How we ensure greater safety when lifting and lowering with Automated Guided Vehicle Systems
Automated Guided Vehicle Systems (AGVS) are currently more in demand than ever before. They are a key component of modern intralogistics solutions.
What is their core task?
- They automatically transport loads from A to B.
- They lift and lower loads.
Wherever they are in operation, so too are people to be found. SAFETY is therefore the top priority so that people are not endangered.
Sticking points when lifting and lowering that can become a danger to people:
Safety: AGVs drive freely through the hall. There are people here. For this reason, the raised elements must be secure and must not simply fall down in case of an EMERGENCY STOP. Otherwise, people's lives are at risk.
Our safe solution: our screw jacks are self-locking. In case of a power failure, the screw jacks don't simply collapse, but maintain a stable position. The load thus remains safely at the previous level. For additional safety, the use of four support points, i.e. a lifting system with four linear drives, is recommended so that the AGV cannot tip over if the load is unevenly distributed. Advantage: no additional elements need to be used for the lifting movement.
Stability: in order to lift heavy loads, the lifting table must be stable. Stability is provided, for example, by the scissors in the lifting table.
Our solution: the spindle is so stable that it absorbs shear forces (for instance due to the acceleration of the applied mass). Complex guidance in the lifting table is unnecessary – the scissors can be dispensed with. However, it should be noted that shear forces during long strokes can be a challenge for compressively loaded spindles. If the energy from the acceleration of the mass becomes too great, plastic deformation of the spindle can occur - at least when extended. However, since most AGVs only implement lifting movements of up to 200 mm, there are two advantages: the customer has more space and costs are lowered.
Speed: modern manufacturing systems demand the shortest cycle times and high speeds. A 24 V motor quickly reaches its limit.
Our solution: We can vary the speed through different reduction ratios, spindle pitches and spindle types. In general, screw jacks are not showcase elements in terms of high efficiencies. Nevertheless, due to self-locking or a currentless brake on the motor, the lifting system does not consume any energy as long as no lifting movement is being carried out. Since the AGV uses only a fraction of the cycle time for the lifting movement, it is relatively easy to calculate the energy requirement. Advantage: short cycle times and high speeds are possible. Self-locking makes it easier to plan the energy requirement.
For the design, we therefore recommend that the following points be explicitly observed:
- Long strokes endanger the buckling safety. Compressively loaded spindles run into stability problems with a long length. A calculation according to Euler or Tetmajer provides an indication here. In combination with a lateral acceleration, the calculation of the reference stress must be used
- Higher speed can be achieved by a higher pitch. In addition, you can also achieve better efficiency through higher pitches. Please note, however, that self-locking of the spindle is no longer possible with a spindle pitch of more than 4.5°.
- We recommend linear chain systems for longer strokes. In order to keep the AGV as narrow as possible, linear chains can provide the appropriate solution. These make sense from lifting heights of more than 300 mm. The advantage of this is that the linear chain can be deflected 90° behind the drive housing and thus requires much less space. CAUTION: Linear chains cannot perform any guidance tasks. See also GROB Trade Fair News - Day 1 - YouTube
