GB2197933A

GB2197933A - Roller structure

Info

Publication number: GB2197933A
Application number: GB8722833A
Authority: GB
Inventors: Shigeo Takahashi
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-09-30
Filing date: 1987-09-29
Publication date: 1988-06-02
Also published as: GB8722833D0; GB2197933B

Abstract

A miniature roller structure e.g. for guiding a tape in a video or tape recorder, comprises a shaft (15), a small roller (10) including an elastic rubber cylinder (11) and a sleeve (12), and a plurality of bearing balls (30). The sleeve (12) is integral with the inner periphery of the elastic rubber cylinder (11), and is mainly composed of polytetrafluoroethylene (fluoroplastics). The shaft (15) is fitted in the roller (10). The bearing balls (30) are fitted in a circumferential or annular groove (16) formed in the shaft (15). The bearing balls (30) are in rolling contact with the inner periphery of the roller sleeve (12) and the base of the groove (16) in the outer periphery of the shaft (15). The groove (16) is at a middle point between the opposite ends of the roller (10). The depth of the groove (16) is such that the bearing balls (30) protrude slightly from the groove, so that a slight gap is formed between the inner periphery of the roller (10) and the outer periphery of the shaft (15). The axes of the roller and shaft are thus slightly tiltable in relation to each other. In an alternative embodiment the groove 16 is formed in the inner periphery of the roller sleeve 12. <IMAGE>

Description

DESCRIPTION ROLLER STRUCTURE This invention relates to miniature roller structures, such as guide rollers and pinch rollers for guiding tapes in tape recorders and video recorders and also other small rollers used for guiding soft tapes and printer tapes of computers, word processors, etc.

Fig. 10 of the accompanying drawings shows a known small or miniature roller A, which may be used as a guide roller or a pinch roller for guiding magnetic tapes of a tape recorder or a video tape recorder. The miniature roller A consists of a light metal cylinder 1 and an elastic rubber layer 2 provided thereon. The light metal cylinder 1, which may be made of aluminium, is fitted on a shaft 3 via a super-small or miniature ball bearing 4 or a radial bearing. Oil seals 5 are provided on the opposite sides of ball bearing 4. The miniature roller A is automatically tiltable over a small range of about 10 or less with respect to the shaft 3.

Although a super-miniature ball bearing 4 of high precision has recently been manufactured by mass production, it does not meet user's requirement as to production costs. Further, because it is a type of radial bearing, it does not meet optitn#ti.ni requirements by users especially with respect to automatic tilt or self-aligning properties. The reason why the radial bearings are utilized in this field is only that they happen to provide an automatic tilting action although the action is achieved over a relatively narrow range.

Further, since the radial ball bearings require inner and outer races 6 and 7, it is impossible to reduce the outer diameter of such rollers, and therefore, it is impossible substantially to reduce the size of apparatus utilizing these ball bearings.

Recently, rollers using tetralfuori.de resins as bearing material have been announced. However, such rollers are incapable of automatic tilting because they are of the sliding journal type, and hence they cannot be used as small rollers of the said type exhibiting automatic tilting properties.

Further, with respect to the PV value and the coefficient of friction, materials having mechanical strength are liable to cause wear of the opposing member, and they also cause heat generation. (The PV value is the product of P and V, P being unit pressure of the shaft on the bearing that is obtained by dividing the load on the bearing by the projected bearing area; and V being the velocity of rubbing at the wear surface). Materials having a low coefficient of friction, on the other hand, have insufficient mechanical strength. Therefore, neither of such materials can be used advantageously as miniature rollers of the type noted above.

Particularly, rollers used for guiding video tapes in tape recorders have to meet strong demands for high speed rotation, capability of being used for a long time, light weight (use of aluminium shaft), freedom from lubrication, prevention of heat generation, low noise and low cost. Development of a small roller which can meet the above demands has been awaited in the pertinent art.

An object of the invention is to provide a miniature roller of simple construction, which may use fluoroplastics as a main material of the inner periphery of roller, makes use of character of slide bearing and has an automatic tilting effect.

