GB1593164A

GB1593164A - Electro magnetic spring clutch

Info

Publication number: GB1593164A
Application number: GB5165377A
Authority: GB
Original assignee: Reell Precision Manufacturing Corp; Reell Precision Manufacturing
Current assignee: Reell Precision Manufacturing Corp; Reell Precision Manufacturing
Priority date: 1976-12-13
Filing date: 1977-12-12
Publication date: 1981-07-15
Also published as: DE2753012B2; JPS5550211B2; DE2753012C3; FR2373717A1; JPS5374657A; FR2373717B1; NL7713732A; NL179940B; DE2753012A1; NL179940C

Description

(54) ELECTRO MAGNETIC SPRING CLUTCH (71) We, REELL PRECISION MANUFAC TURING CORPORATION, a corporation organised and existing under the laws of the State of Minnesota, United States of America, of 1939 West County Road B-2, Saint Paul, Minnesota 55113, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to electromagnetically actuated spring clutches wherein a helical torque-transmitting clutch spring carried by a rotating hub is caused to wrap down onto an axially adjacent hub by means of an applied magnetic field. Such clutches are useful in the controlled intermittent operation of numerous mechanical devices, e.g. printing or copying machines and other paper feed devices.

One method of operation of helical spring clutches, as shown for example in U.S. Patent No. 3,926,286, involves releasing the spring from its initially driving contact with the input hub by means of an exterior floating sleeve which contacts the free end of the spring. Stopping the rotation of the sleeve expands or unwraps the spring so that torque is no longer transmitted to the output hub.

Analogous systems in which the action of the sleeve is employed to initiate wrapdown rather than release of the spring are also known. One such device, in which actuation of the sleeve is accomplished electromagnetically, is shown in U.S. Patent No. 3,185,276.

In this device the magnetic attraction between fixed and rotative components is applied axially between the poles of the fixed electromagnet and a radially extended end of the rotative control sleeve. As a result, frictional drag is introduced between fixed and rotating components, resulting in decreased efficiency and in eventual frictional wear.

It has now been found possible to reduce drag and wear, increase efficiency, and at the same time simplify and otherwise improve the structure of small electromagnetically actuated spring clutch mechanisms, by employing as the spring control element a ferromagnetic ring mounted directly adjacent and attached to the free end coil of the helical spring, and by applying the magnetic flux radially between fixed and rotative components. Accordingly, the present invention provides an electromagetically actuatable spring clutch comprising first and second substantially coaxial hubs; a helical spring carried by the first hub and overlying an end portion of the second hub; a rotatable ferromagnetic control first ring slidably supported axially adjacent and in torquetransmitting association with the free end of the spring around the second hub; a ferromagnetic second ring mounted on the second hub and fixedly supported axially adjacent the first ring, and opposing nonrotatable polepiece means for directing peripherally angularly balanced magnetic lines of flux directly to the first and second rings in a direction radially of the rings to apply a braking force to the free end of the spring to contract the spring around the second hub. Normally, the hubs are both mounted on a common shaft, the first hub being rotatably mounted and the second hub being fixedly mounted.

Other features of the invention will become apparent from the following description, by way of example, of embodiments thereof, in which reference will be made to the accompanying drawings wherein: Figure 1 is a sectional side elevation of an electromagnetic spring clutch in accordance with the invention; Figure 2 is an end elevation, showing four quadrants sectioned as indicated in Figure 1; and Figure 3 is a sectional detail view showing a portion of a modified structure.

In the embodiment shown in Figures 1 and 2, the magnetic clutch 10 comprises a tubular shaft 11, a fixed hub assembly 12, a coaxially disposed hub 13, a helical clutch spring 14 affixed to hub 13 and overlying a portion of hub assembly 12, a control ring 15, and an annular electromagnet assembly 16.

The tubular shaft 11 is provided with a keyway 17 for use in keying to a shaft, not shown, which is to be inserted within the shaft 11 for receiving torque therefrom.

