Pattern recognition apparatus

Abstract: A pattern recognition apparatus includes a pattern memory unit for storing a pattern set constituted by a plurality of reference patterns and a comparison unit for comparing an input pattern with each reference pattern stored in the pattern memory unit in the re­ cognition mode. In the pattern recognition apparatus, the pattern memory unit includes first and second pattern memory sections (14A, 14B), a switch (SW2) is provided to select one of the first and second pattern memory sections (14A, 14B), the comparison unit (16) is constituted to compare the input pattern with a desired reference pattern stored in one (14A) of the pattern memory sections which is selected by the switch (SW2) in the registration mode, and a pattern modifying unit (13) is provided to copy the pattern set stored in one (14A) of the pattern memory sections which is selected by the switch (SW2) into the other pattern memory section (14B) in the registration mode, and modify the desired reference pattern in one of the first and second pattern memory sections (14A, 14B) according to the comparison result obtained from the comparison unit (16).

Description: This invention relates to a pattern recognition apparatus, and more particularly to a pattern recognition apparatus having a registration mode in which a pattern used as a recognition reference is registered. Fig. 1 shows an example of a conventional speech recognition system designed for a small number of non-specified speakers. The speech recognition system includes a speech pattern detection section for frequency-analyzing an input speech and detecting a characteristic speech pattern thereof, and a pattern recognition apparatus for recognizing the speech pattern input from the speech pattern detection section. The pattern recognition apparatus includes a pattern memory section for storing a plurality of reference patterns, a comparing section for recognizing the speech pattern from the speech pattern detection section based on the similarity between the speech pattern and each of the reference patterns stored in the pattern memory section, and a switch for selectively connecting the speech pattern detection section to one of the pattern memory section and the comparing section. In the registration mode, a speech pattern is supplied from the speech pattern detector to the pattern memory section via the switch and registered into the pattern memory as a recognition pattern. On the other hand, in the recognition mode, a speech pattern is supplied from the speech pattern detector to the comparing section via the switch and then compared with a plurality of reference patterns registered in the pattern memory section. In a case where a plurality of speech patterns of a specified speaker are registered as recognition patterns in the pattern memory, it becomes difficult to attain a high rate of pattern recognition for a non-specified speaker. If additional recognition patterns are registered into the pattern memory section and consequently the number of speech patterns to be recognized is increased, the difference between the reference patterns becomes small so that the pattern recognition rate may be lowered. For this reason, the recognition operation is effected in the recognition mode by use of reference patterns registered in the pattern memory section and some of the reference patterns are modified to correctly recognize speech patterns which are difficult to recognize, thus enhancing the recognition rate. However, modification of the reference patterns cannot be always effected with good results, and sometimes the recognition rate may become lower than that which may be obtained without the modification. In the conventional speech recognition system, a new speech pattern is written over the reference pattern which requires modification and the reference pattern is removed from the pattern memory. Therefore, if the modification is made in fail, the content of the pattern memory section cannot be returned to the state prior to the modification. For example, substantially the same reference pattern as that obtained before the modification can be registered into the pattern memory section by inputting a speech to the speech pattern detection section, but this needs a long time and much labor. EP-A-0 025 685 discloses a signal pattern recognition system which includes a reference pattern memory storing plural reference data patterns against which input patterns are compared for recognition. A scoring circuit compares training patterns with a reference data pattern stored in the reference pattern memory to generate a score signal indicative of the similarities therebetween. A merging circuit combines a reference data pattern with a training pattern to produce a new reference data pattern. A minimum score gate replaces the reference data pattern with the new reference data pattern in the reference pattern memory, if the score signal exceeds a predetermined level. Prior, not prepublished EP-A-0 342 630 discloses a speaker adaptation type speech recognition apparatus which operates to recognize inputted speech patterns produced by a particular speaker according to reference patterns produced by a standard speaker. This apparatus is adapted to the particular speaker by converting the reference pattern to normalized pattern through learning operation using training pattern produced by the particular speaker. Both of these documents, however, do not adress the problem of a modification leading to a lowered recognition rate. An object of this invention is to provide a pattern recognition apparatus in which an optimum reference pattern set can be easily obtained. The above object can be obtained by a pattern recognition apparatus comprising a pattern recognition apparatus comprising: input means for receiving a plurality of input patterns; memory means for storing a set of reference patterns; selection and comparison means, responsive to a first input pattern, for recognizing as the first input pattern one of said set of reference patterns stored in said memory means which has the closest similarity to said first input pattern, in a recognition mode; and buffer and modifying means, responsive to a second input pattern, for registering a new set of reference patterns in said memory means in a registration mode; whereby said memory means includes a plurality of pattern memory sections each for storing a set of reference patterns; said buffer and modifying means includes modifying means for copying a reference pattern set stored in a first one of said pattern memory sections into a second one of said pattern memory