The miniature roller structure of the invention comprises a miniature tiltable roller including an elastic rubber cylinder and a sleeve integral with the inner periphery of said elastic rubber cylinder and mainly composed of fluoroplastic, a shaft received in said roller, said shaft or said roller sleeve having a circumferential or annular groove, and a plurality of bearing balls fitted in said groove, such that they are in rolling contact with the inner periphery of said roller sleeve and the base of the groove in the shaft or with the outer periphery of said shaft and the base of the groove in the roller sleeve, said groove being located substantially at a middle point between the opposite ends of said roller, the depth of said groove being such that said bearing balls protrude slightly from said groove so that a slight gap is formed between the inner periphery of said roller and the outer periphery of said shaft, whereby the axes of said roller and shaft are slightly tiltable relative to each other.

With the above construction according to the invention, the roller and the shaft can tilt or rock slightly relative to each other over a range according to the gap dimension between them, about the row of bearing balls, and the roller can rotate about the shaft while they are undergoing instantaneous changes in their relative orientation.

With the above construction and effect, correspondingly to forces received externally by them, the roller and the shaft may be supported only by the row of bearing balls contacting with a mid portion of the inner periphery of the sleeve, or supported by both the bearing ball row and a portion of the inner periphery of the sleeve which is nearer either one of the two ends of the sleeve. This bearing ball row has the action of a roller bearing and also contributes to obtain an automatic tilting effect, while the opposite side sleeve portions have the action of a slide bearing.

Therefore, a great load is not applied solely to the bearing ball row, and wear of components is kept at a lower level. Further, since the circumferential or annular groove is provided mid way between the opposite ends of the roller, the tilting angle range is symmetrical on the opposite sides.

Further, since the roller consists of the elastic rubber cylinder and the sleeve formed directly on the inner side the.reof, it is simplified in construction and reduced in weight in comparison with the prior art roller, so that the roller is reduced to inertia.

Therefore, there can be provided a small roller suitable for using as a tape guide roller of a tape recorder, as noted abbve, which is required to frequently repeat operations of start, stop and reversal and also to be used continuously for long periods.

Further, as the roller can be reduced in size, it is best suited as a miniature roller of the said type.

Further, since the inner side of the roller is constituted by the sleeve having a low friction coefficient and a low wear coefficient, the roller will rotate smoothly and will not be worn partially.

Still further, the gap between the inner periphery of the sleeve and the outer periphery of the shaft can be chosen freely to obtain a required inclination angle of automatic tilting, because they may be moulded parts. Further, the groove, when formed in the sleeve, can be easily processed to obtain a desired depth prior to assembling according to the diameter of the bearing balls used. Thus, it is possible to ensure very high freedom of design and to reduce cost.

The invention will be further described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 is an enlarged-scale elevational view, partly in section, of a first embodiment of miniature roller in accordance with the invention; Fig. 2 is an elevational view showing a shaft in the embodiment of Fig. 1; Fig. 3 is an enlarged-scale elevational view, partly in section, showing a second embodiment of the invention, without a cage for the bearing balls; Fig. 4 is an enlarged-scale plan view showing a cage with bearing balls fitted therein; Fig. 5 is a plan view, partly in section, showing the cage; Fig. 6 is a side view showing the cage of Fig. 5; Fig. 7 is an enlarged-scale front view, partly in section, showing a third embodiment of the invention; Fig. 8 in an enlarged-scale front view, partly in section, showing a fourth embodiment of the invention;; Fig. 9 is a fragmentary view, partly in section, illustrating exaggeratively the roller of the embodiment of Fig. 8 in a tilted state; and Fig. 10 is an enlarged-scale front view, showing the prior art miniature roller described above.

The sleeve 12 used in the miniature roller 10 is composed of polytetrafluoroethylene (fluoroplastics) as main composition and incorporating special fillers.

Physical properties of the sleeve are shown in Table 1.

