Driving device for a vibration type motor

This invention relates to a driving device for a vibration wave motor and, more particularly, to a driving device for setting the level of a driving periodic signal to a low level in driving within a predetermined range of high driving frequencies, and to a high level in driving within a predetermined range of low driving frequencies, thereby reducing the power consumption.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a driving device for a vibration type 
motor and, more particularly, to a driving device for a vibration type 
motor that changes driving conditions by a driving frequency. 
2. Related Background Art 
Conventionally, a driving device for a vibration type motor such as a 
vibration wave motor controls the rotation speed by changing the driving 
frequency, as disclosed in Japanese Patent Application Laid-Open No. 
63-154074. Alternatively, the driving device controls the rotation speed 
by setting a plurality of driving voltages, selecting an arbitrary one in 
advance, and changing the driving frequency, or by setting an input power 
by PWM in advance in accordance with variations in driving voltage and 
changing the driving frequency. 
In any of the above-mentioned driving devices for a vibration wave motor, 
the rotation speed of the vibration motor is controlled by changing the 
driving frequency during a series of operations from the start to end of 
driving. Driving is inefficient such that the power consumption is almost 
uniform regardless of the rotation speed or the input power increases for 
a lower motor rotation speed. 
An element (output transistor such as a switching element) on the output 
side in the motor driving circuit must have a large output, which 
increases the mounting area and the cost. 
When the driving frequency becomes lower than the resonant frequency, the 
conventional vibration wave motor suddenly stops. This problem is solved 
by the following method. 
More specifically, the vibration state of the vibration member of the 
vibration wave motor is monitored to detect a shift from the resonant 
frequency. If the driving frequency comes near the resonant frequency, the 
driving frequency is generally changed not to be lower than the resonant 
frequency. 
According to the conventional method for acheiving above, the arrangement 
for always detecting the above shift is provided. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a driving device for 
changing driving conditions in accordance with the rotation speed of a 
motor to increase/decrease the power consumption and particularly to 
reduce the power consumption during low-speed rotation. 
It is another object of the present invention to provide a device for 
controlling the frequency not to be erroneously lower than the resonant 
frequency even with the above arrangement of reducing the power 
consumption. 
To achieve the above objects, one aspect of the application is to provide a 
driving device for a vibration type motor for generating a vibration of 
the vibration member and obtaining a driving force by applying a driving 
periodic signal to an electro-mechanical energy conversion element portion 
arranged on the vibration member, comprising a frequency setting circuit 
for setting a frequency of the periodic signal, and an adjusting circuit 
for adjusting a level of the periodic signal applied to the 
electromechanical energy conversion element portion in accordance with the 
frequency set by the frequency setting circuit, the circuit adjusting the 
level of the signal which is set as a high frequency to a level lower than 
the level of the signal which is set as a low frequency. 
To achieve the above objects, one aspect of the application is to provide a 
vibration type motor in which an electromechanical energy conversion 
element portion is arranged on a vibration member, and a periodic signal 
is applied to the element portion to generate a vibration of the vibration 
member, thereby obtaining a driving force, comprising driving force 
control means for changing a frequency of the periodic signal to change 
the driving force, regulating means for regulating or changing the 
frequency by the control means in accordance with a shift from a resonant 
frequency of the motor that is detected by detecting means, condition 
setting means for setting a driving condition of the vibration type motor, 
and switching means for changing over between operative and inoperative 
states of the regulating means in accordance with the driving condition 
set by the condition setting means. 
To achieve the above objects, one aspect of the application is to provide a 
vibration type motor in which an electromechanical energy conversion 
element portion is arranged on a vibration member, and a periodic signal 
is applied to the element portion to generate a vibration of the vibration 
member, thereby obtaining a driving force, comprising driving force 
control means for changing a frequency of the periodic signal to change 
the driving force, regulating means for regulating or changing the 
frequency by the control means in accordance with a shift from a resonant 
frequency of the motor that is detected by detecting means, and control 
means for suspending an operation of the regulating means when the 
frequency of the periodic signal is higher than a predetermined frequency, 
and a voltage of the periodic signal is lower than a predetermined 
voltage, and for activating the operation of the regulating means when the 
frequency of the periodic signal is lower than the predetermined 
frequency, and the voltage of the periodic signal is higher than the 
predetermined voltage.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
First Embodiment 
FIG. 1 is a block diagram showing the first embodiment of the present 
invention. 
