Robotic lawn mowers
A robot lawn mower (or robot lawn mower for short ) is a service robot that can mow the lawn by itself. Robot lawn mowers are not remotely controlled, but mow the specified area independently: they work autonomously.
Robot lawn mowers have been commercially available since the mid- 1990s . After vacuum cleaner robots, they are the first household robots that have also found widespread use in private households.
A typical lawnmower robot is designed, depending on the model, to cultivate an area of approx. 150 to 20,000 m² of lawn.
These robots are increasingly equipped with complex sensors that charge themselves and can also detect rain showers. This means that after the machine has been set up, human interaction is usually no longer necessary. With the increased use of smartphones, automation functions have been integrated into some models that can be configured using an app and also controlled manually.
history
After the first devices from 1995, the Automower G1 from Electrolux and Husqvarna, which has been available since 1998, is considered to be the first real robot lawn mower. This robot not only mowed the area to be processed independently, but was also able to automatically go back to a charging station for the first time to recharge its batteries. As a result, apart from maintenance work, he was able to take care of lawn care for any length of time without human control .
The main competitor is the Israeli company Friendly Robotics , which manufactures the Robomow .
However, there are now a large number of manufacturers who offer partly in-house developments and partly licensed replicas . Especially Husqvarna Automower and Friendly Robotics Robomower are used with z. T. modified housing shapes or different colors sold under the name of well-known garden tool manufacturers.
At the end of 2005, robotic lawn mowers represented the second largest category of robots in the household. The growth rate of the robotic lawnmower market, which has been dominated by the Swedish company for more than a decade, is 15 times that of conventional lawnmowers; this attracts the competition.
Design and mode of operation
Robot lawn mowers are almost exclusively battery-powered and cut the stalks of lawn with sharp knives. They are mulching mowers because they cut the grass so finely that no residue has to be collected and nutrients are returned to the soil.
The robotic lawnmower's mowers are significantly less powerful than those of hand-held lawnmowers. Cutting off the stalk with knives (instead of chopping it off as with conventional lawnmowers) is not suitable for high lawns.
For these reasons, the robot lawn mower drives the lawn constantly or at least very frequently in the typical application scenario, only interrupted by charging pauses. This means that the lawn is always short enough to remain workable with the relatively weak mowers. Because of the long duration of use, all areas are finally mowed despite the fact that the lawn is usually not very systematic.
Most devices are relatively quiet due to the low power of the mowers, so that they can usually be used in continuous operation without any annoyance.
It is mostly driven by two separately motorized and controllable wheels that are responsible for driving and steering. The wheels are not actually steerable; Steering is only done via different rotational speeds of the drive wheels. In extreme cases (one wheel turns forwards, the other backwards), robotic lawnmowers can turn on the spot. Another pair of running wheels, less loaded and with a smaller track width, also (passive) swivel castors - on some models just a centrally mounted ball wheel - supports the robot at the front or back.
For particularly steep terrain, robots with 4 driven wheels have also been available since 2019; these steer using articulated steering , i.e. the twisting of two halves of the housing. These robots are supposed to manage gradients of up to 70%, while with two driven wheels a maximum of approx. 35% can be driven.
Orientation using the boundary wire
The area to be mowed is usually surrounded by a wire loop, the so-called boundary wire. This loop carries a signal that sensors in the robotic lawnmower pick up and use it to recognize when they approach the wire. This allows the robot to turn before it passes over the wire and thus remains in a clearly defined area.
In this area, the robot moves back and forth more or less in a disorderly manner. Depending on the manufacturer, various strategies are pursued, such as spiral travel, changes in direction after a certain time or just straight ahead until the boundary wire is reached again and then reversing at a random angle.
Obstacles are automatically detected by shock sensors or ultrasound , but can also be left out with the help of the boundary wire (beds, ponds, trees, etc.). However, obstacles that are flat enough to be run over by the robot, e.g. B. small stones, shoes, toys or items of clothing left lying around.
Search wires can also be used to guide the robot lawn mower to remote areas of a lawn. In extreme cases, unrelated areas can be mowed by programming the robot in such a way that it creates a second area, e.g. B. in 50 percent of all missions by following a search wire. Since the boundary wire and the search wire can usually be buried up to 10 centimeters deep, the robotic lawn mowers can also cover longer distances over paved paths and normal traffic areas such as terraces or streets to get to the second lawn area when the search wire is under the paving was relocated.
The problem with demarcation using a perimeter wire is the reliable detection of the wire. Some devices do not reliably detect the perimeter wire; this can cause damage to the device or leave the intended mowing area. Many manufacturers therefore recommend that particularly critical points such as B. to provide ponds or swimming pools with an additional border that is high enough to trigger the mower's shock sensors (e.g. 15 centimeters)
More sensors
Depending on the manufacturer, robotic lawn mowers are provided with numerous additional sensors that determine whether the robotic lawn mower has been tilted, monitor the battery temperature, interrupt mowing when it rains, stop the blades when pets are approaching, try to determine the height of the lawn and then adjust the speed and the like . As an alternative to the use of a perimeter wire, there have also been models in recent years that try to use capacitive sensors to detect whether they are on a lawn or not. However, this requires a clear separation between lawns and other vegetation zones such as B. Flower borders .
More expensive models have a GPS for orientation , which is usually not used for control on the lawn, but to locate the robot on large properties or in the event of theft. For this purpose, GSM modules are built in, which call automatically to report the departure of a certain area or can be called to give the robot e.g. B. to command to drive back to the base station or to transmit its position.
