Power lawnmowers of the rotary blade type include a housing within which at least one cutting blade is mounted for rotation. Commonly, a grass collector is provided, and a chute connects the housing to the collector; typically for a garden tractor arrangement, the chute may have a length of about one meter, and in the event that the collector is not emptied when full, the chute becomes blocked and is difficult to clear.
Various proposals have been made for the provision of indicators for the fullness of the collector. Thus, in accordance with one proposal, the collector is supported on one or more springs which deflect under the weight of the load. This proposal utilizes a normally OFF momentary contact switch, which contacts close under a predetermined load, and which serve to cut-off the ignition system of the mower.
In accordance with other proposals, optical or sound transducers or electrical resistance sensors are used which change the state of a switch responsive to blockage at the outlet of the chute, and the changed output is indicated either by the operation of an alarm or by changing the operation of the lawnmower, for example.
One of the problems encountered with the above proposals is that of transient conditions which trigger spurious signals. This problem was recognized in at least one of the prior art proposals wherein an electronic delay circuit was incorporated to overcome the problem. However, this delay circuit necessitated a delay reset circuit, to overcome the problem of accumulated delays. Other problems are related to the widely differing responses that may be encountered under different conditions such as wetness and length of grass cuttings, and the tendency of the grass cuttings to mat onto all surfaces with which they come into contact and to thereby change the operating characteristics of the transducing elements and eventually to render them inoperative unless carefully and frequently cleaned.
It is an object of this invention to provide in a lawnmowing apparatus a simple and robust detection means that is responsive to the state of fullness of the grass collector.
It is another object of this invention to provide in such apparatus detection means that has a relatively delayed response time whereby it is inherently less likely to be affected by transient conditions.
It is yet another object of this invention to provide in such apparatus, detector means which is disposed in a position in which it is relatively shielded and unaffected by grass cutting build-up and contamination.
It is still another object of this invention to provide in such apparatus, detector means is integrated into the operating system of the mower.