JPH0428638B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] This invention relates to a vehicle type crane.

[Technical background of the invention]

Generally, vehicle type cranes are equipped with a jib to compensate for the length of the boom.

This jib is extended to the front of the boom by having its base end supported by the tip of the boom and rotating around the base end.When not in use, the jib's base end is directed toward the boom tip, and the jib is extended toward the front of the boom. It is stored along the boom with the side facing toward the base end of the boom.

Vehicle-type cranes equipped with this jib include those that store the jib along the underside of the boom, and those that store the jib along the side of the boom. Vehicle-type cranes that store the jib can extend the jib by rotating the jib vertically under the boom, so the jib can be extended even in tight spaces. During work, there is a problem that the view from the crane operator's cab is obstructed by the jib under the boom, and in the case of self-propelled cranes where travel and crane operations are performed in the same cab, the boom must be retracted and laid down. The jib below the boom obstructs the view from the operator's cab when driving in a state of disrepair.In order to widen the view from the operator's cab, the boom should be mounted high and stored along the bottom of the boom. Since the position of the jib must be raised, the center of gravity of the vehicle-type crane becomes higher, resulting in poor stability.

On the other hand, with the jib that is stored along the side of the boom, there is no jib under the boom, so it is possible to have a wide field of view from the driver's cab without having to install the boom at a high height. Considering only the visibility from the operator's cab, this is more advantageous than a system in which the jib is stored along the bottom of the boom, but conventionally,
Because the jib, which is stored along the side of the boom, can be rotated laterally and extended to the front of the boom, the jib cannot be moved in places where there is no space on the side of the boom that is equal to or larger than the length of the jib. The problem was that it was not possible to extend the area.

Therefore, recently, the jib is stored along the side of the boom, and when using the jib, the jib that is stored along the side of the boom is first moved to the bottom of the boom. A vehicle-type crane has been considered in which the jib is placed under the boom and rotated vertically to extend it out.

This vehicle-type crane is equipped with a jib transfer mechanism that rotates the jib stored along the side of the boom around the boom axis and transfers it from the side of the boom to the bottom. After extending the boom and retracting the sheave block at the tip of the boom forward from the base end of the jib, the jib transfer mechanism transfers the jib from the side of the boom to the bottom side of the boom, and the boom is retracted to move the sheave block forward from the base end of the jib. After engaging the jib support shaft provided on the side with the fork part at the base end of the jib, rotate the jib around the jib support shaft to extend the boom forward. When retracting the jib, move the jib to the boom. After the boom is tucked into the underside, the boom is extended and the sheave block at the tip of the boom is retracted forward from the base end of the jib, and then the jib is moved from the underside of the boom to the side of the boom and stored using the jib transfer mechanism. This vehicle-type crane stores the jib along the side of the boom, allowing for a wide field of view from the operator's cab without having to install the boom high. Also,
Since the jib can be extended by rotating vertically, the jib can be extended even in narrow spaces. As this type of vehicle-type crane, the
A crane described in Japanese Patent No. 59-57890 is known, and in this vehicle type crane, the jib is held and stored in a jib holder which is pivotably supported on the boom so as to be able to rotate between a downward position and a sideways position. The jib is transferred by hooking the winch's winding cable to the jib at a location different from the jib holder, and by hoisting or letting out the winding cable to raise or lower the jib.

[Problems with background technology]