Base station
Almost all models currently on the market can find their own way to the charging station if necessary so that they can charge themselves. Many models look for the boundary wire and drive along it until they come to the base station, which usually also feeds the wire with the signal mentioned. Here the robots drive against charging contacts and then switch off for the duration of the charge. Some models offer additional "search wires" that lead to the base station. You do not follow the search wire directly, but drive in a corridor next to the search wire in order to avoid the same lanes in the lawn. In addition, the base station itself emits a signal that the robot receives when it is close to the station.
safety
Many providers recommend not to let children near robotic lawn mowers. Robotic lawn mowers should stop the mower blade immediately in dangerous situations. For this purpose, the devices usually have sensors that detect lifting or excessive angles of inclination. However, some devices do not switch off immediately, which can lead to injuries, especially to feet or fingers.
Robot lawnmowers were classified as poor in terms of safety by Stiftung Warentest in 2018, and limbs such as children's feet or outstretched hands were not recognized. Small animals are also at risk, especially if the devices are operated at dusk or at night.
The Fraunhofer Institute for Microelectronic Circuits and Systems has introduced an optical sensor in 2018, the mower is to make them safer. It works with Light Detection and Ranging (LIDAR) and detects approaching obstacles such as B. Children. Of the seven branded robotic lawnmowers tested by Stiftung Warentest in 2020, however, none had such a sensor.
Many models permanently check the function of the perimeter wire and recognize whether they are within the mowing area. If there is no signal, the robot stops. In addition to mowing unintended areas, this also prevents “busting out”, i.e. leaving the area in an uncontrolled manner and mowing outside the boundary or even the property.
Area performance
There are robotic lawn mowers for areas from approx. 150 m² to 20,000 m². Several robotic lawn mowers are used for larger areas. Especially in the area of 800 to 5000 m², the robots often only differ in the installed battery power and the performance of the charging electronics, in order to enable the longest possible uninterrupted mowing. In the case of models for small areas in particular, the maximum mowing time and thus area coverage is even only artificially limited by the software. H. an identical model is offered in several versions with different prices and different area coverage, but with the cheaper models the maximum mowing time is reduced by the software.
There were also models with solar cells on the housing, which increased the service life by recharging the batteries when exposed to light, but these models are currently no longer available.
Typically gradients of up to 35%, in models with 4 driven wheels up to 70%, are conquered, but mostly turning on such an incline is not possible, i. H. the boundary wire must not lie on such a slope.
In most cases, however, the robots do not travel the lawn in the same paths as people would use manually guided devices. For example, most robot models do not try to ensure that straight travel is actually straight, for example by actively correcting small deviations in direction caused by bumps. At best, some models try to roughly compensate for drift caused by inclines or slopes. This is why most robotic lawn mowers have a sometimes chaotic mowing pattern. Difficult-to-access corners of an irregularly shaped lawn are sometimes only reached after a long period of operation. Therefore, a robot lawn mower should work the lawn more or less daily in order to ultimately achieve a uniform lawn height.
disadvantage
- Not every garden shape is suitable for robotic lawn mowers. Very winding lawns with many bottlenecks (passages less than 1.20 meters wide) sometimes cause problems. Very uneven surfaces and many or steep inclines are also problematic.
- The lawn must always be free of objects of all kinds that the robot can run over (e.g. branches, larger spruce cones, clothing, larger stones, toys, blankets or flat pillows, cables, tools, garden hoses). Objects that are taller than about 15 centimeters, on the other hand, are usually not a problem.
- The installation of the boundary wire, which is usually required, can be quite time-consuming, especially with more complex shapes.
- Although robotic lawn mowers are significantly quieter than normal lawn mowers, the longer mowing times required or inconvenient mowing times can be a noise problem.
- Robot lawn mowers are designed to maintain well-tended lawns with regular mowing passes. They are not suitable for mowing overgrown "wild" meadows.
- Areas tended by robotic lawn mowers form a relatively short, dense, even lawn . Biodiversity in flora and fauna, such as blooming herbs in the meadow, which are habitat for insects, is suppressed. (Keyword: flower meadow , insect death , monoculture )
- The principle of mulching mowing used also has some potential disadvantages. See: Possible problems when mulching
- Robotic lawn mowers can injure or kill smaller animals (e.g. hedgehogs, blindworms, fire salamanders and toads). You should therefore only let them drive during the day under supervision.
Open source projects
As in many other technical areas, there are also open source projects in the robotic lawnmower area that enable inexpensive replicas.
Web links
Individual evidence
- ↑ "The history of the lawnmower robot" (sic!) ( Memento from September 15, 2016 in the Internet Archive ) and product presentation of the first manufacturer ( page no longer available , search in web archives ) Info: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice. , both accessed on September 19, 2016.
- ↑ Background on the development of the Robomow ( Memento from July 30, 2009 in the Internet Archive )
- ^ Rise of the Lawn-Cutting Machines . In: Bloomberg.com . ( bloomberg.com [accessed June 19, 2018]).
- ↑ The fully automatic gardener , in: Spectrum of Science , Issue 9/2008, p. 94, ISSN 0170-2971
- ↑ a b Robot lawn mower: good models from 1,500 euros , Test.de from May 2, 2014, accessed on October 28, 2014.
- ↑ Stiftung Warentest 2018: Robotic lawnmower in the test: Two endanger children's feet , accessed on June 12, 2020
- ↑ Peter Carstens: How robotic mowers become deadly traps , in GEO , accessed on June 12, 2020
- ↑ NABU Lower Saxony: Lawn mowers and robotic lawn mowers are dangerous for animal gardeners , accessed on June 12, 2020
- ↑ More safety for children when mowing the lawn. August 1, 2018, accessed June 5, 2020 .
- ↑ Stiftung Warentest: Lawn Mower Robots: Comparison of Branded Devices 2020 , accessed on June 13, 2020
- ↑ See e.g. B. the Ardumower project based on the Arduino platform .
