Drawworks control apparatus

In combination with a drawworks assembly having a work piece suspended from, and applying tension to, a cable, one end of the cable being wound on a drum, the rotation of which is controlled by a power brake mechanism, a control apparatus comprising:

• cable tension sensing means connected to the cable, the cable tension sensing means sensing the tension in the cable and producing a tension signal the level of which is proportional to the sensed cable tension;
• pulse generating means for producing a pulsed control signal;
• and
• brake control means connected to the pulse generating means and to the cable tension sensing means, the brake contol means receiving the control signal and the tension signal and applying the tension signal to the power brake mechanism in response to the pulses of the control signal, whereby the power brake mechanism is actuated in a pulsed manner, the strength of the pulses being proportional to the tension in the cable wherein the pulse generating means is further defined to include:
• a set-reset gate receiving a pulse-initiate signal and a pulse-terminate signal, and producing a memory signal in the low state in response to receiving the pulse-initiate signal and a memory signal in the high state in response to receiving the pulse-terminate signal;
• a memory element connected to the set-reset gate, the memory element receiving an activate signal and the memory signal, and, in response to the received activate signal, continuously producing an output signal in the same state as the state of the last received memory signal;
• a NOT gate connected to the memory element, the NOT gate receiving the activate signal and the memory element output signal and in response to the received activate signal, producing an output signal in the high state in response to receiving the memory element output signal in the low state and an output signal in the low state in response to receiving the memory element output signal in the high state, wherein one of the signals output from the memory element and the NOT gate may be applied to the brake control means as the pulsed control signal;
• a pulse initiate time delay connected to the memory element and the set-reset gate, the pulse initiate time delay receiving the memory element output signal and producing the pulse-initiate signal a predetermined time period after receiving the memory element output signal in the high state;
• a pulse terminate time delay connected to the NOT gate and to the set-reset gate, the pulse terminate time delay receiving the NOT gate output signal and producing the pulse-terminate signal a predetermined time period after receiving the NOT gate output signal in the high state;
• and
• a control gate connected to the cable tension sensing means and to the memory element, the control gate receiving the tension signal and providing the activate signal when the level of the received tension signal exceeds a predetermined level.