Referring to FIG. 1, a control circuit 1 comprises a microcomputer (CPU) 2, 
an oscillating circuit (VCO) 3, a comparing phase circuit 6, comparator 
circuits 7 and 8, and a driving logic circuit 12 for a vibration wave 
motor as a vibration type motor. 
The microcomputer (CPU) 2 controls the whole operation. The oscillating 
circuit (VCO) 3 is turned on/off by an output VCOON from the microcomputer 
2 and changes the oscillated frequency by an output VCODAC. 
In changing the oscillated frequency, an internal set voltage is determined 
by an 8-bit output (VCODAC) from the microcomputer 2. Next, the current 
value of a current used for the oscillated frequency is determined by the 
internal set voltage and a resistor 4. An oscillated frequency 
corresponding to the current value is determined by charging/discharging 
the current to/from a capacitor 5. This oscillated frequency is a 
frequency 4 F four times a driving frequency F of the vibration wave 
motor. 
The relationship between the 8-bit output (VCODAC) from the microcomputer 2 
and the oscillated frequency will be exemplified. 
EQU VCODAC=00H 4F=160 kHz 
EQU VCODAC=32H 4F=156 kHz 
EQU VCODAC=FFH 4F=139.6 kHz 
Changing the resistance value of the resistor 4 can correct changes in 
oscillated frequency caused by circuit variations. 
The output 4 F from the oscillating circuit (VCO) 3 is input to the driving 
logic circuit 12 for the vibration wave motor. 
The driving logic circuit 12 outputs a driving output to a motor driver 13 
based on a reception of an output USMON from the microcomputer 2. The 
driving output has a frequency F whose time phase is shifted by 90.degree. 
from the output 4 F of the oscillating circuit (VCO) 3 by an output DIR 
from the microcomputer 2. 
The output DIR from the microcomputer 2 changes the phase relationship to 
90.degree. and -90.degree.. The motor driver 13 amplifies the driving 
output power and outputs it to a vibration wave motor 19 via coils 14 and 
15 and capacitors 16 and 17. A capacitor 18 adjusts the phase relationship 
between the S and A phases. 
The motor driver 13 receives an output from a battery 34 via a voltage 
regulator 35. An output voltage from the voltage regulator 35 is changed 
by an output VDAC (8 bits) from the microcomputer 2. 
For example, for VDAC=A9H, the output voltage is 3.3 V, and for VDAC=8 AH, 
the output voltage is 2.7 V. 
Operation of the comparing phase circuit 6 will be described. 
The comparing phase circuit 6 is constituted by a counter circuit for 
counting outputs from the comparator circuits 7 and 8, and a comparing 
circuit for comparing the counter value of the counter circuit with a 
comparison value variable by the setting of the microcomputer 2. The 
comparing phase circuit 6 detects the phase difference between the S phase 
output as a sensor output that changes depending on the driving state of 
the vibration wave motor and the A phase input as a driving input in the 
vibration wave motor 19, as the time difference between outputs from the 
comparator circuits 7 and 8 via a voltage divider/high-pass filter circuit 
formed from resistors 25 to 30 and capacitors 31 to 33. When the phase 
difference reaches a predetermined value, the comparing phase circuit 6 
sends an output PLE to the microcomputer 2. 
The microcomputer 2 changes the output VCODAC based on the output PLE to 
control the vibration wave motor. A driving start switch 36 starts driving 
the vibration wave motor 19, and a switch 37 determines the rotation 
direction of the vibration wave motor 19. The vibration wave motor 19 is a 
known motor in which piezoelectric members serving as electromechanical 
energy conversion elements are arranged on a vibration member, and 
periodic signals (AC signals) having different phases are applied to the 
conversion elements formed as A and B phases to excite the vibration 
member. 
