Summary of the Invention
This invention contains two modifications of my earlier invention disclosed in U.S. Pat. No. 4,476,358. In particular one of the two elements of the electric contact, previously consisting of pairs of metal strips mounted on the isolated back plate, is now replaced by a metal back plate. In addition a plurality of plastic levers are fitted next to each other on the upper side of the frame of the pad, so as to transfer to the front plate any vertical force exerted by a backstroke swimmer.
Brief Description of the Drawings
In the drawings,
FIG. 1 shows a front view of the pad with the perforated plate partially removed.
FIG. 2 is an amplified view of one strip and spring.
FIG. 4 is a cross section showing the two plates, seagull wing shaped spacers and the frame.
FIG. 5 is a side view of the levers mounted on the upper side of frame.
FIG. 3 is a front view of a strip with two springs and insulating sheath.
Description of the Invention
Compared with other known types, the invention has the following characteristics:
(1) the signal is transmitted without any delay, unlike other systems;
(2) the sensitivity of the pad is quite a constant over its entire surface, since its operating principle is based on the use of approximately 500 mechanical contacts;
(3) it requires no sealed envelope which might cause seepage during a prolonged length of time;
(4) even strong localized forces may be applied without causing damage;
(5) the pad is insensitive to wave motion;
(6) contacts are of the self-cleaning type.
The technical particulars of the invention are outlined hereinafter.
The pad is composed of two plates located face to face, the back plate "D" being made of conductive metal, resting against the vertical wall of the swimming pool, whereas the front plate "E" consists of a plastic sheet with perforations "I" over its entire surface so as to reduce the front plate's resistance to motion in water. The front plate is loosely inserted in a frame "A" consisting of channel sections on the four sides and movable towards the metal back plate.
A contact/spacer spring system is mounted on the back plate covering its whole surface as illustrated in the drawings. The metal strips "B" are mounted, but insulated by rubber sheaths "E", onto the back metal plate whereas the metal contact springs "C" are welded onto strips "B".
The contact springs "C" have a dual purpose: they must close the contact between the strips "B" and the back plate "D" under external forces applied to the perforated sheet "E" and they must serve as an elastic spacers between the two plates "D" and "E".
Furthermore, the contact springs have a self-cleaning action on the contact areas, due to the flattening of their terminal sections.
It should be noted that any pressure on the plate "E" will cause its local deformation and the transfer of the force onto the contact springs nearest to the pressure point. In this way, almost the whole thrust applied by the swimmer is transferred to the contact springs.
While swimming on his back, the swimmer's arms may strike vertically the pad on the upper side where there is no reaction; to obviate this lack of sensitivity, a plurality of plastic levers "G", horizontally pivoting on plastic "H" elements mounted on the upper side of the frame, will permit these striking actions to the front plate "F" thus achieving an electric connection.
The electrical impedance of the water immersed pad depends on various factors, but its operation is always achieved by impedance variation caused by closing of one or more contact springs "E" between the strips "B" and the plate "D".
The voltage and frequency of the energy supply will be determined after tests are carried out in practical environment conditions.
In its practical implementation, the invention may also take shapes other than described above. For instance the configuration and arrangement of the elastic elements and strips, as well as plastic levers may be changed, while remaining within the scope of this Patent.