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Abstract: Forklift is the main tool for material transportation, with various specifications. Each type of forklift has its own applicable environment, and the wrong choice will cause inefficiency and accidents in warehousing operations. This paper systematically introduces eight types of forklifts commonly used at present, such as manual pallet truck, electric pallet truck, balanced forklift truck and forward forklift truck, and analyzes the characteristics of each type and its applicable environmental occasions. At the same time, the test and calculation method of forklift handling capacity are illustrated with examples, and the quantity requirements of various types of forklifts needed to maintain the normal work of the warehouse are obtained. There are many factors that affect the selection of forklift trucks, including floors, frequency of entering and leaving the warehouse, etc. This paper also expounds this.
Key words: manual hydraulic pallet truck, electric pallet truck, electric stacker, counterweight forklift, forward forklift, overhead stacker, picking truck, working cycle time.
With the development and progress of socialized production, the professional division of labor and machinery are becoming more and more detailed, and the matching and connection of various professional equipment make the whole logistics system run orderly and the efficiency increase exponentially.
In the traditional storage system, because there are no more choices, all the transportation, stacking and loading and unloading may be completely solved by a forklift, which is manifested in the warehouse, such as large area, low space utilization, large number of people, scattered stacking of goods, slow delivery during peak hours, vehicle queuing and other shortcomings. At present, the whole process of goods from warehousing, shelving, picking and distribution to warehouse can be completed by balancing forklift, various indoor handling machinery or automatic unmanned handling equipment, conveyor belt, automatic sorting equipment and other professional equipment. , various devices can complete instructions and connections through spreadsheets or wireless transmission. A warehouse environment as bright, clean, fast, efficient and orderly as an office can be realized at any time.
Since the invention and use of pallets, forklifts (including indoor and outdoor forklifts) have been used as the main tools for material transportation. Forklift trucks with innovative functions and higher automation will still occupy the leading position in the transportation field for a long time to come. Next, we will discuss how to choose the right forklift according to the environment, and some factors that need to be considered when choosing a forklift.
First, let's look at the classification of forklifts.
According to the use environment of forklift trucks, they can usually be divided into indoor and outdoor. Outdoor forklifts are usually large-tonnage diesel, gasoline or liquefied gas forklifts, such as container forklifts and cranes used in docks or container transfer stations. Indoor forklifts are basically battery cars. At present, the world's major forklift manufacturers can provide hundreds of specifications, and we usually divide these different specifications into several series. Take JUNGHEINRICH, a German company that ranks the top four in the world in total sales volume and the first in indoor equipment, as an example. Its main products can be roughly divided into eight series:
* Manual hydraulic pallet truck (manual pallet truck)
* electric pallet truck (electric pallet truck)
It can also be divided into three types: self-propelled, standing driving and sitting driving.
* Electric stacker (supporting arm stacker) can be divided into three types: self-propelled, standing driven and sitting driven.
* Electric balance car (electric balance car)
It can also be divided into three wheels and four wheels, rear wheel drive and front wheel drive.
* Diesel/LPG balance truck.
* Forklift extending forward
* Overhead stacker (overhead stacker)
It can also be divided into master students and master students.
* Picking trucks (order pickers)
It can also be divided into two types: plane picking and high-level picking.
All the above series have their most suitable occasions and environments, and some functions overlap, such as balanced forklift, forward forklift and overhead stacker, which can be connected to the shelf area. So what are the benefits for users to choose which model?
To give a simple example: suppose such a warehouse requires that the goods stored in each pallet can be accessed at any time, so it must be placed on both sides of the forklift aisle. On the premise of only considering the plane area, let's take a look at the plane utilization rate of different types of forklifts in this warehouse.
* If the channel width of the forklift used is roughly equal to the length of the carrier (1500mm), the plane utilization rate can reach 66%;
* If the passage width of the forklift truck used is equivalent to twice the length of the carrier (2700mm), the plane utilization rate can reach 50%;
* If the channel width of the forklift truck used needs to be 3 times the length of the carrier (3500mm), the plane utilization rate can reach 40%;
Obviously, if the plane area of the warehouse to store goods is 1000m2, then in the first case,1000/0.66 =1515m2 land is needed. This situation is equivalent to the scheme of adopting overhead stacker or track stacker.