FIG. 2 is a graph showing the driving characteristics of the vibration wave 
motor 19 according to the first embodiment. The abscissa represents the 
driving frequency, and the ordinate represents the following three 
characteristics. 
The upper stage shows a current Iout (A) flowing through a transistor on 
the output side of the motor driver 13. 
The middle stage shows a voltage V (V) applied to the motor that is changed 
by the voltage regulator 35. 
The lower stage shows a rotation number N (rpm) of the vibration wave motor 
19. 
The vibration wave motor 19 is driven using a higher frequency range than 
the resonant point. Accordingly, the rotation number N of the motor 
decreases for a higher driving frequency and increases for a lower driving 
frequency. 
If the driving frequency is decreased too much, for example from FRQ4 to 
FRQ3 in FIG. 2, the rotation number N abruptly decreases. The 
microcomputer 2 changes the output VCODAC based on the output PLE to 
control the vibration wave motor, as described above, in order to prevent 
an abrupt decrease in rotation number. 
As the voltage applied to the motor is higher, the current Iout flowing 
through the transistor on the output side is larger, and the rotation 
number N is larger. 
The dotted line between FRQ1 and FRQ2 indicating the current Iout flowing 
through the transistor on the output side is for 3.3 V, and the solid line 
is for 2.7 V. 
A resonant frequency FRE of an electrical circuit made of the sum of the 
capacitance between A and -A phase electrodes 21 and 22 of the vibration 
wave motor 19 and the capacitance of the capacitor 16 and the inductance 
of the coil 14 is set higher than FRQ1. The resonant frequency of an 
electrical circuit made of the sum of the capacitance between B and -B 
phase electrodes 23 and 24 and the capacitance of the capacitor 17 and the 
inductance of the coil 15 is similarly set. 
Accordingly, the current Iout flowing through the transistor on the output 
side increases as the driving frequency increases (comes near FRE). Since 
the current Iout flowing through the transistor on the output side is 
large in an operation region with a small rotation number N of the motor, 
the power consumption becomes large. 
In this embodiment, the applied voltage V=2.7 V is applied between the 
driving frequencies FRQ1 and FRQ2, and the applied voltage V=3.3 V is 
applied between the driving frequencies FRQ2 and FRQ3. This can decrease 
the current Iout flowing through the transistor on the output side in an 
operation region with a small rotation number N of the motor, thereby 
reducing the power consumption. 
In activation, the vibration wave motor 19 is driven at the applied voltage 
V=2.7 V and the driving frequency FRQ1. After that, the driving frequency 
is decreased from FRQ1 to FRQ2. 
At the driving frequency FRQ2, the applied voltage corresponding to the 
value VDAC is changed such that changes per time in rotation number N of 
the motor in decreasing VDAC=8 AH (output voltage=2.7 V) to VDAC=A9 H 
(output voltage=3.3 V) coincide with changes per time in rotation number N 
of the motor in decreasing the driving frequency from FRQ1 to FRQ2. 
At VDAC=A9 H (output voltage=3.3 V), the driving frequency is decreased 
from FRQ2 to FRQ4. The driving frequency is controlled between FRQ2 and 
FRQ4 by the aforementioned phase detection. When the driving frequency 
decreases to FRQ4, the motor reaches the maximum rotation number. Note 
that the vibration wave motor 19 is stopped by control reverse to 
activation control. 
Second Embodiment 
FIGS. 3 to 5 show the second embodiment. FIGS. 3 and 4 correspond to FIGS. 
1 and 2 showing the first embodiment. 
The second embodiment shown in FIG. 3 is different from the first 
embodiment shown in FIG. 1 in the following point. In FIG. 1, the power 
supply voltage of the motor driver 13 is changed by the voltage regulator 
35. To the contrary, in the second embodiment, the voltage of a battery 34 
is detected by an internal AD converter circuit of a microcomputer 2, and 
the pulse width of an output from a motor driver 13 is changed by a pulse 
width modulation (PWM) function of a driving logic circuit 12 for a 
vibration wave motor, instead of changing the power supply voltage. 
