Rotating speed detecting device of a rotary type electrostatic spray painting device

A rotating speed detecting device of a rotary type electrostatic spray painting device comprising an annular permanent magnet fixed onto the rotary shaft of the spray painting device, and a detecting head mounted on the housing of the spray painting device. The detecting head has an induction coil enclosed by electrically insulating material.

BACKGROUND OF THE INVENTION 
The present invention relates to a rotating speed detecting device of a 
rotary type electrostatic spray painting device. 
The speed of rotation of a rotary shaft is normally detected by sensing a 
change in the reluctance of a magnetic circuit which is formed between an 
electromagnetic pick-up and a nut screwed onto the rotary shaft, or 
between an electromagnetic pick-up and a spacer fixed onto the rotary 
shaft. The sensing function is performed by the electromagnetic pick-up. 
However, it is necessary in such known systems to arrange the 
electromagnetic pick-up at a position near the nut or the spacer. 
Consequently, situations where a large space cannot be provided around the 
rotary shaft, such as in a rotary type electrostatic spray painting 
device, it is difficult to detect the rotating speed of a rotary shaft by 
using such an electromagnetic pick-up. In addition, in order to use an 
electromagnetic pick-up in a rotary type electrostatic spray painting 
device to which a negative high voltage is applied, it is necessary to 
enclose the electromagnetic pick-up with an electrical insulating material 
so that the negative high voltage does not have an adverse effect on the 
output signal. However, enclosing the electromagnetic pick-up causes its 
size to become even larger. Consequently, it is difficult to arrange an 
electromagnetic pick-up at a position near the rotary shaft of a rotary 
type electrostatic spray painting device, and it is therefore difficult to 
detect the rotating speed of the rotary shaft by using such a conventional 
electromagnetic pick-up. 
It is, therefore, an object of the present invention is to provide a 
rotating speed detecting device which is suited for a rotary type 
electrostatic spray painting device to which a negative high voltage is 
applied. 
SUMMARY OF THE INVENTION 
According to the present invention, a rotating speed detecting device for a 
rotary type electrostatic spray painting device of the type having a 
housing and a rotary shaft arranged in said housing is provided with an 
annular permanent magnet which is fixed onto the rotary shaft and arranged 
coaxially with a rotation axis therefore. A detecting head which is 
mounted on the housing is arranged to be radially spaced from the rotary 
shaft, and contains an induction coil enclosed by electrically insulating 
material. The induction coil produces an output signal which corresponds 
to the rotating speed of the rotary shaft. 
The present invention may be more fully understood from the detailed 
description of a preferred embodiment of the invention, set forth below, 
together with the accompanying drawings.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
Referring to FIG. 1, a rotary type electrostatic spray painting device, 
generally designated by reference numeral 1, comprises a generally hollow 
cylindrical front housing 2 made of metallic material, and a generally 
hollow cylindrical rear housing 3 made of metallic material. The front 
housing 2 and the rear housing 3 are firmly joined to each other by bolts 
4. A support rod 6, made of electrical insulating material, is fitted into 
a cylindrical hole 5 formed in the rear housing 3, and this rear housing 3 
is fixed onto the support rod 6 by bolts 70. The support rod 6 is 
supported by a base (not shown). A rotary shaft 8 is inserted into the 
front housing 2. This rotary shaft 8 comprises a hollow cylindrical 
portion 8a located in the middle thereof, a shaft portion 8b formed in one 
piece on the front end of the hollow cylindrical portion 8a, and a shaft 
portion 8c fixed onto the rear end of the hollow cylindrical portion 8a. A 
spray head 9 made of metallic material is fixed onto the shaft portion 8b 
of the rotary shaft 8 by a nut 10. The spray head 9 comprises a spray head 
supporting member 12 forming therein an annular space 11, and a cup shaped 
spray head body 13 fixed onto the spray head supporting member 12. As 
illustrated in FIGS. 1 and 2, a plurality of paint outflow bores 16, each 
opening into the annular space 11 and being smoothly connected to an inner 
wall 15 of the spray head body 13, is formed in an outer cylindrical 
portion 14 of the spray head supporting member 12. As illustrated in FIG. 