The second case requires 1000/0.50=2000m2 of land. This is equivalent to using a forklift extending forward.
In the third case, land of 1000/0.40=2500 m2 is needed. Equivalent to the case of using a balanced forklift.
Therefore, choosing the right forklift can greatly save the investment in land and construction, which is the most intuitive benefit.
Let's take a look at the characteristics and applicable environment of various forklifts.
Both manual pallet trucks and electric pallet trucks are plane point-to-point transportation tools. The compact and flexible shape makes the manual pallet truck suitable for almost any occasion. However, due to manual operation, it is difficult to transport heavy goods of about 2 tons, so it is usually used for short-distance frequent operations of about 15 meters, especially in loading and unloading areas. In all aspects of logistics in the future, manual pallet trucks will also play a role in connecting all transportation links. Every truck or truck is equipped with a manual pallet truck, so the loading and unloading operation will be faster and more convenient, and it is not limited by the site.
When the plane transportation distance is about 30 meters, the walking electric pallet truck is undoubtedly the best choice. The driving speed is controlled by the stepless speed change switch on the handle, which follows the walking speed of the operator, thus reducing the fatigue of personnel and ensuring the safety of operation. For example, when the distance of the main transportation route is more than 30 meters to about 70 meters, the electric pallet truck with folding pedals can be used, and the driver can stand and drive, and the maximum speed can be increased by nearly 60%. Take Forever Forklift as an example, its brand-new ERE20 can reach 65,438+00 km/h when it is empty.
Electric stacker is a kind of light indoor lifting stacking equipment, and its body is relatively light. The arm of the counterweight is lengthened by the supporting arm at the front of the car body to balance the load. Because the fulcrum is outside the center of gravity of the load, and the gravity arm is much larger than the load arm, a smaller counterweight can lift a larger load. Take the electric stacker EJC 14 of Eternal Force as an example. Its rated load is 1.4 tons, but its own weight is only 955 kilograms, and its length, width, height and turning radius are relatively small. Eternal Force has its patented slow button device, which can operate slowly in the vertical braking position. These characteristics make it especially suitable for ground warehouses or other storage environments with small space. The load range of this series is 1 ~ 1.6 tons, and the maximum lifting height is 5350. Back-to-back heavy pallet shelves of 3-4 meters are the most commonly used and effective environment, and are the economic choice for small warehouses.
The use of electric stacker is also limited, because the fork and the support arm need to extend into the bottom of the pallet at the same time to operate the pallet, so double panels cannot be used; Similarly, when using the drive-in shelf (or corridor shelf), for the sake of balance and load-bearing, one side on both sides of the pallet is usually used as the forklift operation surface, and the electric stacker cannot be used at this time. In the shelf design of electric stacker, beams are often installed at the bottom about 100mm from the ground, and the first floor of goods is placed on the bottom beam instead of the ground, which is convenient for forklift positioning.
In fact, we often refer to the balance forklift as forklift, which is also the most widely used and used series. Because there is no supporting arm, it needs a long wheelbase and a large counterweight to balance the load, so the body size and weight of three-wheeled, four-wheeled, electric and diesel are very large, which requires a lot of working space. At the same time, the fork directly forks the goods from the front wheel, which has no requirement for the container; The chassis is high, and rubber tires or pneumatic tires are used to make it have strong climbing ability and ground adaptability. Therefore, balanced forklifts are widely used for loading and unloading goods and outdoor transportation.
In the electric balance forklift, it can also be divided into three wheels and four wheels, front wheel drive and rear wheel drive. Steering and driving are both called rear wheel drive. Compared with front wheel drive, rear wheel drive has the advantages of lower cost and easier positioning. The disadvantage is that when walking on the smooth floor and slope, the pressure of the driving wheel will be reduced when loading, and the driving wheel may slip. At present, most electric balance forklifts are driven by double-motor front wheels. Compared with the four-wheel balanced forklift, the three-wheel balanced forklift has smaller turning radius and is more flexible, which is most suitable for unpacking containers. Now, Eternal Power Company applies AC technology to the electric balance forklift, which greatly improves the overall performance of the forklift and greatly reduces the later maintenance cost. This technology is called the future technology of forklift.
