Interesting applications from the field of machine tools
The requirements from the field of machine tools are extremely diverse and generally require maximum performance from the sensor technology used.
From extremely high speeds in milling spindles with the requirement for high signal bandwidth for the controller through to the need to measure a position with maximum precision within a boring tool – the boring tool must naturally withstand the adverse conditions in the processing plant.
In the case of machine tools, sensor performance is often crucial for the performance of the entire machine.
Speed sensor in high-speed spindle Speed and position measurement in an air-bearinged high-speed spindle
Air-bearinged high-frequency spindles are particularly well suited to very high speeds of over 80,000 rpm. The air bearings, with a very narrow tolerance, enable an extremely high process quality in mechanical surface processing. Here, the air is supplied to the shaft at high pressure via many small air nozzles and held on an air cushion. A brushless motor drives this shaft. As the shaft moves completely freely and without contact, it would seem obvious to use a non-contacting and highly-dynamic sensor concept on a magnetic basis.
Because of the high speed of the engine shaft, some requirements arise that necessitate special structural adjustments to the sensors as regards the measurement scale.
For example, no additional mass may be applied to the shaft if possible. No imbalance may be present and the measurement scale must be able to withstand the peripheral speed.
Furthermore, the sensor system must deliver a high signal quality at very high input frequencies.
- The measurement scale is implemented by means of drill holes arranged in a circle. This results in a tooth structure with 80 “teeth” at the circumference.
- At this tooth structure, the sensor system EBR7811 delivers 80 signal periods with sine and cosine signals as well as one reference pulse per rotation of the shaft.
- The signals with 1VSS are directly used by the controller to control and/or position the shaft.
- Non-contacting, wear-free operating principle on a tooth structure
- No extra pole ring is necessary. The shaft itself serves as the measurement scale
- The high signal quality allows a very high measurement resolution in the controller
- Customized sensor housing for adjustment in the spindle
Length measurement in a boring tool High-resolution and precise path measurement in a boring tool
Boring tools are used to bore precise holes, such as cylinder bores for engines. In principle, a hole is pre-drilled and then the difference to the target dimension is determined. This difference is set on the boring tool and the hole is drilled to the desired dimension.
The traditional boring tool has a setting thread and a vernier scale, as are used in calipers for instance. For some years, electronics has also been moving forward in this area and boring tools have received an integrated measurement system with a display or data interface.
The generally harsh environmental conditions are contrasted by the demands for highest accuracy and precision. However, the modern and highly integrable sensor technology and electronics make digitization possible in this field.
- AMR FixPitch sensor with extremely compact design on a flexible circuit board for integration into the boring tool.
- Durable and high-precision magnetized hard ferrite scale for optimum performance of the overall system.
- The AMR sensor can be activated and clocked quickly for measurement only so that the power consumption remains at a minimum.
- In the relative adjustment range of approx. 300 µm, accuracies of < 1 µm are possible.
- High signal accuracy and low-noise signals for very high-resolution path calculation
- AMR sensors can be affixed or cast in the boring tool
- Sensor pitch (FixPitch design) and magnetization are matched, making high levels of accuracy possible
- The AMR sensor enables path calculations with low power consumption and with energy-saving design.
Tension monitoring for tools Measurement system for monitoring the tool clamping position
The number of machine tools operating unattended is constantly growing. It is therefore often necessary to monitor these machines automatically. As a result, during an automatic retooling, a tool may sometimes not be installed correctly. For the generally very high-speed tools, the resulting chance of damage is very high and there is a risk of considerable material damage.
In these cases, various monitoring concepts can be implemented. Vibrations can be detected in order to detect an incorrectly clamped tool. However, in this case processing has already started and the detection is therefore too late.
Another concept is involves direct measurement of the clamping device so a tool that is not correctly clamped (e.g. tilted) can be detected immediately during clamping on the basis of the incorrect tension.
- Sensor integration in the clamping mechanism is possible with the compact sensor concept.
- Optimized arrangement of the sensor system for a wide measurement range.
- Analog sensor signal across the entire clamping path (from to up to).
- Sensor signal conditioning and clamp positions that can be programmed for correct clamping with the interface to the upstream controller.
- Non-contacting measurement principle and direct mapping of the clamping path
- Entire clamping is recorded by the sensor, so that the correct clamping point can be “taught” for any tools.
- Very compact and integrable
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