WO1995001622A1

WO1995001622A1 - A magnetic vibrator

Info

Publication number: WO1995001622A1
Application number: PCT/US1994/006155
Authority: WO
Inventors: Douglas Fitzpatrick
Original assignee: Motorola, Inc.
Priority date: 1993-06-30
Filing date: 1994-06-02
Publication date: 1995-01-12
Also published as: AU7244194A

Abstract

A magnetic vibrator functioning as an annunciator in a radio communication device is obtained as follows. The magnetic vibrator includes a permanent magnet (24), partially disposed in a coil (21), and fixed to a spring (15) and two metal elements (22 and 23). A current, applied to the coil, initiates a resultant force that acts on the magnet, the spring and the two metal elements. The resulting oscillations of the magnet, the spring, and the two metal elements pass onto a casing (11) as vibrations. These vibrations serve as a non-audible annunciation by providing tactile sensory stimuli to a user of a communication device incorporating the vibrating annunciator.

Description

A MAGNETIC VIBRATOR

Technical Field

This invention relates generally to radio communications devices, and more particularly to non-audible annunciators.

Background of the Invention

Vibrators exist in the art, and one such prior art vibrator comprises a motor with an off-centered weight that vibrates when an electrical current is applied to the motor. When used as a non-audible annunciator, the vibrator passes on the vibrations to a user as a tactile sensory stimulus.

Radio communication devices, such as pagers and two-way radios, have many operating features. These radio communication devices are typically powered by batteries, and therefore are limited to operating for a certain duration only. Hence, a continual need exists for radio communication devices to use energy efficient components (such as vibrators), in order to conserve energy so as to prolong their operating duration.

Brief Description of the Drawings

FIG. 1 is a cross-sectional view of a prior art vibrator. FIG. 2 is a cross-sectional view of a vibrator in accordance with the present invention.

FIG. 3 is a block diagram of a communication device in accordance with the present invention. Detailed Description of a Preferred Embodiment

FIG. 1 illustrates a prior art vibrator (10) that comprises a coil (12) fixed to a casing (11), a permanent magnet (13) disposed in an iron core (14) and movable, together with the iron core (14), in a substantially vertical direction within the casing (11 ), and a circular leaf spring (15) coupled to the casing (11). (The coil (12) is indicated with a diameter (19).) Two flux paths (16 and 17), the coil (12), the magnet (13), and the iron core (14) forms a magnetic circuit. A third flux path (18) is also indicated that goes through the casing (11 ). The directions of a current applied to the coil (12) and that of the flux path (17) determine the direction of a resultant force vector (this resultant force vector is explained below). The above vibrator (10) operates according to the principles of electromagnetic flux theory and mechanics. Basically, the following four equations are relevant to the vibrator's (10) operations. A first relevant equation is as follows:

Fe = i(l xB) - Equation 1 where Fe is the resultant force vector, i is the magnitude of the current, 1 is a vector indicating the direction of the current on the coil (12) and the magnitude of the coil's (12) total length, and B is the magnetic flux density vector at the coil (12).

When the current (i) flows through the coil (12), Equation 1 relates the resultant force vector (Fe) to the current (i), the coil (12), and the magnetic flux density (B) at the coil (12). This resultant force vector (Fe) provides an excitation force that overcomes the frictional losses within the vibrator (10) and, in addition, moves a weight (comprising primarily the magnet (13) and the iron core (14)) from a resting equilibrium to an oscillating steady state. During the steady state, the vibrator (10) will oscillate at a frequency that depends on the weight's mass and on a spring's (15) constant. This frequency relates to the mass and the spring's (15) constant by the following equation:

W₀ = (Vk) / m - Equation 2

where w₀ is the resonant frequency predetermined by a designer (for a good tactile stimulus w₀ ^a 2P (90Hz)), k is the spring's (15) constant, and m is the mass of the weight.

The actual vibration force of the vibrator (10) is related to the mass (m) of the weight and a maximum acceleration of this weight at steady state. The vibration force is determined by a third relevant equation as follows:

F_v = m x a - Equation 3

where F_v is the vibration force, m is the mass of the weight, and a is the acceleration given by a fourth equation: a = x₀ Wo² Sin (w₀t) - Equation 4

where x₀ is a displacement of the weight from a predetermined reference point, w₀ is the resonant frequency as mentioned in Equation 2, and t is time in seconds.

All the above considerations apply towards the design of the vibrator (10), and determine how the vibrator (10) operates. In addition, when used as an annunciator, the vibrations have to be sufficiently strong to be effectively sensed.