Diesel and liquefied gas forklifts are divided into two types according to different transmission modes: hydraulic mechanical transmission type and hydrostatic transmission type. Hydromechanical transmission is a traditional transmission mode with low cost, but hydraulic torque converter has low transmission efficiency, high energy consumption and high maintenance cost. Hydrostatic transmission is the most ideal and advanced transmission mode of internal combustion forklift at present. Its main features are soft start, stepless speed change, quick commutation, simple maintenance and high reliability. The use efficiency of hydrostatic transmission internal combustion forklift truck is obviously improved when it is frequently transported back and forth in short distance outdoors.
Since 1953, Dr. Jungheinrich in Germany invented Reach truck, this series of equipment has gradually become the main tool for indoor overhead access, and its stable load lifting performance has enabled the three-dimensional warehouse to break through the boundary of 6.5 meters height for the first time. At present, the maximum lifting height of the forward-extending forklift reaches 1 1.5m, and the load ranges from 1 ton to 2.5 tons. Special products such as multi-forward-extending forklift for storing and taking out long pipe fittings and indoor and outdoor universal forward-extending forklift have been developed.
Forward-extending forklift combines the advantages of electric stacker with supporting arm and forklift without supporting arm counterweight. When the gantry (the gantry extends forward in European design and the fork extends forward in American design) extends to the top, and the load center of gravity falls outside the fulcrum, it is equivalent to a counterweight forklift; When the gantry is fully retracted, the center of gravity of the load falls on the inside of the fulcrum, which is equivalent to an electric stacker. The combination of these two characteristics ensures the flexibility of operation and high load performance, and at the same time, the volume and self-weight will not increase too much, which saves the working space to the maximum extent.
The most effective working height of the forward forklift is 6 to 8 meters, which is equivalent to the building height of about 10 meter. This height is also the most common building height for shops, distribution centers, logistics centers and enterprise central warehouses. In this height range, the operator can see that the positioning is fast and efficient. When the working height exceeds 8 meters, it is necessary to use the forward forklift slowly and carefully to locate the fork. Usually, auxiliary devices such as height indicator, height selector or camera can be added.
If the warehouse is small in area and high in height, but it needs large storage capacity and high transportation efficiency, and if you don't want to spend huge investment on the automated warehouse, then the overhead stacker is the only and best choice. Usually, the overhead stacker and the high-position pickup truck are called VNA(Very Narrow Aisle), whose main feature is that the fork can rotate in three directions, or directly fork the goods from both sides, without turning in the roadway, so the required roadway space is minimal. The maximum lifting height of VNA series exceeds 14m, the roadway width is usually around 1600mm, and the maximum load capacity is1.5t. VNA series is widely used in pharmaceutical industry and electronic appliance industry.
Overhead stacker can be divided into two types: indoor type and non-indoor type. The cockpit is called the main room type, and as the main elevator, it rises with the gantry. Its advantages are that it can keep horizontal operating sight at any height, ensure the best visual field and improve operating safety. At the same time, because the operator can touch the goods at any position on the shelf, it can be used for picking and counting at the same time.
In order to keep the overhead stacker running straight all the time, there are two ways: magnetic guidance and mechanical guidance. Magnetic guide, because it is necessary to cut and bury magnetic wires in the center of roadway, it is easy to destroy the floor and it is difficult to move and adjust, so mechanical guide is the most widely used at present. Mechanical guidance should be coordinated with the shelf, tracks should be installed on both sides of the roadway, and auxiliary devices such as guide wheels should be used to guide the roadway and drive along a straight line.
VNA forklift trucks, also known as system trucks, need to consider various factors and influencing factors, so each situation needs to be designed separately, so I won't go into details here.
Picking trucks are widely used in distribution centers or third-party logistics warehouses.
Each forklift has its corresponding handling capacity, expressed by the number of pallets operated per hour or per day. For different use environments and different operators, this number is also different, so it is necessary to conduct targeted tests. Here is a simple calculation method of forklift handling capacity.