More specifically, the pulse width is changed by an output PWM (8 bits) 
from the microcomputer 2. For example, when the voltage of the battery 34 
is 5 V, the pulse width is controlled to a pulse width corresponding to an 
output voltage of 3.3 V in the first embodiment for PWM=A9 H, and to an 
output voltage of 2.7 V for PWM=8 AH. In other words, the pulse width is 
set to correspond to an output voltage of 3.3 V for PWM=A9 H and an output 
voltage of 2.7 V for PWM=8 AH regardless of the voltage of the battery 34. 
FIG. 5 shows the waveform of the output voltage of the motor driver 13 in 
this case. The solid line represents a pulse width corresponding to 2.7 V, 
and the dotted line represents a pulse width corresponding to 3.3 V. 
Changing this pulse width changes the applied voltage of a driving periodic 
signal. The -A phase shifts from the A phase by 180.degree., the B phase 
shifts by 90.degree., and the -B phase shifts by 270.degree.. 
To reversely rotate the motor, the relationship between the B and -B phases 
is reversed. In this arrangement, a pulse width corresponding to 2.7 V is 
set at a driving frequency from FRQ1 to FRQ2. The pulse width is gradually 
changed to one corresponding to 3.3 V at FRQ2, and set at one 
corresponding to 3.3 V from FRQ2 to FRQ4. 
Third Embodiment 
FIG. 6 is a block diagram showing the third embodiment of the present 
invention. 
Referring to FIG. 6, the same reference numerals as in the second 
embodiment of FIG. 3 denote the same parts, and a description thereof will 
be omitted. A comparing phase circuit 6 will be explained in detail. 
The comparing phase circuit 6 is constituted by a counter circuit for 
counting outputs from comparator circuits 7 and 8, and a comparing circuit 
for comparing the counter value of the counter circuit with a comparison 
value variably set by a microcomputer 2. The comparing phase circuit 6 
detects the phase difference between the S phase output as a sensor output 
and the A phase input as a driving input in a vibration wave motor 19 that 
changes depending on the driving state of the vibration type motor 
(vibration wave motor), as the time difference between outputs from the 
comparator circuits 7 and 8 via a voltage divider/high-pass filter circuit 
formed from resistors 25 to 30 and capacitors 31 to 33. When the phase 
difference reaches a first value K1 (on the lower stage in FIG. 7), the 
comparing phase circuit 6 sends an output PLE1 to the microcomputer 2. 
When the phase difference reaches a second value K2 (on the lower stage in 
FIG. 7), the comparing phase circuit 6 sends an output PLE2 to the 
microcomputer 2. The microcomputer 2 changes an output VCODAC based on the 
signal PLE to control the vibration wave motor. 
Values such as VCODAC under each driving condition are stored in an 
erasable memory means (EEPROM) 40. 
Note that when the erasable memory means 40 is used for, e.g., an 
interchangeable lens of a single-lens reflex camera, if the lens is 
removed during a write in the erasable memory means (EEPROM) 40, the power 
supply becomes unstable to write erroneous information. 
For this reason, information can only be written when the power supply is 
stable, e.g., in shipment from the factory or in adjustment in the service 
section. 
An external circuit 41 performs communication via a communicating means 42. 
The vibration wave motor (vibration type motor) is constituted by arranging 
an electromechanical energy conversion element portion such as a 
piezoelectric member on an elastic member. Periodic signals (different in 
phase) are applied to generate the vibration of the elastic member, 
thereby obtaining a driving force. The vibration wave motor has a ring or 
bar shape. 
FIG. 7 is a graph showing the driving characteristics of the vibration wave 
motor (vibration type motor) 19 according to the present invention. 
The abscissa represents the driving frequency, and the ordinate represents 
the following three characteristics. 
The upper stage shows a current Iout (A) flowing through a transistor on 
the output side of the motor driver 13. 
The middle stage shows a rotation number N (rpm) of the vibration type 
motor (vibration wave motor) 19. 
