This document describes an improvement on the boom/mast safety control system of mobile shipping container handlers. A mobile shipping container handler comprises a chassis that is connected to a container spreader via a boom or mast, with such handlers more commonly referred to as reach stacker or top pick container handlers.
Mobile shipping container handlers are used worldwide and are manufactured by numerous companies. They are commonly found at rail intermodal yards or container shipping ports. Operation of a container handler is performed by a person referred to as the operator. The operator uses various controls including a joystick to maneuver the spreader. Over the years, safeties have been built into the machine using electric relays and timers and/or computer systems, such as a PLC (Programmable Logic Control), to decrease the number of accidents caused by operator error. The safety logic surrounding hoist function is typically limited based on the following situations:
1) Is the machine locked onto a container? (Green light)
2) Is the machine unlocked from a container? (Red light)
3) Is the machine within its safety envelope?
The locked and unlocked information is determined by proximity sensors on the twistlocks that are located in the four corners of the spreader (some older machines use only two sensors, one for each arm). The machine safety envelope is determined based on the type of machine. On a typical top pick, the safety envelope is simply the maximum capacity of the machine and weight is measured with a load cell or a pressure sensor on one or both of the lift cylinders. On a reach stacker, the safety envelope is more complex due to significant changes in the center of gravity caused by the reach capability of the machine. The envelope is determined based on three sensor readings. These readings are:
a) Boom angle—Inclinometer sensor
b) Boom length—Cable reel with a potentiometer
c) Weight of the load—Load cells or pressure sensors on the lift cylinders
A calculation of the boom angle and length readings is performed repeatedly and the maximum lift capacity is adjusted based on that calculation. The weight of the load is then logically compared to the maximum lift capacity to ensure that the machine is still within its safety envelope. If any one of the aforementioned situations are not met, boom/mast function is limited. In the event of situation 1 or 2 failing to be met, all boom/mast hoist and lower functions are locked. In the event of situation 3 failure, boom/mast hoist is locked.
One area of limitation that has been overlooked is in the regulating of hoist function immediately after attaching the spreader to a shipping container. The machine manufacturers expect the operator to operate the controls smoothly and slowly when initially hoisting a load. However, the increased demand for faster operation and higher container lifts per hour has resulted in many operators ignoring this expectation. This results in significant strain and impact forces on the spreader that were not intended. Embodiments of this document may resolve this discrepancy between manufacturer expectations and operator's actions. Through the use of existing sensors, additional programming logic may be added to the machine to limit the hoist functionality of the machine subsequent to attaching onto a shipping container.
A method is disclosed of operating a mobile container handler, which has a spreader mounted on an extendable boom or a mast and carriage assembly, the method comprising: a. monitoring whether the spreader is locked to the shipping container; b. monitoring whether the spreader is landed on the shipping container; c. limiting a hoist function of the mobile container handler when both of the following conditions are satisfied: i=the spreader is locked to the shipping container; and ii=the spreader is landed on the shipping container; and d. resuming a normal mode of the hoist function of the mobile container handler when all of the following conditions are satisfied: iii=the spreader is locked to the shipping container; and iv=the spreader is not landed on the shipping container.
A method is disclosed for use with a mobile container handler of the reach stacker or top pick type in which the limitation of hoist function immediately subsequent to attaching the container spreader to a shipping container is achieved by the following logic: a. Monitoring the locked or unlocked signals from the spreader twistlock position sensors, b. Monitoring the landed signal from the spreader seated pin position sensors, c. Limiting hoist function if the results from a & b are: i. a=spreader attached to a shipping container, ii. b=spreader landed on a shipping container, d. Resume normal hoist function once the result from b becomes negative and the elapse of a prescribed amount of time (presumably 2 seconds but adjustable based on machine).