1, an end plate 17 is fixed onto the front end of the front housing 2, and 
a paint injector 18 is mounted on the end plate 17. The paint injector 18 
is connected to a paint reservoir 20 via a paint feed pump 19, and a 
nozzle 21 of the paint injector 18 is directed to the cylindrical inner 
wall of the outer cylindrical portion 14 of the spray head supporting 
member 12. 
A pair of non-contact type tilting pad radial air bearings 22 and 23 is 
arranged in the front housing 2, and the rotary shaft 8 is rotatably 
supported on the front housing 2 via a pair of the tilting pad radial air 
bearings 22 and 23. Both the tilting pad radial air bearings 22 and 23 
have the same construction and, therefore, the construction of only the 
tilting pad radial air bearing 22 will be hereinafter described. Referring 
to FIGS. 1 and 3, the tilting pad radial air bearing 22 comprises three 
pads 24, 25, 26 arranged to be spaced from the outer circumferential wall 
of the hollow cylindrical portion 8a of the rotary shaft 8 by an extremely 
small distance, and three support pins 27, 28, 29 supporting the pads 24, 
25, 26, respectively. Spherical tips 30, 31, 32 are formed in one piece on 
the inner ends of the support pins 27, 28, 29, and are in engagement with 
spherical recesses formed on the rear faces of the pads 24, 25, 26, 
respectively. Consequently, the pads 24, 25, 26 can swing about the 
corresponding spherical tips 30, 31, 32, each functioning as a fulcrum. A 
bearing support frame 33 is fixed onto the outer circumferential wall of 
the front housing 2 by means of, for example, bolts (not shown), and the 
support pins 28, 29 are fixed onto the bearing support frame 33 by means 
of nuts 34, 35, respectively. In addition, one end of a support arm 36 
having a resilient plate shaped portion 36a is fixed onto the bearing 
support frame 33 by means of a bolt 37, and the other end of the support 
arm 36 is fixed onto the support pin 27 by means of a nut 38. 
Consequently, the pad 24 is urged onto the hollow cylindrical portion 8a 
of the rotary shaft 8 due to the resilient force of the support arm 36. 
In the tilting pad radial air bearings 22, 23, when the rotary shaft 8 is 
rotated, ambient air is sucked into the extremely small clearances formed 
between the hollow cylindrical portion 8a and the pads 24, 25, 26. Then, 
the air thus sucked is compressed between the hollow cylindrical portion 
8a and the pads 24, 25, 26 due to a so-called "wedge effect" of air, and 
therefore, the pressure of the air between the hollow cylindrical portion 
8a and the pads 24, 25, 26 is increased. As a result of this, the force 
which radially supports the rotary shaft 8 is generated between the hollow 
cylindrical portion 8a and the pads 24, 25, 26. 
Turning to FIG. 1, a pair of disc shaped runners 39, 40 is inserted into 
the shaft portion 8c of the rotary shaft 8 and fixed onto the shaft 
portion 8c via a spacer 41 and a turbine wheel 42 by means of a nut 43. A 
stationary annular plate 44 is arranged between the runners 39 and 40, and 
the runners 39, 40 and the annular plate 44 construct a non-contact type 
thrust air bearing. As illustrated in FIG. 1, each of the runners 39, 40 
is arranged to be spaced from the annular plate 44 by a slight distance. 