The lower stage shows a phase difference .theta. (.degree.) between the A 
and S phases. 
The driving characteristic of the vibration wave motor 19 is that the 
rotation number N of the motor decreases for a higher driving frequency 
and increases for a lower driving frequency. If the driving frequency is 
decreased too much (from FREQ4 to FREQ3), the rotation number N abruptly 
decreases. 
To prevent this, the phase is conventionally controlled. However, at a 
driving voltage of 2.7 V, the phase difference between the A and S phases 
on the lower stage has already reached a phase difference K as in 
resonance. Although the driving state is not an actual resonance state, 
phase control undesirably limits the driving frequency. 
As the voltage applied to the motor is higher, the current Iout flowing 
through the transistor on the output side is larger, and the rotation 
number N is larger. 
The dotted line between MFL21 and MFL1 indicating the current Iout flowing 
through the transistor on the output side is for 3.3 V, and the solid line 
is for 2.7 V. 
A resonant frequency FRE of an electrical circuit made of the sum of the 
capacitance between A and -A phase electrodes 21 and 22 of the vibration 
wave motor 19 and the capacitance of a capacitor 16 and the inductance of 
a coil 14 is set higher than MFL2. The resonant frequency of an electrical 
circuit made of the sum of the capacitance between B and -B phase 
electrodes 23 and 24 and the capacitance of a capacitor 17 and the 
inductance of a coil 15 is similarly set. As a result, the current Iout 
flowing through the transistor on the output side increases as the driving 
frequency increases (comes near FRE). 
Since the current Iout flowing through the transistor on the output side is 
large in an operation region with a small rotation number N of the motor, 
the power consumption becomes large. 
For this reason, the applied voltage V=2.7 V is applied between the driving 
frequencies MFL2 and MFL1, and the applied voltage V 3.3 V is applied 
between the driving frequencies MFL1 and FREQ3 as an applied voltage 
higher than an applied voltage in a high frequency region. This can 
decrease the current Iout flowing through the transistor on the output 
side in an operation region with a small rotation number N of the motor, 
thereby reducing the power consumption. 
Each vibration wave motor 19 has different resonant and activation start 
frequencies. To decrease Iout, the activation start frequency MFL2 and 
driving condition switching frequency MFL1 are desirably adjusted for each 
vibration type motor (vibration wave motor) 19. 
This can be achieved by adjusting the resistance value of a resistor 4 for 
each vibration type motor (vibration wave motor) 19. 
It is, however, difficult to adjust the resistance value of the resistor 4 
for each vibration type motor (vibration wave motor) 19. 
The resistance value of the resistor 4 is therefore adjusted for a 
frequency at a specific value of VCODAC. 
Since a frequency value by VCODAC, which has a larger difference from a set 
value in adjustment, increases an error, the frequency in adjustment is 
set to one requiring high precision. 
Further, a frequency changeable from a set value in adjustment is minimized 
not to erroneously operate the vibration type motor (vibration wave motor) 
19 even if information in the erasable memory means (EEPROM) 40 is wrong. 
VCODAC values for setting the activation start frequency MFL2 and driving 
condition switching frequency MFL1 for each vibration type motor 
(vibration wave motor) 19 are stored in the erasable memory means (EEPROM) 
40. Using these values, the vibration wave motor 19 is controlled. 
The values in the erasable memory means (EEPROM) 40 are used to calculate 
and determine the activation start frequency MFL2 and driving condition 
switching frequency MFL1. 
For example, only the activation start frequency MFL2 is stored, and the 
driving condition switching frequency MFL1 is determined from the value of 
the activation start frequency MFL2, which can reduce the memory capacity 
of the erasable memory means (EEPROM) 40 and the communication time with 
the erasable memory means (EEPROM) 40. 
The stored value can be reset by the external circuit 41 via the 
communicating means 42. 