In various embodiments, there may be included any one or more of the following features: The mobile container handler comprises a chassis with a drive axle and a steer axle, and that is connected to the spreader by an extendable boom. The mobile container handler comprises a chassis with a drive axle and a steer axle, and that is connected to the spreader by a mast and carriage assembly. The method is performed using control signals from a controller. The controller comprises a PLC (Programmable logic control). The controller controls the hydraulic hoist directly by means of a PWM (Pulse Width Modulation) value. The hydraulic hoist is controlled indirectly by means of a pilot control valve. The pilot control valve is located inline on a hoist pilot pressure from a joystick that controls a hoist valve. The pilot control valve comprises a pressure control valve. The pilot control valve comprises a flow control valve. The pilot control valve comprises a directional control valve and a pressure relief valve. Performing the method using electric relays and timers. Resuming further comprises resuming the normal mode of the hoist function of the mobile container handler when all of iii, iv, and the following condition are satisfied: v=a prescribed non-zero amount of time has elapsed after condition iv has occurred. The prescribed non-zero amount of time comprises two or more seconds. The spreader comprises twistlocks for locking the shipping container. Monitoring whether the spreader is locked is performed using signals from position sensors on the twistlocks. Monitoring whether the spreader is landed is performed using signals from landed pin position sensors on the spreader. Limiting the hoist function comprises reducing the maximum power of the hoist function to 25% or less relative to the maximum power of the hoist function when in the normal mode. Retrofitting the mobile container handler with a controller programmed to carry out the method. The mobile container handler comprises a reach stacker or a top pick. A mobile container handler configured to perform the method. A controller programmed to carry out the method when installed on the mobile container handler. A reach stacker in which the machine comprises a chassis with a drive axle and a steer axle that is connected to the container spreader by an extendable boom. A top pick in which the machine comprises a chassis with a drive axle and a steer axle that is connected to the container spreader by a mast and carriage assembly. The logic is performed by a PLC (Programmable logic control) or similar computer system designed for use on mobile industrial equipment. The PLC or computer system controls the hydraulic hoist directly by means of a PWM (Pulse Width Modulation) value. The PLC or computer system controls the hydraulic hoist directly by means of a PWM (Pulse Width Modulation) value. The PLC or computer system controls the hydraulic hoist indirectly by means of a pilot control valve, comprises a pressure control valve, located inline on the hoist pilot pressure from the joystick that controls the hoist valve. The logic is performed using electric relays and timers. The electric relays and timers controlling the hydraulic hoist indirectly by means of a pilot control valve, comprising a pressure control valve, located inline on the hoist pilot pressure from the joystick that controls the hoist valve. The electric relays and timers controlling the hydraulic hoist indirectly by means of a pilot control valve, comprising a pressure control valve, located inline on the hoist pilot pressure from the joystick that controls the hoist valve. The pilot control valve comprises a flow control valve. The pilot control valve comprises a directional control valve and a pressure relief valve.
These and other aspects of the device and method are set out in the claims, which are incorporated here by reference.
Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:
a. a pressure control valve,
b. a flow control valve or,
c. a directional control valve and a pressure relief valve.
a. a pressure control valve,
b. a flow control valve or,
c. a directional control valve and a pressure relief valve.
Immaterial modifications may be made to the embodiments described here without departing from what is covered by the specification.
Embodiments of this document are advantageously designed to address damage caused by abrupt operator inputs on the joystick of a reach stacker or top pick container handler when initially hoisting a shipping container.
Based on conventional logic, there is no limitation in the hoist provided the aforementioned situations are met. A lack of limitation to boom/mast hoist is the cause of significant spreader damage. The situation in question occurs immediately after the spreader is attached to a container. The machine is within its safety parameters and full hoist function is allowed. The operator can pull full power on hoist resulting in a sudden upward jolt on the spreader. This is a problem due to space between the spreader arms 15 and the spreader body 10. The space exists to facilitate movement of the spreader arms inside the spreader body. Some of this space is removed with the wear pads 20, but as the pads wear, the space increases. The sudden hoisting of the spreader causes impact points on various parts of the spreader body and/or the spreader arms based on the orientation of the spreader. On most models, the spreader body comprises two square tubes joined together with additional reinforcing steel, although other variations of spreaders may be used. The spreader arms can be in one of several orientations, including:
1) Oriented for 20′ containers,
2) Oriented for 40′+containers.
Referring to
Referring to
Embodiments of this document may eliminate the damage being caused by sudden hoist inputs by the operator subsequent to attaching to a shipping container. This may be achieved by adding additional logic to the safety system of the machine. Referring to
In previously mentioned embodiments, with the addition of the previously described logic, the operator will no longer be able to pull at full power on hoist and cause impact forces on the spreader 45 immediately after attaching to a shipping container 30. This may in turn eliminate or reduce the damage cause by impact forces that were previously commonplace.
Referring to
Referring to
Referring to
a. a pressure control valve,
b. a flow control valve and/or,
c. a directional control valve and a pressure relief valve.
In the example shown, operator input on the joystick 300 may be transmitted to a pilot control valve 320 via hydraulic pilot pressure. PLC 305 may transmit an electronic signal to the pilot control valve 320 if hoist function is permitted. Pilot control valve 320 may receive a signal from PLC 305 indicating that hoisting is permissible and thus valve 320 may allow pilot pressure from the input on the joystick 300 through the pilot control valve 320 to a hydraulic valve 310. Hydraulic valve 310 may be a suitable valve, such as a directional control valve that delivers hydraulic fluid to the hoist cylinders 315.
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
Referring to
The hoist function may be provided by operating one or more actuators, such as hoist cylinder 315 and extendable boom 64 (
In the claims, the word “comprising” is used in its inclusive sense and does not exclude other elements being present. The indefinite articles “a” and “an” before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.
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