TIMER MECHANISM WITH IMPROVED INTERVAL ACCURACY

摘要

TIMER MECHANISM WITH IMPROVED INTERVAL ACCURACY A timer comprising a control cam having a first and second cam track with the second cam track having three arcuate segments of progressively shorter fixed radius lengths defining a three step cam track profile. Drive means are provided for rotating the control cam about an axis and switch means comprising first and second resilient arms carry opposing contacts and extend generally adjacent the first cam track and the first arm extending between the second arm and the first cam track and the second arm having a lateral projection in the direction of the second cam track. The cam following member extending between the second arm and first cam track is biased into a cam-following engagement with the first cam track by the second arm. A rocker arm having at one end a cam follower portion and at the other end a lifter portion with a pivot point between the ends thereof and spring biased to force the cam follower portion in the cam-following engagement with the second cam track. During rotation of the control cam, cam following member and first cam track are operative to prevent closing the contacts when the rocker arm cam-follower portion is riding on the arcuate segment having the longest radius length. The cam following member and first cam track are also operative to release the cam following member from the first cam track and support the first arm on the rocker arm cam follower portion and prevent closing the contacts when the rocker arm cam follower portion is riding on the arcuate segment having the longest radius length. The cam following member and first cam track further being operative to release the cam following member from the first cam track and close the contact when the rocker arm cam follower portion is riding on the arcuate segment having the second longest radius length. The rocker arm and second cam track being operative to pivot the rocker arm when the cam follower portion is riding on the arcuate segment having the shortest radius length and the lifter portion engages the lateral projection of the second arm and opens the contacts. In addition, there is means to reset the timer for subsequent cycling as mentioned above. By this arrangement instantaneous and precise making and breaking of the contacts respectively is achieved to provide timer interval accuracy.