1. Field of the Invention
The present invention relates to a brushless motor driving apparatus and a printing apparatus including the brushless motor driving apparatus and, more particularly, to a DC brushless motor driving technique of driving a carriage on which a printhead is mounted.
2. Description of the Related Art
Recently, printing apparatuses require higher image qualities. Possible measures are, for example, to increase the printing medium conveyance accuracy, the printhead printing accuracy (for example, for an ink-jet printer, ink discharge amount and discharge timing), and the operation accuracy of the carriage on which the printhead is mounted.
Of these measures, attention is paid to the carriage operation accuracy. An ink-jet printer or the like simultaneously performs carriage operation control and printhead printing control, because the printhead prints while the carriage operates. Hence, the carriage operation accuracy, with respect to a control signal from the controller, affects the printing accuracy.
At present, the carriage often uses, as a driving source, a DC brushless motor which is quiet and which has a long service life. Hence, improvement of the operation accuracy of the DC brushless motor results in higher carriage operation accuracy and higher image quality of the printing apparatus.
A general DC brushless motor takes, for example, an arrangement as shown in FIG. 3. A plurality of (for example, three at every 120°) Hall elements arranged around a magnet (rotor) detect the magnetic pole of the rotating magnet. The obtained voltage is output to a motor driver, and driving of the rotor is controlled via coils based on outputs from the Hall elements. This arrangement has many error factors such as a Hall element mounting position error, an unbalanced voltage of the Hall element itself, the hysteresis of the Hall element itself, an offset of a differential amplifier input, the magnetization accuracy of the magnet, and the mechanical decentering of the rotor. To solve this problem, for example, Japanese Patent Publication No. 61-20232 and Japanese Patent Laid-Open No. 2009-240041 have been proposed.
The invention of Japanese Patent Publication No. 61-20232 pays attention to the error of the unbalanced voltage of the Hall element itself. One of the differential outputs of the Hall element is connected to GND or the power supply line so that the unbalanced voltage is corrected to be low.
In the invention of Japanese Patent Laid-Open No. 2009-240041, the Hall element switching position is estimated from the timing of an induced voltage generated in a coil.
The DC brushless motor inevitably generates errors, such as the dimensional tolerance between building components and the magnetization error of the rotor. In this situation, for example, when the mounting position of the Hall element itself shifts, the operation cannot be corrected by only correcting the unbalanced voltage of the Hall element, as in the invention of Japanese Patent Publication No. 61-20232.
In a printing apparatus, the carriage prints while frequently repeating acceleration and deceleration, and the DC brushless motor needs to be driven accurately even in acceleration/deceleration. However, when the Hall element switching position is estimated from the timing of an induced voltage generated in a coil, as in the invention of Japanese Patent Laid-Open No. 2009-240041, correction accuracy obtained from the estimation becomes poor in a driving form in which acceleration and deceleration are repeated frequently.