Double-masted crane with improved brake arrangement

Lifting apparatus comprising

• first and second generally vertical masts,
• an assembly including a frame moveable along said masts, and a load engaging mechanism mounted on said frame,
• a first brake mechanism which, upon actuation, engages said first mast to prevent downward movement of said frame relative to said first mast,
• a second brake mechanism which, upon actuation, engages said second mast to prevent downward movement of said frame relative to said second mast,
• a first overspeed mechanism for sensing the downward velocity of said assembly and for actuating said first brake mechanism when said overspeed mechanism senses that the downward velocity of said assembly exceeds a first predetermined value,
• a second overspeed mechanism for sensing the downward velocity of said assembly and for actuating said second brake mechanism when said second overspeed mechanism senses that the downward velocity of said assembly exceeds a second predetermined value,
• a first electrical device for providing a first electrical signal when said first brake mechanism is actuated, and
• a second electrical device for causing said second overspeed device to actuate said second brake mechanism in response to said electrical signal, and for providing a second electrical signal when said second brake mechanism is actuated in response to said second overspeed mechanism sensing that the downward velocity of said assembly exceeds a predetermined value,
• wherein said first electrical device causes said first overspeed mechanism to actuate said first brake mechanism in response to said second electrical signal.

Lifting apparatus comprising

• first and second generally vertical masts,
• an assembly including a frame moveable along said masts, and a load engaging mechanism mounted on said frame,
• a first brake arrangement which, upon actuation, prevents downward movement of said frame relative to said first mast, said first brake arrangement including a first member movable between actuating and non-actuating positions,
• a second brake arrangement which, upon actuation, prevents downward movement of said frame relative to said second mast, said second brake arrangement including a second member movable between actuating and non-actuating positions,
• a first solenoid operably connected to said first member such that energization of said first solenoid moves said first member to said actuating position,
• a first switch for generating a first electrical signal when said first member moves to said actuating position,
• a second solenoid operably connected to said second member such that energization of said second solenoid moves said second member to said actuating position, and
• a second switch for generating a second electrical signal when said second member moves to said actuating position,
• said first signal energizing said second solenoid and thereby moving said second member to actuate said second brake arrangement, and
• said second signal energizing said first solenoid and thereby moving said first member to actuate said first brake arrangement.