The annular plate 44 is fixed onto the front housing 2 via a pair of 
O-rings 45, 46. As illustrated in FIGS. 1 and 4, an annular groove 47, 
extending along the outer circumferential wall of the annular plate 44, is 
formed on the inner wall of the front housing 2 and connected to an air 
feed pump 49 via a compressed air supply hole 48 which is formed in the 
front housing 2. A plurality of air passages 50, each extending radially 
inwardly from the annular groove 47, is formed in the annular plate 44. In 
addition, a plurality of air outflow bores 51, each extending towards the 
runner 40 from the inner end portion of the corresponding air passage 50, 
is formed in the annular plate 44, and a plurality of air outflow bores 
52, each extending towards the runner 39 from the inner end portion of the 
corresponding air passage 50, is formed in the annular plate 44. In this 
thrust air bearing, compressed air is fed into the air passages 50 from 
the air feed pumps 49 via the annular groove 47. Then, the compressed air 
is injected from the air outflow bores 51 into the clearance between the 
annular plate 44 and the runner 40 and also injected from the air outflow 
bores 52 into the clearance between the annular plate 44 and the runner 
39. As a result of this, the pressure, which is necessary to maintain the 
above-mentioned clearances formed on each side of the annular plate 44, is 
generated between the annular plate 44 and the runners 39, 40. 
As illustrated in FIG. 1, a turbine nozzle holder 53 is fixed onto the 
front housing 2 at a position adjacent to the annular plate 44, and an 
annular air supply chamber 54 is formed between the turbine nozzle holder 
53 and the front housing 2. The air supply chamber 54 is connected to a 
compressor 56 via a compressed air supply hole 55. The air supply chamber 
54 comprises a compressed air injecting nozzle 57 having a plurality of 
guide vanes (not shown), and turbine blades 58 of the turbine wheel 42 are 
arranged to face the compressed air injecting nozzle 57. A housing 
interior chamber 59, in which the turbine wheel 42 is arranged, is 
connected to the atmosphere via a discharge hole 60 which is formed in the 
rear housing 3. The compressed air fed into the air supply chamber 54 from 
the compressor 56 is injected into the housing interior chamber 59 via the 
compressed air injecting nozzle 57. At this time, the compressed air 
injected from the injecting nozzle 57 provides the rotational force for 
the turbine wheel 42 and, thus, the rotary shaft 8 is rotated at a high 
speed. Then, the compressed air injected from the injecting nozzle 57 is 
discharged to the atmosphere via the discharge hole 60. 
A through-hole 62 is formed on an end wall 61 of the rear housing 3, which 
defines the housing interior chamber 59, and an electrode holder 63 
extending through the through hole 62 is fixed onto the end wall 61 by 
means of bolts 64. A cylindrical hole 65 is formed coaxially with the 
rotation axis of the rotary shaft 8 in the electrode holder 63, and a 
cylindrical electrode 66, made of wear resisting materials such as carbon, 
is inserted into the cylindrical hole 65 so as to be movable therein. In 
addition, a compression spring 67 is inserted between the electrode 66 and 
the electrode holder 63 so that the tip face 68 of the electrode 66 is 
urged onto the end face of the shaft portion 8c of the rotary shaft 8 due 
to the spring force of the compression spring 67. An external terminal 69 
is fixed onto the outer wall of the rear housing 3 by means of bolts 70 
and connected to a high voltage generator 71 used for generating a 
negative high voltage ranging from -60 kV to -90 kV. Consequently, the 
negative high voltage is applied to both the front housing 2 and the rear 
housing 3, and it is also applied to the spray head 9 via the electrode 66 
and the rotary shaft 8. 
In operation, paint is injected from the nozzle 21 of the paint injector 18 
onto the circumferential inner wall of the outer cylindrical portion 14 of 
the spray head supporting member 12. Then, the paint, injected onto the 
circumferential inner wall of the outer cylindrical portion 14, flows out 
onto the inner wall 15 of the spray head body 13 via the paint outflow 
bores 16 due to the centrifugal force caused by the rotation of the spray 
head 9. After this, the paint spreads on the inner wall 15 of the spray 
head body 13 and flows on the inner wall 15 in the form of a thin film. 
Then, the paint reaches the tip 13a of the spray head body 13. As 
mentioned previously, a negative high voltage is applied to the spray head 
9. Consequently, when the paint is sprayed from the tip 13a of the spray 
head body 13 in the form of fine particles, the particles of the sprayed 
paint are charged with electrons. Since the surface to be painted is 
normally grounded, the paint particles charged with electrons are 
attracted towards the surface to be painted due to electrical force and, 
thus, the surface to be painted is painted. 
