How it Works – Self Levelling Laser
This is the first of the “How it Works” series of articles. This time I am looking at how self-levelling works in laser levels, outlining the different technologies and their pros and cons.
There are basically three types of mechanisms used in self-levelling lasers. Firstly wire suspended compensators, Secondly, pendulum mechanisms using a gimbal and thirdly electronic self-levelling.
Wire Suspended Compensators
This technology goes back to the beginnings of levelling technology and is based on the trusty pendulum plumb bob and is commonly found in auto levelling dumpy optical levels, and some older technology rotating laser levels. Wire suspended compensators and how it works for self-levelling in laser levels. The principle is that light enters the compensator at one end and then enters a prism or mirrors on a floating platform, the light then exits through more prisms and lenses. The floating platform moves like a plumb bob with gravity and through clever geometry compensates the exiting light to be always level, this light can be a laser beam or the light entering into a dumpy level.
Pros and Cons
The pros of this method of self-levelling are first that it is simple and so there is less to go wrong, the method can be extremely accurate when using quality components and manufactured well, it is relatively inexpensive to manufacture and it continually self-levels within gravity. The cons are that as the name suggests the platform is hanging on fairly fine wires and so a drop of this type of equipment will often damage or destroy the compensator or at the very least require re-calibration. Secondly, the device will often have limited self-levelling range often around 1 degree compared to other methods that can have about 5 degrees of self-levelling. Finally, the nature of the delicacy of the mechanism means that regular calibration checks are a must.
Pendulum or Gimbal type mechanism
This technology is found in the majority of line and dot lasers plus also some inexpensive rotating lasers. You can generally tell a pendulum based system as the laser level will generally have a locking knob to protect it when in transit, although, there are some out there that are continually floating around and rely on internal rubber bumpers to prevent damage.
The principle is similar to the wire suspended compensator in that a central pendulum is mounted on a gimbal bearing assembly. So, the pendulum floats freely within gravity in order to self-level. Something worth mentioning with both wire suspended compensators and pendulum mechanisms is that they are both dampened to slow and stop bouncing or swaying. The dampening is usually achieved with the use of magnets but occasionally air dampening mechanisms are used. If there was no dampening then the pendulum or compensator would continue moving for many minutes. With compensation, this movement stops in seconds.
Pros and Cons
The pros of this method are similar to wire suspended compensators. They are inexpensive to manufacture and simple so generally quite reliable. It is also fast at self-levelling literally within a handful of seconds and continuously self-levels. This method generally provides a more robust mechanism compared to the wire suspended compensator and a greater self-levelling range. The main con is that it relies on a friction fee bearing for its accuracy. So, any damage to this bearing or wear or dust can seriously impair its performance.
Electronic Self Levelling
This method is generally found in most modern rotating lasers plus some larger line lasers. The principles are similar to the pendulum method above except the pendulum is not free-floating. The pendulum has an electronic sensor mounted on it and motors to move the pendulum to the position that the sensor tells it to go. There are two sensors, two motors because there are two axis for horizontal levelling.
The sensors are often a simple spirit vial with a light source on one side of the vial and a light detector on the other side of the vial. When the bubble is central the maximum amount of light is allowed through to the sensor. This indicates that that sensor is level and so tells the motor to stop adjusting. These axis are at 90 degrees to each other and are normally referred to as the “X” and “Y” axis. When both axis are levelled then the complete horizontal plane of 360 degrees is level.
Pros and Cons
The pros of this method are that it is generally very accurate. The mechanism is very durable to knocks and drops and resistance to calibration changes. This is because it is not relying on delicate wires or friction-free bearings. Being electronic the device can be programmed for more features. For example, such as switchable between continuous self-levelling or not, TILT movement warning, Grade/Slope setting and more. The cons are that they can be much slower at self-levelling compared to the other two methods. The mechanism is much more complicated and involves mechanical and electronic components. This means that IF it is not manufactured to high standards reliability may be a problem. Finally, it’s more expensive to manufacture, although the cost is reducing year on year.
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