sections and for modifying only said copied reference pattern set stored in said second pattern memory section, as the new reference pattern set, according to the result of a comparison between said second input pattern and a reference pattern stored in said first pattern memory section; and said selection and comparison means includes selection means for selecting any one of said pattern memory sections which is used for recognition. In the above pattern recognition apparatus, a reference pattern set is read out from one of the pattern memory sections, and stored in to another pattern memory section with modification. Therefore, even if the modification of the reference pattern set is not adequately effected and the recognition rate becomes lower than before the modification, the original reference pattern set prior to the modification can be used for the recognition operation in the recognition mode. Further, the original reference pattern set can be modified again without effecting complex process. Therefore, with the pattern recognition apparatus of this invention, the optimum reference pattern set can be easily obtained. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a diagram showing the construction of a conventional speech recognition system designed for a small number of non-specified speakers; Fig. 2 is a diagram showing the construction of a pattern recognition apparatus according to one embodiment of this invention; Figs. 3 and 4 are flowcharts for illustrating the operation of modifying the reference pattern into an optimum form in the pattern recognition apparatus of Fig. 2; and Fig. 5 is a diagram showing a modification of the pattern recognition apparatus shown in Fig. 2. There will now be described a pattern recognition apparatus according to one embodiment of this invention with reference to Figs. 1 to 4. The pattern recognition apparatus may be used in such a speech recognition system as described above, for example. Fig. 2 shows a circuit of the pattern recognition apparatus according to one embodiment of this invention. The pattern recognition apparatus includes first and second switches SW1 and SW2, a buffer memory section 12, a pattern modifying unit 13, first and second pattern memory sections 14A and 14B, and a comparison unit 16. The switch SW1 is used to connect an input terminal IN to the buffer memory section 12 in the registration mode and to the comparison unit 16 in the recognition mode. The switch SW2 is used to selectively connect the comparison unit 16 to one of the pattern memory sections 14A and 14B in the registration or recognition mode. Speech patterns are supplied to the input terminal IN from a speech pattern detector 1, for example. The buffer memory section 12 stores each input speech pattern supplied from the input terminal IN via the switch SW1 in the registration mode, and supplies the same to the pattern modifying unit 13 and comparison unit 16. When a pattern set constituted by a plurality of reference patterns is registered into one of the pattern memory sections 14A and 14B, the pattern modifying unit 13 stores speech patterns supplied from the buffer memory section 12 into a corresponding one of the pattern memory sections as the reference patterns. The comparison unit 16 receives an input speech pattern supplied from the input terminal IN via the switch SW1 in the recognition mode, compares the input speech pattern with a plurality of reference patterns stored in one of the first and second pattern memory sections 14A and 14B which is connected thereto via the switch SW2, and recognizes one of the reference patterns which has the largest similarity as the input speech pattern. In a case where a reference pattern set stored in one of the first and second pattern memory sections 14A and 14B is modified in the registration mode, the comparison unit 16 receives a speech pattern supplied from the buffer memory section 12 and compares the speech pattern with the desired reference pattern stored in one of the first and second pattern memory sections 14A and 14B which is connected thereto via the switch SW2. The pattern modifying unit 13 reads out the pattern set containing the desired reference pattern from one of the pattern memory sections and stores the readout pattern set into the other pattern memory section, with the desired reference pattern being modified according to the comparison result from the comparison unit 16 or the difference between the compared speech patterns. In this case, the desired reference pattern is modified into a reference pattern which can be obtained by averaging the desired reference pattern and the speech pattern from the buffer memory section 12. Next, the operation of optimizing the reference pattern in the pattern recognition apparatus is explained with reference to the flowchart shown in Figs. 3 and 4. Assume that no reference pattern is registered in the first and second pattern memory sections 14A and 14B. In this case, the switch SW1 is operated in the step S1 shown in Fig. 3 to select the buffer memory section 12 and the switch SW2 is operated in the step S2 to select one of the first and second pattern memory sections 14A and 14B, for example, the pattern memory section 14A. Then, a plurality of speech patterns of a specified speaker are stored into the buffer memory section 12 via the switch SW1 in the step S3. The speech patterns are supplied to the pattern modifying unit 13 but are not processed here and are stored as reference patterns into the pattern memory section 14A which is selected by the switch SW2 in the step S4. After this, the switch SW1 is operated in the step S5 to select the comparison unit 16. The comparison unit 16 receives a speech pattern of a non-specified speaker supplied via the switch SW1, and compares the speech pattern with the reference patterns stored in the pattern memory section 14A in the step S6. As a result, a reference pattern corresponding to a speech pattern which is difficult to recognize is specified as an object to be modified. Then, the switch SW1 is operated in the step S7 to select the buffer memory section 12, and a speech pattern of another speaker is stored into the buffer memory section 12 in the step S8. The comparison unit 16 compares the speech pattern supplied from the buffer memory section 12 with the to-be-modified reference pattern stored in the first pattern memory section 14A. The pattern modifying unit 13 copies the content of the first pattern memory section 14A into the second pattern memory section 14B, and modifies the to-be-modified reference pattern in the second pattern memory section 14B according to the comparison