| 摘要 |
660,392. Balling - machines. UNITED STATES RUBBER CO. March 16, 1949 [April 30, 1948], No. 7174/49. Class 120(ii). [Also in Group XXXV] In a system such as that described in Specification 631,956 for maintaining a preselected tensile stress in a rubber thread wound for example on a golf ball by detecting the frequency of vibration of a certain length, the vibration detector according to this invention comprises a piezo-electric or like contact microphone, instead of a photo-electric detector. The moving thread passes over a roller 21 and support bar 22 defining the test length and is caused to vibrate at its natural frequency by an airjet 48. The vibrations are detected by a piezo-electric crystal 45 on which the support bar 46 is mounted. Change in frequency due to change in cross-section of the thread are detected by a frequency-discriminator which controls a solenoid type brake operating motor as in the prior Specification to vary the load on the thread and maintain the tensile stress constant.
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