The fixed hub assembly 12 is shown to consist of an inner tubular barrel 18 having a cylindrical outer surface 19, and a radially extending ferromagnetic ring 20, the two being fitted tightly together. The two-piece structure provides for convenience in manufacture and makes possible the use of nonmagnetic material for the barrel component which magnetically isolates the control ring 15 and the ferromagnetic ring 20 from the shaft 11. Less desirably, the two may be combined in a unitary ferromagnetic structure. The ring portion is undercut at the inner edge 21 as shown, providing a relief void. The hub assembly is tightly affixed on the shaft 11, either by keying or preferably by a press fit.

Hub 13, which desirably is non-ferromagnetic, is rotatable about the shaft 11 and against the end of barrel 18. It has a cylindrical surface 22 equal in diameter to that of surface 19 of the barrel 18, which surface 22 carries a portion of the helical clutch spring 14 tightly wound thereon. The remainder of the spring is normally of slightly greater diameter so as to be freely rotatable about the barrel 18. Alternatively, the spring may have a constant diameter, the diameter of hub surface 22 then being appropriately increased to provide for the required tight fit. The free portion of the spring terminates in an axially extending tang 23 which fits into an opening 24 provided in the side of the control ring 15.

The ring 15 fits closely but rotatably about the cylindrical surface 19 of the hub assembly 12 and adjacent the radially extending inner end surface of the ring 20. The end surface 25 of the ring 15, or the surface of the ring 20 contacting the same is optionally lightly roughened, scored or grooved to provide additional relief voids, which assist in preventing or removing any slight accumulation of gummy deposits or other debris at the contacting end surfaces of ring and hub.

The magnet assembly 16 comprises a tubular shell 26, a centrally perforate endpiece 27 carrying a hard steel ring bushing member 28, an opposing endpiece 29 carrying a bushing member 30 and having an inner tubular axial extension 31, and an electromagnetic coil 32. The coil is solidly embedded within the ferromagnetic assembly in a hardened resinous matric 33 and is provided with extended terminals, not shown, for connection to a control circuit.

A split ring 34 holds the assembled components in place.

In one mode of operation, the assembly is mounted with the shaft 11 supported on and keyed to a shaft of a device, such for example as a paper feed device, which is to be intermittently operated. The hub 13 is continuously rotated, for example by a source of power acting through a spur gear or a pulley, not shown, attached over the exposed large-diameter portion of the hub.

The magnet assembly is anchored to a stationary frame, by means not shown, and the coil is connected through a suitable switch to an appropriate source of EMF. Upon activation, a magnetic circuit is established, the magnetic lines of flux passing radially between endpiece 27 and hub member 20 and between extension 31 and ring 15. The ring 15 is attracted to and held in contact with the member 20, causing the rotating clutch spring 14 to wrap down onto and grip the surface 19 and resulting in rotation of the hub assembly 12 and shaft 11. Deactivation releases the ring 15 from the member 20, permitting the free portion of the spring 14 again to expand to its normal diameter and out of driving contact with the hub 12.

It will be seen that a reverse mode of operation is equally possible, wherein the shaft 11 and hub assembly 12 serve as the input function and hub 13 as the output function.

Concentricity of components is assured by forming the relatively softer endpiece 27 to a slightly lesser internal diameter than that of the hard steel ring 28 and then reaming the endpiece to match the diameter of the ring. The composite bearing surface thus produced provides uniform radial spacing, an accurate fit and a long life. The uniform radial spacing results in balanced magnetic attraction around the periphery, again tending to reduce or eliminate mechanical drag and wear.

A particular advantage of the structure described is the minimizing of drag induced during activation. The magnetic forces, being applied substantially entirely in a radial direction and angularly balanced around the periphery, are effectively balanced or neutralized insofar as the introduction of mechanical drag is concerned. The small size and resulting minimal inertia of the control ring 15 also contributes to the minimizing of drag.