Table 1

Sample Physical Property Unit Sample No. 1 No. 2 Density lbs./ft.# 118.6 124.8 (kg/m') (1900) (1999) Hardness Durometer D 63 65 Tensible Strength lbs./in.2 995.4 346.3 (MPa) (6.863) (16.178) Tensible Elongation ( Ó) 100 200 Compressive Strength lbs./in.2 (MPa) 1 % deformation 1094.9 1166 (7.549) (8.04) 5 Ó deformation 3598 2744 (24.81) (18.92) 0.2 % offset 2503 1820 (17.26) (12.55) Compressive Elastic lbs./in.2 109494 116604 Modulus (MPa) (754.96) (803.98) The material used for sample No. 1 had the friction coefficient K; K = 1.4 x 10 11 (in.# 3 ~min)/(1b. ,ft.. hr.) 28 x 10-19 m2N-1 when the PV value was 28 x 10 lbs./in.2 . ft./min.

(0.35 kPa.ms -1),opposing member was an aluminium shaft made of ADC (Aluminium Die Casting)-12, and its hardness was HRC-22 (Hardness in Rockwell C-scale), and its surface roughness Rmax was 0.433 mil to 0.512 mil (11.00 jim to 13.00 jim).

On the other hand, the material used for sample No. 2 has coefficient friction of K; -12 K = 2.8 x 10 (in.'-min.)/(lb.ft.hr.) 5 6 lo~l9 2N-1 when the PV value was 84 x 10' lbs. ,in.2#ft./min.(2.9 kPa.

ms 1) and the opposing member was the same as that of sample No. 1.

However, it is sufficient for the coefficient of friction K to be less than 1.4 x 10-11 (in. .min.)/coefficient (lb..ft..hr.), when the PV value is 28 x 10' lbs./in. 2 sft./min.

As a material for the sleeve "Excelide 9550-No.5" or "9550-No. 7" of Ni chias Co., Ltd. meets the above requirements, but this material is by no means limitative, and any material may be used so long as the above requirements are met.

The coefficient of friction was calculated on the basis of an equation; K = (W)/(P.VTpS) where, W: Worn-out Weight (lbs.) P: Load on unit projected area of sample (lbs./in.2) V: Surface (Peripheral) Velocity (ft./min.) T: Time (hr.) P: Density of sample (lbs./in.') S: Projected area of sample (in.2) Embodiment 1 Figs. 1,2,4 and 6. illustrate a first embodiment.

A surface layer of the roller 10 is constituted by an elastic rubber cylinder 11. An inner layer of the roller 10 consists of a sleeve 12, which is mainly composed of polytetrafluoroethylene having the said physical properties and incorporating a special filler. The two members, namely the cylinder 11 and the sleeve 12, may be formed as respective one-piece mouldings and then subsequently made integral.

Alternatively, one of these members may be first formed by moulding, and then the other member may be formed by insert moulding method. The sleeve 12 has a uniform inner diameter over the entire length.

A shaft 15 has a circumferential or annular groove 16 on a.;niddle portion thereof, which is positioned at a middle point or mid-way between the opposite ends of the roller 10 when the shaft 15 is fitted in the roller 10. Bearing balls 30 are disposed in the groove 16 in a row. The row of bearing balls 30 is formed such that the bearing balls 30 are in rolling contact with the inner periphery of the roller 10 and with the bottom of the groove 16. The rolling surface 17 of the bottom of the groove 16 has an arcuate or U-shaped sectional shape, which has a radius equal to that of the bearing balls 30. The groove 16 has a width b which is greater than the diameter of the bearing balls 30.

The shaft 15 has a pair of tapered surface portions 18 which are formed at the opposite sides of the groove 16 and taper towards the opposite ends of the roller 10. The diameter of each tapered surface portion 18 becomes greater towards the groove 16 and becomes smaller towards the corresponding end of the roller 10. The angle 0between a generation line or generatrix 02 of the tapered surface portion 18 and the axis 0, of the shaft 15 may be about 0.50 to 150.

In the case of this embodiment, it is set within a range of 0.50 to 50. An imaginary extension of each tapered surface portion 18 touches the spherical surfaces of said bearing balls 30 or lies slightly inside such spherical surfaces.

