Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-02-07
2002-04-02
Waks, Joseph (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S156380, C340S007600
Reexamination Certificate
active
06365995
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the structure of a small flat brushless motor and its assembly method.
BACKGROUND OF THE INVENTION
Portable information equipment (hereafter referred to as “equipment”) including, for example, cellular telephones are desired to be smaller, lighter, and thinner, to give a sophisticated impression, and to endure longtime use. Equipment manufacturers are making various efforts to meet these demands. They are attempting to reduce the size and power consumption of electronic parts integrated into the equipment, to use multilayer wiring substrates to allow electronic parts to be densely integrated while increasing productivity, and to configure enclosures using light metal such as magnesium to reduce the thickness of the equipment and give it a sophisticated impression. There are similar demands on flat brushless motors used as a drive source for the equipment.
A vibration generating function for silent calls is now essential for cellular telephones. The vibration generating function is generally implemented by a vibrating motor with an eccentric weight. This is because such a motor has excellent characteristics such as a small size, a low power consumption, and a low price and is thus advantageous in reducing the weight of the equipment. The vibrating motor must also serve to improve the value of the equipment.
Requirements on vibrating motors and flat brushless motors used as equipment drive sources (hereafter, these motors may be collectively and simply referred to as “brushless motor” or “motors”) that should to be met to improve the value of the equipment will be considered. First, brushless motors must be adapted for the improved degree of integration of the equipment. Thus, as in other solid electronic parts, the brushless motor can desirably be mounted on a substrate of the equipment using “surface mount technology.” This is because in case of a multilayer substrate, the degree of integration may decrease if terminals are passed through holes formed in the substrate. In order to improve the degree of integration, the brushless motor is desirably configured by being mounted close to adjacent electronic parts so as to achieve a high density.
Second, the brushless motor must be adapted for the same mounting process as other solid electronic parts in order to increase the productivity of the equipment. Thus, the brushless motor desirably has a configuration and a heat resistance compatible with a reflow soldering method. It is also desirably configured by being efficiently mounted using the same assembly machine as other solid electronic parts.
Third, the brushless motor must be adapted for the reduced size and weight of the enclosure of the equipment. Thus, it desirably has a high impact resistance.
The reasons for the demand for the high impact resistance will be described. Of course, the high impact resistance is required to ensure that the equipment will not be destroyed even if it is inadvertently dropped. Conventional common methods provide a certain amount of space inside the equipment and integrate the motor into the equipment via an elastic body. In recent years, however, the demand for reduced size and thickness prevents a space for the elastic body from being provided. If an attempt is made to surface-mount the motor on the same substrate as other electronic parts in order to meet the demand, the brushless motor is directly fixed to the substrate, thereby preventing impacts to be absorbed as in elastic support structures.
Furthermore, attempts are being made to form the enclosure of the equipment of light metal such as magnesium or aluminum, as described above. Despite its small weight, such metal has a much higher rigidity than resin so its buffering capability is insufficient. Consequently, an unprecedentedly large impact is effected on the substrate fixed to the enclosure and is directly transmitted to the motor fixed to the substrate. As a result, a very high impact resistance is required of the motor and its coupling. Therefore, the desired value of motor impact resistance is conventionally between 3,000 and 5,000 G but now between 10,000 and 20,000 G.
Besides, this impact resistance is desirably met by simply heating and melting a solder on the substrate to solder-connect the motor to the substrate (reflow) without passing terminals through holes formed in the substrate (surface mount). Even enduring a reflow heating temperature (about 250° C.) is difficult. The inventor attempted to find a conventional technique that meets these requirements, but in vain. Thus, through many examinations, the inventor has completed the present invention. A motor according to the present invention is of a flat type having a height smaller than the breadth, so it is sometimes referred to as a “flat vibrating motor” or a “flat brushless motor.”
Next, brushless motors will be described by focusing on conventional assembly methods.
A small flat brushless motor generally comprises a metal base on which various parts are assembled. Since the motor is a rotational power source for the equipment, it must be mounted in the equipment so as to maintain a sufficient rigidity and the metal base must be formed accurately so as to be suitable as a criterion for motor assembly. To assemble the motor, the base is placed on a palette (a positioning working table) and the parts are then mounted on the base.
According to this assembly method, before placing the base on the palette, whether or not the base is located upside down is checked and its direction and position are adjusted. The time required for this operation, however, tends to increase with decreasing size of the motor. This is because it is more difficult to handle smaller parts.
This tendency is found not only in the positioning of the motor base but also in the assembly of electronic parts on a printed circuit board. The electronic parts are difficult to efficiently mount on a small printed circuit board.
In addition to the reduced size, there is a strong demand for the reduced weight of the motor for portable equipment. However, in attempting to reduce the size and weight of the motor, the characteristics of the motor must not be sacrificed. Thus, a rotor and a stator must naturally have a specified size and weight. Accordingly, it is now necessary to reduce the volume and weight of peripheral members including structures other than the rotor and stator, that is, a structure for holding the rotor and stator and a structure for electrically connecting the stator and external device together.
The printed circuit board assembly method called the “connected substrate” is conventionally commonly used to produce built-in circuits for various equipment. When printed circuit boards have small or different external shapes, this method arranges a large number of such circuit boards and connects them together using bridges or frames so as to form a shape that is easily handled by an electronic parts mounting machine. After electronic parts have been mounted on these circuit boards, the bridges are cut and removed to obtain printed circuit board assemblies in order to complete assembly.
This method, however, is still disadvantageous if further size reduction is required. In addition, as the size of the printed circuit board decreases, the area occupied by the bridges or frames relatively increases to reduce the usage of material resources. In addition, despite a demand for further reduction of the size of the printed circuit board, when a shearing machine is used to cut the bridges, contacts with the cutting edge and stress caused by shearing must be avoided. As a result, no part can be placed near the sheared position. The bridges may be folded or ruptured, but the separated portion form a rough rupture surface to degrade the appearance and dimensional accuracy. Due to these disadvantages, this method is unsuitable for small parts. Furthermore, since the separation is carried out after the completion of assembly, an impact associated with shearing may degrade the quality of finished produc
Fujinaka Hiroyasu
Fukuda Yoshiaki
Itakura Kazuhito
Kuyama Koji
Sato Noriyoshi
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
Waks Joseph
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