A patent when it is drafted contains some definite parts which are generally an abstract, specification, claims and one or more drawings. There may be other parts of a patent which are required by different country laws. When a question as to infringement of a patent is raised, it has to be the infringement of one or more claims. Claims are the details of the claimed invention set out in definitive bullet points and determine the scope of invention on which the monopoly is being claimed by the inventor. So in order to hold infringement, the impugned practice, machinery, process, compound etc. (‘infringing material’) should be read into one or more of these claims.

The first step to find infringement in a case is to read the claim to see of everything set out in it is found the infringing material. If the claim sets out something more than what is present in the infringing material, it will generally be held not infringing. On the other hand, if one or more of the claims are covered under the infringing material, it is held to be infringement. This is known as literal infringement and if this is found in a case, it is usually the end of the enquiry. But why will such an infringement happen? If someone tries to infringe a patented invention, doing it literally will be dull and an invitation to trouble. In Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 607, 70 S.Ct. 854, 856, 94 L.Ed. 1097, the Supreme Court held that  “One who seeks to pirate an invention, like one who seeks to pirate a copyrighted book, or play, may be expected to introduce minor variations to conceal and shelter the piracy. Outright and forthright duplication is a dull and very rare type of infringement”.  In this opinion the Court goes on to point out that the doctrine of equivalents evolved in response to this type of infringement and reiterates (339 U.S. at page 608, 70 S.Ct. at page 856) that 'if two devices do the same work in substantially the same way, and accomplish substantially the same result, they are the same, even though they differ in name, form or shape."

Doctrine of equivalent when applied to patent infringement becomes an exercise to investigate the degree of similarity between the two practices, machineries, processes, compounds etc and when the difference remains only in structure, design or other trivial aspects, it is safe to hold it as infringement. The rule laid down by US Supreme Court above provides it too simply. In reality, this depends on the opinions of the experts and putting up scientific and engineering facts. In one well- known case, the patent included claims for welding rods having a flux containing a major proportion of "alkaline earth metal silicate." The accused welding rods included a flux composed principally of "manganese silicate," which is not an alkaline earth metal silicate. Nevertheless, the accused welding rods were held to infringe because of testimony that manganese and magnesium were similar in many of their reactions and that they served the same purposes in fluxes. 

Let’s analyse few cases landmark judgments to see how this doctrine has been treated and developed.

In Karl ZYSSET and New-Nel Kitchen Products Company v. POPEIL BROTHERS, INC 124 U.S.P.Q. 250, 125 U.S.P.Q. 152 the US Court of Appeals 7^th Circuit analysed the patents and concluded that infringement is not avoided by making into one part that which has been shown as two where there is no change in the function or manner of operation of the element

The evidence on the issue of infringement showed that the defendant manufactured and sold two devices. The first form of device was copied directly from plaintiff shredder with only such slight variations as would effect economy in large scale manufacture. Instead of a plurality of holes in the sinuous blade, which defendant used without other change, it attached the blade to the blade carrying rod by the use of slots rather than to project the rod through holes. A 'ring' and 'sleeve' described in the claims of the patent in suit were made as one part rather than two. No change in functioning or manner of operation resulted.

As is clear, the changes made in the shredder by the defendants were trivial and the functioning  and manner of operation remained the same. In Apex Electrical Mfg. Co. v. Maytag Co., 7 Cir., 122 F.2d 182, 187  the court built upon the principle that a patent is not the best way to perform the invention, but it is one of the ways to perform it. If the defendant’s method of performing the plaintiff’s invention does not differ substantially from the plaintiff’s patent, it can be held as infringement. The Court held that patents are not limited to the structure described and shown, but the invention may be embodied in various forms. A transposition or rearrangement of the parts as set forth in a patent is an embodiment of the patented invention and does not avoid infringement unless form, location or sequence is essential to the result or to the novelty of the claims. Infringement is not avoided by combining two elements of a claim in one part.

In Royal Typewriter Co. v. Remington Rand, Inc., 2 Cir., 168 F.2d 691, 693 the court had occasion to observe that courts have with curious unanimity held that it does not avoid infringement to combine into one member that which the patent discloses as two, if the single member performs the duties of both in the same way. The decisions are so numerous that we don’t fine ourselves to citing those which over the past thirty years we have passed ourselves.