By the way, with this vehicle-type crane, when transferring the jib from the side of the boom to the bottom side of the boom when extending the jib, or when moving the jib that has been tucked under the bottom of the boom to the side side of the boom when storing the jib, , the boom must be extended until the sheave block at the tip of the boom is retracted forward from the base end of the jib before the jib transfer mechanism is activated. Because the crane operator is alone in the operator's cab, the crane operator may become depressed and operate the jib transfer mechanism without extending the boom, or may operate the jib transfer mechanism before the boom is fully extended. If the jib transfer mechanism is operated before the sheave block is retracted from the base end of the jib, the jib transfer mechanism may be accidentally activated. The base end hits the sheave block at the tip of the boom and is prevented from rotating, so if you continue to operate the jib transfer mechanism, excessive force will be applied to the jib and sheave block, causing damage to them. It was also on. Moreover,
The conventional vehicle-type crane described in the above-mentioned Japanese Patent Application Laid-Open No. 59-57890 is designed to change the jib by hooking the winch winding cable to the jib at a location different from the jib holder. When transferring the jib, the jib holder holding the jib rotates while creating resistance to the jib being pulled up.
There is a problem in that a torsional moment acts between the rope hooking part of the jib and the jib holder attachment part, causing the jib to be twisted and deformed.

[Purpose of the invention]

This invention was made in view of the above-mentioned circumstances, and its purpose is to prevent the start switch of the jib transfer mechanism from being operated before the sheave book at the tip of the boom is retracted from the base end of the jib. In such cases, it is possible to prevent damage to the jib or the sheave block at the tip of the boom by disabling the jib transfer mechanism due to incorrect jib transfer operations, and also to prevent the jib transfer from occurring without twisting or deforming the jib. The object of the present invention is to provide a vehicle-type crane that can carry out various operations.

[Summary of the invention]

That is, in this invention, a jib for supplementing the length of the boom is stored along the side of the boom with its base end facing the boom tip side and its tip facing the boom base side, and the boom is extended. After retracting the sheave block at the tip of the boom forward from the base end of the jib, the jib is moved from the side of the boom to the bottom side, and then the boom is contracted and the jib installed on the side of the sheave block is moved. In a vehicle-type crane in which the base end of the jib is engaged with the support shaft, the jib is rotated around the jib support shaft to extend the boom forward, and the jib is attached to the lower edge of one side of the boom. The jib holder is removably held by a jib holder which is pivotably supported and rotated downward when the jib is moved to the bottom side of the boom, and rotated sideways when the jib is stored along the side of the boom. , connects a jib transfer mechanism that rotates the jib holder between a downward state and a sideways state, and includes a starting operation section for operating the jib transfer mechanism, and a detection value and set value of a boom length detector. A boom extension detection means detects that the boom has been extended until the sheave block at the tip of the boom retracts forward from the base end of the jib by comparing the A circuit for operating the jib transfer mechanism by operating the starting operation section.

According to this invention, even if the crane operator operates the starting operation part, the jib transfer mechanism will not operate until the boom has been extended until the sheave block at the tip of the boom is retracted forward from the base end of the jib. This prevents damage to the jib and sheave block at the tip of the boom due to incorrect jib transfer operations.

Moreover, in this invention, a jib transfer mechanism is connected to a jib holder that holds a jib, and the jib transfer mechanism rotates the jib holder between a downward state and a sideways state, so that the jib held by the jib holder can be rotated. Since the winding line is transferred to the side and bottom sides of the boom, there is no torsional moment on the jib, such as when the winch winding cable is hooked to the jib at a location different from the jib holder and the jib is raised or lowered. Therefore, the jib can be transferred without causing torsional deformation of the jib.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a jib transfer error prevention device, and FIG. 2 shows a vehicle-type crane equipped with a jib.

First, to explain a vehicle type crane equipped with a jib, in Fig. 2, 1 is a car body, 2 is a swivel base, and 3 is an extendable boom that is raised and lowered by a boom hoisting cylinder 4. A sheave block 5 having sheaves 6a and 6b is provided at the tip of the sheave block 3, and a rooster sheave 7 is provided at the end of the sheave block 5. In addition,
8 is a driver's cabin that doubles as a driving operation and a crane operation room;
9 is an outrigger.

Reference numeral 10 denotes a jib that supplements the length of the boom 3. This jib 10 is supported at its base end and tip side by a jib holder and a jib support bracket, which will be described later, provided on the boom 3, so that the base end is attached to the boom tip side. It is stored along one side of the boom 3 with the tip facing toward the boom base end. When in use, it is transferred from the side of the boom to the bottom side of the boom, and then the base end is The boom 3 is extended in front of the boom 3 by being supported by the distal end and rotating about the base end.