The shaft 15 is provided with a pair of non-contact shaft portions 19 between the groove 16 and each tapered surface portion 18. The non-contact shaft portion 19 has a considerably smaller outer diameter than the inner diameter of the roller 10. The ratio between the axial length R, of tapered surface portion 18 and the axial length Q 2 of the non-contact shaft portion 19 may be about 1 : 5 to 5 : 1, and it is preferably 1 : 2 to 2 : 1.

Although the material of the shaft 15 is not limited, annealed steel or stainless steel is preferred in view of wear resistance and cost. Aluminium is partially suitable to reduce the shaft weight and to obtain a required heat radiation property. Brass and other materials may also be used.

Stainless steel balls, synthetic resin balls and ceramic balls are used as the bearing balls 30 suitably in dependence on the material and hardness of the shaft 15. Usually, balls having substantially the same hardness as the shaft 15 are used.

A cage or retainer 25 for holding the bearing balls 30 at a predetermined interval from one another in the groove 16 of the shaft 15 is of a ring-like form. The cage 25 is split or open in a direction at right angles to the axis thereof, so that it has opposite butt ends 26 which are connected to each other.

When no external force is applied to the cage 25, the radius R of curvature of its inner surface is substantially the same as the radius of the largest diameter portion of the shaft 15. When the butt ends 26 are connected to each other, the cage 25 forms a perfect ring. At this time, the inner diameter of the cage is greater than the diameter of the bottom of the groove 16 of the supporting shaft 15, and the outer diameter of the retainer 25 is smaller than the inner diameter of the roller 10. Ball-receiving holes 27 are radially formed in the cage in a circumferentially spaced relation to one another such that the bearing balls 30 can be supported at uniform angular intervals.

The material of the cage 25 is not limited so long as it has slightly elastic deformablity, low coefficient of friction, excellent heat resistance to the friction heat, and low coefficient of thermal expansion.

Polyamidoimed (PAI) resins of thermoplastic have been found to be suitable.

When the bearing balls 30 are inserted in the ball-receiving holes 27, they are capable of sliding rotation in the ball-receiving holes 27. The butt ends 26 of the cage are provided with a tenon 28 and a mortise 29 respectively, which can be interconnected by hooking with each other.

The upper end of the supporting shaft 15 is provided with a flange 20, and the lower end of the shaft 15 is provided with a flange 21, each flange having a diameter greater than the inner diameter of the roller 10 so that the roller 10 will be restrained vertically. The end surface of each of the flanges 20 and 21 facing on the end surface of the roller 10 has a second tapered surface 22 of an acute angle, which is formed at right angles to the generation line or generatrix 02 of the tapered surface portion 18. When the roller 10 is inclined or tilted, the ends of the roller 10 will not strike the flanges 20 and 21, but they are supported at the second tapered surfaces 22.

The flange 20 at one end of the shaft 15 is detachably mounted on the shaft 15 by a small bolt 23 screwed into the axis portion of the shaft 15.

In assembling the above components, the cage 25 is moved axially from one end of the shaft 15 up to the position of the groove 16 by increasing its diameter while making use of its elastic deformability. Then, the tenon 28 and the mortise 29 of the respective butt ends 26 of the cage 25 are hooked to each other in the groove 16 so as to obtain the cage 25 of a perfect ring-like form. Then, the roller 10 is gently fitted on the shaft 15 from the top end thereof up to a position, at which the roller 10 strikes the flange 21 integral with the shaft 15.

Then the other flange 20 is fitted on the top end of the shaft 15, and the small bolt 23 is screwed via a suitable washer 24, thus securing the flange 20 to the shaft 15.

In using the assembled roller as a tape guide roller of a video tape recorder, an angular stem 15a of the shaft 15 is secured to a particular position of the chasis of the video tape recorder.

Operation and Effects of Embodiment 1 When the miniature roller structure of this embodiment is used, the following operation and effects are obtained in addition.