The judgment in Specialty Equipment & Machinery Corp. v. Zell Motor Car Co., 4 Cir., 193 F.2d 515, 518 supports this theory where the Court observed that while it is true that the function of a machine is not patentable and that there is infringement only where the same result is reached by substantially the same or similar means, it is also true that one using the substance and essentials of a patented combination does not avoid infringement by varying nonessential details. Neither the joinder of different elements of a patented combination into one, nor the separation of one integral part into two or more doing together substantially what was done by the single element will evade a charge of infringement.

Therefore, we can conclude in other words, that the changes made by the alleged infringer should not be obvious to the plaintiff’s patent. At the time of infringement, if the changes made by the infringer in his machine, process etc vis-à-vis the plaintiff’s patent (essentially the claims), are obvious and not novel enough to stand out of the plaintiff’s patent and what those changes actually constitute are the embodiment, structure or design in which the invention is performed, it shall fall under the scope of the doctrine of equivalent and hence held infringement.

The above analyses  assumes that the defendant has started with the plaintiff’s patented invention and made changes to it. Another scenario could be if the defendant/infringer has developed the same invention from scratch and came to light when actually it was marketed or published. Assuming the plaintiff has prior rights, the court would obviously consider the validity of the patent on the grounds of obviousness, but the principles underlining the doctrine of equivalent will apply as they apply above.

In the UK, the three most celebrated cases on patent claim interpretation have been Catnic Components V. Hill, Improver v. Remington and Kirin Amgen case. While Catnic and Improver lay down the principle, Kirin Amgen takes a stock of the legal position in US, UK and EU and suggests the best way forward, in light of the new EPC.

Catnic Component laid the foundation of what is called the ‘Purposive construction of claims. In this case, the plaintiffs were the registered proprietors of a patent in respect of steel lintels; the lintels were novel and proved to have been a commercial success. The defendants examined the brochures issued by various manufacturers including the plaintiff’s and having decided that the plaintiffs' lintel was the best, copied it and manufactured a number of lintels in accordance therewith. The defendants had obtained plaintiff’s brochure illustrating their lintels before making drawings for lintels which they proposed to manufacture; they had subsequently been sent a copy of a drawing of one of plaintiff's experimental lintels by an employee of the plaintiff, who had applied for a position in the defendant company. Certain dimensions were then placed on the defendants' drawings and from them the defendants made a number of lintels. After receiving a writ from the plaintiffs for infringement of patent, the defendants produced a second form of lintel which differed from both the one which they made before and the plaintiffs' commercially produced lintel only in that the rear support member, instead of being perpendicular to the base, was inclined 6° or 8° from the vertical. Claim I of the Plaintiff’s patent required that the rear member should “extend vertically”. An angle of 6° reduced the load bearing capacity of the member by 0·6 per cent and an angle of 8° by 1·2 per cent. From the point of view of function, a reduction of this order was negligible.

For the Patents granted before 1977, the patent law in UK was governed by the common law, the terms of the royal grant and general principles of construction. It was these principles which Lord Diplock set out in the present case.

The Patent Act 1977, effectuated the European Patent Convention in the UK. The UK Courts now are bound by Article 69 of the Convention which provides that the extent of the protection conferred by a European patent or a European patent application shall be determined by the claims. Nevertheless, the description and drawings shall be used to interpret the claims. 

The rationale that the courts of UK have follow is to first interpret the claims literarily and thereafter decipher if the infringement would fall under the scope of the claims, given that whether a person skilled in the relevant art would interpret the claims so as to conclude that the patentee intended to have the infringing material included in the scope of the claims. The Court held that: 

(1)    That textual infringement and infringement of the “pith and marrow” of an invention are not separate causes of action but a single one.

(2)    That a patent specification should be given a purposive rather than a purely literal construction.

(3)    That the question in each case was whether persons of relevant practical knowledge and experience would understand that strict compliance with a particular descriptive word or phrase was intended by the patentee to be an essential requirement of the invention so that any variant would fall outside the monopoly claimed, even though it could have no material effect upon the way the invention worked.

(4)    That such question would only be answered in the negative when it would be apparent to a reader skilled in the art that such a descriptive word or phrase could not have been intended to exclude minor variants which would have no material effect upon the working of the invention.

