Safety device for crane

Claim 2

A sefety device for a crane comprising boom length detecting means for detecting a boom length including means for generating a first electric signal corresponding to boom length, work radius detecting means for receiving said first signal and for generating directly a second electric signal corresponding to work radius, said second signal being a product of said first signal and a third cosine signal corresponding to a boom inclination angle, said cosine signal being generated in said work radius detecting means, lifted load detecting means for detecting a lifted load including means for generating a fourth electric signal corresponding to the lifted load, a rated load determining means including means for converting said second signal received therein to a fifth electric signal indicating a rated load corresponding to said work radius, said rated load determining means including a polygonal line function generator having an operational amplifier circuit and diode switches for changing amplification factors according to said second signal, and comparator means for comparing said fifth signal with said fourth signal to produce a sixth output signal providing information concerning safe crane operation when said lifted load is equal to or more than said rated load.

Claim 3

A safety device as set forth in claim 1, wherein said boom length detecting means (1) comprises a cord reel (12) adapted to extend and retract a cord according to a boom length, a helical potentiometer (13) responsive to the movement of said cord to convert the boom length to an electric resistance, and a negative feedback amplifier circuit connected to the electric resistance for providing an electric voltage signal comprising said first signal.

Claim 4

A safety device as set forth in claim 1, wherein said work radius detecting means (2) comprises a potentiometer, the resistance winding of which is wound in a cosine manner and a slider interlocKed with a main boom (14) wherein a turned angle of the slider is proportional to a boom inclination angle ( theta ), an output voltage signal (L) from said boom length detecting means (1) being applied to the ends of said resistance winding of said potentiometer for producing a signal (L cos theta ), corresponding to a work radius, which is generated from the turning angle of the slider, said signal (L) comprising said first signal and said signal (L cos theta ) comprising said second signal.

Claim 5

A safety device as set forth in claim 1, wherein said lifted load detecting means (4) comprises a load cell (11) in which a real stress acting on a wire rope for lifting is converted into an electric signal which is applied to an amplifier to obtain a signal of electric voltage (WL) corresponding to the lifted load, said voltage (WL) comprising said fourth signal.

Claim 6

A safety device as set forth in claim 1, wherein said rated load determining means (3) comprises an operational amplifier circuit and diode switches for changing amplification factors according to an input voltage (L cos theta R) comprising said second signal, said amplification factors being (W2-W1)/(R2-R1), (W3-W2)/(R3-R2), and (W4-W3)/(R4-R3) corresponding to respective ranges of work radii, wherein R1 - R4 are work radii and W1 - W4 are corresponding rate loads.

Claim 7

A safety device as set forth in claim 1, wherein said comparator means (5) comprises a differential amplifier, to the respective input terminals of which the fourth signal (WL) and a rated load signal (WO) comprising said fifth signal are supplied to discriminate the positive or negative value of the difference between the signals (WO) and (WL) and wherein when the lifted load is equal to or more than the rated load, said differential amplifier produces an output signal comprising said sixth signal to operate an alarm device (6).

Claim 8

A safety device as set forth in claim 6, wherein said alarm device (6) comprises a relay adapted to be operated by said output signal from said differential amplifier to close its contacts so that an alarm buzzer sounds.

Claim 9

A safety device as set forth in claim 6, wherein said alarm device (6) comprises a relay adapted to be operated by said output signal from said differential amplifier to close its contacts so that the operation of the crane is stopped.

Claim 10

A safety device as set forth in claim 6, wherein said alarm device (6) comprises a relay adapted to be operated by said output signal from said differential amplifier to close its contacts so that an alarm lamp is lighted.

Claim 11

A safety device for a crane comprising boom length detecting means (1) including a cord reel (12) adapted to extend and retract a cord according to a boom length, a first helical potentiometer (13) responsive to the movement of said cord to convert the boom length to an electric resistance, and a first negative feedback amplifier circuit, connected to the electric resistance, for providing a first electric output voltage signal (L), a work radius detecting means (2) including a second potentiometer, the resistance winding of which is wound in a cosine manner, and a slider interlocked with a main boom (14) wherein a turned angle of the slider is proportional to a boom inclination angle ( theta ), the output voltage signal (L) from said boom length detecting means (1) being applied to the ends of said resistance winding of said second potentiometer for producing a second signal (L cos theta ), corresponding to work radius, which is generated from the turning angle of the slider, lifted load detecting means (4) including a load cell (11) in which a real stress acting on a wire rope for lifting is converted into a third electric signal which is applied to a first amplifier to obtain a fourth signal oF electric voltage (WL) corresponding to the lifted load, rated load determining means (3) including a second operational amplifier circuit and diode switches for changing amplification factors according to an input voltage (L cos theta R) comprising said second signal to provide a fifth electric signal corresponding to a rated load signal (WO), said amplification factors being (W2-W1)/(R2-R1), (W3-W2)/(R3-R2) and (W4-W3)/(R4-R3) corresponding to respective ranges of work radii wherein R1-R4 are work radii and W1-W4 are corresponding rated loads, and comparator means (5) including a second differential amplifier, to the respective input terminals of which the fourth signal (WL) and the fifth signal (WO) are supplied to discriminate the positive or negative value of the difference between the signals (WL) and (WO) and wherein when the lifted load is equal to or more than the rated load, said differential amplifier produces a sixth output signal to operate an alarm device (6), said alarm device including a relay adapted to be operated by said sixth output signal from said differential amplifier to close its contacts.

Claim 12

A safety device for a crane comprising boom length detecting means (1) including a cord reel (12) adapted to extend and retract a cord according to a boom length, a first helical potentiometer (13) responsive to the movement of said cord to convert the boom length to an electric resistance, and a first negative feedback amplifier circuit, connected to the electric resistance, for providing a first electric output voltage signal (L), a work radius detecting means (2) including a second potentiometer, the resistance winding of which is wound in a cosine manner, and a slider interlocked with a main boom (14) wherein a turned angle of the slider is proportional to a boom inclination angle ( theta ), the output voltage signal (L) from said boom length detecting means (1) being applied to the ends of said resistance winding of said second potentiometer for producing a second signal (L cos theta ), corresponding to work radius, which is generated from the turning angle of the slider, lifted load detecting means (4) including a load cell (11) in which a real stress acting on a wire rope for lifting is converted into a third electric signal which is applied to a first amplifier to obtain a fourth signal oF electric voltage (WL) corresponding to the lifted load, rated load determining means (3) including a second operational amplifier circuit and diode switches for changing amplification factors according to an input voltage (L cos theta R) comprising said second signal to provide a fifth electric signal corresponding to a rated load signal (WO), said amplification factors being (W2-W1)/(R2-R1), (W3-W2)/(R3-R2) and (W4-W3)/(R4-R3) corresponding to respective ranges of work radii wherein R1-R4 are work radii and W1-W4 are corresponding rated loads, and comparator means (5) including a second differential amplifier, to the respective input terminals of which the fourth signal (WL) and the fifth signal (WO) are supplied to discriminate the positive or negative value of the difference between the signals (WL) and (WO) and wherein when the lifted load is equal to or more than the rated load, said differential amplifier produces a sixth output signal to operate an alarm device (6), said alarm device including a relay adapted to be operated by said sixth output signal from said differential amplifier to close its contacts.