Note that 11 is a guide sheave provided on the base end side of the boom 3, and this guide sheave 11 is used when the jib 10 is extended and retracted.

As shown in FIGS. 3 to 5, the jib holder that holds the base end of the jib 10 includes a jib receiving portion 20a that receives the upper surface of the jib 10, and a rising portion that rises from the center of the jib receiving portion 20a. 20b, and the rising portion 20b of the boom 3 is pivoted on one support shaft 21 provided at the lower edge of one side of the boom 3 along the boom axis direction, allowing vertical movement. possible. The support shaft 20 is a pair of left and right vertical members 2 provided on the side of the boom.
2 and 22 between the lower end portions thereof.

This jib holder 20 is rotated by a jib transfer cylinder 23 provided on the boom 3 between a horizontal position shown by a solid line in FIG. 3 and a downward position shown by a chain line in the figure. The transfer cylinder 23 is installed on the boom 3 with its base end pivotally supported between the upper ends of the vertical members 22, 22, and the rod 23a of this cylinder 23 is located on one end side of the jib receiving part 20a of the jib holder 20. It is pivoted to.

Further, the proximal portion of the jib 10 held by the jib holder 20 has attachments 1 on both side edges thereof in contact with both ends of the jib receiving portion of the jib holder 20.
2 and 12, and a holder mounting bracket 13 that is detachably fixed to the jib holder 20 between the attachments 12 and 12.
is provided.

The proximal end side of the jib 10 is attached to a holder mounting bracket 13 with the attachments 12, 12 received at both ends of the jib receiving portion 20a.
is held by the jib holder 20 by being connected to the jib holder 20 by a pin 24, and removed from the jib holder 20 by removing the pin 24. In addition, in FIG. 5, 25 and 26 are the holder mounting brackets 13.
and a pin insertion hole provided in the jib holder 20.

Further, a lock pin insertion hole 27 is provided near the cylinder connecting portion of the jib holder 20, and the jib holder 20 is provided with a lock pin insertion hole 27.
By aligning 7 with the lock pin insertion hole 28 provided in the vertical members 22, 22 and inserting the lock pin 29, the lock pin 29 can be locked in a horizontally rotated state.

Figure 6 shows the jib 1 installed on the base end side of the boom 3.
Jib support bracket 30 that supports the tip side of 0
The jib support bracket 30 is fixed to the lower end of a vertical rib 31 provided on the side surface of the boom 3, and the jib support bracket 30 is fixed to the lower end of a vertical rib 31 provided on the side surface of the boom 3. 30
a bracket mounting plate 14 that is removably pivoted to the bracket mounting plate 14;
is provided. The bracket mounting plate 14 is rotatably supported on the jib support bracket 30 by a pin 32 extending along the axial direction of the boom 3. By removing this pin 32, the jib support bracket 14 can be attached to the jib support bracket 30. It is adapted to be removed from the bracket 30.

Next, we will explain the operation for extending the jib 10 stored along the side of the boom 3 to the front of the boom. Jib to the side 1
0, the sheave block 5 is retracted forward from the base end of the jib 10 so that the base end of the jib 10 does not hit the sheave block 5. In this state, the jib transfer cylinder 23 is extended and the jib holder 20 is moved. Rotate it to the downward position shown by the chain line in FIG. When the jib holder 20 is rotated downward, the jib 10, whose proximal end is held by the jib holder 20 and whose distal end is pivotally supported by the jib support bracket 30, aligns with the rotation center of the jib holder 20 and the jib support bracket. It rotates around the jib pivot point 30 and is held on the lower surface side of the boom 3.