(5)    That no plausible reason had been advanced why a limitation should have been intended excluding a back plate not positioned at precisely 90° to both horizontal plates yet close enough to make no material difference to the working of the lintel.

Therefore, “Extending vertically” was in context capable of meaning `near enough to vertical to enable the back plate to perform satisfactorily all the functions that it could perform if it were precisely vertical'. It would be obvious to a builder that the patentee did not intend to make exact verticality of the back plate an essential feature of the invention.

The next case was Improver v. Remington. In this case, The plaintiffs had invented and were granted a European patent for a depilatory device marketed  as “Epilady.” It consisted of an electric motor in a hand-held housing to which was attached a helical steel spring held by its ends and stiffened by a guide-wire to form a loop. The sharp form of the spring caused the gaps between the windings to open on the convex side and be pressed together on the concave side. When the spring was rotated at high speed and held close to the skin, hairs entered the gaps on the convex side and were gripped between the windings as the rotational movement brought them round to the concave side. The effect was to pluck the hair from the skin. The defendants on the other hand produced a rival device known as “Smooth and Silky which instead of a helical metal spring, the element attached to the motor and used to extract the hair was a cylindrical rod of elastomerised synthetic rubber held by its ends to form an arc sub tenting about 60 degrees. The effect was the same that is to pluck the hair from the skin.

Hoffman J. applied the principles laid down in Catnic Components and sort of gave them a shape of a checklist now famously known as “Lord Diplock's three questions”:

1. Does the variant have a material effect upon the way the invention works? If yes, the variant is outside the claim. If no:— [question of materiality considered]

2. Would this (i.e.: that the variant had no material effect) have been obvious at the date of publication of the patent to a reader skilled in the art? If no, the variant is outside the claim. If yes:— [the variant should be obvious to be covered in the claims]

3. Would the reader skilled in the art nevertheless have understood from the language of the claim that the patentee intended that strict compliance with the primary meaning was an essential requirement of the invention? If yes, the variant is outside the claim. [whether the patentee intended to have a strict literal meaning of the claim]

These questions bring out the essential difference between the Doctrine of equivalents and the principles followed in UK and EU. The UK/EU law draws on the intention of the patentee as the base which is in turn deciphered from the language of the claim. The language of the claims should suggest that an extended meaning has to be given to the substance of the invention and if that meaning covers what the infringing material offers, it is held to be infringing.

It is also to be noted that the question of materiality and the onus of proof that whether the patentee wanted the claims to be interpreted literarily or purposively have been placed on the Plantiff-patentee. This is exactly the opposite of Doctrine of equivalents where the onus of proving that whether the variant is material enough to stand out is on the Defendant-infringer.

Kirin Amgen V. TKT discussed the doctrine and its application in EU in greater detail and took a complete stock of position since Catnic till the Art. 69 of the EPC.

The European Patent Convention follows what has been the law in the UK before it came into force. During the course of the 18th and 19th centuries, practice and common law had come to distinguish between the part of the specification in which the patentee discharged his duty to disclose the best way of performing the invention and the section which delimited the scope of the monopoly which he claimed: see Fletcher-Moulton LJ in British United Shoe Machinery Co Ltd v. A. Fussell & Sons Ltd, (1908) 25 RPC 631, 650. The best-known statement of the status of the claims in UK law is by Lord Russell of Killowen in Electric and Musical Industries Ltd v Lissen Ltd, (1938) 56 RPC 23, 39: “The function of the claims is to define clearly and with precision the monopoly claimed, so that others may know the exact boundary of the area within which they will be trespassers. Their primary object is to limit and not to extend the monopoly. What is not claimed is disclaimed. The claims must undoubtedly be read as part of the entire document and not as a separate document; but the forbidden field must be found in the language of the claims and not elsewhere.”

In Germany, however, the practice before 1977 in infringement proceedings was commonly to treat the claims as a point of departure (“Ausgangspunkt”) in determining the extent of protection, for which the criterion was the inventive achievement (“erfinderische Leistung”) disclosed by the specification as a whole. Likewise in the Netherlands, Professor Jan Brinkhof, former Vice-President of the Hague Court of Appeals, has written that the role of the claims before 1977 was “extremely modest”: see Is there a European Doctrine of Equivalence? (2002) 33 IIC 911, 915. What mattered was the “essence of the invention” or what we would call the inventive concept.