In the modified structure illustrated in Figure 3, the inner surface of the extension 311 is increased in diameter about the clutch spring but remains of smaller diameter at the free end portion surrounding most of the control ring 151. The outer surface of the ring 151 is reduced in diameter beneath the end ot the extension 311, and extends past the smalldiameter portion of the extension. With thls slightly more complicated structure a slight further reduction in drag may be accomplished.

WHAT WE CLAIM IS: 1. An electromagnetically actuatable spring clutch comprising first and second sub

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. keyway 17 for use in keying to a shaft, not shown, which is to be inserted within the shaft 11 for receiving torque therefrom. The fixed hub assembly 12 is shown to consist of an inner tubular barrel 18 having a cylindrical outer surface 19, and a radially extending ferromagnetic ring 20, the two being fitted tightly together. The two-piece structure provides for convenience in manufacture and makes possible the use of nonmagnetic material for the barrel component which magnetically isolates the control ring 15 and the ferromagnetic ring 20 from the shaft 11. Less desirably, the two may be combined in a unitary ferromagnetic structure. The ring portion is undercut at the inner edge 21 as shown, providing a relief void. The hub assembly is tightly affixed on the shaft 11, either by keying or preferably by a press fit. Hub 13, which desirably is non-ferromagnetic, is rotatable about the shaft 11 and against the end of barrel 18. It has a cylindrical surface 22 equal in diameter to that of surface 19 of the barrel 18, which surface 22 carries a portion of the helical clutch spring 14 tightly wound thereon. The remainder of the spring is normally of slightly greater diameter so as to be freely rotatable about the barrel 18. Alternatively, the spring may have a constant diameter, the diameter of hub surface 22 then being appropriately increased to provide for the required tight fit. The free portion of the spring terminates in an axially extending tang 23 which fits into an opening 24 provided in the side of the control ring 15. The ring 15 fits closely but rotatably about the cylindrical surface 19 of the hub assembly 12 and adjacent the radially extending inner end surface of the ring 20. The end surface 25 of the ring 15, or the surface of the ring 20 contacting the same is optionally lightly roughened, scored or grooved to provide additional relief voids, which assist in preventing or removing any slight accumulation of gummy deposits or other debris at the contacting end surfaces of ring and hub. The magnet assembly 16 comprises a tubular shell 26, a centrally perforate endpiece 27 carrying a hard steel ring bushing member 28, an opposing endpiece 29 carrying a bushing member 30 and having an inner tubular axial extension 31, and an electromagnetic coil 32. The coil is solidly embedded within the ferromagnetic assembly in a hardened resinous matric 33 and is provided with extended terminals, not shown, for connection to a control circuit. A split ring 34 holds the assembled components in place. In one mode of operation, the assembly is mounted with the shaft 11 supported on and keyed to a shaft of a device, such for example as a paper feed device, which is to be intermittently operated. The hub 13 is continuously rotated, for example by a source of power acting through a spur gear or a pulley, not shown, attached over the exposed large-diameter portion of the hub. The magnet assembly is anchored to a stationary frame, by means not shown, and the coil is connected through a suitable switch to an appropriate source of EMF. Upon activation, a magnetic circuit is established, the magnetic lines of flux passing radially between endpiece 27 and hub member 20 and between extension 31 and ring 15. The ring 15 is attracted to and held in contact with the member 20, causing the rotating clutch spring 14 to wrap down onto and grip the surface 19 and resulting in rotation of the hub assembly 12 and shaft 11. Deactivation releases the ring 15 from the member 20, permitting the free portion of the spring 14 again to expand to its normal diameter and out of driving contact with the hub 12. It will be seen that a reverse mode of operation is equally possible, wherein the shaft 11 and hub assembly 12 serve as the input function and hub 13 as the output function. Concentricity of components is assured by forming the relatively softer endpiece 27 to a slightly lesser internal diameter than that of the hard steel ring 28 and then reaming the endpiece to match the diameter of the ring. The composite bearing surface thus produced provides uniform radial spacing, an accurate fit and a long life. The uniform radial spacing results in balanced magnetic attraction around the periphery, again tending to reduce or eliminate mechanical drag and wear. A particular advantage of the structure described is the minimizing of drag induced during activation. The magnetic forces, being applied substantially entirely in a radial direction and angularly balanced around the periphery, are effectively balanced or neutralized insofar as the introduction of mechanical drag is concerned. The small size and resulting minimal inertia of the control ring 15 also contributes to the minimizing of drag. In the modified structure illustrated in Figure 3, the inner surface of the extension 311 is increased in diameter about the clutch spring but remains of smaller diameter at the free end portion surrounding most of the control ring 151. The outer surface of the ring 151 is reduced in diameter beneath the end ot the extension 311, and extends past the smalldiameter portion of the extension. With thls slightly more complicated structure a slight further reduction in drag may be accomplished. WHAT WE CLAIM IS:

