Vibration motor

A vibration wave motor has a vibration member of an elastic material, and a sliding member comprising a composite resin having a filler formulated in a resin having a glass transition point of 100.degree. C. or higher secured onto a support comprising an elastic material with good thermal conductivity such as aluminum alloy.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a large output type vibration wave motor which 
moves by friction a movable member comprising a sliding member and a 
supporting member by the vibration wave generated on the vibration member 
by applying an electrical field on an electro-mechanical energy converting 
element. 
2. Related Background Art 
In the prior art, as shown in Japanese Laid-Open Publication No. 62-100178 
(FIG. 4), a vibration wave motor is constituted of the basic elements of a 
vibration member 2A having a super-hard material comprising tungsten 
carbide and cobalt flame sprayed on an elastic material and a movable 
member 3A made of an aluminum alloy in pressure contact with one surface 
of the vibration member surface and subjected to hard alumite treatment, 
the motor further includes an electro-mechanical energy converting element 
1A arranged and secured on the other surface of the vibration member 2A 
which generates a surface wave in the circumferential direction of the 
vibration member in response to an alternating current applied thereto, 
thereby rotating the movable member 3A in pressure contact with the 
surface of the vibration member 2A through frictional driving. 
However, the vibration wave motor having the movable member 3A with the 
hard alumite treated film on the surface of the vibration member 2A with 
the super-hard material film of the above-mentioned prior art example is a 
medium output type with the starting torque of about 1 kg-cm, and when 
pressurizing force between the vibration member 2A and the movable member 
3A is attempted to be made greater so as to obtain a large output of with 
a starting torque of about 5 kg-cm abrasion of the hard alumite film of 
the movable member will abruptly proceed, whereby there is the problem 
that torque performance is lowered in consequence of the consumption of 
the film leading to a short useful life for output type vibration wave 
motors. 
To cope with such abrasion of sliding surfaces, there is also a prior art 
example, in which the movable member is constituted by securing a sliding 
member of a thin synthetic resin on a support having flexibility (Japanese 
Laid-Open Publication No. 62-262092). 
However, such synthetic resin, as different from a metal material, 
generally suffers from remarkable fluctuations in material characteristics 
to temperature changes. For example, in the case of a vibration wave motor 
of the large output type having rated outputs of 4 kg-cm of torque and 
about 100 rpm of rotational number, the input is about 15 W, and the 
temperature of the vibration member becomes as high as 100.degree. C., but 
the temperature of the sliding member in pressure contact with the sliding 
surface of the sliding member has been also confirmed to become at least 
about 100.degree. C., partially because of heat generation accompanied 
with sliding friction. 
Now, if a 66 polyamide resin (hereinafter called nylon 66) belonging to 
general purpose engineering plastics is employed among crystalline 
thermoplastic resins for the sliding member material, although the melting 
point of nylon 66 is high as 260.degree. C., because the glass transition 
point is about 65.degree. C., physical properties will be markedly lowered 
and, for example, longitudinal modulus coefficient at 100.degree. C. will 
become as low as 30% or lower. 
FIGS. 2(a) and 2(b) show the sliding surface contact state between the 
vibration member and the sliding member, FIGS. 2(a) and 2(b) showing the 
contact state on driving initiation (room temperature) between the metal 
vibration member 2A and the sliding member 3b comprising nylon 66, 
indicating the state that the sliding member 3b is slightly lowered by a 
constant pressurizing force relative to the wave head of the vibration 
member 2A. 
When the temperature of the vibration member 2A reaches steady state of, 
for example, about 100.degree. C. via a predetermined time after 
initiation of driving, the flexural modulus of the nylon 66 sliding member 
3b becomes smaller. 
FIG. 2(b) shows the contact state between the metal vibration member 2A and 
the nylon 66 sliding member 3b under steady state of, for example, 
100.degree. C., and the stress of the nylon sliding member 3b received 
from the metal vibration member 2A does not change, but only the flexural 
modulus of the nylon 66 sliding member 3b becomes smaller, whereby the 
amount of nylon 66 sliding member lowered relative to the metal vibration 
member 2A becomes greater. 
Under the contact state shown in FIG. 2(b), the shearing force which 
separates the cohesion has become also smaller because the flexural 
modulus of the nylon 66 sliding member 3b becomes smaller, but the 
frictional coefficient between the metal vibration member 2 and the nylon 
66 sliding member 3b has become greater because the sliding surface area 
becomes markedly greater, and consequently the frictional driving force 
becomes greater. 