The Indian Scene

The Indian law has still to be developed as far as the doctrine is concerned. The Patent Act, 1970 provides that a patent should contain a title, specification, one or more drawings if any and claims. Section 10 (4) and (5) provide that the complete specification should fully and particularly describe the invention and its operation or use and the method by which it is to be performed, disclose the best method of performing the invention which is known to the applicant and for which he is entitled to claim protection; and end with a claim or claims defining the scope of the invention for which protection is claimed. Further the section provides that the claims should stick to the unity of invention rule, shall be clear and succinct and shall be fairly based on the matter disclosed in the specification. The Courts have sadly not read into what all is included in the scope of invention, and therefore it is open to adopt either the European or American approach.

India has only had one precedent recently on this doctrine. Ravi Kamal Bali v. KalaTech, 2008(5) BomCR138 dealt with the alleged infringement of a registered patent in respect of tamper proof locks and seals. The primary argument of the Plaintiff was that the improvements to the originally patented invention would be entitled to an independent patent which would vest in the inventor of that particular addition. This was based on Sec.2(i)(a), which requires that every invention must have an inventive step or in other words be non-obvious and novel, to  merit the grant of a patent.  The facts of the case were that one of the former employee had access to the technical details of the patented invention. He was assisting the defendants in the production of the patented products. In order to prevent fraud on the patent, the court applied the doctrine of equivalence.

The Court emphasized on Indian Patent Act 1970, Section 54 of the and held that only the patentee of the main invention is entitled to improve or modify the main invention and claim patent for such or else it would permit anybody to benefit from it by exploiting the main invention. The court opined that a mere carrying forward of an existing product involving change of form, proportion or degree or the substitution of an equivalent is not an invention, thus applying the doctrine of equivalent.

Conclusion

Kirin Amgen discussed in detail about the doctrine and its application in US. It was stated that due to the application of the Doctrine, some judges have expressed that, it is not easy to know where its limits should be drawn. In Warner-Jenkinson Co v Hilton Davis Chemical Co 520 US 17, 28–29 (1997) the United States Supreme Court expressed that the doctrine has “taken on a life of its own, unbounded by the patent claims.”

The American courts have somehow restricted the scope of the doctrine by what is known as prosecution history or file wrapper estoppel. The File wrapper estoppel states that the equivalence cannot be claimed for those elements restricting the monopoly which have been included by amendment during the prosecution of the application in the patent office. The patentee is estopped against the world from denying that he intended to surrender that part of the monopoly.

The Court of Appeals in order to further clarify the legal position and settle the dust laid down a rule that any amendment for reasons of patent validity was an absolute bar to any extension of the monopoly outside the literal meaning of the amended text. But the Supreme Court reversed this retreat to literalism on the ground that the cure was worse than the disease: Festo Corporation v Shoketsu Kinzoku Kogyo Kabushiki Co Ltd (28 May 2002) US Supreme Court.

Lord Hoffman further stated that there are two options to deal with the problems of fair protection to the patentee. The first one is to stick to literary construction of claims and develop a doctrine which enhance the claims by giving protection to equivalents. This is what courts have been doing so far in US. The other is to abandon literalism. That is what the House of Lords did in the Catnic case, where Lord Diplock said that “Both parties to this appeal have tended to treat ‘textual infringement’ and infringement of the ‘pith and marrow’ of an invention as if they were separate causes of action, the existence of the former to be determined as a matter of construction only and of the latter upon some broader principle of colourable evasion. There is, in my view, no such dichotomy; there is but a single cause of action and to treat it otherwise … is liable to lead to confusion.” The solution, said Lord Diplock, was to adopt a principle of construction which actually gave effect to what the patentee wanted the claims to say and not any artificial extension of claim language.

Giving a simple solution to the entire issue, rather sarcastically, Lord Hoffman states that ‘’I cannot say that I am sorry because the Festo litigation suggests, with all respect to the courts of the United States, that American patent litigants pay dearly for results which are no more just or predictable than could be achieved by simply reading the claims.