1. Field of the Invention
The invention generally relates to an electric hair cutter. More particularly, the invention relates to an electric hair cutter and a control method for its motor rotational speed, in which a brushless DC (BLDC) motor is used and the counter-electromotive force pulses of the motor are detected and used to calculate the motor speed so as to keep the motor rotating at a fixed speed and in which a comfortable grip is provided.
2. Descriptions of the Related Art
Electric hair cutter has been used to cut hair. The hair cutter has a cutting unit and a screen unit. The reciprocating motion of the cutting unit enables it to cut hair.
Because the cutting unit plays a crucial role in haircutting, improvements of the cutting unit (such as the use of different materials and the inclination angle of the small blades of the cutting unit) have been made.
The inventor has worked in the relevant field for 20 years. From his talks and chats with the customers and hairdressers, he found out that, aside from the improvements in the use of different materials for the cutting unit and different designs of the main body of the hair cutter, the following disadvantages have not been addressed in the prior art:
(1) Motor has a relatively shorter service life because of the wear and tear of the carbon brushes. When the motor of a hair cutter is damaged, its user often purchases another one to replace it even though other components of it are still usable. Therefore, users have to spend more money and such discarded hair cutters are not environmentally friendly.(2) The cutting unit has a relatively shorter service life. Conventionally, because the carbon brushes are easily worn, this affects the motor speed and the motor can not rotate at a fixed speed. In addition, after a period of use, its battery can store a less amount of current; this affects the motor speed too. Therefore, these factors affect the haircutting performance of the cutting unit and the service life of the cutting unit is shortened.(3) Unable to provide comfortable grip: Because the conventional motor rotates at lower, unstable speeds, the hair cutter of the prior art can not provide comfortable, stable grip. This would affect the haircutting performance of hairdressers.
From the above, we can see that the prior art motor for the electric hair cutter needs to be improved.