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Jerk-free linear motions – from the steering wheel to the fork

drylin® linear drives for Jungheinrich special forklifts
 

There is a lot of work for creative designers in the Jungheinrich plant in Lüneburg. This plant is exclusively responsible for special forklifts and modified serial-production devices, and manufactures a variety of industrial trucks that handle special tasks, such as transport of paper rolls. Lubrication free linear drives from igus® are used in the special designs as needed – on the operator workstation and in the load-handling equipment.
 
Jungheinrich AG of Hamburg is officially cited as the the world's number three manufacturer of industrial trucks, such as forklifts and other vehicles for the inner-company material flow. The company's six plants produced approximately 73,200 industrial trucks in 2012.

Specialized in special forklifts
 
In the production network the Lüneburg plant is responsible for special forklifts and small-lot production. In some cases, existing devices from the large-scale production are modified in the Lüneburg plant to meet special customer requirements. However, many devices newly developed from the ground up; naturally in this process the engineers can avail themselves of the complete design construction set of the serial production.
 
In the forklift market this is an offering that is not entirely self-evident, yet it is in high demand, the capacity of the plant founded in 1990 is well utilised. Last year the approximately 230 employees manufactured 8000 special forklifts and 6000 modified devices. In this regard genuine craftsmanship is demanded, as designer Dipl.-Ing Aimo Helbach explains: "The average lot size for special forklifts is two forklifts. If we receive in order for five identical devices, this is large-scale production for us. “

Special forklifts

The special forklift is used to "gather-in" trolleys in a large dairy facility and feed them into the washing system. (Source: igus GmbH)

 

A special type of industrial truck
 
At first glance, the special low-stroke vehicle that Jungheinrich recently built in Lüneburg and delivered to a large dairy in Scandinavia, has an irritating effect. Where every "normal" low-stroke device has a double fork as load-handling equipment for taking up pallets, in this case there is only a single fork and a single castor. Considered from the chassis perspective this is sort of a "turned around" three-wheel forklift. And the missing second fork is compensated through an additional boom-like load-handling device in the third dimension.
 
The purpose of this design becomes clear when Aimo Helbach explains the intended purpose: "The vehicle gathers in trolleys throughout the entire dairy facility, these trolleys can be pushed inside of each other, and the vehicle transports them to the infeed point of an automated washing system. "For this task a single fork suffices; the operator drives the single fork between the rollers of the trolley. When the operator activates the lift function he clamps the trolleys against the upper, fixed load handling device, and can even safely drive over longer distances without losing a trolley.

Supplemental function: Lubrication free linear system swivels out "wings"
 
Jungheinrich has already built these types of machines several times for various dairies. However, for the current project the responsible parties desired an additional function. Aimo Helbach: "The washing system accommodates ten trolleys. To also ensure that the forklift only transports ten trolleys, a triangular sheet metal element that limits the number of trolleys that are taken along is mounted at the front on the clamping device. However, there are also other destinations to which more trolleys should and can be transported. In this case the wings are designed to pivot. “

drylin SHT

The drylin® SHT linear axis works wear free and lubrication free. A DC motor and an end position scan ensure optimal integration in the movement sequences of the forklift when taking up and setting down the trolleys. (Source: igus GmbH)

 
Jet-Pilot

The position of the Jet-Pilot can be adapted to the operator's body size via an additional drylin® linear unit. (Source: igus GmbH)

 

The designer thus is faced with the task of moving the triangular sheet metal element up and down, through motor force. This occurs with an igus® linear axis from the drylin® SHT product range with trapezoidal thread and 60 mm travel. The ball bearing supported, lubrication free lead screw unit was delivered by igus® ready to install with a compact DC motor and end position scan. A wedge made of wear-resistant plastic translates the linear motion into a pivot motion and ensures that the wing-shaped sheet metal elements pivot downward 30°. The operator gives the appropriate command on the Jet-Pilot.

Trapezoidal threads

A trapezoidal thread with handwheel ensures fast adjustment of the Jet-Pilot in the vertical axis. (Source: igus GmbH)

 
End of the boom

The motion of the drylin® SHT linear axis causes the pivoting of the wing-shaped sheet metal elements on the end of the boom. (Source: igus GmbH)

 

If the pair of wings should be pivoted upward, the drylin® system moves in the opposite direction, the wedge enables the motion and a spring ensures retraction of the wings to the "Up" position. The ideal slide pairing of aluminium guidance and plain bearing elements made of the high-performance polymer iglidur® J ensures a quiet run, the spindle itself is made of steel. The system is activated by a multi-function micro-controller that Jungheinrich developed expressly for the special vehicles.
 
High requirements imposed on ergonomics
 
This drive, designed by Aimo Helbach translates one motion into the other twice (from the rotative motion of the motor into the linear motion of the linear system, and from the linear system into the pivot motion). The system has proven itself to be ideal in all test runs – and it is not the only system that uses an igus® linear axis. An individual solution was also designed for the arrangement of the operator workstation. Aimo Helbach: "Conventional low stroke vehicles are operated via a drawbar and have a hinged operator platform. However, because this special device travels over long distances, operators desire an operator platform that they can lean against. “
 
Operating unit can be conveniently adjusted
 
In this case, for ergonomic reasons the forklift functions can be better moved with a multi-function Jet-Pilot steering wheel than they can be with a drawbar. So that forklift operators of different sizes and statures find the perfect operating and working position. The Jet-Pilot can be moved in the longitudinal direction, i.e. in its distance to the operator, by 50 mm This linear motion is likewise executed by a drylin® axis.

igus Sales Consultant

Dipl.-Ing. Aimo Helbach, designer at the Jungheinrich Lüneburg plant, explains the structures surrounding the igus® linear guide to igus® Sales Consultant, Christian Wille. (Source: igus GmbH)

 

In this area Jungheinrich decided on a drylin® SHT-S system with high helix thread, which however is moved via a hand wheel. This axis is also characterized by maintenance-free dry operation, as is the electric motorized drive in the fork. In this regard the excellent gliding properties of the linear system are particularly important. When the operator adjusts the position of the Jet-Pilot, he is exerting lever forces that are not optimal, relative to the laws of physics. However the drylin® unit is "good-natured" – in other words capable of sliding – sufficiently to allow this, and to bring the Jet-Pilot into the desired position without jerking motions.

Directly after the driving and function tests, to which each special forklift is subjected, and acceptance by the customer the device was already en route away from Lüneburg headed north. In the meantime the forklift fleet of the large dairy, which also includes several other Jungheinrich forklifts is now being supplemented with a genuine specialist among the industrial trucks.