GB2185153A - Mounting arrangement for miniature rotary electric motor - Google Patents

Abstract

A rotary electric motor has a generally cup-shaped motor case 1 having a generally cylindrical side wall and a bottom 3. The bottom incorporates a bearing housing having an outer circumferential surface 4 for a bearing 11 which rotatably supports the rotor shaft. Both surfaces are hand finished and/or machined until the outer surface 3 of the bottom forms a surface which is essentially perpendicular to the axis of the shaft and the surface 4 is coaxial with the shaft 2. The invention can make use of conventional inexpensive mass-produced miniature electric motors to produce motors having a shaft 2, the axis of which makes an angle of 90 DEG +/- 6' to the outer surface 3 of the bottom of its casing, and which are thus acceptable for use as the drive unit of a compact disc unit. Preferably the surface 4 is within 0.02 mm concentric with the shaft 2. <IMAGE>

Description

SPECIFICATION Rotary electric motor This invention relates to rotary electric motors.

So-called "miniature" electric motors of the permanent magnet field type are widely employed in various pieces of electrical equipment as drive motors,forexample in gramophones, tape recorders and players, optical equipment, office equipment, and also for computer-related equipment.

More recently, the possibility of employing these miniature electric motors has been considered for compact disc drive units.

In order to achieve volume production at a sufficiently low price to be competitive in the world's markets, it is the general practice for miniature electric motors of the permanent magnet field typeforthem to have a generally cup-shaped motor case manufactured by drawing and stamping metal sheets.

Compact disc equipment require close tolerances in the mounting of any drive motor. This has made it necessa ryfor the Applicant company, as a major manufacturer of mass-produced electric motors of this kind,to subjectan entire production run to inspection, with a consequent sacrifice in overall efficiency, whereby to select those motors from any production run which would meet the aforementioned dimensional requirements. In an attempt to improve efficiency, the present Applicants have proposed to provide a conventional miniature electric motor with a spacer machined to a high accuracy, thereby enabl ingthestrictdimensional requirementstobe achieved.Both because of the need to manufacture spacers at all, and also because their manufacturing process involves considerably close tolerances, this proposal has resulted in increased production costs.

In the production and sale of miniature electric motors, it is the cost element which is paramount.

Thus, until the present invention, there has been no satisfactory solution to the problem of providing mass-produced, and thus inexpensive, miniature el ectricmotorsfordriving compactdiscunits.Thepre- sent invention has arisen from ourwork seeking to provide a solution to this problem.

In accordance with the present invention, there is provided a rotary electric motor having a generally cup-shaped motor case comprising a generallycylindrical sidewall and a bottom,the bottom incorporat ingabearing housingforabearingrotatablysup- porting the rotor shaft, the bearing having an outer circumferential surface,the said surface and also the outer surface of said bottom being hand finished and/or machined so that the said outer surface of the bottom forms a surface which is essentially per pendicularto the axis of the shaft.

The invention is hereinafter more particularly described by way of example only with reference to the single figure of the accompanying drawing which shows an embodiment of electric motor constructed in accordance with the present invention in side elevation, and partly in section, mounted upon a surface of a piece of external equipment.

The internal construction of the motor illustrated in the single figure ofthe accompanying drawing is essentially conventional. The motor has a generally cup-shaped motorcase 1 prnvideqwith a bottom surface 3, a central portion of which in effect forms a housing for a bearing 11 for the rotor shaft 2, which bearing housing has an outer circumferential surface 4. A second bearing 11 is mounted'in an end closure 9 for the otherwise open end of the motor case 1. The end closure 9 also mounts brush gear for the motor, insulated from the surface ofthe motor case 1 and the end closure 9 by means of an insulator 12.The brush gear comprises terminals 5 which extend ex ternally of the end closure for connection in an ex- ternal electric circuit and brushes 8 positioned to makecontactwith a commutator 10 mounted on the rotor shaft together with a rotor 7. Permanent magnets 6forming the statorare mounted on the interior surface of the side wall of the motor case 1.

Thus far, the motor illustrated in the single figure of the accompanying drawing is entirely conventional.

Thus, in orderto provide an embodiment of motor in accordance with the present invention, any of a broad variety of mass-produced electric motors (of which that illustrated is but one example) may be employed, such motor necessarily having a bearing such as bearing 11 mounted in the bottom of the motor case. The shaft 2 of such a conventional massproduced electric motor, whether in its finished or semi-finished state is then fitted to a jig and machined both on the outer bottom surface 3, which, as shown in the single figure of the accompanying drawing serves as a motor mounting surface, and on the outer circumferential surface 4 of the bearing housing. Such machining may be by way of cutting, or grinding and polishing. The alternative of hand finishing by similar processes is labour intensive and therefore not to be preferred.

The machining or hand finishing is continued until the perpendicularity ofthe bottom surface 3 to the axis of the shaft is within 900i 650 that the motor mounting surface 3 is essentially perpendicularto the axis of the shaft or, to put it anotherway,the axis of the shaft extends substantially exactly at 900 to the outer surface of the bottom of the motor case. The outer circumferential surface 4 of the bearing housing should be machined so that the concentricity between this circumferential surface and the axis of the shaft is within 0.02 mm. forthe miniature motorto be fully acceptable for use as the drive unit for a compact disc unit.

As can be seen from the singlefigure of the accompanying drawing, the motor is mounted to a su rface 13 of an external equipment such as a compact disc unit in which the motoristo be installed, by meansofscrews 14 which are received in respective threaded openings formed in the bottom surface of the motor case.

