Claims
- 1. In a motor bell alarm for generating a clear ringing sound having an electric motor for generating a rotational motion, a shell, a plunger for striking said shell, said plunger being positioned such that there is a space between said shell and the end of said plunger adjacent said shell when said plunger is in the at-rest position, and linkage means, having a lever arm, for translating the rotational motion of said electric motor to a longitudinal oscillating motion of said plunger, the improvement wherein said linkage means comprises:
- a pushrod, connected at one end to said lever arm and bearing at the other end against said plunger when said plunger is in the at-rest position, for transmitting the oscillating motion of said lever arm to said plunger to cause said plunger to move from the at-rest position towards said shell;
- means for connecting said one end of said pushrod to said lever arm so as to provide longitudinal freedom of movement of the pushrod relative to the lever arm in the direction away from the shell when the plunger rebounds from striking the shell; and
- a tension coil spring concentrically surrounding said pushrod for returning said plunger to its at-rest position after said plunger has rebounded from striking said shell, one end of said spring being connected to the pushrod and the other end of said spring being connected to said plunger, said spring being sufficiently resilient to permit the plunger to move towards the shell, under the momentum imparted thereto by said lever arm and said pushrod, out of bearing engagement with said other end of said pushrod to strike said shell, such that a gap exists between said plunger and said other end of said pushrod when said pushrod strikes said shell.
- 2. The improvement according to claim 1, wherein said pushrod is connected to said lever arm by a pin inserted through a hole in said lever arm and secured to said pushrod, the diameter of said pin being smaller than the diameter of said hole so as to provide longitudinal freedom of movement of the pushrod.
- 3. The improvement according to claim 2, wherein said pushrod has a slotted end for inserting an end of said lever arm through which said pin can link said pushrod to said lever arm, said slotted end being sufficiently long so as to provide longitudinal freedom of movement of the pushrod for the range of longitudinal motion provided by the difference in diameter between said pin and said hole in said lever arm.
- 4. The improvement according to claim 1, wherein said pushrod is constructed of a material substantially less dense than the material of the plunger so as to minimize the mass of said pushrod.
- 5. In a motor bell alarm for generating a clear ringing sound having an electric motor for generating a rotational motion, a shell, a plunger for striking said shell, said plunger being positioned such that there is a space between said shell and the adjacent end of said plunger when said plunger is in the at-rest position, and linkage means, having a lever arm, for translating the rotational motion of said electric motor to a longitudinal oscillating motion of said plunger, the improvement wherein said linkage means comprises:
- a pushrod interposed between the lever arm and the plunger for transmitting the oscillating motion of said lever arm to said plunger to cause said plunger to move from the at-rest position towards said shell;
- means including a lost-motion coupling for connecting one end of said pushrod to said lever arm so as to provide longitudinal freedom of movement of the pushrod in the direction away from the shell when the plunger rebounds from striking the shell; and
- means for connecting the other end of said pushrod to said plunger.
- 6. The improvement according to claim 5, wherein said pushrod is connected to said lever arm by a pin inserted through a hole in said lever arm and secured to said pushrod, the diameter of said pin being smaller than the diameter of said hole so as to provide longitudinal freedom of movement of the pushrod.
- 7. The improvement according to claim 6, wherein said pushrod has a slotted end for inserting an end of said lever arm through which said pin can link said pushrod to said lever arm, said slotted end being sufficiently long so as to provide longitudinal freedom of movement of the pushrod for the range of longitudinal motion provided by the difference in diameter between said pin and said hole in said lever arm.
- 8. The improvement according to claim 5, wherein said pushrod is constructed of a material substantially less dense than the material of the plunger so as to minimize the mass of said pushrod.
- 9. The improvement according to claim 5 and further comprising:
- a support member for guiding the movement of said plunger; and
- a rebound spring concentrically surrounding a portion of said plunger and compressed between said support member and a shoulder on the said plunger for urging said plunger away from said shell so as to prevent said plunger from coming to rest against said shell and dampening the ringing sound when said motor stops.
- 10. The improvement according to claim 5 wherein said plunger is oriented substantially vertically upwardly so that the force of gravity acting on said plunger prevents said plunger from coming to rest against said shell and dampening the ringing sound when said motor stops.