FIG. 3 shows the time fluctuation of torque when the amplitude of the 
vibration member 2 of the vibration wave motor by use of the nylon 66 
sliding member 3b is made constant by a control circuit, and the 
rotational number is fixed at, for example, 100 rpm, and the torque on 
initiation of driving becomes greater with lapse of time, until indicating 
an equilibrium state after about 20 minutes, but also indicating 
generation of sudden abrupt torque down (see the arrowhead D) during the 
equilibrium state. 
The phenomenon of such torque fluctuation or abrupt torque down is seen in 
a thermoplastic resin sliding member having a glass transition point of 
the steady state temperature (for example, 100.degree. C.) of the sliding 
member 3b, and if the temperature dependency of the material physical 
properties such as flexural modulus, etc. is great, the torque fluctuation 
between initiation of driving and steady state is great, which is not 
desirable for the sliding member material. 
Also, if the modulus is further lowered and the amount of the sliding 
member 3b lowered relative to the vibration member 2 is increased, until 
lowered to reach 1/2 of the vibration wave of the vibration member 2, the 
frictional driving force will become unstable to generate suddenly abrupt 
torque down phenomenon, which becomes a vital problem to the motor. For 
prevention of such torque down phenomenon, the pressurizing force of the 
sliding surface contact can be also reduced, but by reduction of 
pressurizing force, the important motor performance, namely the rotational 
number at high torque region, will be lowered. 
If the melting point is 100.degree. C. or less, melting of the material 
occurs and therefore a material having such low melting point cannot be 
employed as the sliding member material as a matter of course. 
As the physical properties which are regarded as important in employing a 
synthetic resin member for a vibration wave motor, in addition to heat 
resistance, there are sliding characteristic, thermal conductivity, 
fatigue resistance, creep resistance, etc. 
As the sliding characteristic of a synthetic resin material as the sliding 
member material, abrasion resistance is important, and also the frictional 
coefficient value is also an important characteristic in the point of 
motor performance. 
Also, since thermal conductivity of a synthetic resin as the sliding member 
material is by far smaller than metals, and it is necessary to improve the 
characteristic so as to dissipate the local heat at the sliding portion, 
make the temperature distribution of the resin material distribution 
uniform and lower. 
Further, it is necessary to consider sufficiently the fatigue resistance 
and the creep resistance of a synthetic resin as the sliding member 
material in the points of life and performance of the sliding member. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide a vibration motor with 
little torque fluctuation. 
Another object of the present invention is to provide an abration resistant 
vibration motor. 
Still other objects of the present invention will be apparent from the 
detailed description given below.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1(a) and 1(b) are sectional view and front view of the principal part 
of the large output type vibration wave motor, wherein 1 is an 
electro-mechanical energy converting element polarized into a plurality of 
thin rings, for example, a piezoelectric element, which are secured 
concentrically with a heat-resistant epoxy type adhesive on a metal 
vibration member 2, which is shaped in a ring and has flexibility, such as 
stainless steel. 
The vibration member 2 is fixed on the casing of the vibration wave motor 
(not shown) in the vicinity of the central portion, and on the sliding 
surface which is the opposite surface to the surface where the 
piezoelectric element 1 is fixed, a plurality of comb-shaped grooves for 
accomodating large vibration amplitude are provided radially toward the 
axial center. 
3a is a ring-shaped support comprising a metal having high thermal 
conductivity such as aluminum alloy, etc. a ring-shaped sliding member 3b 
comprising a composite material of a thermoplastic resin is secured on the 
support 3a concentrically with a heat-resistant epoxy type adhesive 
material having a glass transition point of 100.degree. C. or higher 
movable member 3 is formed with these 3a, 3b, and the sliding surface of 
the sliding member 3b contacts the sliding surface of the vibration member 
2 under a pressure of a load of 9 kg concentrically by a means which is 
also not shown. 
In FIGS. 1(a) and 1(b), when frequency voltages different in phase from 
each other by 90.degree. are applied on the electrodes 1a and 1b subjected 
alternately to the polarization treatment in the thickness direction, a 
travelling vibration wave is generated in the circumferential direction at 
the vibration surface of the vibration member, and by the vibration wave, 
the movable member 3 in pressure contact with the surface of the vibration 
member 2 is rotated through the frictional force of the sliding surface 
between the vibration member 2 and the sliding member 3. 
