JPS6133493A - Jib shifting malfunction informer for car type crane - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a jib relocation erroneous operation notification device for 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, making it possible to extend the jib 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 traveling and crane operations are performed in the same cab, the boom is retracted and laid down. The view from the driver's cab while driving is obstructed by the jib below the boom, so to widen the view from the driver's cab, the boom must be mounted high.

Since the position of the jib stored along the lower surface of the crane must be raised, the center of gravity of the vehicle-type crane becomes high, resulting in poor stability.

On the other hand, those that store the jib along the side of the boom,
Since there is no jib under the boom, the boom can be mounted in a high position to provide a wide view from the operator's cab. This is more advantageous than the jib that is stored along the bottom of the boom, but in the past, the jib that was stored along the side of the boom was rotated laterally and extended to the front of the boom. However, there was a problem in that the jib could not be extended in locations where there was no space on the sides of the boom that was at least the length of the jib.

Therefore, recently, the jib is stored along the side of the boom, and when the jib is used, the jib that is stored along the side of the boom is moved to the underside of the -H boom. Therefore, a vehicle-type crane has been considered in which the jib is placed under the boom and rotated in the vertical direction to extend the jib.

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. Extend the boom and retract the sheave block at the tip of the boom forward from the base end of the jib, then use the jib transfer mechanism to transfer the jib from the side of the boom to the bottom of the boom, retract the boom, and 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. In this vehicle-type crane, the jib is stored along the side of the boom, so the boom can be installed to provide a wide field of view from the driver's cab without having to raise it higher. Moreover, since the jib can be rotated vertically and extended, the jib can be extended even in narrow spaces.

[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 activate the jib shifting mechanism without fully extending the boom, or the jib shifting mechanism may be activated before the boom is fully extended. If the jib transfer mechanism is activated before the sheave block is retracted from the base end of the jib, the base end of the jib that is rotated around the boom axis will The jib transfer mechanism hits the sheave block at the tip of the boom and is prevented from rotating, so if the jib transfer mechanism continues to operate, there is a problem in that excessive force will be applied to the jib and sheave block, damaging them.

[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 turned on before retracting the sheave book at the tip of the boom from the base end of the jib. If the crane operator continues to operate the jib transfer mechanism without knowing about the erroneous operation, the sheave at the tip of the jib or boom may be damaged. To provide a jib transfer erroneous operation alarming device for a vehicle type crane capable of preventing block damage.

[Summary of the invention]

That is, in this invention, the sheave block at the tip of the boom retracts forward from the base end of the jib.

When the start switch of the jib transfer mechanism is turned on before the crane is extended, an alarm is activated to notify the crane operator of an erroneous jib transfer operation.

[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 erroneous operation alarm system, 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. Sheaves 6a and 6b are installed at the tip.
A sheave block 5 is provided, and a rooster sheave 7 is provided at the end of the sheave block 5.

In addition, 8 is a driver's cabin that also serves as a driving operation and a crane operation room,
9 is an outrigger.

10 is a jib that supplements the length of the boom 3, and this jib 10
The boom 3 is supported at its proximal end and distal end by a jib holder and jib support bracket, which will be described later, provided on the boom 3, with the proximal end facing the boom distal end and the distal end facing the boom proximal end. It is stored along one side of the boom, and when in use, it is moved from the side of the boom to the bottom of the boom.
Thereafter, the base end is supported by the boom tip and rotated around the base end, so that it is extended to the front of the boom 3.

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 proximal end of the jib 10 has a section 20a that receives the upper surface of the jib 10, and this jib holder that rises from the center of the section 20a. The boom 3 is approximately T-shaped with a rising portion 20b, and the rising portion 20b is pivoted to a support shaft 21 provided at the lower edge of one side of the boom 3 along the boom axis direction. It is rotatably provided. Note that the support shaft 2
0 is the side of the boom.

It is provided between the lower end portions of a pair of left and right vertical members 22, 22 provided in the.

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 same figure. The cylinder 23 is installed on the boom 3 with its base end pivotally supported between the upper ends of the vertical members 22 and 22, and the rod 23a of this cylinder 23 is connected to the jib holder 2.
The jib holder 0 is pivotally attached to one end side of the portion 20a.

