Speed reducer

A speed reducer in which a shaft for supporting a plurality of pinion gears is provided on the closed end of a cylindrical gear mounting plate having one end closed, a reduction gear in meshing engagement with the pinion gear is contained in the cylindrical gear mounting plate, a single stage speed reducing unit is constituted by the gear mounting plate, the pinion gear and the reduction gear, and the gear mounting plates of the respective stages are closely joined together, and the cylindrical inner peripheral surface of the gear mounting plate is formed with ribs for intercepting sounds produced by the meshing engagement between the gears.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a speed reducer for decelerating the rotation of 
the rotary shaft of a motor and obtaining a desired speed. 
2. An apparatus of the construction shown in FIG. 1 of the accompanying 
drawings is known as a speed reducer. The construction of FIG. 1 is such 
that a first spur gear 2 having a toothed portion 2A is fixed to the shaft 
1 of a motor, a second spur gear 6 supported by a case 4 and having a 
toothed portion 6A is in meshing engagement with the first spur gear and 
an output shaft 8 is fixed to the second spur gear. In the case of the 
above-described construction according to the prior art, the axis O.sub.1 
of the shaft of the motor and the axis O.sub.2 of the reduction output 
shaft are not coincident with each other, but have an amount of deviation 
therebetween and therefore, it has been difficult to transmit the 
revolution of the motor to the output shaft 8 without causing eccentricity 
and run-out. Further, in the above-described construction, the outer 
diameters of the spur gears which perform the speed reducing action are 
great and it has been difficult to incorporate such apparatus into 
instruments which are required to be compact. 
That is, in the conventional apparatus of FIG. 1, the distance between the 
shaft 1 of the motor and the axis of the output shaft 8 is determined by 
the mounted position of a motor case (not shown) and the speed reducing 
case 4 and the mounted position of the unshown bearing of the output shaft 
8, and adjustment of these mounted positions is accomplished as by 
adjustment of mounting holes and mounting screws, and attainment of 
accurate mounted positions has been difficult. Furthermore, because of the 
tolerance of the finish dimensions of parts, there has been more or less 
irregularity in the individual speed reducers. Therefore, when the 
revolution of the motor is to be transmittted to the drive shaft of an FA 
(factory automation) instrument, not shown, through the speed reducer, it 
has been difficult for the revolution of the motor to be smoothly 
transmitted to the drive shaft, and this has also seriously affected the 
performance of the FA instrument. 
Further, in the conventional speed reducer, where reduction gears are 
constructed in multistage to increase the reduction gear ratio, fastening 
means such as screws or caulking has been resorted to for the arrangement 
and coupling of the speed reducing units, and this has led to errors in 
the assembled position, which in turn has resulted in the lack of 
smoothness of the rotation transmitting portion. Also, if the number of 
stages of engagement between gears is increased to increase the reduction 
gear ratio, there are produced great sounds by the meshing engagement and 
rotation of the gears and thus, the conventional speed reducer has 
suffered from an undesirable problem as a speed reducer to be incorporated 
into a business machine. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to overcome the above-noted 
disadvantages and to provide a speed reducer in which the shaft of a motor 
and an output shaft are made coincident with each other, whereby the 
diametrical dimension of the apparatus can be reduced. 
It is another object of the present invention to provide a speed reducer in 
which the torque of the output shaft can be amplified as desired. 
It is still another object of the present invention to provide a speed 
reducer in which even if the number of speed reduction stages is made 
multiple and the number of meshing portions of gears is increased, the 
production of meshing and rotation sounds is minimized. 
It is yet still another object of the present invention to make the speed 
reducing portions into units and thereby eliminate the necessity of taking 
the trouble of coupling the speed reducing units even if the number of 
couplings of such units is increased. 
Other objects of the present invention will become apparent from the 
following detailed description of an embodiment thereof taken in 
conjunction with the accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
An embodiment of the present invention will hereinafter be described with 
reference to the drawings. 
Referring to FIG. 2 which is an exploded view of the essential portions of 
a speed reducer, reference numeral 10 designates a motor and reference 
character 10A denotes the rotary shaft of the motor. Reference numeral 12 
designates a pinion gear fixed to the motor shaft 10A. Reference numeral 
14 denotes a seat plate attached to the motor 10. The seat plate 14 is a 
plate for mounting on the motor 10 a speed reducer B which will be 
described later. The seat plate 14 is provided with several types of 
threaded holes 14a, 14b, . . . at a distance from the center position of 
the central through-hole 14A thereof so as to enable a speed reducer which 
will be described later to be mounted on different types of motors. 