Referring to FIGS. 1 and 5, the spacer 41, inserted between the turbine 
wheel 42 and the runner 40, has an annular flange portion 41a, and an 
annular permanent magnet 73 is fitted into an annular groove 72 formed on 
the annular flange portion 41a. As illustrated in FIG. 6, the annular 
permanent magnet 73 is magnetized in the direction illustrated by the 
arrow A. Consequently, in FIG. 6, the polarity of the upper portion of the 
annular permanent magnet 73 is "N", and the polarity of the lower portion 
of the annular permanent magnet 73 is "S". As illustrated in FIG. 1, a 
cylindrical bore 74 is formed on the front housing 2 at a position located 
above the annular permanent magnet 73, and a rotating speed detecting head 
75 is fitted into the cylindrical bore 74. The detecting head 74 has an 
annular flange 75a formed in one piece thereon, and the annular flange 75a 
is secured onto the front housing 2 by means of a nut 76. 
As illustrated in FIG. 7, the detecting head 75 comprises a body 77 made of 
an electrical insulating material, such as hard polyvinyl chloride, a 
bobbin 78 made of magnetic material, an electrical wire 80 wound around 
the bobbin 78 for forming an induction coil 79, and a pair of external 
terminals 81, 82. One end of the wire 80, wound around the bobbin 78, is 
connected to the external terminal 81, and the other end of the wire 80 is 
connected to the external terminal 82. As illustrated in FIG. 1, the 
external terminals 81 and 82 are connected to a frequency detector 85 via 
leads 83 and 84, respectively. When the rotary shaft 8 rotates and, 
accordingly, the annular permanent magnet 73 rotates, a rotating field 
generates around the permanent magnet 73. The generation of the rotating 
field causes the induction coil 79 to generate an induced electromotive 
force and, as a result, a sinusoidal voltage, having a frequency which is 
proportional to the rotating speed of the rotary shaft 8, is produced 
between the external terminals 81 and 82. This sinusoidal voltage is 
applied to the frequency detector 85 and, thus, the rotating speed can be 
detected. 
As mentioned above, since the rotating field, generated by the annular 
permanent magnet 73, is detected by the detecting head 75, the spacer 41, 
the turbine nozzle holder 53 and the front housing 2, which are arranged 
around the annular permanent magnet 73, are formed of non-magnetic 
metallic material so that they do not shield the rotating field. In 
addition, as mentioned above, a negative high voltage of -60 KV to -90 KV 
is applied to the front housing 2. Therefore, the body 77 has a thickness 
of about 5 mm to 15 mm so that the negative high voltage does not 
influence the induction coil 79 within the detecting head 75. However, 
since the detecting head 75 is formed by directly covering the bobbin 78, 
having a small size, by the body 77 made of electrical insulating 
material, the size of the detecting head 75 becomes rather small. 
According to the present invention, since the detecting head detects the 
rotating field generated by the permanent magnet, it is not necessary to 
arrange the detecting head at a position near the rotary shaft for 
detecting the rotating speed of the rotary shaft. Consequently, the 
detecting head according to the present invention is suited for a rotary 
type electrostatic spray painting device in which a large space is not 
present around the rotary shaft. In addition, in a rotary type 
electrostatic spray painting device, in the case wherein the detecting 
head is attached to the housing of the device, it is necessary to insulate 
the detecting head from the housing of the device. However, in the present 
invention, since the detecting head has such a construction that an 
induction coil, having a small size, is directly covered by electrical 
insulating material, the size of the detecting head becomes rather small 
and, thus, there is an advantage that the detecting head can be easily 
attached to the housing of a spray painting device. 
While the invention has been described by reference to a specific 
embodiment chosen for purposes of illustration, it should be apparent that 
numerous modifications could be made thereto by those skilled in the art 
without departing from the spirit and scope of the invention.