Referring now to FIG. 2, an embodiment of a vibrator (20) in accordance with the present invention shows parts with similar functions to those in FIG. 1 , such as a coil (21 ), a metal disc (22), a metal cup (23), and a permanent magnet (24). Importantly, however, the two magnets (13 and 24), in FIGs. 1 and 2 respectively, are disposed and shaped differently (the magnet (24) is partially disposed within the coil (21)). FIG. 2 also shows two flux paths (25 and 26) that form a magnetic circuit together with the four parts above (the coil (21 ), the disc (22), the cup (23), and the magnet (24)). The vibrator (20) functions somewhat similarly to the prior art vibrator

(10). However, there are improvements in the vibrator (20) compared to the prior art vibrator (10), and these will be explained as follow.

First, the coil (21) in the magnetic vibrator (20) has a larger diameter (27) than the prior art coil's (12) diameter (19). As a result, and with a same number of windings, the coil (21 ) is longer than the prior art coil (12). This longer coil (21) increases the resultant force vector (Fe), assuming the current (i) and the magnetic flux density (B) remains the same. Second, the disposition of the coil (21), the disc (22), the cup (23), and the magnet (24) provides the two flux paths (25 and 26) that have a lower reluctance compared to the prior art vibrator's (10) flux path (17). Both flux paths (25 and 26) couple to the magnet (24); the first low reluctance flux path (25) is disposed exterior to the coil (21), and the second low reluctance flux path (26) is disposed within the coil (21). Those skilled in the art will know that reluctance is a characteristic of a magnetic circuit that determines the magnetic flux density (B). Generally, a lower reluctance will provide a better magnetic flux density (B).

Third, the vibrator (20) better utilizes the magnet (24) by providing a magnetic circuit with a lesser flux leakage. (In the prior art vibrator (10), the magnetic flux path (18) is a leakage path that does not contribute to the resultant force vector (Fe)). Hence, more of the magnetic flux goes through the coil (21), and this increases the magnetic flux density (B) at the coil (21) for the vibrator (20). Equations 1 , 2, 3, and 4 all affect the performance of the vibrator (10 or 20). Equation 1 is an electromagnetic coupling equation that determines the maximum efficiency by relating the resultant force vector (Fe) to the current (i), the coil (12 or 21), and the magnetic flux density (B). A measure of the output vibration strength, with regard to all the above, is commonly known in the art as a coupling efficiency. The inventor has determined that for the vibrator (20), the disposition and differing features of the elements have resulted in a better coupling efficiency. As a result, and taking into account all the above considerations, the vibrator (20) operates more efficiently. An embodiment, in accordance with the present invention, of a magnetic vibrator (20) into a communication device (30) is shown in the block diagram of FIG. 3. The communication device (30) comprises a radio receiver (31), a logic unit (32), a power source (33), and a vibrating annunciator (34). The communication device (30) can be a pager, a radio telephone, or any other communication device (30) where some type of vibrating annunciation is used to alert a user of such devices when a predetermined signal is received. Typically, when the predetermined signal is detected, the radio receiver (31 ) provides a signal to the logic unit (32) (for example a decoding unit in a pager) that then enables the power source (33) to provide the current to the vibrating annunciator (34) to initiate the oscillations of the magnetic vibrator (20).

The trend in technological developments indicates that future radio communication devices (30) will continue to reduce in size, especially when portability is a factor. Typically, such portable radio communication devices (30) are powered by batteries, and incorporate many operating features, including non-audible annunciators. As a result, energy consumption becomes a prime consideration in battery- powered radio communication devices (30). Therefore, a need exists for radio communication devices (30) to use more efficient components, such as magnetic vibrating annunciators.

Claims

1. A vibrator, comprising: A) a casing; B) a coil fixed with respect to the casing;

C) a spring coupled to the casing;

D) a magnetic circuit fixed to the spring, the magnetic circuit comprising: i) a magnet at least partially disposed inside the coil; and ii) a flux path coupled to the magnet; such that the magnet will oscillate within the coil when an alternating current is applied to the coil and thereby impart mechanical vibration to the casing.

The vibrator of claim 1 , wherein the spring comprises a circular-shaped leaf spring.

3. The vibrator of claim 2, wherein: the magnetic circuit further comprises: i) a permanent magnet at least partially disposed inside the electric coil; and ii) a first low reluctance flux path coupled to the permanent magnet and being disposed exterior to the electric coil; and iii) a second low reluctance flux path coupled to the permanent magnet and being disposed within the electric coil.