Stacker cranes are a great asset in the world of logistics because they help automate the operating cycle. They are the backbone of automated warehouses, thanks to which many companies are able to improve performance, speed up the handling of goods and increase their productivity.
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Stacker cranes are machines used to automatically store and pick various types of goods such as pallets, boxes, containers, tyres. They are robots and, thanks to control systems integrated into them and warehouse management software, stacker cranes are able to execute all commands given to them.
These machines are programmed to store products automatically at the pre-determined location, guaranteeing error-proof and low-cost work. Stacker crane operated warehouses can be over 150 metres long and up to a maximum of 45 metres high.
What does a stacker crane consist of and how does it move?
- By a mobile frame that moves by means of belts, chains or supporting ropes, along a vertical structure and within an aisle, typically bounded by two racks;
- The vertical structure actually consists of one or more columns in turn anchored to a beam running along a rail on two supporting wheels, one driving and one driven. In some cases, machines with several driving wheels are designed for high-performance machines;
- There are contrast wheels at the top that keep the sideshifter upright.
Depending on the goods to be handled, there are different types of stacker cranes: stacker cranes for pallets or for larger and heavier goods, and miniloads, for handling lighter and smaller loads.
In addition, they can handle single- or double-deep and multiple-deep warehouses, i.e. with a variable number of containers per side.
Stacker cranes for pallet
Stacker cranes for pallet are designed for the automatic storage and pick of pallets, boxes and other bulky loads. They move along aisles according to the commands of specific software that allows an operator to manage them.
The dimensions of the pallet stacker cranes can reach a height of 45 metres in their self-supporting warehouse version, with load capacities of over 10 tonnes.
The strengths of automatic stacker cranes include:
- the precise automation of pallet entry and exit,
- improving the management of inventories by constantly updating them,
- the elimination of errors typical of manual operations,
- the speed of picking, regardless of unit size,
- the guarantee for operators to work in complete safety,
- the possibility of being equipped with mechanisms for recovering energy during braking
- their energy efficiency,
- the versatility, which allows them to adapt to almost all types of goods and different temperatures, even as low as -35 °C in a cold store.
There are two main types of pallet stacker cranes: single-column and double-column.
Single-column stacker cranes
Single-column pallet stacker cranes, as the name suggests, consist of a single column and are most suitable for warehouses with lighter loads. In this sense, we can indicate an ideal pallet weight of between 1,000 and 1,500 kg.
Double-column stacker cranes
In this type of stacker crane, the structure with two vertical columns corresponds to an elevation cradle in the centre, which allows access to all storage levels. As double-column stacker cranes are stronger than single-mast cranes, they are well suited to handling heavy or bulky loads.
Miniloads
The miniload is a machine similar to the stacker crane but with a tendentially lighter structure, designed to handle boxes or plastic crates. The advantages to be found in this type of stacker crane are the same as those already mentioned in those for pallets, simply related to smaller loads and dimensions.
As far as their configuration is concerned, the miniload stacker cranes also come in single-column and double-column variants. The twin-column stacker cranes for containers can be up to 20 metres high, moving up to four containers weighing over 50 kg each at the same time.
LCS Group’s automated storage solutions
LCS Group, operating since in the fields of internal logistics and industrial automation, designs and manufactures automatic warehouses that can also be customised on request. Since the stacker cranes represent the focal point of the system that makes up the automatic warehouse, it is important to be able to count on a wide choice of products that vary according to the load capacity, the size of the goods and the type of height to be reached for storage.
What is the pallet size? How many pallet locations do you need? How much throughput will you require? How many SKU will be kept in your ASRS?
When I get a project, I always ask customer questions as this order. There is no doubt, pallet size is the basic point in ASRS design, which decides the racking structure, and pallet location is related with how big area will this ASRS need. Today I need to discuss about throughput.
About Throughput
Throughput means cargo inbound and outbound frequency. In other words, how many pallets inbound and outbound per hour in ASRS? I would like know such data from customer, 120 pph (pallets per hour) inbound 8 hr per day, 100 pph outbound 10 hr per day. The amount of inbound and outbound for a day should be almost the same, for if inbound is more than outbound, the ASRS will be full finally, if outbound is more than inbound, the ASRS will empty forever. Usually we take the peak throughput as our design target to make sure it can work at any time.