In this case, the jib holder 20 that holds the base end of the jib 10 is pivotally supported on the lower edge of one side of the boom 3, so the base end of the jib 10 is centered around the lower edge of the one side of the boom 3. It rotates, and the jib 1
The tip side of the boom 3 is also pivotally supported by a jib support bracket 30 fixed to the lower edge of one side of the boom 3, and therefore rotates around the lower edge of one side of the boom 3. It can be moved to the lower surface side of the boom 3 without interfering with the boom 3.

Figure 8 shows the jib 10 relative to the boom 3 at this time.
In this figure, the jib 10 is held diagonally relative to the boom 3 with its base end located directly below the boom 3 and its distal end protruding to the side of the boom 3.

After the jib 10 is transferred to the bottom side of the boom 3 in this way, the boom 3, which was extended when the jib 10 was transferred to the bottom side of the boom, is retracted as shown in FIGS. 9 and 10. , jib support shafts 15, 15 protruding from both sides of the sheave block 5 are connected to fork portions 16, 1 provided at the tip of the jib 10.
6, and a pin 17 is inserted into the tips of the fork parts 16, 16 to prevent the fork parts 16, 16 from coming off from the jib support shafts 15, 15.

After this, the lifting rope 18 of the crane is looped around the guide sheave 19 on the jib 10 side and the guide sheave 11 at the base end of the boom, and its tip is attached to the rope hooking part 10a of the jib 10 (see Fig. 11). )
The jib holder 2
By removing the pin 24 that fixes the holder attachment bracket 13 of the jib 10 to the jib holder 20 and the pin 32 that pivots the jib 10 to the jib support bracket 30, the jib holder 20 and the jib support bracket 30 are removed. I'll remove jib 10.

After this, the lifting rope 18 is let out while raising the boom 3, and the jib 1 is raised as shown in FIG.
0 by its own weight around the jib support shafts 15, 15 as fulcrums to make the jib 10 hang down from the tip of the boom, then remove the lifting rope 18 from the guide sheave 11 at the base end of the boom and wind up the lifting rope 18. The jib 10 is extended to the front of the boom.

After the jib 10 is extended in front of the boom in this way, with the boom 3 lowered close to the ground,
The base end is pivoted to the tip side of the jib 10, and the tip is attached to the jib 10.
The tip of the tension rod 33 attached to the jib 10 is removed from the rod support 34, and the tip of the tension rod 33 is attached to the boom 3 as shown in FIG. After installing the tension rod set pin 35 on the sheave block 5,
Remove the lifting rope 18 from the rope hooking part 10a of the jib 10, and attach the hook 35 to this lifting rope 18.
All you have to do is install it and perform crane work.

In addition, when storing the jib 10, the tip of the lifting rope 18 hung on the guide sheave 19 of the jib 10 is hooked on the rope hooking part 10a of the jib 10, and the tension rod 33 is attached to the sheave block 5.
After removing it from the jib 10 and temporarily fixing it to the rod support 34 of the jib 10, let out the lifting rope 18 and attach it to the jib 10.
is suspended from the tip of the boom under its own weight, and then the lifting rope 18 is attached to the guide sheave 1 at the base end of the boom.
1 (the tip of the lifting rope 18 is attached to the jib 10)
By winding up the lifting rope 18, the jib 10 is rotated and the jib 10 is held under the boom 3, and then the jib 10 is attached to the holder. By inserting the pin 24, the bracket 13 is attached to the jib holder 20.
At the same time, the tip side of the jib 10 is fixed to the pin 3.
2 to the jib support bracket 30.

After this, the boom 3 is slightly extended and the sheave block 5 at the tip of the boom is retracted forward from the base end of the jib 10 (at this time, the jib support shafts 15, 15 of the sheave block 5 are also 1
6), then contract the jib transfer cylinder 23 and rotate the jib holder 20 sideways to store the jib 10 along the side of the boom 3, and move the jib holder 20 to the lock pin 2.
9 to lock the boom 3 and at the same time retract the boom 3.