Since the bearing balls 30 are held by the cage at predetermined angular intervals in the groove 16 of the shaft 15, they will never be brought into contact with one another. They will never be displaced in the groove 16 also in the width direction of the groove 16. Further, since the cage 25 is made of the material as noted above, even if the bearing balls 30 are in sliding contact with the bearing sleeve 12 and the supporting shaft 15, frictional resistance may be kept at a lower level, and hence, there is no possibility of impairing of mechanical characteristics, even if heat is generated of the contact portions on account of friction heat.

Further, since the second tapered surfaces 22 on the upper and lower shaft flanges 20 and 21 are formed such that their generatricesincline at right angles to those of the tapered surface portions 18, the ends of the sleeve 11 of the roller 10 are supported by the second tapered surfaces 22 with sliding on the generatrices of the second tapered surfaces 22.

Therefore, even if the roller 10 is tilted in relation to the supporting shaft 15, it does not cause any substantial increase in the frictional resistance.

Further, since the sleeve 12 made of the above material is fitted into the rubber cylinder 11 in order to constitute the inner periphery of the roller 10, the frictional coefficient is very low. Therefore, even if a tape running speed which is several times (i.e. 3 to 5 times) that of a known ordinary video tape recorder may be adopted, a sufficiently normal operation can be ensured for the permissible life period of the video tape.

Further, when annealed steel is used as the material for the shaft 15, the shaft 15 will not be worn at all. When aluminium is used for the shaft 15, satisfactory heat conduction can be obtained.

Therefore, no heat is retained or accummulated on the bearing balls 30 and the taper surface portions 18, and there is no possibility of thermal seizure at all.

The illustrated structure is enlarged in scale.

In the case of this embodiment, the actual length of the roller 10 is about 0.196 to 0.787 inch (4.89 to 19.99 mm) and the roller 10 has an inner diameter of 0.118 to 0.196 inch (3.00 to 4.98 mm) and an outer diameter of 0.196 to 0.393 inch (4.98 to 9.98 mm), and the bearing ball 30 has a diameter of 39.3 mil to 59 mil (1.00 to 1.50 mm) and the shaft has an outer diameter of 0.114 to 0.188 inch (2.90 to 4.78 mm) at the said non-contact shaft portion 19.

The miniature roller structure of the sizes noted above was actually rotated at a speed of 2,000 r.p.m. or more, but no phenomenonoccurred such as would cause thermal seizure or defective rotation.

Embodiment 2 Fig. 3 shows a second embodiment. In this embodiment, the cage 25' used in the first embodiment is omitted. Parts designated by the same reference numerals as those in the first embodiment are those having like operation and effect.

In this case, when the same sizes as in the first embodiment were selected, no actual troubles occured in use at a speed of 2,000 r.p.m. or below.

In each case of the embodiment 1 and the embodiment 2, since an actual contact surface velocity between a shaft and an inner periphery of a guide or pinch roller of a visual video tape recorder is relatively -l low, such as 11/8 ins./sec. to 2 inc./sec. (34.9 mm.s to 50.8 mm.s 1), and an acutal contact surface pressure therebetween is 1.98 lbs. to 3.09 lbs., the rotation speed of the roller is 140 r.p.m. to 204 r.p.m. when the inner diameter of the roller, for example is 2/16 inches (3.17 mm). This value is very low in comparison with the above permissable rotational speed, and hence it is well understood that the miniature roller structure of the invention has an adequate utility and usefulness.

Embodiment 3 Fig. 7 shows a third embodiment. In this embodiment, the taper surface portions 18 of the shaft 15 are omitted so that the shaft 15 has a uniform diameter except for the groove 16. The gap D between the outer periphery of the shaft 15 and the inner periphery of the roller 10 is set about A mil to 8 mil (0.10 to 0.20 mm) so that the roller 10 is tiltable by about 10 to either side with respect to the shaft 15.

In order that the roller 10 will not be detached from the shaft 15, a washer 37 is in contact with the end surface of the roller 10, and the washer 37 is held by a spring lip 36 which is fitted in an engagement groove 35 provided at the end of the shaft 15.

In Fig. 7, parts designated by the same reference numerals as those in the first embodiment are those having the same operation and effects as in the first embodiment.

