Multi-Axis sensors are precision transducers designed to measure multiple forces and moments simultaneously. Unlike a traditional load cell that measures force in only one direction, a multi-axis sensor can capture the complete loading condition of an object in real time.
The selection of the appropriate force-torque sensor is initially based on the measuring ranges for forces and moments in the three coordinate axes.
Other boundary conditions include geometry, installation conditions, accuracy, weight, and stiffness.
This article aims to help you make the right choice when selecting a sensor. Our sales team will be happy to assist you in making your selection based on the specific operating conditions of the sensor.
The measuring range is the primary factor in the selection process: The force/torque sensor (6A sensor) must not be used above its so-called service forces and torques. Above these forces or torques, the sensor can be destroyed by plastic deformation. The measurement signals would then be outside the range that the measuring electronics can still evaluate.
A special feature of force/torque sensors, unlike 1A force or torque sensors, is that the operating forces and torques are often not in the range of 150% to 200% of the measuring range, but usually up to 300% of the measuring range.
A very good overview of the utility forces is provided in the document 6A-Comparison-Table.pdf
For 6A sensors, additional overload protection usually does not need to be planned. On the contrary, a deliberate exceedance of individual force or torque components can be factored in.
In addition to the forces and moments involved, the resolutions are also specified. Here, resolution is understood to mean the noise amplitude at a measurement frequency of 10 Hz.
The forces are usually applied at a certain distance from the sensor’s front surface (from the “origin of the force sensor”). This distance (usually in the positive z-direction) can range from, for example, 50 mm to 1000 mm. If a force of, for example, 1 kN acts on the sensor at a distance of, for example, 100 mm from the front surface, then a moment of 100 Nm must be taken into account when selecting the sensor.
It is rare to find a standard 6A sensor that is designed for both forces up to, for example, 100 N and moments above 100 Nm. Physically, this would only be possible with a very large sensor diameter, as the moments must be absorbed by the sensor using a force couple.
In these cases, calibration is performed under partial load.
Another selection criterion for force-torque sensors is the diameter of the sensor: The diameter should be chosen to be as large as possible.
Therefore, if the choice has to be made between the 6A27 and the 6A40, the sensor model with the larger dimensions should definitely be chosen.
Accordingly, this rule can be applied to all other models 6A80, 110, 130, 150, 175, 225, 300.
The torque measurement range of the 6A sensor is largely determined by its diameter. Selecting a larger diameter generally reduces torque crosstalk on the force signal display.
The highest accuracy with a 6A sensor is achieved when the forces are introduced in the area of the sensor’s front surface up to a distance of approximately 1× the sensor diameter from the front surface.
As the distance of the force application from the front surface increases, the pattern of the signals becomes “less clear,” because a superposition of forces and moments is always introduced into the 6A sensor.
Particularly stringent requirements are placed on the sensor mounting. Local deformations of the force application flanges inevitably lead to measurement errors. The thickness of the mating flanges must be selected to minimize local deformations. Recommendations for the minimum thickness of the flange plates are provided on the 6A Assembly page. If even a single one of the typically six mounting screws is not tightened or is omitted, a measurement error will occur. Local deformations of the flange plates can occur, especially when moments are applied. Care must be taken to ensure the flanges are as symmetrical as possible.
If this is not possible, calibration under the specific installation conditions may be necessary.
The calibration matrix of the 6A sensor represents the relationship between the sensor’s 6 (or 12) output signals and the applied forces and moments. The optimal calibration matrix is
Often, individual forces or moments are applied in later applications at only a fraction of the rated forces and moments of the 6A sensor. Calibration with, for example, 10% of the rated load of the 6A sensor is readily possible.
Due to the high resolution / low noise amplitude of the BX8 measuring amplifier, there is no reduction in accuracy due to partial load.
However, the relative, temperature-related drift of the sensor is based on the sensor’s nominal loads. If the drift is related to a partial load of, for example, 10%, the relative drift increases accordingly by a factor of 10.