1. A rotary electric motor having a generally cupshaped motor case comprising agenerallycylindri- cal sidewall and a bottom, the bottom incorporating a bearing housing for a bearing rotatably supporting the rotor shaft, the bearing housing having an outer

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (4)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Rotary electric motor This invention relates to rotary electric motors. So-called "miniature" electric motors of the permanent magnet field type are widely employed in various pieces of electrical equipment as drive motors,forexample in gramophones, tape recorders and players, optical equipment, office equipment, and also for computer-related equipment. More recently, the possibility of employing these miniature electric motors has been considered for compact disc drive units. In order to achieve volume production at a sufficiently low price to be competitive in the world's markets, it is the general practice for miniature electric motors of the permanent magnet field typeforthem to have a generally cup-shaped motor case manufactured by drawing and stamping metal sheets. Compact disc equipment require close tolerances in the mounting of any drive motor. This has made it necessa ryfor the Applicant company, as a major manufacturer of mass-produced electric motors of this kind,to subjectan entire production run to inspection, with a consequent sacrifice in overall efficiency, whereby to select those motors from any production run which would meet the aforementioned dimensional requirements. In an attempt to improve efficiency, the present Applicants have proposed to provide a conventional miniature electric motor with a spacer machined to a high accuracy, thereby enabl ingthestrictdimensional requirementstobe achieved.Both because of the need to manufacture spacers at all, and also because their manufacturing process involves considerably close tolerances, this proposal has resulted in increased production costs. In the production and sale of miniature electric motors, it is the cost element which is paramount. Thus, until the present invention, there has been no satisfactory solution to the problem of providing mass-produced, and thus inexpensive, miniature el ectricmotorsfordriving compactdiscunits.Thepre- sent invention has arisen from ourwork seeking to provide a solution to this problem. In accordance with the present invention, there is provided a rotary electric motor having a generally cup-shaped motor case comprising a generallycylindrical sidewall and a bottom,the bottom incorporat ingabearing housingforabearingrotatablysup- porting the rotor shaft, the bearing having an outer circumferential surface,the said surface and also the outer surface of said bottom being hand finished and/or machined so that the said outer surface of the bottom forms a surface which is essentially per pendicularto the axis of the shaft. The invention is hereinafter more particularly described by way of example only with reference to the single figure of the accompanying drawing which shows an embodiment of electric motor constructed in accordance with the present invention in side elevation, and partly in section, mounted upon a surface of a piece of external equipment. The internal construction of the motor illustrated in the single figure ofthe accompanying drawing is essentially conventional. The motor has a generally cup-shaped motorcase 1 prnvideqwith a bottom surface 3, a central portion of which in effect forms a housing for a bearing 11 for the rotor shaft 2, which bearing housing has an outer circumferential surface 4. A second bearing 11 is mounted'in an end closure 9 for the otherwise open end of the motor case 1. The end closure 9 also mounts brush gear for the motor, insulated from the surface ofthe motor case 1 and the end closure 9 by means of an insulator 12.The brush gear comprises terminals 5 which extend ex ternally of the end closure for connection in an ex- ternal electric circuit and brushes 8 positioned to makecontactwith a commutator 10 mounted on the rotor shaft together with a rotor 7. Permanent magnets 6forming the statorare mounted on the interior surface of the side wall of the motor case 1. Thus far, the motor illustrated in the single figure of the accompanying drawing is entirely conventional. Thus, in orderto provide an embodiment of motor in accordance with the present invention, any of a broad variety of mass-produced electric motors (of which that illustrated is but one example) may be employed, such motor necessarily having a bearing such as bearing 11 mounted in the bottom of the motor case. The shaft 2 of such a conventional massproduced electric motor, whether in its finished or semi-finished state is then fitted to a jig and machined both on the outer bottom surface 3, which, as shown in the single figure of the accompanying drawing serves as a motor mounting surface, and on the outer circumferential surface 4 of the bearing housing. Such machining may be by way of cutting, or grinding and polishing. The alternative of hand finishing by similar processes is labour intensive and therefore not to be preferred. The machining or hand finishing is continued until the perpendicularity ofthe bottom surface 3 to the axis of the shaft is within 900i 650 that the motor mounting surface 3 is essentially perpendicularto the axis of the shaft or, to put it anotherway,the axis of the shaft extends substantially exactly at 900 to the outer surface of the bottom of the motor case. The outer circumferential surface 4 of the bearing housing should be machined so that the concentricity between this circumferential surface and the axis of the shaft is within 0.02 mm. forthe miniature motorto be fully acceptable for use as the drive unit for a compact disc unit. As can be seen from the singlefigure of the accompanying drawing, the motor is mounted to a su rface 13 of an external equipment such as a compact disc unit in which the motoristo be installed, by meansofscrews 14 which are received in respective threaded openings formed in the bottom surface of the motor case. CLAIMS

1. A rotary electric motor having a generally cupshaped motor case comprising agenerallycylindri- cal sidewall and a bottom, the bottom incorporating a bearing housing for a bearing rotatably supporting the rotor shaft, the bearing housing having an outer circumferential surface,tbe said surface and also the outer surface of said bottom being hand finished and/or machined so that the said outer surface ofthe bottom forms a surface which is essentially perpendicularto the axis ofthe shaft.

2. A motor according to Claim 1, wherein the said outer bottom surface has at least one threaded opening therein for receiving a screw.

3. A motor according to Claim 1 or Claim 2, wherein the said outer bottom surface is machined bybeingturned on the axis of said shaft.

4. A rotary electric motor substantially as hereinbefore described with reference to and as shown in the accompanying drawing.