Further, the proximal portion of the jib 10 held by the jib holder 20 is provided with attachments 12.12 on both side edges thereof, which contact both ends of the jib receiver of the jib holder 20, and an intermediate portion of the attachment 12.12. A holder mounting bracket 13 is provided which is detachably fixed to the jib holder 20.

The base end side of the jib 10 is attached to this attachment 12.
．． 12 is received at both ends of the jib holder part 20a, the holder can be attached by connecting the bracket 13 to the jib holder 20 with a pin 24, and is held in the jib holder 20, and by removing the pin 24, the jib holder can be attached. It is now removed from 20. In addition, in Fig. 5, 25 and 26 are the brackets 13 for mounting the holder.
and a bottle insertion hole provided in the jib holder 20.

Further, a lock bin insertion hole 27 is provided near the cylinder connecting portion of the jib holder 20, and the jib holder 20 inserts the lock bin insertion hole 27 into the vertical member 22.
Insert the lock bin 2 into the lock bin insertion hole 28 provided in the lock bin 2.
9, it is locked in a horizontally rotated state.

Figure 6 shows the jib 1 relative to the jib support bracket 3o that is provided at the base end of the boom 3 and supports the distal end of the jib 1°.
This shows the support structure of Jib support bracket 3.
0 is fixed to the lower end of a vertical rib 31 provided on the side surface of the boom 3, and a bracket mounting plate 14 is provided on the tip side of the jib 10 to be removably pivoted to the jib support bracket 30. It is being

The plate 14 is attached to the jib support bracket 30 by means of a pin 32 along the axial direction of the boom 3.
The pin 32 is rotatably supported by the pin 32, and can be removed from the jib support bracket 3° by pulling out the pin 32.

Next, jib 1 is stored along the side of boom 3.
0 to the front of the boom. In this case, first, as shown in Fig. 7, the boom 3 is slightly extended, and when the jib 10 is transferred to the bottom of the boom, the base end of the jib 10 is placed under the sheave. The sheave block 5 is retracted forward from the base end of the jib 10 so as not to hit the block 5, and in this state, the jib transfer cylinder 23 is extended and the jib holder 2
0 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, is moved to the jib holder 20.
and the jib pivot point of the jib support bracket 30, and is held on the lower surface side of the boom 3.

In this case, a jib holder 20 that holds the base end side of the jib 10
is pivotally supported on the lower edge of one side of the boom 3, so the base end side of the jib 10 rotates around the lower edge of one side of the boom 3, and the tip side of the jib 10 also rotates around the lower edge of one side of the boom 3. Since the jib 10 is pivotally supported by a jib support bracket 30 fixed to the lower edge of one side of the boom 3, the jib 10 rotates around the lower edge of one side of the boom 3. It is transferred to the bottom side of 3.

FIG. 8 shows the attitude of the jib 10 with respect to the boom 3 at this time. It is held diagonally to 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. , the jib support shafts 15.15 protruding from both sides of the sheave block 5 are inserted and engaged with the fork portions 16.16 provided at the tip of the jib 10, and the fork portions 16.16
Insert the bottle 17 into the tip of the fork part 16.16 and remove it from the jib support shaft 15.15.

Make sure not to.

After this, the lifting lobe 18 of the crane is connected to the guide sheave 19 on the jib 10 side and the guide sheave 1 on the base end of the boom.
1, and its tip is hooked to the rope hooking part 10a of the jib 10 (see Fig. 11).
18 is hoisted up and the lifting rope 18 is kept under tension,
To attach the holder of the jib 10 to the jib holder 20, remove the pin 24 that fixes the bracket 13 and the pin 32 that pivots the jib 10 to the jib support bracket 30. 30
I'll remove jib 10 from it.

After this, the lifting lobe 18 is let out while raising the boom 3, and the jib 10 is rotated by its own weight around the jib support shaft 15.15 as a fulcrum, as shown in FIG.
0 hangs from the tip of the boom, then the lifting row 118 is removed from the guide sheave 11 at the base end of the boom, and the lifting rope 18 is wound up to extend the jib 10 forward of the boom.