1. An electromagnetically actuatable spring clutch comprising first and second sub

stantially coaxial hubs; a helical spnng carried by the first hub and overlying an end portion of the second hub; a rotatable ferromagnetic control first ring slidably supported axially adjacent and in torque- transmitting association with the free end of the spring around the second hub; a ferromagnetic second ring mounted on the second hub and fixedly supported axially adjacent the first ring, and opposing nonrotatable polepiece means for directing peripherally angularly balanced magnetic lines of flux directly to the first and second rings in a direction radially of the rings to apply a braking force to the free end of the spring to contract the spring around the second hub.

2. A clutch according to Claim 1 wherein the hubs are both mounted on a common shaft, the first hub being rotatably mounted and the second hub being fixedly mounted.

3. A clutch according to Claim 2 wherein the control ring is magnetically isolated from the said shaft.

4. A clutch according to Claim 2 or Claim 3 wherein the second ring is magnetically isolated from the shaft.

5. A clutch according to any preceding Claim wherein the polepiece means comprises at least one polepiece with nonrotatable opposite poles, one adjacent the second ring and the other adjacent the first ring, both being angularly balanced around the periphery and defining a magnetic path wherein magnetic lines of flux extend radially between one pole and the second ring and between the first ring and the other pole; and a selectively actuable flux generating means for generating said lines of flux.

6. A clutch according to Claim 5 wherein the polepiece is an annulus and contains an annular flux generating coil.

7. A clutch according to Claim 5 or Claim 6 wherein the polepiece overlies and encloses the spring and ring.

8. A clutch according to Claim 7 wherein the polepiece comprises an outer tubular shell, a centrally perforate first endpiece fitting over and bearing on the second ring, and an opposing endpiece fitting over and bearing on the first hub and having an inner tubular axial extension overlying the spring and terminating about the first ring and spaced from the first endpiece.

9. A clutch according to Claim 8 wherein the internal diameter of said axial extension is uniform.

10. A clutch according to Claim 8 wherein the internal diameter of said axial extension is greater about the spring than about the central width of the first ring, and wherein the first ring is of reduced external diameter adjacent the second ring.

11. A clutch according to any of Claims 8 to 10 wherein each endpiece includes a hard wear-resistant ring bushing.

12. A clutch according to any preceding Claim wherein the free end of the coil terminates in an axially extending tang, the first ring being perforate to accommodate the tang.

13. A clutch according to any preceding Claim wherein the second ring comprises a radially extending annular ferromagnetic shoulder on the second hub.

14. A clutch according to Claim 13 wherein the face of the shoulder adjacent the first ring is undercut to provide a relief void.

15. A clutch according to Claim 13 or Claim 14 wherein the first ring is provided with relief voids on the end surface contacting the shoulder.

16. An electromagnetically actuatable spring clutch substantially as described herein with reference to and as illustrated by the accompanying drawings.