About Single Circle and Combine Circle
Single circle means stacker crane takes 1 pallet from inbound point and unload at defined location, then back to inbound point or stacker crane gets order from WMS to defined location take the pallet and go back to outbound point. It deals with 1 pallet operation in 1 circle.
Combined circle means stacker crane takes 1 pallet from inbound point and unload this pallet at defined location, then move to next defined location, taking the cargo and move to outbound point.
It deals with 2 pallet operation (1 inbound and 1outbound) in 1 circle.
Parameter Explains
Stacker Crane Travelling Path and Lifting Path
According to FEM 9.851 Performance data of SRMs: Cycle time, throughput calculation will use 2 point inside of ASRS. Point A(1/5L,2/3H) and point B(2/3L, 1/5H), L is racking length, H is distance from first layer bottom to top layer bottom.
Inbound and outbound Offset
Inbound point and outbound point are not on the same floor in some project. In our Hengshun Vinegar project, FG are palletize by robot hands and sent to ASRS by conveyor, its inbound point was installed on mezzanine floor. It effects stacker crane circle mode.
Max. SRM Travelling Velocity and Average Acceleration
Our HUADE brand stacker crane travelling speed range is from 120-160m/min and average acceleration is 0.3 to 0.5 m/s2. There are 2 situation when we calculate how long will stacker crane arrive at defined location in X direction (horizontal direction). Situation 1: The travelling path is not long enough, stacker crane cannot reach to max velocity before half point, when it passes half point, it will slow down and stop at defined location. Situation 2: The travelling path is long enough, stacker crane can reach the max velocity before half point. It will do uniform motion and then slow down until it arrives at the defined location.
Max. SRM Lifting Velocity and Average Acceleration
HUADE brand stacker crane lifting speed range is from 40-60m/min and average acceleration is 0.3 to 0.5 m/s2. Lifting calculation also should consider 2 situations, and method is the same as the travelling.
Fork Velocity, Travelling Path, Creeping and Position period
HUADA fork telescopic speed range is from 30-60m/min, full loaded speed and empty loaded speed will be different. Fork travelling path is equal to stroke length, and our fork need 3.28 seconds to finish creeping lift or down operation.
Responding Time
Every move of stacker crane follows orders from WMS, it need to analyze and finish these operations which need responding time. We suppose this period is 12 seconds in every circle.
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Single Circle
We need to judge whether the stacker crane can reach Max. Velocity before half point in X direction, it calculation will go like following:
0.5*a*(Vmax/a)≥0.5*L/5, it is situation 1.
Stacker crane reach to Point A defined location in X-direction period calculation will go like following:
If 0.5*a*(Vmax/a)＜0.5*L/5, then it is situation 2. The calculation method will go like following:
Accelerated motion/Decelerated motion period:
T=Vx/ax
Uniform motion period:
S=0.5*ax* T2
Tu=(L/5-2S)/Vx
Tx= 2Ta+ Tu
We need to calculate the lifting period, the method is the same with travelling period. First, judge it is situation 1 or 2.
0.5*a*(Vmax/a)≥0.5*2H/3, it is situation 1.
Stacker crane reach to Point A defined location in Y-direction period calculation will go like following:
If 0.5*a*(Vy/ay)＜0.5*2L/3, then it is situation 2. The calculation method will go like following:
Accelerated motion/Decelerated motion period:
T=Vy/ay
Uniform motion period:
S=0.5*a* T2
Tu=(L/5-2S)/Vy
Ty= 2Ta+ Tu
Stacker crane does travelling and lifting at the same time, so we should compare Tx and Ty, and take the max one as stacker crane from O to A period in Y direction.
Fork velocities are different in empty and unloaded situations, also they have different acceleration. The calculation will goes like following:
T=Vze/aze
Uniform motion period:
S=0.5*a* T2
Tu=(L/5-2S)/Vz
Tze= 2Ta+ Tu
And Full load calculation method is the same.
Tz=Tze+Tzf+Tcr*2
Finally, Ta=Tx/Ty+Tzr+Tr, T=( Ta+ Tb)/2
Combined Circle
Ta and Tb calculation method is the same. The Period of Point A to Point B, we can called it Tab
Finally, T= Ta+ Tb +Tab+2*Tz+Tr
According to experience, the practical throughput is 80% of theoretical throughput. So we can do the rough calculation by this method.
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