T: Time required to complete a work cycle (test value)
T = T 1+T2+T3+Th
T 1: the time required for one working cycle in the length direction.
T2: Time required for one working cycle in the width direction.
T3: Time required for one working cycle in the direction of entry.
Th: Time required for one working cycle in the height direction.
1. Assuming that the distance from point A to point B is a standard test distance, testing a working cycle time includes the following processes:
1. Drive the forklift to point A for positioning, lift the pallet and drive out of point A..
2. accelerate, drive to point b and brake.
3. Drive into point B, locate the tray, put down the tray and drive out of point B..
Step 4 speed up and go back to the starting point
The above test results are the time required for the planar working cycle.
2. Take 1/2 of the total shelf height as a working cycle distance, lift the pallet to this height, and then lower it to the ground. This test time should be calculated from the time when the fork is inserted into the pallet to the time when the fork exits the pallet, that is, it does not include the fork picking time, but only the lifting time.
Take VNA overhead stacker as an example, because it only works in The shelf area, the total cycle time includes T 1, T2 and th.
The standard test distance of T 1 is S2, and S2= 1/4 shelf area length.
The standard test distance of T2 is S3, and S3= 1/2 shelf area width.
The standard test distance of Th is 1/2 shelf height.
Therefore, T=T 1+T2+Th.
Forklift capacity per hour =3600 seconds/ton
Assuming a shift operation, the operation time is 8 hours, and the forklift utilization rate is 60%, the transportation capacity that can be completed by one shift can be obtained.
Cmax = 8x3.600x60%/t = 7,280/t cycle/shift.
Through the above calculation, we can get the number of forklift trucks used in a warehouse, or decide whether to use spare batteries to maintain the normal operation of the warehouse.
Traditional warehouse design, usually building first, then considering layout planning and mechanical equipment, often leads to waste of investment. By analyzing and anticipating the production plan, choosing the appropriate storage mode of logistics form, and then designing and planning the civil works, or both, the best investment income can be obtained. The choice of forklift is inseparable from the design of storage form. Errors in equipment selection often lead to inefficiency or accidents in actual operation, and in serious cases, it is necessary to dismantle and rebuild. Therefore, in the initial design and equipment selection of the storage system, we should not only consider the applicable height and roadway space of the above-mentioned series of vehicles, but also consider other factors in combination with our own conditions. There are many influencing factors. The following are just some examples:
Pallet: Most forklifts are operated by pallets, so the size and form of pallets often affect the choice of forklift forms and specifications. Operating pallets with different depths and widths requires different road space. More importantly, if the center of gravity of the pallet and the goods it carries exceeds the design load center of the forklift, the load will drop. Therefore, it is usually recommended to adopt the standard pallet form. At present, the four-way fork pallet of European standard 800x 1200 or 1000x 1200 is widely used. It can be applied to various vehicles.
Floor: the smoothness and flatness of the floor greatly affect the use of forklift trucks, especially when using high-lift indoor forklift trucks. Assuming that the lifting height of the forklift is 10 meter, if there is a height difference of 10 mm between the left and right wheels of the forklift, it will cause an inclination of nearly 80 mm at 10 meter, thus causing the danger of shelf use. There are usually three kinds of surface conditions of the floor, and the most influential is the uneven ground, which should be avoided as far as possible; If the ground fluctuates, there is a certain height difference at a certain distance, which is allowed; The best floor is flat and smooth, usually a concrete floor with surface treatment. Factors that need to be considered in the floor include bearing capacity, wheel pressure of forklift, etc.
Elevator, container height, etc. If forklift trucks need to get in and out of elevators or work in containers, the entrance heights of elevators and containers should be considered. There are several types of gantry for forklift trucks to choose from. At this time, it is usually necessary to choose a gantry with large free lift.
Daily workload: The frequency of goods entering and leaving the warehouse and the daily workload of the forklift are related to the selection of forklift battery capacity or forklift quantity to ensure normal operation.
Others should also be considered, such as the peak period of warehouse operation, wheel materials, building restrictions and so on.