OTX the new transmission for precise wheel balancing and accurate acoustic monitoring
Recent developments in the grinding machine industry have shown an increase in the rotation speed of spindles, as well as an enhancement in the capacity to achieve superior levels of surface finish. In order to ensure optimal performance levels, it is essential to continuously monitor vibrations caused by mechanical parts and the grinding wheel.
The balancer is a system that aims to reduce the intensity of vibrations on the grinding wheel, by automatically compensating for any imbalances and improving the quality of the parts produced, specifically the surface finish and geometry. For example, ring gears, input shafts, intermediate shafts, pinions, and all the planetary elements are ground with surface profile and surface finish being important targets. Advanced gear grinders are designed to control the twist and texture of gear tooth surfaces. Grinding wheel vibration is eliminated by the active control provided by Marposs Dittel Wheel Balancer systems, which continuously monitor and compensate for this.
Better surface quality demands an increased frequency of dressing cycles for every operation. Marposs Dittel AE (Acoustic Emission) ultrasound acoustic sensors are the most effective tool for monitoring and controlling the dressing cycle. They optimise wheel wear by limiting the amount of abrasive material removed from the grinding wheel in each dressing pass, thereby guaranteeing the integrity of the wheel surface after each cycle. Acoustic monitoring systems detect and measure noise levels when the grinding wheel comes into contact with either the workpiece or the dresser. Monitoring the sound produced during the machining process enables any potential issues to be identified and corrective actions to be implemented on the machine. For optimal effectiveness, the sensors should be positioned as close as possible to the machining area. Acoustic emission sensors can be integrated directly inside the wheel balancing head, placing them close to the contact point between the grinding wheel and the workpiece or dresser.
As the balancing head is installed inside the spindle, contactless transmission is required to supply power and exchange data with it. The new OTX transmission system comprises elements that perform two basic functions:
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Drive the balancing masses to remove the wheel unbalance in accordance with commands from a Marposs control system
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Detect, elaborate and transmit the acoustic signal generated by an AE transducer housed in the rotating body to the Marposs control system
In the case of OTX, BLÚ – the latest Marposs modular and distributed monitoring system – is the controlling system. BLÚ actually features a node designed specifically for this purpose. The OTX transmission was developed by combining the expertise of Marposs and Dittel in wheel balancing and acoustic monitoring. The balancing procedure begins with an analysis of the unbalance, as detected by the accelerometer and integrated RPM sensor. Then, the control system manages the wheel balancers using different strategies; the balancing algorithms are hosted in the supervising electronics. Commands to drive the masses are sent to the rotating head via the OTX transmission.
Marposs Dittel balancing systems can manage different strategies:
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Heuristic (balancing head without encoder position)
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Deterministic (balancing head with encoder position)
And different spindle layouts:
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Single plane
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Double plane
The OTX enhances the capabilities of the conventional MiniCT system, improving performance and optimising the layout.
In fact, in MiniCT transmission, three nodes are required for a single-plane application: an ACC node to detect the accelerometer, a WBTX node to drive the transmission, and an AE node to sense the acoustic waves. However, OTX improves this layout, as only one node is needed to connect the accelerometer and the stator. In fact, the WB and AE signals are both digitalised and then transmitted through a single cable.
Performance is improved in terms of noise reduction thanks to acoustic conversion and processing within the rotor. In fact, AE sampling and processing inside the rotor enables reliable digital transmission to the stator and BLÚ.
OTX will also allow for greater flexibility in terms of different machine layouts. The new hardware components are mechanically compatible with the previous MiniCT rotor and stator (axial Ø42 mm and Ø38 mm). In addition, new dimensions are available, such as an axial transmission with a diameter of 32 mm, which can drive balancing heads down to Ø24 mm, as well as a ring transmission.
The transmission and the balancing heads attached to it are suitable for high-speed applications of up to 30,000 RPM, depending on the specific design.
All the components also include an improved embedded diagnosis system to monitor the system itself, as well as the machining process.
Main features of the new OTX transmission:
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Optimised layout
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One node for WBTX, AE and ACC communication channels
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Embedded AE elaboration – AE signal directly elaborated into the spindle near the sensor
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FFT analysis and fully digital transmission for the best signal quality
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Heuristic and Deterministic balancing heads management
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Single and double plane management
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Suitable for super-compact applications (down to Ø32mm transmission and Ø24mm head)
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Suitable for high-speed applications (up to 30,000 RPM)
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Suitable for ring transmissions
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Mechanically compatible with former MiniCT solutions
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Improved diagnosis
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Available for both BLÚ and BLÚ LT