After the jib 10 is extended in front of the boom in this way, with the boom 3 laid down close to the ground, the base end is attached to the jib 10.
The tip of the tension rod 33 attached to the jib 10 is removed from the rond support 34 by being pivotally attached to the rond support 34 and the tip of the tension rod 33 is attached to the rond support 34 provided on the base end side of the jib 10. After attaching the tip of the jib 1 to the tension rod set bin 35 provided on the sheave block 5 of the boom 3 as shown in FIG.
One lifting rope 18 may be removed from the rope hooking portion 10a of 0, and the hook 35 may be attached to this lifting rope 18 to 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 removed from the sheave block 5. After temporarily fixing the jib 10 to the rod support 34, the lifting loaf 18 is let out so that the jib 10 hangs from the tip of the self-weight boom, and then the lifting rope 18 is attached to the guide sheave 1 at the base end of the I-m.
1 (leaving the tip of the lifting rope 18 hooked to the rope hooking part 10a of the jib 10) and hoisting the lifting rope 118, the jib 10 is rotated and placed under the boom 3. After the jib 10 is held in place, the jib 10 is attached to the jib holder 20 by fixing the bracket 13 to the jib holder 20 by inserting the pin 24 and pivoting the tip end of the jib 10 to the jib support bracket 30 by the pin 32.

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 shaft 15.15 of the sheave block 5 also extends from the fork section 16. 16), then the jib transfer cylinder 23 is reduced and the jib holder 20 is
By rotating the rigid jib 10 sideways, the rigid jib 10 is stored along the side of the boom 3, and the jib holder 20 is attached to the lock bin 2.
9 to lock the boom 3 and at the same time retract the boom 3.

In addition, in the above-mentioned vehicle type crane, the cylinder 23 is used to transfer the jib 1° from the side side of the boom to the bottom side, but the jib transfer is used to transfer the jib holder 2o from the side side of the boom to the bottom side. The mechanism is not limited to one that uses a cylinder, but a dedicated winch is provided above the jib holder 20 of the boom 3, and the jib holder 20 is pulled up and rotated to the side of the boom by the hoisting rope of this winch, and the jib holder 20 and the jib 10 are jib holder 2 due to its own weight.
0 may be rotated toward the lower surface of the boom.

By the way, when extending and storing the jib 10,
When moving the jib 10 stored along the side of the boom 3 to the bottom side of the boom 3, or when moving the jib 10 tucked into the bottom side of the boom 3 to the side side of the boom 3, the boom There is no problem if the jib transfer mechanism is operated after the sheave block 5 at the tip of the boom is retracted forward from the base end of the jib 10 by extending the sheave block 3, but in reality, as mentioned above, the crane operator The jib transfer mechanism may be inadvertently activated without the boom 3 being fully extended, or the jib transfer mechanism may be activated before the boom 3 is fully extended. If the jib transfer mechanism is operated by mistake before the block 5 is retracted from the base end of the jib 10, the base end of the jib 10 that is being transferred and rotated between the side and bottom sides of the boom will be transferred to the sheave at the tip of the boom. If the jib transfer mechanism continues to operate because it hits the block 5 and is prevented from rotating, excessive force may be applied to the jib 10 and the sheave block 5, damaging them.

Therefore, in this vehicle-type crane, a jib transfer system that issues a warning to the crane operator when the crane operator turns on the start switch of the jib transfer mechanism before retracting the sheave book 5 at the tip of the boom from the base end of the jib 100. A changing operation error notification device is installed to notify the crane operator of an incorrect jib transfer operation.

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

The configuration of this jib relocation erroneous operation notification device 40 will be explained with reference to FIG. 1. In FIG.
This cylinder 23 is for transferring the jib from the side side of the boom to the bottom side of the boom, and this cylinder 23 is expanded and contracted by pressure oil sent from a hydraulic unit by switching an electromagnetic switching valve 41. In addition, 42a
, 42b is pylon 1 ~ check valve, 43a
, 43b is an aperture.

Reference numeral 44 denotes a cylinder drive circuit equipped with a switching valve drive power source 45, and this cylinder drive circuit 44 is opened and closed by a cylinder start switch 46 which is manually operated by the crane operator. This cylinder drive circuit 44 operates the electromagnetic switching valve when the cylinder start switch 46 is turned on to extend or contract the jib transfer cylinder 23. It is extended by switching the switch 46 upward or downward, and it is reduced by switching the switch 46 upward.

On the other hand, 48 is a boom length detector provided in an overload prevention device 47 provided in the vehicle type crane, and this boom length detector 48 measures the extension length of the boom 3 using a potentiometer or the like. It is designed to detect and output the detected value signal.