A particular feature of isis embodiment is that the roller 10 is tiltable with respect to the shaft 15 in a range of about 10 until the end of the inner periphery of the roller 10 is brought into contact with the supporting shaft 15. In this embodiment, since the shaft 15 and inner periphery of the roller 10 are brought into contact with each other only at the opposite ends, the contact surface area is reduced so as to decrease loss by friction.

When operation has continued for a long time, the sleeve 12 constituting the inner periphery of the roller 10 becomes worn. A tapered surface 12a whose diameter increases towards the opposite ends of the roller is formed, as shown in Fig. 9, and the contact surface area is also increased, so that subsequent wear is reduced. In this way, when the sleeve 12 becomes worn, the tilting angle of the roller 10 with respect to the shaft 15 is increased, but this does not cause any adverse effect upon the operation of the roller.

Embodiment 4 Fig. 8 shows a fourth embodiment. A particular feature of this embodiment is that the inner periphery of the sleeve 12 is formed with a circumferential or annular groove 16 for receiving the bearing balls 30.

The sleeve 12 has a uniform inner diameter over the entire length except for the groove 16, and the shaft 15 has a uniform diameter over its entire working length.

The gap D is substantially of the same size as in the third embodiment. Parts designated by the same reference numerals as those in the other embodiments are those having the same operation and effects.

In this embodiment, since the shaft 15 is free from any groove 16, the shaft 15 may be more stout.

Therefore, in providing the same mechanical strength of the shaft 15 as in the other embodiments, the diameter of the shaft can be reduced. For the rest, the same effects as in the third embodiment can be obtained.

Claims

1. A miniature roller structure comprising a miniature tiltable roller including an elastic rubber cylinder and a sleeve integral with the inner periphery of said elastic rubber cylinder and mainly composed of fluoroplastics, a shaft received in said roller, said shaft or said roller sleeve having a circumferential or annular groove, and a plurality of bearing balls fitted in said groove such that they are in rolling contact with the inner periphery of said roller sleeve and the base of the groove in the shaft or with the outer periphery of said shaft and the base of the shaft groove in the roller sleeve, said groove being located substantially at a middle point between the opposite ends of said roller, the depth of said groove being such that said bearing balls protrude slightly from said groove so that a slight gap is formed between the inner periphery of said roller and the outer periphery of said shaft, whereby the axes of said roller and shaft are slightly tiltable relative to each other.

2. A miniature roller structure according to claim 1, wherein said groove is formed in the outer periphery of said shaft and said shaft has tapered surface portions at the opposite sides of said groove and adjacent to the opposite ends of said roller, said tapered surface portions each being tapered towards the end of the shaft, the imaginary extensions of said tapered surface portions touching or being slightly inside the surfaces of said bearing balls, portions of said shaft between said tapered surface portions and said groove being non-contact portions having a diameter incapable of contact with the inner periphery of said roller.

3. A miniature roller structure according to claim 2, wherein the length ratio between said tapered surface and non-contact portion is 1 : 5 to 5 : 1.

4. A miniature roller structure according to claim 2 or 3, wherein the angle between the generatrix of the tapered surface portion and the axis of said shaft is 0.50 to 150.

5. A miniature roller structure according to any of claims 1 to 4, wherein the coefficient of friction is 1.4 x 10-11 0.50 (in. .min.)/(lb.*ft.hr.) or below, preferably 2.8 x 10-12 (in.'.min.)/(lb.fta hr.) at a PV value of 84 x 10' lbs./in.2.ft./min., wherein said fluoroplastic sleeve mainly composed of polytetrafluoroethylene is fitted on an aluminium shaft of ADC-12, and its surface roughness Rmax is 0.433 to 0.512 mil, and its hardness is HRC-22 or below.

6. A miniature roller structure according to any of claims 1 to 4, wherein said shaft is made of annealed steel, aluminium, stainless steel or brass.

7. A miniature roller structure substantially as herein described with reference to and as illustrated in Figs. 1 to 9 of the accompanying drawings.