| Number | Date | Country | Kind |
|---|---|---|---|
| 3-267833 | Oct 1991 | JPX |
| Number | Name | Date | Kind |
|---|---|---|---|
| 2791492 | Isbell | May 1957 | |
| 2865156 | Wolfson | Dec 1958 | |
| 3233778 | Cobb et al. | Feb 1966 | |
| 3348733 | Johnson | Oct 1967 | |
| 3431890 | Ulary | Mar 1969 | |
| 3511409 | Huck | May 1970 | |
| 3680736 | Viessmann | Aug 1972 | |
| 3841351 | Shida | Oct 1974 | |
| 4129230 | Billett et al. | Dec 1978 | |
| 4263932 | Laar et al. | Apr 1981 | |
| 4306649 | Berge | Dec 1981 | |
| 4377368 | Koch | Mar 1983 | |
| 4405059 | Kull | Sep 1983 | |
| 4533225 | Shiga | Aug 1985 | |
| 4705379 | Kobayashi et al. | Nov 1987 |
| Entry |
|---|
| Patent Abstracts of Japan, vol. 13, No. 355 (P-914) Aug. 9, 1989 & JP-A-01 113 766 (Ricoh) May 2, 1989. |
| Patent Abstracts of Japan, vol. 12, No. 156 (P-701) May 13, 1988 & JP-A-62 273 537 (Konishiroku Photo Ind.) Nov. 27, 1987. |