BACKGROUND OF THE INVENTION
This application is a continuation-in-part of U.S. patent application Ser. No. 281,257, filed Dec. 7, 1988, now abandoned.
The present invention relates to a motor bell alarm in which the rotational motion of an electric motor is transduced to a longitudinal oscillating motion of a plunger for striking a bell shell, thereby creating a clear, loud ringing sound.
A conventional motor bell alarm is shown in FIG. 1. Conventional motor bell alarm designs use an electric motor 10 to generate a rotational motion at a motor shaft 12. This rotational motion is converted to a reciprocating motion by means of an eccentric cam 14 and a lever assembly 16 that link the motor shaft 12 to a plunger 18. The plunger 18, as a result of the reciprocating motion imparted to it by the cam-lever linkage, cyclically strikes a shell 20 to generate a ringing sound. The plunger 18 passes through and is guided in its longitudinal reciprocating motion by the alarm housing 22.
Inasmuch as the free vibration of the shell 20 is vital to the production of a clear, loud sound, it is important to minimize the time in which the striking plunger 18 is in contact with the shell 20. While the plunger 18 is in contact with the shell 20, the mass of the plunger 18 and other components in the plunger drive linkage dampens the vibrations of the shell, which, in turn, muffles the ringing sound. Ideally, the plunger 18 should strike the shell 20 at the apex of its reciprocating path and then instantaneously rebound towards its at-rest position.
In the prior art motor bell of FIG. 1 a resilient coil spring 24 is interposed between the lever assembly 16 and the plunger 18. The momentum imparted to the plunger 18 toward the shell 22 by the motion of the lever assembly 16 and the compression force of the spring 24 is such that the plunger overcomes the tension in the spring 24 to allow the plunger 18 to strike the shell 20 without the plunger 18 having to be pushed mechanically against the shell 20 by the lever assembly 16. As a result, the action of the plunger 18 striking the shell 20 more closely resembles an elastic collision. In other words, the plunger 18 rebounds off the shell 20 as a result of the collision. Without the spring 24, the plunger 18 would not rebound as a result of the collision but would instead retreat only after the reciprocating cycle reached its apex of motion toward the shell. By using the spring 24, the apex of the reciprocating cycle of the lever does not directly dictate when the plunger 18 retreats.
Although the spring 24 reduces the time that the plunger 18 is in contact with the shell 20, it does not minimize the rest mass in contact with the shell 20, and thus does not fully isolate the shell 20 from the dampening effect of the plunger 18. An object of the present invention, therefore, is to minimize the rest mass in contact with the shell 20, thereby further reducing the dampening effect on the shell 20 and enhancing the clarity and volume of the ringing sound. A further drawback to the use of a spring 24 in a conventional motor bell results from the spring 24 being an inefficient medium for transferring momentum to the plunger 18. Accordingly, another object of the present invention is to provide a more efficient means for imparting momentum to the plunger 18.
A motor bell alarm constructed generally in accordance with FIG. 1 is disclosed in U.S. Pat. No. 4,183,018. Other prior art motor bells are disclosed in U.S. Pat. Nos. 4,300,128, 4,305,066, 4,308,529, 4,310,834 and 4,368,458.
The present invention attains the foregoing and other objects by utilizing a linkage means that minimizes both the time of contact between the plunger and the shell and the magnitude of rest mass in contact with the shell while the shell is vibrating for generating the ringing sound. This is accomplished by use of a linkage that embodies a series of gaps between the various components, so that when the plunger strikes the shell it is not in driving contact with any other component. Furthermore, the present invention utilizes a drive arrangement that maximizes transfer of momentum to the plunger while still minimizing the collision time between the plunger and the shell. As the plunger rebounds from striking the shell, a gap exists either between the plunger and the pushrod or between the pushrod and the lever arm. As a result, the rest mass in contact with the vibrating shell is minimized, which in turn minimizes the dampening of the vibrations. Ultimately, such a characteristic leads to a clearer and louder ringing sound.
US Referenced Citations (3)
Continuation in Parts (1)
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7281257 |
Dec 1988 |
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Patent Grant
4970490
