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Photoelectric sensors functionality

 

Diffuse sensor with background suppression
 

 

By using the triangulation principle, diffuse sensors with background suppression not only measure the light intensity reflected by the target, but also determine the distance of the object from the sensor. In this way, objects with the minimum size of the light beam located within the adjustable sensing distance can be detected regardless of their color and surface.

The diffuse sensors with background suppression and laser light source were developed specifically for applications in which exact positioning is important. With the precisely focused beam, even very small objects such as the wires of a resistor or threads can be clearly detected or counted.

   Characteristics and advantages

  • Adjustable sensing distance 
    The switching point can be adjusted accurately between the object and the interfering background using a set screw or Teach-in method
  • Largely independent of color
    The sensing distance remains constant even if the color of the objects changes. Readjustment is therefore unnecessary. Objects changing in the background also have no effect.
  • Small spot size  
    Laser sensors can detect objects with a size of just 0,1 mm. Sensors with pinpoint diodes have a spot of only 2 mm diameter at the focus.
  • Red light emitters
    Visible red light permits simple adjustment of the sensor to small objects by eye.
  • Short response time 
    Small, quickly moving objects are reliably detected due to the short response time.

   Mounting and adjustment

The diffuse sensor must be aimed at the object. The sensing distance must be set to a distance between the target and the background. The background must be located behind the adjusted sensing distance by at least the distance of the sensing distance reduction of the sensor to black.

 

Diffuse sensor with background suppression
 

 

By using the triangulation principle, diffuse sensors with background suppression not only measure the light intensity reflected by the target, but also determine the distance of the object from the sensor. In this way, objects with the minimum size of the light beam located within the adjustable sensing distance can be detected regardless of their color and surface.

The diffuse sensors with background suppression and laser light source were developed specifically for applications in which exact positioning is important. With the precisely focused beam, even very small objects such as the wires of a resistor or threads can be clearly detected or counted.

   Characteristics and advantages

  • Adjustable sensing distance 
    The switching point can be adjusted accurately between the object and the interfering background using a set screw or Teach-in method
  • Largely independent of color
    The sensing distance remains constant even if the color of the objects changes. Readjustment is therefore unnecessary. Objects changing in the background also have no effect.
  • Small spot size  
    Laser sensors can detect objects with a size of just 0,1 mm. Sensors with pinpoint diodes have a spot of only 2 mm diameter at the focus.
  • Red light emitters
    Visible red light permits simple adjustment of the sensor to small objects by eye.
  • Short response time 
    Small, quickly moving objects are reliably detected due to the short response time.

   Mounting and adjustment

The diffuse sensor must be aimed at the object. The sensing distance must be set to a distance between the target and the background. The background must be located behind the adjusted sensing distance by at least the distance of the sensing distance reduction of the sensor to black.


Through beam sensor


An emitter in a separate housing transmits the light to a separate receiver. The object is detected when it breaks the emitted beam.





The active area (A) of a through beam sensor is equal to the diameter of the lens of  the receiver or emitter. The acceptance zone (B) of the emitter and receiver is larger. However, this is only important for adjustment and for operation close to glossy surfaces. With focused through beam laser sensors, the active area is the diameter of the laser beam if this is smaller than the receiver lens or the front opening at the receiver end.

 

   Characteristics and advantages

Due to the separated configuration, long ranges with large signal excess gain can be achieved in comparison with equivalent retro-reflective systems. Through beam-sensors are therefore most suitable for operation in unfavorable ambient conditions such as dirt, dust and moisture.

  • The clearly defined, consistent active zone permits highly constant repeatability throughout the entire sensing distance.
  • The switching point is independent of the surface properties of the object.

   Mounting and adjustment

The emitter and receiver must be aimed at each other. The narrower the angle of radiation and reception, the more accurately this must be conducted.


 

Retro-reflective sensors
 

 

The emitter and receiver are installed in the same housing. The emitted infrared, red or laser light is returned by a triple reflector or a reflective film to the receiver. The output changes its state when the object breaks the light beam (sensor receives no light).

   Characteristics and advantages

  • Single-lens optics 
    Because the emitted and received beams are on the same axis, the direction of approach of the object is irrelevant, and it is possible to look through small openings. Reflectors can also be used in close-range without signal breakdown
  • Short response times 
    Retro-reflective laser sensors with response times of 0,05 ms and focused laser beams correctly detect the smallest, fast-moving objects (0,1 mm in diameter).

   Mounting and adjustment

Each sensor has a separate excess gain curve. As the operating reliability depends heavily on the ambient conditions, it must be ensured that the sensor operates with the highest possible excess signal gain.


 

SmartReflect – the light barrier without reflector
 

Contrary to diffuse or through beam sensors, SmartReflect light barriers feature a closed light beam which is set up between the sensor and machine. The sensor switches when an object interrupts the light beam. The only requirement is the presence of a defined background, e.g. a machine part, within the sensing range of the sensor, which closes the light beam.

