Accordingly, the art contains many inventions intended to protect the equipment or the person from the effects of this sudden, and sometimes violent, discharge associated with ESD.
For instance, in the logging industry where chains are lowered by helicopter to loggers waiting on the ground to fasten fresh-cut timber to them so it could be airlifted to the sawmill or nearby waterway, track access point or the like, the loggers are often reluctant to grab the chain because of a painful shock that may occur as a result of a buildup of static electricity which will be discharged to ground through their bodies. This particular problem has been solved by incorporating a resistance in the line from the charge-carrying object, such as the helicopter, to the person on the ground. The high resistance causes the current to be low enough that the discharge will not be painful.
However, this is cumbersome. This solution may be even more cumbersome if the person is an office worker who moves around a great deal. Accordingly, this solution to the ESD problem has serious shortcomings.
Accordingly, there is a need for a system that protects a person against the effects of ESD but can do so in a manner that does not interfere with any task the person may be performing and further will not be cumbersome or burdensome for the person to use.
Still other inventions are directed to protecting electronic equipment from the effects of ESD. For example, many computers include touch pads or touch areas for the user to touch before touching the remainder of the computer. The touch pads are grounded so the ESD will pass from the person via a spark or the like directly to ground without going to or through the computer.
While many of these devices work well, there are several problem areas not addressed thereby. This results in drawbacks and disadvantages for such devices when a person or equipment are situated in certain environments or subject to certain conditions.
First, no matter how effective a touch pad is it will be totally ineffective if the person does not use it. That is, if the person carrying a large ESD charge forgets to touch the touch pad and proceeds to touch a computer, the ESD will discharge through the computer and the touch pad will have been useless. Thus, a shortcoming of such touch pads is that they require the person to remember to use it.
Furthermore, no matter how effective the ESD protection device is, the current level and/or the change in current level may be so high that either the person or the equipment can be damaged.
Still further, while placing a touch pad on a computer may protect the computer it does not protect the user from the effects of an electrostatic discharge.
As mentioned above, the majority of applications for the prevention of ESD are in the manufacturing or medical fields and are largely concerned with protecting the ‘manufacturing’ process or sensitive components for ESD damage. Examples include moving mediums such as the manufacture of rolls of paper, the assembly of delicate electronic chips and circuitry and surgeon-patient contact during an operation.
An analysis of each of the above will help illustrate the shortcomings of the prior art. In the manufacture or printing of paper, long rolls of paper may move at high speed. Often the path may involve rubber or other rollers and guides. As the paper rubs across such items a static electricity charge may be generated. Since the paper path is well controlled, it is an easy process to place grounded conductive brushes or flat metal springs in contact with the moving paper since the paper stays in a fixed path. Such electrodes are connected directly to the grounded frame of the associated machinery or to another path eventually leading to earth ground or other equalizing means.
Another common application of ESD control is in the production or repair of fragile electronics such as computer circuit boards. Even a slight electrostatic discharge through a sensitive device may destroy it. Therefore, significant effort and cost is devoted to eliminating the possibilities of electrostatic potentials in the vicinity of the sensitive electronics. Typically, a single ground point is provided that all associated elements are connected to so that no electrostatic potential can exist between them that might flow through the sensitive electronics. For example, an assembly person is connected to a ground, typically by a wrist strap tether. The tether generally consists of a wrist pad and grounding wire that is eventually connected back to the single ground point. For operator safety, the ground wire typically contains a 1 Meg resistor to limit current flow to safe levels should the operator come in contact with 120 volts AC. This tethering restraint is inconvenient and not considered suitable for a typical office worker or call center operator. The single ground point is eventually connected to true earth ground or other equalizing point by another conductor.
Applications are similar in the medical field, employing similar tethers and/or foot/shoe connectors also considered impractical for the typical office worker environment.
Today, a new set of ESD problems is emerging in the typical work place or home office environment. Today, a typical worker may exist in a virtually electrically isolated environment—a plastic computer case, plastic keyboard, plastic control knobs on a molded plastic control panel, plastic office chair with man-made fabric and plastic wheels, non-conductive flooring or carpeting and even a headset with foam or molded plastic earpieces and plastic microphone tube.
As the operator moves in his/her chair, there are many opportunities for a very large electrostatic charge to build up on his/her body. Friction between dissimilar materials is the classical means for generation of electrostatic voltages. There are many such situations that exist continually in the operator environment today—the operator's clothing sliding against the chair back or arm rests, the operator's shoes sliding on the carpet, the plastic chair wheels sliding against the carpet are a few examples. The effects can be cumulative over a long period of time, and can become quite high.
Eventually a discharge or equalization to (true earth) ground must take place. The higher the value of the electrostatic voltage charge, the greater the distance the charge may ‘jump’ to discharge, and the more ‘catastrophic’ the event to the
Gernstein Terry M
Ngo Hung V.
LandOfFree
Grounding elements for eliminating ESD via floor coverings... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Grounding elements for eliminating ESD via floor coverings..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Grounding elements for eliminating ESD via floor coverings... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3268017