System for controlling energy output of combustion-powered, fastener-driving tool

摘要

A system for controlling the energy output of a combustion-powered, fastener-driving tool, in which a fan is arranged to produce turbulence in a combustion chamber when the fan is driven, in which a direct current motor is arranged to drive the fan when a driving voltage is applied across the motor, and in which a battery provides a battery voltage not less than the driving voltage. A voltage divider includes a settable resistance, either a potentiometer or two parallel, fixed resistances that can be alternatively selected, and is used to provide a setpoint voltage. A comparator, an inverter, and a transistor switch are arranged to sample a voltage proportional to the rotational speed of the fan, to compare the sampled voltage to the setpoint voltage, to apply the driving voltage across the motor if the sampled voltage is less than the setpoint voltage, and to remove the driving voltage from across the motor if the sampled voltage is not less than the setpoint voltage. The voltage divider also includes a permanently grounded resistance, two selectively groundable resistances, and two photoelectric switches, each including a phototransmissive diode and a photoreceptive transistor and being arranged to ground one of the selectively groundable resistances if a fastener between the phototransmissive diode and the photoreceptive transistor blocks phototransmission therebetween but not if the fastener does not block phototransmission therebetween. The photoelectric switches can be thus used for discriminating among relatively short, intermediate-length, and relatively long fasteners.