   Characteristics and advantages

 Maximum security

  • Most secure object detection due to the barrier principle
  • Higher process reliability by eliminating the reflector as the weak spot
  • No functional impairment due to contamination

Reduced operating costs

  • Time savings during installation, as no separate reflector / receiver is necessary
  • No regular reflector exchange necessary
  • Expensive reflector cleaning is not required

   Mounting and adjustment

The SmartReflect light barrier has to be aligned with a machine part within its sensing range. This machine part is then set using the teach-in.



 

Colour sensors
 

The sensor operates by the three-stage principle, meaning that it emits the three colors red, green and blue and then measures the color proportions of the three colors reflected by the object.

The color of an object is programmed in the Teach-in procedure. If the sensor recognizes this color again during operation, it activates the corresponding output. Optional tolerances permit it to detect large or small differences in color.

   Characteristics and advantages

  • Simple operation
    Four different colors can be programmed with just three buttons.
  • Finest color graduation
    One of five tolerance stages can be chosen for each color.
  • Short response time
    With a response time of only 0.34 ms, high detection rates can be achieved.
  • Synchronization input
    Allows controlled measurement of the color.
  • External Teach-in input
    Allows complete remote control of all Teach-in functions by serial data transfer. An RS 232 interface transducer with galvanic isolation is available as an accessory.

   Mounting and adjustment

The use of the color sensor is as simple as for a diffuse sensor. Only the points below must be observed.

  • For glossy objects, tilt the sensor to the side by approve. 15 °.
  • If you wish to detect very fine differences in color, the sensing distance of 40 mm ha to be adhered.


 

Diffuse contrast sensors

 

Diffuse contrast sensors can detect finest differences in contrast. Contrasts arise when surfaces bear bright and dark areas (e.g. a dark color mark on a bright primary color), or by structures on a surface (e.g. a weld seam).

Diffuse contrast sensors are based on the intensity difference principle with a clearly defined small light spot. At the ideal operating distance the sensor is optimized so that the finest contrast differences are detected almost independent of small changes in distance.

   Characteristics and advantages

  • White light sensor
    The narrow white light line allows precise detection of color marks
  • Laser sensors
    Thanks to the focused beam, even the slightest edge up to 0.1 mm in height can be detected.
  • Fast response time
    Very short response times up to 50 μs allow "real time" recording of marks and thus increase the process accuracy.
  • Sensor with analog signal
    Allows to import desired nominal values and to detect deviations thereof.

   Mounting and adjustment

The sensor should usually be mounted inclined by 5° to 20° to the object surface, especially when shiny material is scanned. When scanning edges, grooves or indentations, the sensor must be aligned so that the direct reflection is detected when the indentation, groove, or edge enters the light beam.

 

Difference sensors
 

The range of difference sensors opens new perspectives in the field of sensing. The patented functions provide the user with new, innovative solutions in the detection of objects, monitoring of tolerances or the comparison of object sizes and object positions. With the fine laser beam and the high insensitivity of the sensor to colors, objects are accurately detected. Five different sensors with different functions are available according to the application:

  • Step analysis
  • Window analysis
  • Tolerance analysis
  • Min./max. analysis
  • 2-point comparisons

Characteristics and advantages

   Difference sensors with step analysis

In step analysis, objects are detected by their height difference (stage) and reported in the form of a digital output signal. The sensor evaluates the positive or negative height difference within a specified time window of max. 5 ms. If the height difference is greater than 50 % of the taught-in value, an impulse of at least 10 ms is issued at the output. When the value is less than 50 %, the sensor switches back to the OFF state. If height differences are smaller than 50 % of the taught value within the time window (e.g. fluctuation of the conveyor belt), the sensor remains in the OFF state.

Advantages:

  • The stage / edge from which the objects are detected can be adjusted (minimum object height 0,2 mm)
  • Defined output impulse of 10 ms (can also be read by a normal PLC)
  • Detection of objects on a fluctuating conveyor belt
  • Detection of stages or edges
  • Positioning of objects by an edge, regardless of the distance

   Difference sensors with min/max analysis

With min/max analysis, objects can be inspected and monitored according to their scanned contour or shape. The scanning of the objects is activated by an external control signal. At the end of detection sequence, the measured values are evaluated and the difference between the minimum and maximum values is determined. If the difference exceeds a nominal difference previously taught into the sensor, this is reported in the form of an ON signal. This signal remains active until a new detection sequence is started. When this starts, the output returns to the OFF state. If the difference is smaller than the nominal difference, the output remains in the OFF state.

Advantages:

  • Difference is detected regardless of the distance
  • Start and stop of the measuring cycle can be determined independently
  • Round true running or knock of wheels / discs can be checked regardless of the distance
  • Deformation of plastic parts after cooling can be checked

   Difference sensors with tolerance analysis

The dimensional tolerance of objects can be determined by tolerance analysis. In the continuous detection of object distances, all measured values are checked to determine if it is between the specified maximum and minimum tolerances. In the case of if being between, an ON signal is issued at the output. If the distance remains within the tolerance range, the sensor remains in the OFF state.

