Types of CNC Machine Sensors


CNC machine sensors measure physical conditions or activity on machines and convert these readings to electrical signals that can then be analyzed to establish their status. What do you think about custom sensor components.

Previous advances included condition monitoring, which used internal PRBS signals to detect differences between theoretical and actual speed and feed, then adjusted cutting “on the fly.” Unfortunately, such sensors require external hardware in order to function.

Hall Sensor

Hall effect sensors detect magnetic fields by sensing conductors with magnetic flux density measured in Gauss or G units; their output changes according to this quantity, and more vital magnetic fields generate higher output values from them, making these sensors ideal for measuring currents ranging from milliamps up to thousands of amperes without expensive transformers or coils.

A Hall element’s primary benefit lies in its direct sensing of magnetic fields without contact, making it ideal for use in environments hostile to other sensors, such as water, dust, or oil. Furthermore, vibration and shock tolerance make this sensor suitable for placement near moving parts; additionally, it allows users to distinguish the polarity of magnetic fields through changing output voltage, which enables position/direction detection.

Linear Hall devices generate output proportional to the magnetic flux density presented to their IC case. A shunting effect occurs between the vane and magnet, with the latter covered by the case; as its leading edge approaches it, magnetic fields intensify, and the output voltage rises progressively until reaching its limit and gradually declines as more magnets are exposed.

An average circuit typically features three terminals – usually constant current drive or logic low), two ground terminals, and an output terminal that could either be constant current drive or reason high – and an output terminal shorted directly to the circuit common; when switched on, current flows through it. Some digital Hall switches include current limiting to prevent excessive output currents from damaging devices. When selecting a Hall device in your application, its operation and release points will determine its sensitivity and maximum output current. Operation point and release point refer to magnetic flux density levels that allow a switch to turn on and remain on, respectively, while hysteresis, which measures the difference between operate and release points, can be reduced by placing a resistor between the sensor and power supply.

Speed Sensor

Speed sensors (also referred to as velocity sensors or vehicle speed sensors, VSS for short) are crucial components in vehicle control systems such as traction control, wheel slide protection, registration, train control, and door control. Speed sensors use magnetic fields to detect rotational movements of targets in their vicinity and generate an electrical signal proportional to this rotational speed.

Different kinds of speed sensors work differently. A passive sensor generates its voltage, while active ones require external power from either the Hall effect or magneto-resistive sources and usually feature either the Hall effect or magneto-resistive technology. All speed sensors read targets known as reluctor wheels or exciter rings, but each has its own method for doing this.

Passive speed sensors, also known as inductive or variable-reluctance sensors, are among the most widely used types. They typically feature a coil of wire with a voltage source and magnet inside. When reluctor wheels or exciter wheels pass by, changes in the magnetic flow of the ring are detected, leading to an alternating current that fluctuates according to the rate of rotation, then translated into digital signal output.

Active speed sensors are more complex than passive ones and typically consist of a pair of hall-effect or magneto-resistive sensors, a rare-earth magnet, and evaluation electronics. As target teeth pass by and modulate their magnetic field, the sensors record this variation and produce a voltage proportional to their angular speed, then transmit this signal to a computer for processing.

Easybom recommends performing routine maintenance by unplugging and testing its sensor plug with an oscilloscope to check whether its output signal voltage is within acceptable limits – 0.25V AC to 1.2V AC is ideal, and its waveform should match Figure 3; otherwise, it may need replacing. If results indicate otherwise, replace the speed sensor.

AE Sensor

Acoustic emission (AE) is a non-destructive technique for identifying damage and failures in structural components. Based on elastic wave propagation caused by microscopic deformations within materials, an AE sensor detects elastic waves that travel outward before being converted to electrical signals by an AE sensor. Acoustic emission can help identify defects in metal and composite structures during their service lives as its signs may come from corrosion fatigue, mechanical overload, dented parts, impact damage crack formation/growth matrix cracking delamination, and internal stress events, among many other events/situations/sources//. Acoustic emission is an excellent technique for identifying defects/damages as its signals can come from any event/occurrence/situation/situational phenomenon that causes elastic waves to propagate outward and be converted back into electrical signals by an AE sensor.

Compared to vibration analysis, Acoustic Emission (AE) provides superior detection capability of defect-related activity at meager energy release rates. This makes AE particularly helpful when applied to rotating machinery where damage often develops slowly and is difficult to detect through traditional means. Furthermore, it enables tracking defects over time – thus providing a basis for Predictive Based Maintenance (PBM), but further research may be required in this regard.

AE sensors are designed to be cost-effective and user-friendly. Their compact form factor does not include an onboard computer or specific input/output ports, making setup straightforward and hassle-free. They can easily be integrated into existing and new machines without impacting structural integrity – attached with tape, glue, or elastic ties or clamps – while data processing and monitoring capabilities can be easily connected via portable PC or tablet PCs or tablets.

Event curves of AE data can be used for fault detection by comparing its amplitude with an established reference value, such as that found with good-condition samples. Furthermore, different sensors’ registered signals can also be analyzed; calculation results display validation accuracy values gathered using algorithms that use a Super Vector feature set to classify AE signals, while colored lines represent which sensor has provided optimal classification results.

Vibration Sensor

Vibration sensors are devices designed to track the movement of machines, particularly their shaft supports (bearings). Their purpose is to minimize unplanned outages by identifying minor maintenance issues before they grow into major ones, thus increasing productivity, financial gains, and asset health.

Sensors come in three main varieties: displacement, velocity, and acceleration sensors. Displacement sensors feature a probe that threads into holes drilled and tapped into a machine’s frame, while velocity and acceleration sensors have their electronic processing engines to measure frequency properties and determine frequency properties via internal sensor engines. An accelerometer is often the go-to vibration sensor as it measures acceleration before converting it to digital signal form.

No matter the type of vibration sensor used, all have their own set of advantages and drawbacks. For instance, displacement sensors use electromagnetic eddy current technology to measure the distance between their sensor probe and metal machine shaft. When powered with high-frequency AC energy, their coil induces eddy currents in its magnetic field that strengthen as closer the post comes towards them – this allows displacement sensors to detect radial imbalances by inducing stronger eddy currents that would enable balancing weights to be applied when necessary.

Piezoelectric sensors are another popular choice for vibration monitoring. Being inherently analog, these sensors require external electronics to digitize vibration data – something which adds cost, complexity, and power consumption to their use. Piezoelectric sensors are helpful for detecting early-onset shocks that might indicate failure in pumps or bearings.

When sensors detect issues, they send digital signals to a CMMS system, which records and alerts a team member of any potential fault. By monitoring and recording these readings, it’s possible to screen for imbalance, misalignment, looseness, and late-stage bearing wear, as well as track trends over time and predict future machine performance – offering advanced condition monitoring services. Vibration monitoring provides another means of condition monitoring that helps avoid costly downtime while increasing uptime efficiency and equipment uptime.

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