The material of the vibration member 2 is an elastic material such as 36% 
nickel having particularly small thermal expansion coefficient (Invar) or 
a martensite type stainless steel having relatively smaller thermal 
expansion coefficient and small internal loss, etc. When the partner 
sliding member is a composite resin which is reinforced, the sliding 
surface is applied with the hardening treatment such as flame spraying of 
a super-hard material comprising tungsten carbide and cobalt or heat 
treatment. 
The material of the sliding member 3b is a thermoplastic resin having a 
glass transition point of 100.degree. C. or a composite resin thereof, 
including specifically natural materials such as amorphous resins such as 
polyether sulfone (PES), polyarylate (), polyether imide (PEI), 
polysulfone (PSF), polycarbonate (PC) and modified polyphenylene oxide 
(modified PPO), etc., crystalline resins such as polyether ether ketone 
(PEEK), polyphenylene sulfide (PPS) and special polyamide (PA), etc., the 
non-reinforcement type sliding materials comprising these filled with a 
fluorine resin such as PTFE, etc. as the lubricant, as well as the 
reinforced type sliding member materials comprising the above amorphous 
resins and the crystalline resins filled with carbon fibers and potassium 
titanate whisker or PTFE. 
Table 1 shows the thermoplastic resins and composite resins thereof and 
their thermal characteristics investigated as the sliding member material 
of the large output type vibration wave motor. 
TABLE 1 
__________________________________________________________________________ 
Glass Heat 
Transition 
Melting 
distortion 
Thermoplastic Filler point point 
temperature 
resin (wt %) (.degree.C.) 
(.degree.C.) 
(layer load .degree.C.) 
__________________________________________________________________________ 
Reference 
6 None 65 260 75 
example 
Examples 
1 PEEK None 143 334 152 
2 None 193 -- 175 
3 PES PTFE(5) 230 -- 203 
4 PEEK Carbon fiber(30) 
144 320 280 
5 " Carbon fiber(30) + 
144 320 280 
PTFE(5) 
6 " Potassium titanate whisker(30) + 
144 320 247 
PTFE(5) 
7 PES Carbon fiber(30) 
230 -- 217 
8 Special Carbon fiber(20) + 
125 320 285 
polyamide 
Potassium titanate 
whisker (20) 
9 Special Carbon fiber(20) + 
100 240 220 
Polyamide 
Potassium titanate 
whisker (20) 
__________________________________________________________________________ 
Reference, Examples 1 and 2 are natural materials, and Example 3 is a 
composite resin of an amorphous polyether sulfone (PES) filled with a 
fluorine resin (PTFE) as the lubricant. 
Examples 4 to 9 are the reinforced type composite resins, and as the 
thermoplastic resin, three kinds of an amorphous polyether sulfone (PES), 
a crystalline polyether ether ketone (PEEK) and a heat-resistant special 
polyamide resin are employed, and together with these, carbon fibers and 
potassium titanate whisker as the reinforcing fibers, and a fluorine resin 
(PTFE) as the lubricant were used. 
Filling of a reinforcing material is first for improvement of abrasion 
resistance of the resin material, and the filling amount for that purpose 
should be desirably as much as possible. However, for accomplishing 
successfully injection molding, the upper limit of the reinforcing 
material filled based on the thermoplastic resin is about 30% in terms of 
weight ratio. 
Accordingly, the amounts of the reinforcing fiber filled in Examples 4 to 9 
were made 30% in terms of weight ratio for single fiber and 40% for a 
mixture of carbon fiber and potassium titanate whisker. 
Filling of a fluorine resin is for improvement of lubricity of sliding, and 
the filling amount is not required to be made much, and it was made 
sufficiently about 5% in terms of weight ratio. 
Table 2 shows comparison of abrasion amount after a predetermined time (24 
hours), time fluctuation of torque, torque irregularity and torque down 
after motor driving, when ring sliding members with a thickness of 1 mm 
(see FIG. 1) are formed with thermoplastic resins or composite resins used 
in Reference example and Examples 1 to 9 shown in Table 1, and the large 
output type vibration wave motor when the pressurizing force is made 9 kg 
is driven under a constant vibration amplitude amount. 