In addition, in the above vehicle type crane, jib 1
The cylinder 23 is used to transfer the 0 from the side of the boom to the bottom, but the jib holder 20
The jib transfer mechanism for transferring the jib holder 20 from the side side of the boom to the bottom side of the boom is not limited to one that uses a cylinder. A dedicated winch is provided above the jib holder 20 of the boom 3, and the jib holder 20 is moved by the hoisting rope of this winch. It may be configured such that the boom is pulled up and rotated toward the side of the boom, and the jib holder 20 is rotated toward the bottom of the boom by the weight of the jib holder 20 and the jib 10.

By the way, when extending and storing the jib 10, the jib 10 stored along the side of the boom 3 may be moved to the bottom side of the boom 3,
When moving the jib 10 that has been tucked under the bottom of the boom 3 to the side of the boom 3, extend the boom 3 and retract the sheave block 5 at the tip of the boom forward from the base end of the jib 10 before moving the jib 10 to the side of the boom 3. There is no problem if the transfer mechanism is operated, but in reality, as mentioned above, the crane operator may become depressed and operate the jib transfer mechanism without extending the boom 3, or the boom may In some cases, the jib transfer mechanism is operated before the sheave block 3 is fully extended, and in this way, the jib transfer mechanism is operated by mistake before the sheave block 5 is retracted from the base end of the jib 10. Then, the base end of the jib 10, which is transferred and rotated between the boom side and the bottom side, hits the sheave block 5 at the boom tip and is prevented from rotating, so the jib transfer mechanism is operated as it is. If this continues, excessive force may be applied to the jib 10 and sheave block 5, causing damage to them.

Therefore, in this vehicle type crane, the boom is extended and the sheave book 5 at the tip of the boom is moved to the jib 10.
A jib transfer erroneous operation prevention device is installed that prevents the jib transfer mechanism from operating even if the crane operator turns on the start switch of the jib transfer mechanism until the jib is retracted from the base end. I'm trying to prevent it.

In FIG. 2, reference numeral 40 denotes a jib transfer erroneous operation prevention device, and this jib transfer erroneous operation prevention device 40 is provided in the driver's cab 8.

The configuration of this jib transfer misoperation prevention device 40 will be explained with reference to FIG. 1. In FIG.
23 is a jib transfer cylinder that transfers the jib 10 from the boom side side to the bottom side, and this cylinder 23 is extended or contracted by pressure oil sent from the hydraulic unit by switching the electromagnetic switching valve 41. It's summery. In addition, 42a, 42
b is a pilot check valve, 43a, 43b
is the aperture.

Reference numeral 44 includes a cylinder start switch 45 which is manually operated by the crane operator, and is closed when the cylinder start switch 45 is turned on to operate the jib transfer cylinder 23, and 46 is a cylinder drive circuit. A power supply circuit that supplies operating power for switching the electromagnetic switching valve 41 to the circuit; 47 is this power supply circuit 4;
The cylinder drive circuit 44 and the power supply circuit 45 are connected to each other by turning on a normally open relay switch 48 interposed therebetween.

The cylinder drive circuit 44 operates the electromagnetic switching valve 41 using the operating power supplied from the power supply circuit 46 when the cylinder start switch 45 is turned on, thereby extending or contracting the jib transfer cylinder 23. The cylinder 23 is extended by switching the cylinder start switch 45 upward in the figure.
5 to the lower side.

On the other hand, 51 is a boom length detector provided in an overload prevention device 50 provided in a vehicle type crane, and this boom length detector 51
is configured to detect the extension length of the boom 3 using a potentiometer or the like and output a detected value signal. The overload prevention device 50 is equipped with a boom angle detector, a load detector, etc. (not shown) in addition to the boom length detector 46, and the crane is controlled based on the detected values of these detectors. The system calculates the load on the crane and automatically stops the crane when it becomes overloaded.