Reference numeral 16 designates a first gear mounting plate in the form of 
a ring having a central through-hole 16A and pins 16a.sub.1, 16a.sub.2, 
16b.sub.1, 16b.sub.2, . . . . The pins 16a.sub.1 and 16a.sub.2 of the 
first gear mounting plate 16 are provided at 180.degree. opposite 
positions equidistant from the center of the through-hole 16A, and the 
other pins 16b.sub.1 and 16b.sub.2 are provided at 180.degree. opposite 
positions in a different diametrical direction from the pins 16a.sub.1 and 
16a.sub.2. These pins are for changing the mounted positions of 
intermediate gears to be described in conformity with the combination of 
the intermediate gears and reduction gears. Reference characters 
16c.sub.1, 16c.sub.2 and 16c.sub.3 denote bosses projected on the 
thick-walled portion 16d of the outer shell of the gear mounting plate 16 
in a direction parallel to the axis thereof. Each of these bosses and the 
thick-walled portion 16d are formed with a through-hole 16e. 
Reference characters 18A and 18B designate intermediate gears supported on 
the pins 16a.sub.1, 16a.sub.2, 16b.sub.1, 16b.sub.2, . . . of the first 
gear mounting plate and rotatable about said pins. Reference numeral 20 
denotes a first reduction gear which is a gear having an internal gear 
portion 20A in meshing engagement with the intermediate gears 18A and 18B 
and a spur gear portion 20B, as shown in FIGS. 3 and 4, said two gear 
portions being formed integrally with each other. 
The pinion gear 12, the intermediate gears 18A, 18B, the first gear 
mounting plate 16 and the first reduction gear 20 together constitute a 
first stage speed reducing unit. Reference numeral 24 designates a second 
gear mounting plate which, like the first gear mounting plate 16, has pins 
24a.sub.1 and 24a.sub.2, a through-hole 24A into which is inserted the 
spur gear portion 20B of the first reduction gear 20, bosses 24c.sub.1, 
24c.sub.2 and 24c.sub.3, thick-walled portions 24d, and a through-hole 
24e. Reference characters 26A and 26B denote second intermediate gears 
supported on the pins 24a.sub.1 and 24a.sub.2, respectively, of the second 
gear mounting plate. 
Reference numeral 28 designates a second reduction gear in meshing 
engagement with the second intermediate gears 26A and 26B and having an 
internal gear portion 28A and a spur gear portion 28B. The second gear 
mounting plate 24, the intermediate gears 26A, 26B and the second 
reduction gear 28 together constitute a second stage speed reducing unit. 
Third, fourth, . . . , sixth gear mounting plates 30, 32, 34, 36, 
intermediate gears 38A, 38B, 40A, 40B, 42A, 42B, 44A, 44B, and third 
stage, . . . , sixth stage reduction gears 46, 48, 50, 52 are combined 
together in succession. The toothed portion of the sixth stage reduction 
gear 52 has an internal gear 52A and does not have a spur gear portion. 
Reference numeral 54 denotes a hollow output shaft which is 
caulking-coupled to the sixth stage reduction gear 52. Reference numeral 
56 designates a case, and a sleeve bearing 56A is caulking-coupled to a 
disc-like case. 
Reference numeral 60 denotes a center pin for making the axes of the output 
shaft 54 and the reduction gears 20, 28, 46, 48, 50 coincident with one 
another. The center pin 60 is fitted to the central through-hole of each 
reduction gear and the center point 54A of the hollow shaft. 
The first gear mounting plate 16, the first reduction gear 20 and the 
intermediate gears 18A, 18B together constitute a first stage speed 
reducing unit, and the respective subsequent gear mounting plates, 
reduction gears and intermediate gears together constitute respective 
stage speed reducing units. 
In the speed reducer of the above-described construction, when the motor 
shaft 10A rotates, the first stage reduction gear ratio is the gear ratio 
of the pinion gear 12 and the internal teeth 20A of the first reduction 
gear 20, the second stage reduction gear ratio is the ratio of the number 
of teeth of the spur gear portion 20B of the first reduction gear 20 to 
the number of internal teeth 28A of the second reduction gear 28, and each 
of the subsequent stage reduction gear ratios is the ratio of the number 
of teeth of the spur gear of the preceding stage reduction gear to the 
number of internal teeth of the succeeding stage reduction gear. The 
reduction gear ratio of the output shaft 54 of the speed reducer B is the 
product of the reduction gear ratios of the respective stages. 
The rotation of the motor shaft is transmitted to the intermediate gears 
18A and 18B through the pinion gear 10A. The intermediate gears 18A and 
18B are rotated about the pins 16a.sub.1 and 16a.sub.2, respectively, of 
the first gear mounting plate 16, and the rotation thereof is transmitted 
to the first reduction gear 20. 
In the construction of the present embodiment, when the rotation is 
transmitted to each of the subsequent stage reduction gears through the 
intermediate gears supported on the pins of the gear mounting plate, the 
intermediate gears do not change their centers of rotation but are rotated 
at predetermined positions and therefore, transmission of the rotation can 
be changed and accomplished. 
The respective stage speed reducing units are serially arranged on the axis 
X.sub.1 -X.sub.2 of the output shaft 10A of the motor. 
