US3299380A - Plunger electromagnet with anti-stick means separating the poles and operating a utilization device - Google Patents

Description

Jan. 17, 1967 B. K. M REYNOLDS PLUNGER ELECTROMAGNET WITH ANTI-STICK MEANS SEPARATING THE POLES AND OPERATING A UTILIZATION DEVICE 2 Sheets-Sheet 1 Filed March 15, 1965 IN VE N TOR Boone K. M Reyno/ds Jan. 17, 1967 'B K. M REYNOLDS 3,299,380

v PLUNGER ELECTROMAGNET WITH ANTI-STICK MEANS SEPARATING THE POLES AND OPERATING A UTILIZATION DEVICE llll Filed March 15,1965 2 Sheets-Sheet 2 Ill 303 am V U 307 PRlOR ART-- United States Patent York Filed Mar. 15, 1965. Ser. No. 439,812 6 Claims. (Cl. 335-420) The invention relates to core assemblies for tractive electromagncts and more particularly concerns a nonferromagnetic actuating pin aguided for longitudinal movement by one piece of a two-piece conical-faced ferromagnetic core. The actuating pi-n has a flared truncated conical end within the coil of the electromagnet to provide a residual gap that mates with the truncated conical ends of the two-piece core.

In known core assemblies for tractive electromagnets, the best force-stroke characteristic curves have been obtained with conical-faced cores. In one such arrangement, the core assembly comprises two conica-1-faced ferromagnetic pole pieces, one of which is movable and the other stationary. A nonferromagnetic actuating pin in the form of a straight pusher pin is guided by means of a hole in the stationary pole. Upon energization of the electromagnet, the movable pole or plunger is attracted to the stationary pole, thereby driving the pusher pin to actuate external mechanism. Problems exist, however, in the provision of a residual gap to prevent continued engagement of the plunger with the stationary pole due to residual magnetism in the poles after de-energization of the electromagnet. In small electromag-nets, it is especially difficult to control the width of the residual gap by an arrangement that may be economically manufactured. Air gaps are difficult to adjust and maintain at correct and consistent widths. Gaps of nonferromagnetic material which are coated or secured in some other manner to the face of one of the pole pieces, necessitate an extra step in the manufacture of the electromagnet. Another serious difficulty found is that repeated impact of the plunger against the pusher pin causes a mushroom deformation at the end of one or both parts. Such deformation often becomes suflicient to cause the mushroomed end of either or both the pusher pin and plunger to jam in the hole in the stationary pole. Still another difliculty is that conventional straight pusher pins have a tendency to fall through the hole in the stationary core when the electromagnet is turned over or otherwise moved about.

According to the invention, a core assembly for a tractive electromagnet is provided in which a first ferromagnetic pole is secured to one end of a nonferromagnetic sleeve about which .acoil is wound.- A second ferromagnetic pole is mounted for movement within the sleeve. A central hole is provided in the stationary pole to guide a nonferromagnetic member for longitudinal movement. The nonferromagnetic member is an actuating pin of nonferromagnetic material and has a flared truncated conical end which remains within the sleeve. The ends of the poles as well as the flared end of the actuating pin are of mating, truncated, conical shapes. Upon energization of the coil, the movable pole engages the conical end of the pin, driving it into engagement with the conical end of the stationary pole. The flared conical end of the pin, being of nonferromagnetic material, provides a residual gap between the poles to permit the movable pole to return to the normal position immediately upon de-energization of the coil. This type of gap is found to be very accurate and economical to manufacture. It is also found that the conical shape of the poles and pin permit distribution of the impact of the pieces over a relatively large area, thereby preventing deformation of any of the pieces of the core assembly. In tests carried out on devices constructed according to the invention, core assemblies have been subjected to 20 million cycles without deformation of any of the pieces or failure of any kind. In prior devices, deformation of either or both the pusher pin and plunger and consequent jamming of one or the other in the hole, occurred in less than 10 million cycles and in some cases as few as 1 million cycles.

Still other advantages are obtained in practicing the invention. No adjustment of the gap between the poles is necessary during assembly nor any time thereafter since the flared, truncated, conical end of the actuating pin provides an automatically determined and easily controlled gap. The conical, gap-forming portion of the pin end also eliminates the need to maintain close tolerances during manufacture and assembly of various pieces as necessitated in previous arrangements. The flared end of the pin also limits the upward travel of the pin, preventing inertial forces from carrying the pin beyond a normal actuated position as is possible with a straight actuating pin.

During assembly of the electromagnet still another advantage is obtained. Insertion of the pin is facilitated by the conical shape of the inner end of the stationary pole which tends to funnel the straight portion of the pin into the hole. Thereafter, the pin due to the flared conical end, will not fall out of the assembly, thereby enabling the electromagnet to be inverted and otherwise moved about.

A primary object of the invention is to reliably operate a tractive electromagnet over extended periods of time.

