GB1593165A - Electro magnetic spring clutch - Google Patents

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 1935 West County Road B-2, Saint Paul, Minnesota 55133, 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. More particularly, this invention relates to an improvement on or modification to a spring clutch of the type described and claimed in our Patent Application No: 51653/77, hereinafter referred to as "the Parent Patent" (Serial No. 1593164). Some clutches are useful in-the controlled intermittent operation of numerous mechanical devices, e.g. printing or copying machines and other paper feed devices.

The parent Patent describes and claims an electromagnetically 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 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, a?nd opposing non-rotatable 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 e free end of the spring to contract the spring around the second hub. In the clutch of the present invention, the two hubs are mounted on a common shaft, the first rotatably and the second fixedly mounted, and the ferro magnetic control first ring is supported axially adjacent and in torque-transmitting association with the free end of the spring on a non-magnetic bushing slidably mounted on the shaft. With this modification, the response time from actuation of the clutch can be reduced.

Accordingly, the present invention provides an electromagnetically actuated spring clutch comprising a shaft; a first hub rotatably mounted on said shaft; a second hub fixedly mounted on said shaft axially adjacent said first hub; a helical clutch spring overlying adjacent portions of both hubs, affixed to said first hub and when in relaxed state free of said second hub; a ferromagnetic control first ring supported on a non-magnetic bushing which is slidably and rotatably mounted on said shaft, said first ring being axially adjacent to and in torque transmitting association with the free end coil of said spring; a ferromagnetic second ring fixedly supported on said shaft axially adjacent said control ring; at least one polepiece with nonrotatable opposite poles, one adjacent said second ring, the other adjacent said first ring, both being angularly balanced around the periphery and defining a magnetic path wherein magnetic lines of flux extend radially between said one pole and said second ring and between said first ring and said other pole; and a selectively actuable flux generating means for generating said lines of flux.

The invention will now be described by way of example, and with reference to the accompanying drawings wherein Figure 1 is a sectional side elevation of an electromagnetic spring clutch in accordance with the parent Patent; Figure 2 is an end elevation, showing four quadrants sectioned as-indicated in Figure 1; Figure 3 is a sectional detail view showing a portion of a modified structure, also in accordance with the parent Patent, and Figure 4 illustrates the modification according to the present invention of the clutch of Figures 1 to 3.

In the clutch illustrated in Figure 1 and 2, the magnetic clutch 10 comprises a tubular shaft 11, a fixed hub assembly 12, a coaxially disposed rotatable 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 rotatably 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 rotatably 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 matrix 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 largediameter 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 of the extension 311, and extends past the small-diameter portion of the extension.

With this slightly more complicated structure a slight further reduction in drag may be accomplished.

Figure 4 illustrates the modification according to the present invention of the structure of Figure 1. A control ring assembly 34, consisting of an outer ferromagnetic control ring 15 affixed to an inner non-magnetic annular bushing 35, is slidably positioned about the shaft 11 and between the appropriately shortened inner tubular barrel 181 and the non-magnetic flanged collar 36, both of which are affixed to the shaft. The flanged end portion of the ferromagnetic ring 20 of Figure 1 has been omitted, the shoulder on ring 201 being fixedly held in place about the shaft by the collar 36 as indicated. As before, the magnetic lines of force pass radially between the ring 201 and the endpiece 27, and between the ring 15 and the extension 31. Braking action between rings 201 and 15, and contraction of spring 14 about the barrel 181, occur within microseconds upon activation of the electromagnet.

WHAT WE CLAIM IS: 1. An electromagnetically actuated spring clutch comprising a shaft; a first hub rotatably mounted on said shaft; a second hub fixedly mounted on said shaft axially adjacent said first hub; a helical clutch spring overlying adjacent portions of both hubs, affixed to said first hub and when in relaxed state free of said second hub; a ferromagnetic control first ring supported on a nonmagnetic bushing which is slidably and rotatably mounted on said shaft, said first ring being axially adjacent to and in torque transmitting association with the free end coil of said spring; a ferromagnetic second ring fixedly supported on said shaft axially adjacent said control ring; at least one polepiece with non-rotatable opposite poles, one adjacent said second ring, the other adjacent said first ring, both being angularly balanced around the periphery and defining a magnetic path wherein magnetic lines of flux extend radially between said one pole and said second ring and between said first ring and said other pole; and a selectively actuatable flux generating means for generating said lines of flux.

2. A clutch according to Claim 1 wherein the ferromagnetic second ring is fixedly supported on a non-magnetic bushing including a radially extending flange and which is fixedly mounted on the common shaft.

3. An electromagnetically actuable spring clutch substantially as described herein with reference to and as illustrated by Figure 4 of the accompanying drawing.

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

Claims (3)

**WARNING** start of CLMS field may overlap end of DESC **. With this slightly more complicated structure a slight further reduction in drag may be accomplished. Figure 4 illustrates the modification according to the present invention of the structure of Figure 1. A control ring assembly 34, consisting of an outer ferromagnetic control ring 15 affixed to an inner non-magnetic annular bushing 35, is slidably positioned about the shaft 11 and between the appropriately shortened inner tubular barrel 181 and the non-magnetic flanged collar 36, both of which are affixed to the shaft. The flanged end portion of the ferromagnetic ring 20 of Figure 1 has been omitted, the shoulder on ring 201 being fixedly held in place about the shaft by the collar 36 as indicated. As before, the magnetic lines of force pass radially between the ring 201 and the endpiece 27, and between the ring 15 and the extension 31. Braking action between rings 201 and 15, and contraction of spring 14 about the barrel 181, occur within microseconds upon activation of the electromagnet. WHAT WE CLAIM IS:

1. An electromagnetically actuated spring clutch comprising a shaft; a first hub rotatably mounted on said shaft; a second hub fixedly mounted on said shaft axially adjacent said first hub; a helical clutch spring overlying adjacent portions of both hubs, affixed to said first hub and when in relaxed state free of said second hub; a ferromagnetic control first ring supported on a nonmagnetic bushing which is slidably and rotatably mounted on said shaft, said first ring being axially adjacent to and in torque transmitting association with the free end coil of said spring; a ferromagnetic second ring fixedly supported on said shaft axially adjacent said control ring; at least one polepiece with non-rotatable opposite poles, one adjacent said second ring, the other adjacent said first ring, both being angularly balanced around the periphery and defining a magnetic path wherein magnetic lines of flux extend radially between said one pole and said second ring and between said first ring and said other pole; and a selectively actuatable flux generating means for generating said lines of flux.

2. A clutch according to Claim 1 wherein the ferromagnetic second ring is fixedly supported on a non-magnetic bushing including a radially extending flange and which is fixedly mounted on the common shaft.

3. An electromagnetically actuable spring clutch substantially as described herein with reference to and as illustrated by Figure 4 of the accompanying drawing.