ALHS is short for Automatic Load Height Sensor. The ALHS used on stretch wrapping machines identifies the top of the load. The sensor can also be used to determine when a load has been placed on the machine. There are several types of load height sensors. Below are a couple examples.
Diffused Light Sensors
This form of sensing is commonly referred to as proximity mode. Light from the emitter strikes the target which causes it to become diffused at arbitrary angles. Some light returns directly to the receiver and the target is detected. Sensing range factors are color, size and finish of the target. The actual sensing range for each model is based upon a “white card test”. The white card has a 90% reflectivity factor and is considered a “standard target”. Darker colored or matte finished targets provide less reflectivity; therefore the sensitivity must be increased or the entire sensor must be positioned closer to the target.
- Diffused with background suppression
- Sensors with background suppression have a defined sensing range for any object regardless of color, reflectivity or finish. They are able to detect dark objects placed on shiny backgrounds and can be easily installed and adjusted.
- Diffused with foreground suppression
- Sensors with foreground suppression define a “dead-band” from the sensor’s optical window. Objects falling inside this minimum sensing distance are ignored.
- Diffused with background evaluation
- Sensors with background evaluation only evaluate the light reflected by the background (i.e. the floor). If the sensor is not able to see the background, the output will change state. This is useful in applications with odd shapes where direct light at the target cannot be reflected back to the sensors.
Digital laser load height sensor
A laser load height sensor enables long distance detection. This is useful for difficult applications where there must be a focused, visible beam spot. The method used to measure distance using a laser is referred to as TOF (Time of Flight).
The TOF method of detection measures distance by calculating the time it takes for a pulse-emitted beam to leave the sensor, hit the target, and then return to the sensor. This enables stable detection that is unaffected by the surface conditions of the work piece that is being detected.
Eagle Stretch Wrappers
Eagle stretch wrapping machines feature load height sensors. Click here to view more information on our stretch wrapping machines.