Manipulator for natural stones: How a gravel plant ergonomically stacks wall stones
A single brick can weigh up to 130 kilograms, with dimensions of up to 80 x 35 x 25 centimeters. At the Weißenburg gravel and stone plant, these blocks are no longer lifted by hand from the conveyor belt onto pallets; since 2021, this task has been handled by a manipulator from Zeilhofer Handling Technology.
In Germany, the amount of weight that is generally considered acceptable for manual lifting is regulated by the Manual Handling Ordinance (Lastenhandhabverordnung) . More information can be found in the article "How many kg can you lift? Limit values and the key indicator method" . Our guide "Industrial Lifting Aids " provides an overview of all types of lifting aids.
One company in focus: Retaining skilled workers, making work easier
A recent BR24 report on the German labor market highlights the challenges facing many medium-sized companies: finding skilled workers, retaining experienced employees, and making jobs future-proof. The report uses the Weißenburg gravel and stone plant as an example. Long-serving employees will be retiring in the coming years, and according to Managing Director Jens Geiger, replacements can't be found overnight. Attractive jobs aren't just created through recruitment strategies, but also directly where employees work every day. This is precisely where our collaboration with the Weißenburg gravel and stone plant begins, a partnership that existed even before the BR24 report.
The manipulator in detail: Column device with recording device
For the project “Stacking bricks onto pallets”, Zeilhofer Handling Technology designed a pneumatic handling manipulator as a stationary column device, firmly anchored to the floor, with a working radius of 3,500 millimeters in relation to the product and a working stroke between 100 and 1,000 millimeters.
The movement is driven by a robust articulated arm, similar to the one used in our articulated manipulator : The main axis can be manually rotated 330 degrees, the arm rotates continuously 360 degrees, and the gripping device itself rotates another 330 degrees. This allows the manipulator to achieve any orientation required for stacking on the pallet. The gripping device secures the bricks laterally with a pneumatic gripper unit, and specially shaped gripper jaws ensure a secure hold on various brick sizes. A dual-circuit smooth-running balancing control automatically switches from the preset empty weight to the respective load weight, enabling the movement of bricks of different sizes without manual readjustment. The control unit is positioned at two different heights and offset by 90 degrees, allowing operators of varying heights and from different positions to use it. With a weight of 420 kilograms and a noise level of less than 70 decibels per double stroke, the manipulator integrates discreetly into the workplace.
From conveyor belt to pallet: the working method
The manipulator picks up the bricks from the conveyor belt and places them on pallets, with each loaded pallet reaching a height of up to 1,000 millimeters. The bricks are picked up from above, along their long sides. For upward and downward movements without a brick, the operator doesn't need to operate any buttons or levers; only when gripping does the operator actively move the gripper towards the brick. Guides and a centering mechanism ensure the correct positioning of the brick before gripping.
The worker guides the movement, while the manipulator bears the weight of the stones, which can weigh up to 130 kilograms. Repeated lifting and balancing results in a controlled, repeatable sequence of movements.
Safe for continuous use
The manipulator features a compressed air reservoir with a check valve, which allows for a controlled termination of the work cycle in the event of a power failure. The gripper only releases after it has been safely lowered and completely relieved of pressure. An additional safety device prevents the boom from snapping upwards in the event of a load break, and further check valves protect against hose rupture.
The design complies with the EC Machinery Directive 2006/42/EC and the harmonized standards EN ISO 12100-1 and EN ISO 12100-2; the risk assessment is carried out according to EN ISO 14121-1.
Like any lifting aid, this manipulator is also subject to annual accident prevention testing according to DGUV Regulation 54; more information can be found in the guide: Accident Prevention Testing for Lifting Aids .
Less effort, more safety: the advantages at a glance
Form-fitting, secure gripping of masonry blocks between 250 and 800 mm in length
Reliable handling for weights up to 130 kg per stone
Automatic switching between empty and loaded weight without manual readjustment
Swing-free, low-effort movement from the conveyor belt to the pallet
quiet operation below 70 dB
Safety devices against load shear and hose rupture
In daily practical use at the Weißenburg gravel and stone plant since 2021
Handling technology that suits the natural stone industry
Natural stones are not standardized building components; they vary in size, shape, weight, and surface. A handling solution must therefore be precisely tailored to the specific task: How heavy is the load, what shapes and sizes are present, how frequently does the handling process occur, and what does the workplace look like? Zeilhofer Handling Technology from Holzkirchen designs manipulators for 18 industries based on precisely this principle. "What is a manipulator?" explains its functionality in detail.
When skilled workers are hard to find and the goal is to retain experienced employees long-term, the question of physically less strenuous workplaces becomes increasingly important. While handling technology cannot provide a complete answer, it can make a significant contribution. Our guide, "Ergonomics at the Assembly Workplace ," shows how to fundamentally reduce strain when lifting.
How to handle your natural stones or wall stones more ergonomically?
Do you move heavy stone blocks, bricks, or other unwieldy loads by hand in your company? Our engineers will develop a custom-designed manipulator for you, from the initial requirements analysis to the fully operational system. Made in Germany, from a single source.
Frequently asked questions about the natural stone manipulator
How does the manipulator work when stacking bricks?
The manipulator picks up the stones from the conveyor belt, and a pneumatic gripper unit grips them securely from the side. The operator guides the movement, and the manipulator carries the weight until it is placed on the pallet.
How heavy and large are the stone blocks that the manipulator handles?
The wall stones are between 250 and 800 mm long, 200 to 350 mm wide and 120 to 250 mm high, weighing up to 130 kg per stone.
What is the working area of the manipulator?
The working radius is 3,500 mm relative to the product, and the working stroke ranges from 100 to 1,000 mm.
Since when has the Weißenburg gravel and stone plant been using the manipulator?
The solution was designed by Zeilhofer Handling Technology in 2021 and has been in daily use ever since.
What safety features does the manipulator have?
A compressed air reservoir with a check valve allows for the safe termination of the work cycle in the event of a power failure; an additional safety device prevents the boom arm from springing upwards in the event of load shear. The design complies with EC Machinery Directive 2006/42/EC.
How loud is the manipulator during operation?
The noise level is below 70 decibels per double stroke, which allows for use close to the workplace without additional noise pollution.
Can the manipulator also be adapted for other natural stone products?
Yes. The receiving device and gripper unit are individually adapted for each project to the dimensions, weight and surface of the respective stone product.
Can the manipulator be operated by different employees?
Yes, the control unit is arranged in two heights and additionally offset by 90 degrees, so that it adapts to different body sizes and working positions.
Does the manipulator need to be checked regularly?
Yes, like any lifting aid, it is subject to the annual accident prevention inspection according to DGUV Regulation 54.
