1. Field of the Invention
The present invention relates to an actuator driving apparatus.
2. Description of the Related Art
Actuator driving apparatuses that operate at a resonance frequency are well known. For example, Jpn. Pat. Appln. KOKOKU Publication No. 62-52282 discloses an actuator driving apparatus described below.
FIG. 6 shows a conventional actuator driving apparatus. As shown, an actuator driving apparatus 20 for driving an actuator 1 comprises a power supply circuit 2, start signal generating circuit 3, switch circuit 4, drive signal generating circuit 5, start control circuit 6, timing signal generating circuit 7 and rock detection circuit 8. The actuator 1 is connected to the drive signal generating circuit 5 and rock detection circuit 8.
The power supply circuit 2 supplies power to each of the above-mentioned circuits of the actuator driving apparatus 20 via power supply lines (indicated by the broken lines in the figure). The rock detection circuit 8 extracts a detection signal from, for example, a signal indicating an electromotive force and generated during the rock motion of the actuator 1. The timing signal generating circuit 7 generates a drive timing signal based on the detection signal from the rock detection circuit 8. The start signal generating circuit 3 generates a start signal of substantially the same frequency as the resonance frequency of the actuator 1.
The switch circuit 4 outputs either the start signal supplied from the start signal generating circuit 3 or the drive timing signal supplied from the timing signal generating circuit 7, based on a switch control signal described later. The drive signal generating circuit 5 generates a drive signal based on the output signal of the switch circuit 4, and supplies it to the actuator 1. The start control circuit 6 generates the above-mentioned switch control signal.
The operation of the above-described structure will be described. At the initial stage of actuator driving, a switch control signal is output from the start control circuit 6, and the switch circuit 4 is ready to output the start signal supplied from the start signal generating circuit 3. The start signal has a frequency close to the resonance frequency of the movable portion of the actuator 1. The drive signal generating circuit 5 generates a drive signal in accordance with the start signal as the output of the switch circuit 4, and supplies it to the actuator 1. Since the drive signal has a frequency close to the resonance frequency of the movable portion of the actuator 1, the actuator 1 is activated to rock, and the rock angle of the actuator 1 is gradually increased.
The rock detection circuit 8 acquires information concerning the rock motion of the actuator 1, and outputs a detection signal. When the amplitude of the detection signal exceeds a preset value, the start control circuit 6 stops the output of the switch control signal to switch the switch circuit 4. The timing signal generating circuit 7 outputs a drive timing signal that has the same frequency as the detection signal supplied from the rock detection signal 8, and has its phase adjusted in accordance with the detection signal. The switch circuit 4 outputs the timing signal that is supplied from the timing signal generating circuit 7. The drive signal generating circuit 5 generates a drive signal in accordance with the drive timing signal, and supplies it to the actuator 1.
As stated above, at the initial stage of the starting operation, the actuator 1 is forcibly driven by substantially the same frequency as the resonance frequency of the movable portion of the actuator 1, therefore can reliably be started. When the rock amplitude of the actuator 1 exceeds a predetermined value, a self-oscillation circuit is formed based on the rock detection signal of the actuator 1, thereby performing driving at the resonance frequency.