Note that the overload prevention device 47 includes a boom length detector 4
In addition to 8, it is equipped with a boom angle detector, load detector, etc. (not shown), and calculates the load on the crane based on the detected values of each of these detectors, and when an overload occurs, the crane is set to stop automatically.

49 also connects the sheave block 5 at the tip of the boom to the jib 10.
50 is a boom extension detection circuit, and this boom extension detection circuit 5
0 consists of a comparison circuit that compares the detected value of the boom length detector 48 and the set value of the setter 49, and when the detected value of the boom length detector 48 is smaller than the set value of the setter 49, In other words, when the boom 3 is in the retracted state, the alarm circuit 5
1, and when the detection value of the boom length detector 48 becomes larger than the setting value of the setting device 49, the boom 3 It is designed to stop outputting the signal when the is expanded.

The alarm circuit 51 is opened and closed by an alarm circuit open/close switch 52. This alarm circuit open/close switch 50 is automatically turned on and off in conjunction with the cylinder start switch 46, and when the cylinder start switch 46 is turned on. When this occurs, the alarm circuit 51 is turned on and the alarm circuit 51 is closed.

53 is an alarm drive circuit equipped with an alarm power supply 54;
This alarm drive circuit 53 is opened and closed by an alarm drive relay switch 55. This alarm drive relay switch 55 is connected to an excitation coil provided in the alarm circuit 51 when the output signal of the boom extension detection circuit 50 flows to the alarm circuit 51 which is closed by turning on the alarm circuit open/close switch 52. 56, the alarm drive circuit 53 is closed and the alarm, e.g. alarm buzzer 57, is turned on.
It is designed to operate.

Further, in FIG. 1, 58 is the cylinder drive circuit 4.
The emergency stop relay switch 59 is a bypass circuit connected to the alarm circuit 51 by bypassing the excitation coil 56, and the bypass circuit 59 includes:
An excitation coil 60 is provided to turn off the emergency stop relay switch 58.

The emergency stop relay switch 58 is of a normally closed type that is normally kept in a state where the cylinder drive circuit 44 is closed. When the output signal of the detection circuit 50 flows, the excitation coil 60 of the bypass circuit 59 turns on, opens the cylinder drive circuit 44, closes the electromagnetic switching valve 41, and extends or contracts the jib transfer cylinder 23. It is designed to stop.

To explain the operation of this jib transfer error operation alarm device,
When the boom 3 is in the retracted state, a signal is output from the boom extension detection circuit 50 to the alarm circuit 51, but if the cylinder start switch 46 is not turned on at this time, the alarm circuit 51 is open. , the alarm buzzer 57 does not operate at this time.

On the other hand, if the crane operator turns on the cylinder start switch 46 when the boom 3 is in the contracted state or when the boom 3 has not been extended to the set extension length, the cylinder start switch 46 is activated. The signal output from the boom extension detection circuit 50 flows to the alarm circuit 51, which is closed by turning on the alarm circuit open/close switch 52, which opens and closes. 55 is turned on and the alarm buzzer
57 is driven. Also, at this time, since the output signal of the boom extension detection circuit 50 also flows to the five bypass circuits connected to the alarm circuit 51, this signal turns on the emergency stop relay switch 58, and the cylinder drive circuit 44 is activated. As a result, the electromagnetic switching valve 41 closes and the jib transfer cylinder 23 is stopped.

When an alarm is issued by the jib relocation erroneous operation alarm device, the crane operator immediately turns off the cylinder start switch 46 and moves the boom 3 to the set length, that is, retracts the sheave block 5 at the tip of the boom from the base end of the jib 10. length, and then turn the cylinder start switch 46 again.
It is sufficient to turn on the jib transfer cylinder 23 to operate the jib transfer cylinder 23.

The jib transfer erroneous operation notification device of the above embodiment is equipped with a mechanism that automatically stops the jib transfer cylinder cylinder 23 when an erroneous operation occurs, so the crane operator does not have to turn off the cylinder start switch 46. The boom 3 may be extended as it is; in that case, the alarm buzzer 57 will continue to sound until the boom 3 is extended to the set length and the output of the boom extension detection circuit 50 is stopped; however, once the boom 3 is extended to the set length. The alarm buzzer 57 stops, and at the same time, the jib transfer cylinder 23 automatically operates to start transferring the jib 10.