Advantages:

  • Sensor form of caliper gauge
  • Simple monitoring of a distance with a tolerance range (pass/fail information)
  • Tolerance range and nominal distance can be taught in separately
  • Material thickness checking after a roller mill
  • Material thickness checking for extruders

   Difference sensors with window analysis

With window analysis, objects can be classified by a specified switching window. For this purpose, the switching window is specified in a simple Teach-in procedure with upper and lower limits. If an object is outside the defined limits, this is reported at the switching output.

Advantages:

  • Foreground and background suppression in a single sensor
  • Positions can be taught in separately
  • Interfering objects in the foreground and background can be suppressed
  • Objects can be detected on a segmented conveyor belt

   Difference sensors with 2-point comparison

In a 2-point comparison, two distances detected at two specifically chosen times are measured and compared. The choice of the time is made using a sync signal. The first distance is measured at the rising flank of the signal and the second distance at the falling flank of the signal. After the second distance was measured, the sensor evaluates the difference between the two distances and compares this with a previously taught-in maximum permissible deviation. If this difference is exceeded, the output switches to the ON state.

Advantages:

  • Object heights can be compared regardless of the distance
  • Deviation can be taught in (min. 0,3 mm)
  • Measuring time can be determined separately by an external signal
  • Checking the pressing depth of pins
  • Comparison of the distances/heights of objects with a reference value

   Mounting and adjustment

The direct reflection from glossy or reflective objects must not impinge on the receiver. This can be avoided by slightly tilting the sensor.

For optimum measurement results, the sensor must be installed at right angles to the movement of the object.

 

Triangulation

 

The distance measurement is based on the triangulation principle. The laser beam strikes the object as a small point. The receiver of the sensor (photodiode line) detects the position of this point. The angle of incidence changes according to the distance, and thereby the position of the laser point on the receiver. The photodiode line is read by an integrated microcontroller. The controller accurately calculates the angle from the light distribution on the photodiode line and then calculates the distance to the object from this. This distance is either issued at the serial port or converted into an output current proportional to the distance. The microcontroller guarantees a high degree of linearity and measuring precision. The combination of a photodiode line and a microcontroller permits interfering reflections to be suppressed and thereby provides reliable data from critical surfaces. The sensor adapts to different colors by adjusting its internal sensitivity, making it virtually independent of the color of the object. A digital output is activated if there is no object within the measuring range or if insufficient light is received to correctly detect the object, e.g. if the sensor is dirty. The possible resolution and accuracy change with the distance. The same distance Δd which causes a large change in the angle α1 close to the sensor produces a much smaller change in the angle α2 at a greater distance (see drawing). This non-linear behavior is corrected by the microcontroller, so that the output signal remains linear to the distance.

   Characteristics and advantages

  • Short response times
    Measuring cycles as short as 0.9 ms permit accurate measurements even on moving parts.
  • Integrated microcontroller
    The integrated microcontroller makes an external processing device unnecessary and makes it simple to place the sensor wherever it is needed.
  • High resolution and linearity
    Precise measurements thanks to a very high linearity of ±6 μm at a resolution of up to 2 μm (measured on matte white ceramic).
  • For any surfaces
    Intelligent signal processing improves the measurements made on critical surfaces.
  • Teach-in function
    The measuring range can be adjusted within the maximum measuring range by the user with the Teach-in button or via the Teach-in cable. The analog output has its full span within this taught-in range. The factory setting is the maximum measuring range.
  • Synchronization/hold function
    The measurements of several sensors can be synchronized using the sync input, or the last value can be held and the laser diode switched off.
  • Insensitivity to external light
    An algorithm makes the sensor insensitive to external light sources.

   Mounting and adjustment

With all distance measuring sensors, it must be ensured that the laser spot can be seen directly by the optical system of the receiver and that no obstructions are in front of the receiver.

 

Time-of-Flight / Run time measurement


With the run time measurement method distances are measured indirectly by measuring the time required by a signal to travel the length of the range to be covered. This translates into the real world as follows: a sender unit is emitting a burst signal which, when reflected by an object, is picked up by the sensor's receiver. The sensor's electronics evaluates the time elapsed and/or the phase-shift encountered which is then converted into distance information. By applying the run time technology objects can be detected precisely and reliably even at long distances.

 


 

Light section technology
 

 

The innovative multi-spot measuring principle by Baumer is based on light section technology. Up to 600 measuring values of an object are determined per measurement in the sensor, and from these values the distance is calculated using the intelligent evaluation process. Thanks to its resolution of up to 2 µm at a measuring frequency of 500 Hz, the sensor offers stable and precise measurement results.