Another object of the invention is to prevent deformation of the pieces of a core assembly of a tractive electromagnet during extended operation of the electromagnet.

Another object of the invention is to arrange a core assembly for a tractive electromagnet in which the residual gap is determined prior to assembly by the shape of the parts.

Another object of the invention is to provide a core assembly that is automatically adjusted upon assembly and thereafter automatically and permanently maintained in adjustment.

Another object is to provide a core assembly for a tractive electromagnet in which the necessity for maintaining close tolerances during manufacture and assembly is reduced.

Another object of the invention is to provide a core assembly for a tractive electromagnet that may be easily assembled and thereafter moved about without any of the pieces falling out.

In order that the invention may be practiced by others, it will be described in terms of an express embodiment, given by way of example only, and with reference to the accompanying drawing in which:

FIGURE 1 is a view, partially in section, of a tractive electromagnet;

FIGURE 2 is a portion of the view of FIGURE 1 shown with the electromagnet energized;

FIGURE 3 is a partial view partially in section of a i tractive electromagnet known in the prior art;

FIGURE 4 is a View of the plunger and pusher pin of the electromagnet of FIGURE 3 after extended operation.

An embodiment of the invention is shown in FIGURE 1 in which a tractive electromagnet 101 comprises a coil 103 wound on a thin nonferromagnetic sleeve 105. A ferromagnetic pole piece 107 is driven into the sleeve to the position shown and is held there by a knurled surface (not shown) on the pole piece. The upper end of the pole 107 is threaded to receive a nut 109. The electro- 3 magnet 101 is secured to a nonferromagnetic framework 111 by means of the threaded portion of the pole 107 passing through a slot in the framework to hold the electromagnet between a shoulder (not shown) in the pole piece and the nut.

Prior to mounting the electromagnet on the framework, a nonferromagnetic actuating or pusher pin 113 is inserted in the lower end of the sleeve. The pin is inserted with the electromagnet inverted from the position shown in FIGURE 1. The pin falls downward, therefore, into a truncated conical shaped hole 115 in the pole 107. The conical hole leads into a cylindrical hole which passes through the pole. The hole 115 tends to funnel the straight portion of the pin into the cylindrical hole. A flared, truncated, conical end 117 is formed on the lower end of the pin 113-. The upper conical surface of the flared end 117 mates with the conical hole 115, while the inner truncated conical surface of pin end 117 mates with an external truncated conical end 119 of a erromagnetic plunger 121 which is inserted into the sleeve following insertion of the pin.

In operation, the electromagnet 101 is mounted in the framework 111 in the position shown in FIGURE 1. With the electromagnet in the de-energized state, the pusher pin 113 and plunger 121 assume the position shown. Upon energization of the electromagnet, the plunger 121 is drawn upward to a position in which the upper conical surface of the pin end 117 is in mating engagement with the conical hole 115 in the lower end of the pole 107. The pin 113 is driven therefore from the position shown in FIGURE 1 to the position shown in FIGURE 2. In FIGURE 1, the plunger end 121 and pin end 117 are shown slightly separated, and in FIG- URE 2 the plunger end, pin end and pole 107 are shown slightly separated. These parts are shown separated to clearly show the various parts. In practice, however, the parts are in intimate mating contact in both figures. When the plunger 121 is drawn upward, the upper end of the pin 113 engages the lower surface of a platform 123 extending from a lever 125. The lever is pivoted at 127 and is urged CCW by a spring 128. Upon energization of the electromagnet, the pin 113 pushes the platform from the position shown to a position 123A, thereby driving a member 129, pivoted at the left end of the lever 125, upward. Upward movement of the member 129 causes engagement of a cam with a power roll of an electric typewriter to drive a typebar. This mechanism (not shown) is comprised of known SCM Corporation Electric Typewriter parts and does not form a part of the invention herein.

In FIGURE 2, the core assembly is shown in an actuating position as a result of the coil 103 being energized, with the pole 107, plunger 121, and pin 113 in mating engagement. The conical portion 117 of the pin, being of a nonferr-omagnetic material such as stainless steel, provides an economical and very easily controlled gap between the poles.

A prior art tractive electromagnet 301 is shown in FIGURE 3 and comprises a conical-faced plunger 303, a conical-faced pole 304 and a straight pusher pin 305. A gap 307 of a nonferromagnetic material may be provided by coating or otherwise securing the material on the conical end of the pole 304. Such an arrangement, however, would necessitate an extra step in the manufaeture of the device. If the gap is of a nonmetallic material, there is a further disadvantage of deterioration under extended use, making it difficult to control the width of the gap. Alternatively, and more commonly, the gap is of air and is obtained by controlling the upward movement of the plunger. One arrangement for achieving such control is by means of threads on the lower end of the plunger 303 for receiving a nut 309 which serves to stop the upward movement of the plunger when the nut is brought into engagement with the lower end of the sleeve 105. The nut may also be adjusted to control the width of the air gap. Adjustment of such a gap by this means, however, is found to be very diflicult during initial assembly and thereafter to require periodic adjustment.

