Electrical generator or motor structure – Non-dynamoelectric – Piezoelectric elements and devices
Reexamination Certificate
1999-03-12
2001-05-01
LaBalle, Clayton (Department: 2834)
Electrical generator or motor structure
Non-dynamoelectric
Piezoelectric elements and devices
C310S323030
Reexamination Certificate
active
06225730
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a vibrating type driving device for obtaining a driving force by press contacting a moving member against a vibration member.
2. Related Background Art
In a vibrating type driving device (vibrating type motor), a moving member is brought into pressure contact with a vibration member made of an elastic member to which an electromechanical energy converting element is joined; an AC voltage is applied to the converting element, and a progressive vibration wave thereby is generated in the vibration member, thereby frictionally driving the moving member.
FIG. 7
shows a conventional vibrating type motor. A ring-shaped stator (vibration member)
102
fixed to a base
101
is constructed in a manner such that an electromechanical energy converting element
122
to which a current is supplied through a connector
110
and a flexible board
111
is joined to the lower surface of an elastic member
121
and a frictional member
123
is adhered onto the upper surface of the elastic member
121
. An outer peripheral portion of a pressurizing spring
106
is attached onto the upper surface of a rotor (moving member)
103
through a rubber plate
107
. An inner peripheral portion of the pressurizing spring
106
is attached to a disk
105
which is shrink fitted to an output shaft
104
.
The output shaft
104
is rotatably supported by a pair of roller bearings
181
and
182
each having an outer ring fixed to the base
101
and an inner ring fitted to the outer circumference of the output shaft
104
. The disk
105
is in contact with the inner ring of the rolling bearing
182
. On the other hand, the inner ring of the rolling bearing
181
is brought into engagement with a snap ring
109
attached to a groove of the output shaft
104
in a state in which the output shaft
104
is pressed onto the stator
102
side together with the disk
105
and the inner ring of the roller bearing
182
by only a displacement amount of the pressurizing spring
106
, thereby bringing the rotor
103
into pressure contact with the stator
102
with a proper force.
As shown in
FIG. 6
, consequently, in the bearing
182
, a preload force acting in the same direction as that of a pressure of the pressurizing spring
106
is applied to the inner ring by the disk
105
, so that a rattle in the radial direction in the bearing
182
is eliminated. On the other hand, in the bearing
181
, a preload force acting in the direction opposite to that of the pressure of the pressurizing spring
106
is applied to the inner ring by the snap ring
109
, so that a rattle in the radial direction in the bearing
181
is eliminated. Since the rattle in the radial direction of each of the bearings
181
and
182
is eliminated, a shake in the radial direction of the output shaft
104
is also suppressed.
Now, assuming that a reactive force of pressure of the pressurizing spring
106
is labeled as F and a preload force of the bearing
181
is labeled P
1
and a preload force of the bearing
182
is called P
2
, the relation
F=P
1
−P
2
is satisfied among those three forces.
As will be understood from the above relation, since the bearing
181
receives the sum of the reactive force of pressure and the preload force of the bearing
182
as a preload force, such a preload force is much larger than the preload force of the bearing
182
.
Usually, a fatigue life of the bearing is inversely proportional to the cube of the bearing load. Therefore, a fatigue life of the bearing
181
which receives a large preload force is much shorter than that of the bearing
182
. Further, since the vibrating type motor is often used at a low speed and it is difficult to form an oil film between the rolling member of the bearing and a raceway surface, it is necessary to set a load of a rolling member of the bearing to be smaller than the ordinary load.
A torque which can be generated by a motor depends on the maximum frictional force between the stator and the rotor. Since the frictional force is determined by a coefficient of friction between the rotor and the stator, and a pressure applied therebetween, it is effective to increase the pressure in order to raise the maximum torque.
In the conventional motor, however, since the bearing
181
bears all of the pressure, in order to increase the pressure without reducing the bearing life, a bearing having a larger load rating has to be used. This results in an increase in size and cost of the bearing.
In recent years, in the fields of OA equipment and FA equipment, high precision is demanded in the positioning of a driving mechanism, the speed control, and the like. A general way to reduce a rotational output of a pulse motor or the like is to use a speed reducing mechanism such as gear, belt, or the like and to perform driving at high resolution and high torque. When the speed reducing mechanism uses gear, however, transfer precision may deteriorate due to a tooth shape error, a pitch circle error, or the like. In order to raise the degree of precision, it is necessary to raise the gear grade, perform a precision grinding, or the like, which results in high costs. Further, since controllability deteriorates due to nonlinearity caused by backlash, it is necessary to provide a countermeasure, such as a non-backlash gear or the like. When the speed reducing mechanism uses a belt, the controllability also deteriorates because of a reduction in transfer precision due to eccentricity, roundness, or the like of a pulley, expansion and contraction of the belt, and reduction of the transfer rigidity due to a bending vibration.
On the other hand, a “direct drive” method, in which a motor shaft is directly attached to a driven member and is driven using a motor which can generate a low speed and a high torque without using a speed reducing mechanism such as a gear, belt, or the like, is an effective drive means. In this “direct drive” method, reduction of the precision using the above transfer mechanism, backlash, and reduction of the rigidity in the transfer system can be prevented and the motor shaft can be driven at high precision.
Since a vibration wave motor can stably generate torque at a low speed, it is a motor suitable for the “direct drive” method. The vibration wave motor is constructed in a manner such that an electromechanical energy converting element (piezoelectric element, magnetostrictive element, or the like) is joined to one side of a vibration member made of an elastic material, an AC voltage is applied to such a piezoelectric element, and a progressive vibration wave is generated in the vibration member, thereby frictionally driving the moving member that is in contact with the vibration member with a pressure. By combining angle detecting means of a high resolution to such a motor, the motor shaft can be driven at high precision, high rigidity, and high resolution.
FIGS. 15A and 15B
show conventional examples of a roller driving device which is used to convey a sheet.
One end of a roller is rotatably supported at a casing of the device by a ball bearing and another end is fixed to an output shaft of a motor fixed to the device. With such a structure, the transfer error occurring in the conventional case of reducing the speed by using a gear or belt driving can be eliminated.
In the case of performing a gear or belt driving method, even if a slight error occurs in an attaching precision between the member to be driven and the transfer mechanism, it can be absorbed by the transfer mechanism. For example, although a change in distance between the shafts occurring when the eccentricity of the gear causes deterioration of the transfer precision, since the displacement of the gear is absorbed between the gears, a surplus load that is caused by an error of each transfer member is not applied to the driven member or the motor. In the case of belt driving as well, since each part precision and an attaching error are converted to a linear velocity of the belt or are absorbed by the extension and contracti
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
LaBalle Clayton
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