result in the step S10, for example. After this, the switch SW1 is operated in the step S11 to select the comparison unit 16 and the switch SW2 is operated in the step S12 to select the second pattern memory section 14B. The comparison unit 16 compares a speech pattern of a non-specified speaker with reference patterns stored in the second pattern memory section 14B in the step S13. If it is detected in the step S14 that the pattern recognition rate is lowered as a result of the modification of the reference pattern, the switch SW2 is operated to select the first pattern memory section 14A instead of the second pattern memory section 14B. On the other hand, if it is detected that the pattern recognition rate is not lowered, the switching position of the switch SW2 is kept unchanged so as to continuously select the second pattern memory section 14B. Further, in a case where it is required to modify the reference pattern stored in the second pattern memory section 14B, the content of the second pattern memory section 14B is copied into the first pattern memory section 14A and then the operation of modifying the reference pattern is effected. In this embodiment, even in a case where the modification of the reference pattern is failed and the pattern recognition rate is lower than before the modification, the modifying operation can be effected again without any trouble since the pattern set is also stored in the form obtained before it is subjected to the modification. Further, since a newly registered speech pattern is determined in the reference pattern registration operation after a difference between the input speech pattern and the registered speech pattern is detected, it becomes possible to set the recognition rate obtained after the modification equal to or higher than that obtained before the modification. When a new reference pattern is simply added, the pattern modifying unit 13 copies the content of one of the pattern memory sections into the other pattern memory section and additionally stores the new reference pattern into the other pattern memory section. The number of the pattern memory sections can be set to three or more in order to hold the reference patterns obtained when two or more preceding modification cycles were effected. In this case, the switch SW3 is operated to select one of the pattern memory sections and connect the same to the comparison unit 16. Further, the pattern memory sections may be provided in a ring buffer configuration in a single chip as shown in Fig. 5, for example, instead of being provided separately. In this case, the switch SW2 can be replaced by a circuit for designating the address of the memory chip to select one of the pattern memory sections. In the above embodiment, a speech pattern is supplied to the pattern recognition apparatus, but an image pattern such as letters and numerals can be supplied to serve the same purpose. Reference signs in the claims are intended for better understanding and shall not limit the scope.

Claims: A pattern recognition apparatus comprising: input means (IN) for receiving a plurality of input patterns; memory means (14A, 14B) for storing a set of reference patterns; selection and comparison means (SW2, 16), responsive to a first input pattern, for recognizing as the first input pattern one of said set of reference patterns stored in said memory means (14A, 14B) which has the closest similarity to said first input pattern, in a recognition mode; and buffer and modifying means (12, 13, SW1), responsive to a second input pattern, for registering a new set of reference patterns in said memory means (14A, 143) in a registration mode; characterized in that said memory means includes a plurality of pattern memory sections (14A, 14B) each for storing a set of reference patterns; said buffer and modifying means (12, 13, SW1) includes modifying means (13, SW1) for copying a reference pattern set stored in a first one of said pattern memory sections (14A, 14B) into a second one of said pattern memory sections (14A, 14B) and for modifying only said copied reference pattern set stored in said second pattern memory section, as the new reference pattern set, according to the result of a comparison between said second input pattern and a reference pattern stored in said first pattern memory section; and said selection and comparison means (SW2, 16) includes selection means (SW2) for selecting any one of said pattern memory sections (14A, 14B) which is used for recognition. A pattern recognition apparatus according to claim 1, characterized in that said buffer and modifying means (12, 13, SW1) further includes buffer memory means (12) for storing said second input pattern. A pattern recognition apparatus according to claim 2, characterized in that said modifying means includes comparing means (16) for performing a first comparison of said first input pattern with said reference pattern stored in said first one of said pattern memory sections (14A, 14B) to determine a reference pattern to be modified, and for performing a second comparison of said input pattern stored in said buffer memory means (12) with said reference A pattern recognition apparatus according to claim 3, characterized in that said modifying means (13, SW1) includes a switching means (SW1) for receiving one of said input patterns from the input means (IN) and for supplying the received input pattern to one of said buffer memory means (12) and said comparing means (16). A pattern recognition apparatus according to claim 3, characterized in that said modifying means includes a modifying unit (13) for copying said reference pattern to be modified, as part of said reference pattern set, into said second one of said pattern memory sections (14A, 14B) and for modifying said reference pattern to be modified according to said first and second comparisons. A pattern recognition apparatus according to claim 5, characterized in that the modified reference pattern is an average pattern of a desired reference pattern and said second input pattern stored in said buffer memory means (12). A pattern recognition apparatus according to claim 1, characterized in that said plurality of pattern memory sections are provided in a ring buffer configuration on a single memory chip, and said selection means includes a circuit for designating an address of said memory chip to select one of said pattern memory sections (14A, 14B).

Inventors: KOYAMA MOTOAKI, KOYAMA, MOTOAKI, KOYAMA, MOTOAKI, C/O INTELLECTUAL PROPERTY DIV.
Applicants: TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA
Application year: 1990
Main classification: G10L5
IPC codes: G10L11, G10L15