In this manner, the jib relocation erroneous operation notification device activates the start switch 4 of the jib relocation cylinder 23 before retracting the sheave block 5 at the tip of the boom from the base end of the jib 10.
6 is turned on, it issues a warning to the crane operator and automatically stops the shifting of the jib 10.If a vehicle-type crane is equipped with this jib shifting malfunction alarm device, Since it is possible to notify the driver of an erroneous jib transfer operation and to automatically stop the operation of the jib transfer cylinder 23, damage to the base end of the jib 10 or sheave block 5 due to an erroneous jib transfer operation can be prevented. can be prevented.

In the above embodiment, the alarm buzzer 57 is used as the 11 alarm.
However, this alarm may be an alarm lamp, or a combination of an alarm buzzer 57 and an alarm lamp may be used.

Furthermore, although the jib relocation erroneous operation notification device of the above embodiment is equipped with a mechanism that automatically stops the jib relocation cylinder 23 when an erroneous operation occurs, this cylinder automatic stop mechanism may not be provided. By notifying an erroneous jib transfer operation using an alarm, the crane operator can stop the operation of the jib transfer cylinder 23, thereby preventing damage to the base end of the jib 10 or sheave block 5 due to an erroneous jib transfer operation. It can be prevented.

Further, in the above embodiment, the jib transfer error notification device for a vehicle-type crane that transfers the jib 10 using the cylinder 23 has been described. It can also be used as an erroneous operation notification device, in which case the cylinder start switch 46 of the above embodiment may be used as a winch start switch, and the winch drive circuit can be opened and closed by this switch.

(Effects of the Invention) According to this invention, when the start switch of the jib transfer mechanism is turned on before the sheave block at the tip of the boom is retracted from the base end of the jib, an alarm is issued and the crane operator is instructed to transfer the jib. It is possible to notify erroneous operation of
It is possible to prevent the crane operator from unknowingly operating the jib transfer mechanism unintentionally and damaging the jib or the sheave block at the tip of the boom.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, in which Fig. 1 is a circuit diagram of a jib relocation erroneous operation alarm system, Fig. 2 is a side view of a vehicle-type crane equipped with a jib in a jib storage state, and Fig. 3 is an enlarged cross-sectional view taken along line A-A in Figure 2, Figures 4 and 5 are side views and vertical cross-sectional views of the jib removed from the jib holder, and Figure 6 is an enlarged cross-sectional view taken along line B-B in Figure 2. Enlarged sectional view along No. 7
The figure is an enlarged side view of the boom extended when the jib is transferred to the bottom of the boom, Figure 8 is a plan view of the jib transferred to the bottom of the boom, and Figures 9 and 10 are the boom. An enlarged plan view and a side view of the state in which the jib is contracted and the jib support shaft is engaged with the fore part at the base end of the jib, Fig. 11 is a side view of the jib in the middle of being extended, and Fig. 12 is a state in which the jib is extended. FIG. 3...Boom, 5...Sheave block, 10...
Jib, 20...Jib holder, 30...Jib support bracket, 15...Jib support shaft, 16...Fork portion, 23...Jib transfer cylinder, 42...Cylinder drive circuit, 44...Cylinder start switch, 46
...Boom length detector, 47...Boom extension length setting device, 48...Boom extension detection circuit, 49...Alarm circuit, 50...Relay switch for opening/closing alarm circuit, 55
...Alarm buzzer. Applicant's representative Patent attorney Takehiko Suzue Figure 2 Figure 3 Figure 111 "°-]U Figure 4 Figure 5 Figure 6 Figure 7 Figure 12

Claims (1)

[Claims] The jib is stored along the side of the boom with the base end facing the boom tip and the tip facing the boom base, and the jib is rotated around the boom axis to move from the side side of the boom to the bottom side. 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 moves the jib from the side of the boom to the bottom of the boom. After this, the boom is retracted and the jib support shaft provided on the side of the sheave block is engaged with the fork part at the base of the jib, and then the jib is rotated around the jib support shaft and the boom is moved forward. This is a device that notifies the occurrence of an erroneous operation of starting a jib transfer before retracting the sheave block at the tip of the boom forward from the base end of the jib in a vehicle-type crane that is extended to a boom length detector. A boom extension detection circuit compares the value with the set value and 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, and this boom extension detection circuit detects whether the boom is extended. A jib transfer error operation alarm device for a vehicle-type crane, comprising an alarm circuit that activates an alarm when a start switch of a jib transfer mechanism is turned on before detection.