As described above, switching driving conditions can decrease the current 
Iout flowing through the transistor on the output side and reduce the 
power consumption. However, the phase difference on the lower stage 
reaches a phase difference as in resonance at an applied voltage of 2.7 V, 
so that the driving frequency is limited by phase control. The third 
embodiment therefore prevents the driving frequency from being limited by 
phase control even upon switching driving conditions. 
Operation in the present invention will be described. 
FIG. 8 is a flow chart showing operation of a microcomputer 2. 
The operation will be explained with reference to this flow chart. The flow 
chart exemplifies the third embodiment applied to a camera system. 
The flow chart starts upon reception of a driving instruction from a camera 
(not shown) at step 100. 
At step 101, the microcomputer 2 sets a terminal DIR to High or Low in 
accordance with a driving instruction from the camera. 
At step 102, the microcomputer 2 sets a maximum driving frequency (MFL2) 
using a driving frequency (FREQ) as an activation frequency. 
At step 103, the microcomputer 2 sets a pulse width (PWM) for determining 
the driving voltage to PWMDT1 corresponding to 2.7 V. 
At step 104, the microcomputer 2 starts activating the vibration type motor 
(vibration wave motor) (USM). 
At step 105, the microcomputer 2 compares the driving frequency (FREQ) with 
a driving condition switching frequency (MFL1). If FREQ=MFL1, the flow 
advances to step 107; otherwise, to step 106. 
At step 106, the microcomputer 2 increments a value FREQ' for determining 
the driving frequency (FREQ) to decrease the driving frequency by one 
step. Note that the driving frequency is lower as the value FREQ' for 
determining the driving frequency is larger. 
By steps 105 and 106, the driving frequency (FREQ) is gradually decreased 
to the driving condition switching frequency (MFL1). 
At step 107, when the driving frequency (FREQ) reaches the driving 
condition switching frequency (MFL1), the microcomputer 2 fixes the 
driving frequency (FREQ), and compares the pulse width (PWM) for 
determining the driving voltage with a pulse width PWMDT2 corresponding to 
3.3 V. If PWM=PWMDT2, the flow shifts to step 109; otherwise, to step 108. 
At step 108, the microcomputer 2 increments PWM to increase the driving 
voltage by one step. 
By steps 107 and 108, the pulse width (PWM) for determining the driving 
voltage is gradually increased to PWMDT2 to switch driving conditions to 
3.3-V driving. 
At step 109, upon completion of switching driving conditions, the 
microcomputer 2 performs a process of starting phase control, thus 
starting phase control. 
At step 110, the microcomputer 2 checks a signal PLE1. If the signal PLE1 
is ON, the flow shifts to step 114; if the signal PLE1 is OFF, to step 
111. 
At step 111, the microcomputer 2 checks a signal PLE2. If the signal PLE2 
is ON, the flow shifts to step 113; if the signal PLE2 is OFF, to step 
112. 
At step 112, since both the signals PLE1 and PLE2 are OFF, the 
microcomputer 2 determines that the driving frequency has not reached the 
resonant frequency yet, and decreases the driving frequency by one step to 
increase the driving speed of the vibration type motor (vibration wave 
motor). Then, the flow returns to step 110. 
At step 113, since the signal PLE2 is determined in step 111 to be ON, the 
microcomputer 2 determines that the driving frequency has reached the 
resonant frequency, and maintains the driving frequency (FREQ). The flow 
returns to step 110. 
At step 114, since the signal PLE1 is determined in step 110 to be ON, the 
microcomputer 2 determines that the driving frequency is very near to the 
resonant frequency, and increases the driving frequency (FREQ) by one step 
to prevent the vibration wave motor from suddenly stopping at a frequency 
becoming higher than the resonant frequency. After that, the flow returns 
to step 110. 
As described above, when the voltage applied to the motor driver is 2.7 V, 
phase control is inhibited. After driving conditions are switched, and the 
voltage applied to the motor driver rises to 3.3 V, phase control starts. 
The vibration type motor (vibration wave motor) can be stably, reliably 
activated and vibrated without receiving erroneous phase difference 
information. 
The above-mentioned operation concerns activation (acceleration) and can be 
similarly adopted to stop (deceleration).