Coupling of the respective stage speed reducing units is accomplished by 
ultrasonic welding. FIGS. 6A and 6B illustrate the ultrasonic welding. In 
FIG. 6A, a boss 32c.sub.1 provided on one end of the thick-walled portion 
32d of the outer shell of the fifth gear mounting plate 32 is engaged with 
an engagement hole 36e provided in the end surface opposite to the boss 
36c.sub.1 of the outer shell of the sixth gear mounting plate 36. The 
length of the boss 32c.sub.1 before welded has a welding allowance 32g 
relative to the depth of the engagement hole 36e. The bosses of the 
respective gear mounting plates are brought into engagement with the 
engagement hole and ultrasonic wave is applied in the directions of arrows 
A and B indicated in FIG. 5 and the bosses are pressed, whereby the tip 
end of each boss is welded to the seat surface of the engagement hole, as 
indicated by dotted line in FIG. 5. 
By this pressing and welding operation, the welding allowance of the boss 
is eliminated and the gear mounting plates are closely welded together. 
The case 56 and the sixth gear mounting plate 36 are caulking-coupled 
together by inserting the bosses 36c.sub.1, 36c.sub.2 and 36c.sub.3 of the 
gear mounting plate 36 into holes 56a, 56b and 56c, respectively, formed 
in the outer periphery of the case 56. 
Where the number of teeth of each intermediate gear and the number of 
internal teeth of each reduction gear and the number of teeth of the spur 
gear portion of each reduction gear are constant in the abovedescribed 
construction, the distance between each reference pitch circle a, b, c, d, 
. . . , e of the meshing portion of each toothed portion and the axis 
O.sub.1 -O.sub.2 of the output shaft is constant. Where the numbers of 
teeth of the toothed portions of the intermediate gears and the reduction 
gears are made to differ from one another in order to make the reduction 
gear ratio great, the gear diameters of the intermediate gears also differ 
from one another. Therefore, pins 16b.sub.1 and 16b.sub.2 or 16c.sub.1 and 
16c.sub.2 discrete and different in mounted position from the pins 
16a.sub.1 and 16a.sub.2 on which the intermediate gears are supported are 
provided on the gear mounting plate. By so providing a plurality of pins 
different in mounted position on the gear mounting plate, there can be 
provided a construction corresponding to the change of the reduction gear 
ratio. 
In the present embodiment, each of said gear mounting plates, the 
intermediate gears and the reduction gears may be formed of a resin 
material such as polylacetal resin to thereby reduce the weights of these 
members and reduce the noise during rotation. 
The sound insulation of the speed reducer of the construction as shown in 
FIGS. 2 to 6 will now be described with reference to FIGS. 7A and 7B. 
The gear mounting plates 16, 24, . . . , 36 each form a cylindrical shape 
having one end closed, and vertical projections or ribs 16h.sub.1, 
16h.sub.2, . . . , 16h.sub.n extending toward the axis X.sub.1 -X.sub.2 
are provided on the inner wall surface of the cylinder. Pinions 18A and 
18B supported on pins 16a.sub.1 and 16a.sub.2, respectively, are in 
meshing engagement with the internal teeth of the reduction gear and are 
further in meshing engagement with the toothed portion of the reduction 
gear and are thus rotated. The meshing portion of each gear is contained 
in the cylinder of the gear mounting plate and the open side of the gear 
mounting plate is closely joined to the next stage gear mounting plate and 
therefore, the mesh engagement of each gear is confined in a hermetically 
sealed chamber and the sound produced by the rotation of the meshing 
portions is reflected by the ribs 16h.sub.1, . . . , 16h.sub.n and thus, 
the volume of sound transmitted along the outer shell of the gear mounting 
plate and leaking outwardly is greatly reduced. 
As described above, according to the present invention, the rotary shaft of 
the motor can be made coincident with the axis of the output shaft of the 
speed reducer by a combination of the gear mounting plates, the 
intermediate gears and the reduction gears, whereby a driving output can 
be obtained, and this leads to the possibility of providing a speed 
reducer which is free of the rotational vibration, irregularity and 
run-out of the output shaft. 
Further, according to the present invention, any free reduction gear ratio 
can be obtained by providing a plurality of combinations of several sets 
(stages) of the gear mounting plates, the intermediate gears and the 
reduction gears and even if a set of these members is serially combined, 
the diametrical dimension of the entire speed reducer does not become 
great, and this is very convenient for the speed reducer to be 
incorporated into an FA instrument or a business instrument in which 
various units are crowded. 
Especially, according to the present invention, the gear mounting plates of 
the respective stage speed reducing units are made by synthetic resin 
molding and their bosses are engaged with and ultrasonically welded to the 
engagement holes and thus, the respective stage gear mounting plates are 
integrally coupled together, and as compared with the conventional 
coupling means using screws, adhesion or the like, this eliminates the 
misalignment and positional deviation during the coupling of the gear 
mounting plates and prevents the fastening portions from being loosened by 
aging and thus, the quality and assured accuracy of the product can be 
enhanced. 
Particularly, according to the present invention, the gear mounting plates 
are closely coupled together and the ribs for reflecting the sounds 
produced from the peripheral surfaces of the gear mounting plates by 
rotational meshing engagement therebetween are formed, whereby the 
transmission of the rotational sounds to the outside can be greatly 
reduced.