Another problem encountered with the electromagnet 301 (FIGURE 3) in which an air gap is used is the requirement that close tolerances be maintained in all parts of the core assembly to prevent a tolerance build-up at the lower end of the electromagnet. Since this part of the electromagnet acts as a stop for the nut 309, close tolerances are necessary to ensure that the plunger is moved the same distance specified in the design. Furthermore, in mass production of the electromagnets of FIGURE 3, it is necessary to assemble the nut 309 onto, the plunger 303 prior to insertion of the plunger into the sleeve 10S. Consequently, the distance between the lower end of the sleeve and the conical recess of the pole 107 must be closely controlled. In contrast, the lower end of the electromagnet 101 (FIGURE 1) does not act as a stop for the plunger 121 so that tolerance build-up at this point may be neglected.

It has also been found that extended operation of the device shown in FIGURE 3 causes a mushroom deformation on the ends of either or both the pusher pin 305 and plunger 303 as indicated in FIGURE 4. This deformation is due to the continual pounding of the plunger 303 against the lower end of the pin 305. Frequently, the deformation becomes so severe that the pin and/ or plunger is jammed into the lower end of the pole 304, causing the pin to stick in the raised position.

From the above description other embodiments of the invention may become apparent. For example, the shapes of the pole faces might be interchanged, or the actuating pin 113 could be arranged to pull rather than push. v

The invention claimed is:

1. A tractive electromagnet for operating a utilization device comprising:

(a) a coil;

(b) a first ferromagnetic pole having one end internal tosaid coil, said end having a recess therein;

(c) a second ferromagnetic pole having one end internal to said coil;

(d) means for holding one of said poles stationary with respect to the other to permit movement of the other pole toward the stationary pole upon energization of the coil;

(e) a nonferromagnetic member positioned between the ends of the poles for movement therebetween, said member having first and second surfaces opposite respective one ends of said poles, each said surface being shaped for mating engagement corresponding one end of a pole;

(f) an opening defined by a third surface, said third surface being on one of said poles, and

(g) an extension secured to one of said first and second surfaces and passing through said opening to enable operative engagement between said member and said utilization device in response to movement of said other pole.

2. A tractive electromagnet according to claim wherein said one end of said first pole has a conical recess therein;

said one end of said second pole has a shape complementary to said conical recess;

each said surface of said nonfer-romagnetic member opposite a respective pole is conically shaped for mating engagement therewith.

3. A tractive electromagnet according to claim 2 wherein said pole ends and said surfaces of said member are in the shape of truncated cones.

4. A tractive electromagnet for operating a utilization device, comprising:

(a) a coil;

(b) a first ferromagnetic pole having one end internal to said coil;

(0) a second ferromagnetic pole having one end internal to said coil;

(d) means for holding one of said poles stationary with respect to the other to permit movement of the other pole toward the stationary pole upon energization of the coil;

(e) a nonferromagnetic member in the shape of an elongated pin flared on one end and positioned between the ends of the poles for movement therebetween, said flared end having surfaces respectively opposite one of said one ends of the poles, each said surface being shaped for mating engagement with a respective one end of a pole; and

(f) means formed in one of said poles to engage the pin portion of said member to guide the member 2 lengthwise within the coil and enable operative engagement between said pin portion of the member wherein said one end of the first pole has a conical recess therein,

said one end of said second pole has a conical shape complementary to said recess,

said flared end of the elongated pin being conically shaped for mating engagement with respective opposite conically haped poles, and

said pin-engaging means formed in one of said poles is a central hole in which said pin member is positioned for guidance.

6. A tractive electromagnet according to claim 5 wherein said pole ends and the flared end of the pin member are in the shape of truncated cones.

No references cited.

BERNARD A. GILHEANY, Primary Examiner. H. A. LEWITTER, Assistant Examiner.

Claims (1)

1. A TRACTIVE ELECTROMAGNET FOR OPERATING A UTILIZATION DEVICE COMPRISING: (A) A COIL; (B) A FIRST FERROMAGNETIC POLE HAVING ONE END INTERNAL TO SAID COIL, SAID END HAVING A RECESS THEREIN; (C) A SECOND FERROMAGNETIC POLE HAVING ONE END INTERNAL TO SAID COIL; (D) MEANS FOR HOLDING ONE OF SAID POLES STATIONARY WITH RESPECT TO THE OTHER TO PERMIT MOVEMENT OF THE OTHER POLE TOWARD THE STATIONARY POLE UPON ENERGIZATION OF THE COIL; (E) A NONFERROMAGNETIC MEMBER POSITIONED BETWEEN THE ENDS OF THE POLES FOR MOVEMENT THEREBETWEEN,

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