| 摘要 |
A ball-throwing machine having a throwing arm rigidly mounted on a rotatable shaft and a crank secured to the shaft for effecting a drive coupling provided with a force mechanism for acceleratedly driving the throwing arm through a portion of its path of travel to throw a ball. An elongated support structure is pivotally mounted with respect to the frame of the machine and supports the force mechanism for movement longitudinally of the structure. In this manner the line of force of tension spring means which comprises the mechanism is varied relative to the path of travel of the throwing arm. Thus, the point of application of the accelerative driving force, which is applied to the throwing arm as the latter reaches an overcenter position in its path of travel, is varied to alter the trajectory of a ball being thrown. A mounting component of the force mechanism has a locking element in the form of spring-biased detent means which is interengageable with a corresponding locking element in the form of a plurality of slots in the support structure. These cooperating elements are selectively interengageable to lock the spring means relative to the supporting frame of the machine. Springs bias the interengageable elements into their normal locking positions and a camming surface of the support structure is movable against the action of one of the springs to disengage the locking elements and permit swinging of the spring means longitudinally of the structure.
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