Further, 52 is a boom extension length setting device that presets the boom extension length necessary to retract the sheave block 5 at the tip of the boom forward from the base end of the jib 10, and 53 is a boom extension detection circuit.
This boom extension detection circuit 53 consists of a comparison circuit that compares the detected value of the boom length detector 51 and the set value of the setting device 52.
When the detected value of the boom length detector 51 is smaller than the set value of the setting device 52, that is, when the boom 3 is in the retracted state, no output operation occurs, and the detected value of the boom length detector 51 becomes larger than the set value of the setting device 52. The signal is output when the boom 3 is extended until the sheave block 5 at the tip of the boom is retracted forward from the base end of the jib 10.

Further, in FIG. 1, 54 is a relay circuit equipped with an excitation coil 49 that turns on the normally open relay switch 48, and this relay circuit 54 is connected to the boom extension detection circuit 53 to detect the boom extension. An excitation coil 49 is excited by the output signal of the circuit 53 to turn on the relay switch 48, and the cylinder drive circuit 44 and the power supply circuit 46 are connected to supply operating power to the cylinder drive circuit 44.

To explain the operation of this jib transfer error prevention device, when the boom 3 is in the contracted state,
Alternatively, when the boom 3 is not extended to the set length, the boom extension detection circuit 53 does not output, and the relay switch 49 is in an open state that cuts off the cylinder drive circuit 42 and the power supply circuit 46. At this time, even if the crane operator turns on the cylinder start switch 44, the jib transfer cylinder 23 will not be operated.

If the jib transfer cylinder 23 does not operate as described above, the crane operator should turn off the cylinder start switch 45 and move the boom 3 to the set length, that is, move the sheave block 5 at the tip of the boom to the jib 1.
Extend it from the proximal end of 0 to the elongated length to be retracted,
After that, it is only necessary to turn on the cylinder start switch 45 again, and when the boom 3 is extended to the set length, the boom extension detection circuit 53 is activated to output,
The relay switch 48 is turned on by the output signal, and operating power is supplied from the power supply circuit 46 to the cylinder drive circuit 44. Therefore, when the cylinder start switch 45 is turned on, the jib transfer cylinder 23 is activated. Start transferring the jib 10.

In this case, the crane operator may extend the boom 3 without turning off the cylinder start switch 45. In that case, the jib transfer cylinder 23 is automatically activated at the same time as the boom 3 is extended to the set length. It operates and starts transferring the jib 10.

In this way, the jib transfer error prevention device prevents the start switch 4 of the jib transfer cylinder 23 from being activated until the boom 3 is extended until the sheave block 5 at the tip of the boom is retracted from the base end of the jib 10.
5 is turned ON, the cylinder 23 for transferring the jib 10 cannot be operated.If a vehicle-type crane is equipped with this jib transfer error prevention device, it will prevent incorrect jib transfer operations. This prevents damage to the jib 10 and sheave block 5. Moreover, in the vehicle-type crane described above, the jib holder 20 that holds the jib 10 is
A jib transfer mechanism (the jib transfer cylinder 23 in the above embodiment) is connected to the jib transfer mechanism, and the jib transfer mechanism rotates the jib holder 20 between a downward state and a sideways state, thereby holding the jib holder 20. Since the jib 10 that has been removed is transferred to the side and bottom sides of the boom 3, the transfer can be performed without causing torsional deformation of the jib 10.

That is, in the conventional vehicle-type crane described in Japanese Patent Application Laid-Open No. 59-57890 mentioned in the [Technical Background of the Invention] section, the winch winding rope is hooked to the jib at a location different from the jib holder. Because the jib is raised or lowered by
The jib holder that holds the jib rotates while creating resistance to the jib being pulled up, and as a result, a torsional moment acts between the jib rope hooking part and the jib holder mounting part, causing the jib to be torsionally deformed. Resulting in.

However, as in the above embodiment, the jib transfer cylinder 23 is connected to the jib holder 20, and the jib holder 20 is rotated by the jib transfer cylinder 23. If the jib 10 is moved between the bottom side and the side side of the boom 3, no torsional moment will be applied to the jib 10 when the jib 10 is moved, so no torsional deformation will occur in the jib 10. The transfer can be done.