TABLE 2 
__________________________________________________________________________ 
Torque 
Abrasion 
Fine irregula- 
Sliding member material 
Amount 
Fluctuation 
rity Torque down 
__________________________________________________________________________ 
Reference 
6 Medium 
Large Small 
" 
Example 
Example 1 
PEEK Large 
-- -- -- 
Example 2 
Large 
-- -- -- 
Example 3 
PES + PTFE(5) Medium 
Small Small 
Small 
Example 4 
PEEK + Carbon fiber(30) 
Small 
Small Medium 
Small 
Example 5 
PEEK + Carbon fiber(30) + 
Small 
Medium 
Medium 
Small 
PTFE(5) 
Example 6 
PEEK + Potassium titanate 
Small 
Medium 
Small 
Small 
whisker(30) + PTFE(5) 
Example 7 
PES + Carbon fiber(30) 
Small 
Small Small 
Small 
Example 8 
Special polyamide + Carbon 
Small 
Medium 
Small 
Small 
fiber(20) + Potassium 
titanate whisker(20) 
Example 9 
Special polyamide + Carbon 
Medium 
Medium 
Small 
Small 
fiber(20) + Potassium 
titanate whisker(20) 
__________________________________________________________________________ 
To observe first the abrasion of the sliding member under low load (300 
g-cm), since both the natural materials of Example 1 are large in abrasion 
amount, the tests under high load were impossible and intermitted. 
On the other hand, 6 of Reference example, Examples 3 and 9 exhibited 
moderate amounts of abrasion, and substantially no abrasion was seen in 
the reinforced type composite resin sliding members of other Examples. 
Next, torque fluctuation was examined under high load of 2.5 kg-cm, 6 of 
Reference example exhibited clearly time fluctuation during driving as 
mentioned above, with moderate torque irregularity (torque variance for a 
short time), and also the phenomenon of torque down was observed. 
In Example 3, there was little torque irregularity and no torque down was 
observed, but the output was considerably small. This is due to small 
frictional coefficient because abrasion resistance was attempted to be 
improved by filling of PTFE as the lubricant, and also due to small 
modulus because of no reinforcement. 
Of the reinforced type in Examples 4 to 9, in Examples 3 and 7 by use of a 
polyether sulfone (PES) which is an amorphous thermoplastic resin and 
excellent in creep resistance characteristic, both time fluctuation and 
torque irregularity were small. This is due to the high glass transition 
point of the polyether sulfone as 225.degree. C., and hence due to small 
temperature dependency of the physical properties such as flexural 
modulus, hardness, etc. 
Thus, during the time lapse from initiation of motor driving to the time 
when the sliding member temperature becomes, for example, 100.degree. C., 
the flexural modulus of the resin sliding member 3b is not lowered, and 
therefore the lowering amount of the sliding member 3b to the vibration 
wave of the vibration member is not increased and also there is no 
lowering in hardness, whereby there is no fluctuation in frictional 
coefficient and consequently no fluctuation in frictional driving force 
during large temperature elevation. 
Next, in Examples 4, 5 and 6 by use of a polyether ether ketone which is a 
crystalline thermoplastic resin and excellent in fatigue resistance 
characteristic, both time fluctuation and torque irregularity are 
relatively smaller, and also no torque down phenomenon is observed, thus 
exhibiting remarkable effects as the heat-resistant resin. The carbon 
fiber and the potassium titanate whisker used as the fillers had 
remarkable effects in aspect of abrasion resistance with reinforcement of 
physical properties such as strength, flexural modulus, etc. 
The carbon fiber as the filler has been expected to have improvement effect 
of fatigue resistance or creep resistance, and additionally, the effect of 
heat dissipation could be also observed due to excellent thermal 
conductivity. The potassium titanate of Example 6 has been expected to 
have the improvement effect of fatigue resistance or creep resistance 
similarly as the carbon fiber, and additionally there was obtained the 
result of small torque irregularity due to smooth sliding surface because 
of finer fibers and small orientation characteristic and also due to small 
variance of frictional coefficient because of uniform reinforcement. 
