Sensors for motion systems

A new portfolio of sensors from Pepperl+Fuchs includes reduction factor 1 capability, simplifying setup and configuration in changing application conditions. The inductive sensors also feature an IO-Link connection for added diagnostic and maintenance capabilities.

Motion systems employ sensors for a variety offunctions, the most common of which are measuring position or speed. Encoders are chiefly used for position measurement (both rotary and linear), while tachometers are common for speed measurement. Proximity sensors are used for both object detection as well as distance measurement.

In fact, many industrial and manufacturing applications use proximity sensors to sense the presence of objects or materials, then either initiate some action or simply flag their presence or absence. Key to their operation is that they don’t require physical contact with the target or object being sensed, and why they’re often called non-contact sensors.

Proximity sensors employ one of several sensing techniques including photoelectric, ultrasonic, capacitive and inductive. Photoelectric sensors operate on the basis of light, detecting light levels present to the detector in the sensor. Ultrasonic sensors work by emitting a high-frequency sound wave. The wave strikes an object and then reflects back to the sensor where the distance of the object can be calculated based on the time it takes for the emitted signal to return. Capacitive sensors operate by detecting a change in capacitance or what is really the dielectric constant between the sensor and the detected object. Inductive sensors are based on the principle of electromagnetic induction and are used to sense metallic objects.

Regardless of sensor type, technological developments across industries are impacting new generations of sensor designs, leading manufacturers to add features to accommodate the changes. For example, the ongoing expansion of IoT and IIoT demands the use of more sensors as data collecting tools and to monitor system operations for both predictive maintenance and condition monitoring. As a result, new sensors have added functions, are easier to program, and include better connectivity.

Manufacturers are also seeing interest in wireless sensors, particularly for smart factory applications. This interest is driven mainly by the cost savings that wireless sensors offer over hard wiring sensors to machines. With better wireless connectivity prevailing, wireless sensors are also beginning to find more use in some applications.

SENSOR SELECTION TIPS

The most important factors for selecting a sensor include the desired variable to be measured, the required accuracy or resolution, the type of output, as well as any size or space restrictions, environmental factors, and product lifetime and cost.

For motion applications, is the motion rotary or linear? Encoders or resolvers can measure rotary position. For linear motion, there are linear encoders using a variety of sensing technologies including optical, capacitive, inductive, and magnetic.

Also, consider the needed precision for the application including factors such as linearity, resolution, and repeatability. Generally speaking, higher precision sensors are more expensive. So knowing the application’s required precision and accuracy helps with not paying for more precision than the application demands.

What is the required measuring range? For linear measurements, is the range on the order of nanometers, a few millimeters, or several feet? For rotary applications, if measured in degrees, is the angular distance more or less than 360 degrees? Is the type of encoder needed a single-turn or multi-turn device?

What type of output is needed? Is it voltage or current? Digital or analog? Many transducers are programmable through a simple data connection, such as a PC-to-USB link. Other interface options can include encoder-specific communication links like SSI (synchronous serial interface), BiSS (bi-directional serial/synchronous), or PROFINET.

There may be other considerations such as any physical size or weight restrictions or special installation or mounting requirements. Environmental conditions are another factor. The sensor should be able to withstand the environmental conditions of the application. Some of the most common conditions to consider are EMI/RFI noise, shock and vibration disturbances, extreme heat or cold, and environmental contaminants such as dirt, dust, moisture, and corrosive chemicals.