1. Field of the Invention
The present invention relates generally to an electrical nailing gun, and more specifically to a driving circuit for an electrical nailing gun, which uses a capacitor to accumulate electrical energy for increasing the power of the electrical nailing gun.
2. Description of the Related Art
Conventionally, high power nailing guns are air nailing guns to be used with an air compressor to fire nails. However, an air nailing gun produces much noise during operation. Further, the air compressor requires much work space. In order to eliminate these drawbacks, electrical nailing guns are developed. An electrical nailing gun uses electricity to energize a coil, thereby producing a magnetic force to attract the piston, and therefore the piston drives the nail into the workpiece. This design of electrical nailing gun produces low noise during operation. Because this design of electrical nailing gun does not use with an air compressor, it requires less work space. However, conventional electrical nailing guns still have drawbacks. A conventional electrical nailing gun requires a heavy transient current when firing the nail, and such a heavy transient current is a heavy burden to the AC power cord. Different AC power cord conditions, such as wire diameter, power cord extension length, or power cord material, cause different transient current to further result in different firing power. Due to the limitation of firing power, there is a limitation to the application of conventional electrical nailing guns, thereby resulting in a barrier to market promotion.
FIG. 7 is a circuit diagram of a driving circuit for electrical nailing gun according to the prior art. According to this design, the driving circuit is a single coil driving circuit where only one half-cycle of AC power source is electrically connected upon each firing action. FIG. 8 is a circuit diagram of another design of driving circuit for electrical nailing gun according to the prior art. According to this design, the driving circuit is a bi-coil driving circuit where AC power source positive half-cycle and AC power source negative half-cycle are respectively applied on two coils that are connected in series. The two coils accelerate the piston, thereby increasing the firing power.
The driving circuit of a conventional electrical nailing gun simply uses one half-cycle or one full-cycle. However, the frequency of city power supply is 60 Hz, and the period of a half-cycle is as short as 8.3 ms. This short period results in a limitation to the action of the magnetic force upon the piston. Because magnetic force varies with the variation of AC power supply waveform, the magnetic force converted from the electrical energy for attracting the piston cannot be optimized, i.e., the piston firing power is limited. Further, in order to increase magnetic force, electrical current must be relatively increased. However, increasing electrical current may cause an overload at the AC power cord, thereby resulting in flashing of fluorescent lamps in the house. Furthermore, if the resistance is increased due to the use of an electrical extension cable, the energizing current will drop, thereby reducing nail firing power. Therefore, the use of an electrical extension cable is limited. Further, if three or more coils are used to increase nail firing power, the length of the electrical nailing gun must be relatively increased, and the weight of the electrical nailing gun will be relatively increased. Further, because every coil works at a saturated status, the temperature of the electrical nailing gun will be greatly increased, not able to meet safety code (for example, UL) requirements.