An Electro Permanent Magnetic work holding system having additional solenoid(s) positioned within the main pole(s) of the working face.

The present invention relates to an electro permanent magnetic work holding system having additional solenoid(s) positioned within the main pole(s) of the working face. As used before and hereinafter in this specification the expression "main pole(s)", unless otherwise specified, signifies the pole (s) positioned above the reversible magnets, and the walls of the apparatus have effectively been utilized as 'secondary' or 'auxiliary' poles. More particularly, this invention relates to an electro permanent magnetic work holding system in which the working surface is made up of a monolithic block of steel and additional solenoids are positioned within the main pole(s) of the working face which enhances the performance of the system.

In the prior art, Electro permanent magnetic (EPM) work holding apparatuses of flux reversal type are known in which a magnetic circuit is activated or deactivated by changing the polarity of the permanent magnets inside the apparatus. These devices use intrinsic energy of the permanent magnetic device but instead of being switched "ON" or "OFF" mechanically, it requires electrical pulse similar to electro magnetic devices but only momentarily delivered by an electrical winding.

Once switched "ON", these devices provide magnetic force for infinite duration of time independent of any external energy source. For instance, US Patent No. 4507635 granted to Michele Cardone of Milan, Italy, pertains to a magnetic anchoring apparatus, comprising in combination: an external ferromagnetic crown provided with a base plate and lateral walls; at least one group of four pole pieces defining pairs of corresponding poles of an anchoring surface, said pole pieces presenting their longitudinal axes at right angles to the base place and in correspondence with the apexes of a square. Moreover, the apparatus comprises a plurality of permanent magnets for feeding the aforesaid poles, interposed between the pole pieces, and between the latter and said ferromagnetic crown.

Since the magnet uses the polarity of permanent magnets a complete demagnetization or switching 'OFF' of the work piece is often difficult. Also the demagnetization is a function of the job being clamped as materials which have more retentively are difficult to be de-clamped from these work holding apparatuses.

For better demagnetization the same inventor proposed the use of another set of electrical winding on an intermediate pole member for better demagnetization as per application EP0345554 titled MAGNETIC GRIPPING APPARATUS HAVING CIRCUIT FOR ELIMINATING RESIDUAL FLUX. The problem of prior art was that the solenoids which were used to demagnetize the job were placed at the intermediate pole member and not on main poles holding the work piece.

Present invention aims at circumventing and finding an effective solution to the difficulties mentioned above.

The principal object of this invention is to provide an electro permanent magnetic work holding system having additional solenoid(s) positioned within the main pole(s) of the working face.

A further object of this invention is to provide a work holding apparatus having a ferrous working face, preferably monolithic in nature, with slots separating the main magnetic poles.

A still further object of this invention is to provide a work holding apparatus having a ferrous working face having additional solenoids positioned within the main poles thereof for better clamping and de- clamping of the work piece.

Another object of this invention is to provide an EPM work holding apparatus having a working face wherein the direction of energising the additional solenoid(s) can be either along or against the direction of the flux emanating from the main poles of the electro permanent magnets, thus ensuring better clamping and de-clamping.

Yet another object of the subject invention is to provide a novel EPM work holding apparatus having additional solenoid(s) positioned within the main pole(s) of the working face which ensures prompt release of the work piece from the said working face owing to proper demagnetisation of the work piece by the said additional solenoid(s).

The foregoing objects are achieved by the intention which relates to an Electro Permanent work holding system characterized in that the said system comprises a work holding face , a base plate ,a set of reversible magnets , solenoid(s)for controlling reversible magnets , main pole(s) positioned above the reversible magnets , a set of non-reversible permanent magnets , set of additional solenoid(s) within the main poles of the working surface and magnetic insulator .

The present invention provides an apparatus that has separate solenoid(s) at the working face which can be energised separately or in conjunction with the EPM assembly in the system.

The solenoids help in improving the following:- 1. Energising the additional Solenoids to provide a magnetic flux which is in the same direction of the flux emerging from the Electro Permanent Magnetic system thereby generating more Magnetic Flux for proper holding of work piece.

2. Energising the additional Solenoids to provide a magnetic flux which is in the reverse direction of the flux emerging from the Electro Permanent Magnetic system thereby reducing the Magnetic Flux. This feature is essential when thin work pieces are involved and high flux is detrimental for the operation.

3. The additional Solenoids can also be used for demagnetizing the work pieces once the Electro Permanent Magnetic system has been switched off. It has been observed that the work piece normally remains stuck to the Electro Permanent Apparatus even when system has been de-energized because of residual magnetism which is more apparent on high carbon steel or hardened steel which has high retentively.

4. As the additional solenoids are directly placed in the working face of the work holding apparatus, it can be used very effectively to monitor Flux to ascertain whether the system has magnetised properly. This can be useful to ascertain whether optimum clamping is achieved prior to operations.

5. The additional solenoids can be used to detect displacement of the work piece from the desired position during operation. This can be interlocked with the machine to reduce accidental damages to the machine and/ or the job.

The placement of additional solenoid on the working face of the apparatus can be done in different ways and has been illustrated in the Figs 2 and 3.

Fig. 1 shows a prior art Electro Permanent Magnetic system.

Fig. 2 shows an Electro Permanent Magnetic system made having additional solenoids in the working face.

Fig. 3 shows additional solenoids placed appropriately on a separate monolithic Plate which matches the working face of the EPM apparatus.

Fig. 4 shows an Electro Permanent Magnetic system made from monolithic working face having additional solenoids which are inserted from the bottom side thus eliminating the use of non magnetic material like Epoxy on the top side.

The invention will be further defined by means of the illustrated drawings accompanying the specification wherein:- Fig. 1 depicts the conventional EPM work holding system in a longitudinal cross sectional view of the top surface in which ( 1 ) is the work holding face, (2) is the bottom surface, (3) stands for electrical windings for controlling reversible magnets, (4) denotes main poles, (5) is the first set of reversible magnets and (6) is the second set of non reversible permanent magnets; Fig. 2 shows a system of this invention having additional in the working face wherein ( 1 ), (2), (3), (5) and (6) have the same significance as in Fig 1 narrated above, (7) shows the additional solenoids and (8) is the magnetic insulator and

Fig. 3 shows additional solenoids placed on a separate plate wherein ( 1 ), (2), (3), (5), (6), (7) and (8) have the same significance as given in Fig 2 and 9 shows additional plate with fixing means ( 10) carrying the solenoids.

Fig. 4 shows additional solenoids inserted from the bottom side of the working surface wherein ( 1 ), (2), (3), (5), (6), (7) and (8) have the same significance as given in Fig 2 and 1 1 shows additional Steel plate. The work holding apparatus has thus no epoxy on the top surface.

The placement of solenoid in the working face of the apparatus can be done in different ways and two such arrangements have been illustrated in Figs. 2 and 3 of the drawings.

Additional modifications and improvements of the present invention may also be apparent to those skilled in the art. Thus the particular combination of parts described and illustrated herein is intended to represent only one embodiment of this invention with a variation and is not intended to serve as limitation of alternative devices or features within the spirit and scope of the invention. Having described the invention in detail with particular reference to the illustrative drawings accompanying both provisional and complete specifications, it will now be made more specifically defined by the claims appended hereafter.