Examples 8 and 9 use a material of a special polyamide (aromatic polyamide) 
particularly excellent in heat resistance and inexpensive filled with 
carbon fiber and potassium titanate whisker, and torque irregularity, 
torque down were extremely small, but the tendency of reduction in torque 
on initiation of driving which was also observed in Example 6 was 
observed. In Examples 6, 8 and 9, in which potassium titanate was filled, 
heat generation at the motor portion was large to give low efficiency. It 
has been found that this is because of low thermal conductivity of the 
potassium titanate whisker, whereby heat generation by input and heat 
dissipation of sliding frictional heat are poor. Accordingly, since the 
potassium titanate whisker is an effective filler in the point of small 
variance in frictional coefficient because it is a fine fiber, it has been 
found the good results can be expected, if it is used in a small amount of 
30% or less in the carbon fiber, or a lubricant of high thermal 
conductivity such as graphite, etc. is used in combination. 
The vibration member 2 used in the above investigations is a martensite 
type stainless steel, with the frictional surface having a super-hard 
material comprising tungsten carbide and cobalt flame sprayed thereon, its 
frictional surface hardness is 800 to 1200 in terms of Vickers hardness 
and its surface roughness is 0.2 S to 0.6 S. Desirably, the frictional 
surface hardness was found to be about 1200 in terms of Vickers hardness, 
and further its surface roughness to be about 0.4 S. (See Japanese 
Industrial Standard, Definitions and Designations of Surface Roughness, 
JIS B 0601-1982 (reaffirmed: 1987), Section 3.4.3) 
When the above-mentioned martensite type stainless steel is subjected to 
heat treatment, the Vickers hardness becomes about 600, but if the 
vibration member made of such heat-treated stainless steel, the abrasion 
amount shown in Table 2 will be generally reduced, and at least all of the 
sliding member materials by use of the fillers in Examples are usable. 
As described above, by use of a thermoplastic resin having a glass 
transition point of 100.degree. C. or higher, the time fluctuation of 
torque is reduced and also the phenomenon of torque down is avoided. 
Also, by filling the carbon fiber at a ratio of 30% which is the upper 
limit capable of injection molding, it has been rendered possible to 
obtain higher abrasion resistance than is aimed at. 
Filling of carbon fiber is used for the purpose of making torque higher 
through improvement of modulus, or improving thermal conductivity, etc., 
but in another thermosetting resin, it has been confirmed that the 
increase of abrasion amount is very little in the case of the vibration 
member made of a stainless steel subjected to the heat treatment as 
mentioned above, even when the filling amount may be reduced from 30% to 
20% or 10%. 
On the other hand, in a composite resin filled with a mixture of 30% or 
less of carbon fiber in terms of weight ratio and 10% or less of potassium 
titanate whisker also in terms of weight ratio, there is a slight problem 
in the point of heat dissipation, but it has been found to be effective in 
the points of reduction of torque irregularity and performance improvement 
in the higher torque region. 
Further, additional filling of a fine fluorine resin of about 5% in terms 
of weight ratio has been found to form a film of the fluorine resin on the 
frictional surface of the vibration member, whereby improvement of 
lubricity can be expected. 
On the other hand, a composite resin comprising about 5% of a fluorine 
resin filled in a thermoplastic resin, although performance may be lowered 
in higher torque region, is effective in little torque irregularity, and 
it has been also found to be usable in a soft material such as phosphorus 
bronze material or a stainless steel material subjected to no heat 
treatment. 
As described above, by forming the sliding member of a composite resin of a 
thermoplastic resin having a glass transition point of 100.degree. C. or 
higher, the vibration wave motor suffers from lowering in flexural modulus 
to negligible extent during the time lapse from initiation of driving to 
the point when the sliding member temperature becomes steady state, 
whereby the amount that sliding member to lower into the vibration wave of 
the vibration member does not change, also without fluctuation of 
frictional coefficient, and therefore there is no fluctuation of 
frictional driving force after initiation of driving and hence no time 
fluctuation of motor torque. Also, no abrupt torque down after 
equilibrated state is observed, and a reliable vibration wave motor with 
stable torque characteristics could be obtained. Also, the sliding member 
of a composite resin comprising carbon fibers or potassium titanate 
whiskers filled as the reinforcing material alone or as a mixture in a 
thermoplastic resin having a glass transition point of 100.degree. C. or 
higher, and further a fluorine resin added as the lubricant therein gave 
the characteristics improved in aspect of abrasion resistance.