Note that although the above embodiment includes a dedicated power supply circuit 46 for supplying operating power to the cylinder drive circuit 44, the output of the boom extension detection circuit 53 may be used for the operating power of the cylinder drive circuit 44. In that case, the cylinder drive circuit 44 may be directly connected to the boom extension detection circuit 53.

Further, in the above embodiment, the cylinder 23 is used as the jib transfer mechanism, but a winch may be used as the jib transfer mechanism. In that case, the winding cable of the winch is connected to the jib holder 20, and A start operation section (for example, a start switch) for operating the jib transfer mechanism is used as the start operation section of the winch, and the start operation section is operated only when extension of the boom 3 is detected by the boom extension detection means. All you have to do is start the winch.

〔Effect of the invention〕

According to this invention, if the operating section of the jib transfer mechanism is operated before the sheave block at the tip of the boom is retracted from the tip of the jib, the jib transfer mechanism is not activated, thereby preventing erroneous jib transfer operations. It can prevent damage to the sheave block at the tip of the jib or boom. Moreover, in this invention, a jib transfer mechanism is connected to a jib holder that holds a jib, and the jib transfer mechanism rotates the jib holder between a downward state and a sideways state, so that the jib held by the jib holder can be rotated. Since the winding line is transferred to the side and bottom sides of the boom, there is no torsional moment on the jib, such as when the winch winding cable is hooked to the jib at a location different from the jib holder and the jib is raised or lowered. Therefore, the jib can be transferred without causing torsional deformation of the jib.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, in which Fig. 1 is a circuit diagram of a jib transfer error prevention device, Fig. 2 is a side view of a vehicle-type crane equipped with a jib, and Fig. 3 is a side view of the jib storage state. is an enlarged side view taken along line A-A in Figure 2, Figures 4 and 5 are a side view and longitudinal sectional view of the jib removed from the jib holder, and Figure 6 is an enlarged side view taken along line B-B in Figure 2. Figure 7 is an enlarged side view of the boom with the boom extended when the jib is transferred to the bottom of the boom, Figure 8 is a plan view of the jib with the jib moved to the bottom of the boom, Figures 9 and 10 are an enlarged plan view and side view of the boom when it is contracted and the jib support shaft is engaged with the fork at the base end of the jib, Figure 11 is a side view of the jib in the middle of being extended, and Figure 12. is a side view with the jib extended. 3...Boom, 5...Sheave block, 10...
... Jib, 20 ... Jib holder, 30 ... Jib support bracket, 15 ... Jib support shaft, 16 ... Fork part, 23 ... Jib transfer cylinder, 44
... Cylinder drive circuit, 45 ... Cylinder start switch, 51 ... Boom length detector, 52 ... Boom extension length setting device, 53 ... Boom extension detection circuit, 46 ... Power supply circuit, 48 ... Normal Open relay switch, 54...Relay circuit.

Claims (1)

[Claims] 1. A jib for supplementing the length of the boom is stored along the side of the boom with its base end facing the boom tip side and its tip facing the boom base side,
After the boom is extended and the sheave block at the tip of the boom is retracted forward from the base end of the jib, the jib is transferred from the side of the boom to the bottom side by the jib transfer mechanism, and then the boom is contracted and the sheave block is moved forward from the base end of the jib. In a vehicle-type crane in which the base end of the jib is engaged with a jib support shaft provided on a side surface of the boom, the jib is rotated around the jib support shaft to extend forward of the boom, It is attached to and detached from the jib holder, which is pivotally supported on the lower edge of one side of the boom, rotates downward when the jib is moved to the bottom side of the boom, and rotates sideways when the jib is stored along the side of the boom. a jib transfer mechanism for rotating the jib holder between a downward state and a sideways state; A boom extension detection means detects that the boom has been extended until the sheave block at the tip of the boom is retracted forward from the base end of the jib by comparing the detected value of the boom with the set value, and the boom extension detection means a circuit for operating the jib transfer mechanism by operating the start operation section only when extension of the jib is detected.