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2D laser protection for checking overhang in a high-bay warehouse

25 April 2016

Sometimes the simplest of things can bring multi-million pound installations grinding to a halt, one such example is a leaning load on a pallet.

Collisions between the crane mechanism and a pallet or load in high-bay warehouses and AS/RS can be serious. In addition to the obvious risk of damage to the goods and crane, such occurrences require manual intervention and time offline to correct, repair and clean-up which can cause significant delays to the logistics operation. Effective palletising procedures are the obvious solution but the reality of the logistics chain often means that there are too many variables to fully control, and too many opportunities for pallets to be damaged, incorrectly packed, or for the product or packaging to move or bend after loading. Pallets that appear perfectly symmetrical when entering the system can, over time, shift and settle after being set down, resulting in product encroaching into the working area. So how can we check for such changes before there is a collision?

The R2000 Class 1 laser sensor helps to avoid these collisions by scanning a 360° area around the sensor, detecting the smallest of objects in its scanning zone and giving a pre-emptive warning during normal operation. The R2000 laser scanner gives protection at up to a 30m distance, allowing plenty of time for the crane to slow down. 

In order to give a highly reliable and accurate scan the R2000 gives a gapless 360° measuring angle with small light spot. At a scanning frequency of up to 30Hz, this gives 54,000 measurements per second.

Depending on the application, the R2000 scanner can be set for either a high resolution to detect small parts or higher speed for faster reaction times. With the 10Hz setting, an angular measurement of 0.071° is achieved for detection of extremely small objects. At a distance of 10m this will give a light spot diameter of 15mm and a step of ~12mm making a gapless detection area. The scan plane is only ±0.05° which enables detection of objects in very tight places. At the same 10m range other scanners could have a light spot of approximately 200mm. For applications where objects may not be so small but speed is more important, the 30Hz setting gives an angular resolution of 0.2°. At a distance of 10m this would still give a light spot of 15mm, but the angular step would be ~35mm.

Four configurable outputs

The R2000 has four configurable outputs attached to four fields. By using the built-in logic you can configure up to 13 different detection zones by overlapping the four fields. These fields are easily configurable using free graphical software and are fully adjustable to suit the application.  Any geometric shape can be used as a field area provided it only has one start and end point. In one recent application the customer was interested in identifying which shelf level the overhang was at, so the four fields were configured into seven zones and a logical output given to each shelf level. 

Interactive graphical display

The R2000 has 24 LEDs mounted on the rotating measurement module which act as a projection service for an interactive graphical display. During commissioning the display is used for menu navigation of parameters such as Ethernet settings, display mode or factory reset etc. During normal operation the display can be used to show the four outputs or field status or even programmed to show a bitmap image such as a company logo or a message.

Accurate distance measurement with PRT

PRT or Pulse Ranging Technology means that the R2000 sensor can achieve accurate and reliable readings over long distances. Rather than a continuous light beam the sensor emits a very short, high-intensity light pulse up to 250,000 times a second. The energy in each single pulse is up to one thousand times more intense than pulses generated by sensors which emit a permanent light beam. The distance to the object is calculated using a time-of-flight method, which measures the time from when the pulse is sent to that of the returning light pulse. By using this method of measurement the housing is much smaller (105 x 105 x 116.5mm) and larger detection ranges are achievable than using a standard triangulation type sensor.

To summarise: the R2000 laser sensor is a compact scanner capable of detecting small overhanging objects at large distances. The four simple outputs can be set logically to create up to 13 zones so the area of the overhang can be easily highlighted and give a pre-emptive warning before a collision, which could be both costly and time consuming, occurs. 

Other typical applications which the R2000 detection scanner can be used for within automated warehousing include:

Broken pallet detection

Defective pallets can also lead to collisions in automatic warehouses causing damage to product, crane or racking. Due to the very narrow beams of the R2000 it can reliably detect small fragments of broken pallet and give a pre-emptive warning.

Skewed pallet detection 

The R2000 laser scanner can also be used to look down on a pallet. In this orientation the sensor can detect if the load is uniform and aligned on the pallet or if it is skewed. Checking that that the pallet is loaded correctly will help reduce the risk of damage caused by a collision of the load and the racking and also prevent oversized loads from being placed on the pallet.

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