PRESS RELEASE
1. Intelligent Sensor for Factory Automation
1.1 Introduction
Proximity sensors are the eyes and ears in factory automation processes. They can be photoelectric type,
inductive type, magnetic type or capacitive type. Of all, inductive proximity sensors are one of the most
popular choices among designers. They come in many shapes and sizes to fit different applications, and
are distinguished by a long operating life and extreme robustness in harsh industrial environment.
Inductive proximity sensors are non-contactless switch triggered by the presence of metal object. The
output signal is mostly ON-OFF type, connected to digital inputs of either PLC (programmable logic
controller) or the distributed input-output (IO) units. The inductive proximity sensor is used either to (a)
detect unidirectional motion (left picture), or (b) detect rotational motion (right picture).
In automation task, the PLC will poll the IO or sensor periodically. For unidirectional motion detection, an
automated task will trigger mechanical movement of the metal target towards the sensor, and activate this
sensor. For rotational motion detection, the inductive sensor generates ON-OFF pulses due to the
rotating movement of the target object. The PLC counts the pulses to determine the speed and
acceleration data, and decide on the next automation task. Rotational motion detection normally requires
more PLC processing bandwidth.
Typically there can be several hundred or several thousands of inductive sensors in factory automation
line. Each sensor may demand bandwidth from PLC. Hence, the PLC has to have enough MIPS to liaise
with all equipment including sensors at the same time. Unfortunately, as automation line gets more
advance where more equipment are demanding the PLC bandwidth, and it may not be able to cope.
1.2 Demands for intelligent sensor
In many factory automation processes, such as steel cable stranding machines, textile weaving, certain
conveyor systems e.t.c, the work-piece quality is highly dependent on shaft rotary speed and
acceleration. Any small deviation can result affect end product quality which result in higher scraps. For
tighter control, each motor on the machine needs a sensor to capture rotational pulses information, and
feed them to PLC.
Classical method is to use a simple inductive ON-OFF proximity sensor to measure the rotation of the
toothed flywheel. The angular speed, acceleration-deceleration computation is dedicated to the PLC. The
PLC “MIPS” has to be high enough to compute all the data simultaneously, and control the process
tightly. Unfortunately this classic method hogs a lot of PLC resources. A typical steel cable stranding
machine uses around forty motors and therefore requires forty inductive sensors. The PLC has to poll all
the sensor and analyse the total number of pulses to determine the angular parameters. This is taxing to
the PLC, which may not be fast enough to handle such tasks. PC-based controller may have to be use
instead. Alternatively, IO modules such as programmable counters attached to the inductive sensor, can
be used to offload the controller, but this can result in escalating system cost.
A more intelligent sensor is required, whereby the PLC can dedicate the task of computing the angular
speed-acceleration data to this intelligent sensor. It can trigger the PLC when some abnormal conditions
are detected.
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1.3 Introducing SAM
The Speed-Acceleration Monitor (SAM) inductive sensor is designed to simplify the automation process,
by offloading the tedious task of computing the speed and acceleration data from the PLC. Briefly, the
SAM is a 4-pin inductive sensor, housed in cylindrical threaded housing. Two housing type are available,
the Ф18 type which has sensing range of 7mm, and the Ф30 type whose sensing range is 10mm. SAM
output is a simple discrete ON-OFF signal like any other inductive.
The SAM can be programmed using an IO-Link-enabled programming box and a Laptop-based user
interface software. The SAM is connected to the programming box as shown in the diagram. (IO-Link is
an input-output technology worldwide (IEC 61131-9) for the communication with sensors. Further
information can be found at http://www.io-link.com). On the user-interface program, designers can setup a
few threshold values to monitor. Once the SAM is setup, it is ready to go, where they can operate either
as a stand-alone sensor, or operate as one unit in a IO-link environment.
M18 and M30 SAM inductive
Programming the SAM inductive
Motor #1
SAM #1
Motor #2
SAM #2
Motor #n
SAM #n
PLC or IO
Application wise, it is straightforward. One SAM inductive is mounted on each motor. Instead of
transferring every single pulse to the PLC, the computation of the speed is directly done in the sensor
itself. The SAM will output a single ON-OFF signal to the PLC once the motor speed or acceleration gets
above the pre-set threshold values. This reduces the traffic and computing time of a PLC dramatically
therefore is a real cost saver.
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1.4 How it works?
The SAM inductive offers two main functions: (a) Speed monitoring, and (b) acceleration monitoring. In
the speed monitoring mode, the SAM checks if the speed of the rotating target reached the upper
threshold, and activate the output if this is true. The upper threshold and a lower threshold can be set
from 6 pulses to 12,000 pulses per min.
Upper threshold
Lower threshold
t
High
Output
High
Application-wise, the upper threshold can emulate the MUST_NOT_EXCEED speed of the motor, while
the lower threshold as the desire operating speed.
In acceleration monitoring mode, the SAM can check for a deceleration of the system between the range
of 0,1…2 pulses/sec². At constant rotating speed, there is no change in acceleration and output remains.
If deceleration is detected, the output is toggled immediately.
Speed
AccelerationDeceleration
t
Acceleration
t
0
Threshold (deceleration)
High
High
Switching output
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Application-wise, the acceleration monitoring mode is perfect for monitoring any machines with regular
speed changes e.g. due format changes in the production process. When using standard speed monitors,
the designers have to adjust the thresholds in accordance with the speed after every format change, in
order to detect motor breakdowns immediately. With the SAMs acceleration monitoring mode, this is not
needed anymore. The acceleration is independent of the absolute speed value. By monitoring the
acceleration ON-OFF data from SAM, the designer can check for motor breakdown in the automation
process.
1.5 SAM Benefits
1.5.1 Simpler Process and lower cost of system
SAM inductive can simplify the whole automation process design. The example below shows an
automated process with many cascading motors’ whose rotation speed and acceleration are coordinated
closely to ensure a smooth process flow. Should one motor breakdown, while all the other motors are still
running, crumpling of the work-piece can happen. To safeguard this, SAM can be used to monitor speed
and acceleration characteristic of mission critical motors, and triggers an ON-OFF command to PLC who
then executes recovery sequences.
With SAM inductives, the system does not need high-end PLC or PC-based controllers. The result is a
simplified control system which is cheaper now.
1.5.2 Simplifies commissioning & calibration
Lastly, SAM inductive shortens commissioning time and effort. During process commissioning, the
engineers need to teach the system when and how to react. When using classic method, the engineers
need to measure the system characteristics. Next, they need to write comparison algorithm and lookup
table for the controller.
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With SAM, commissioning the system is much simpler. The engineers just setup the SAM’s threshold
trigger via IO-Link. No physical information is required on shaft speed and acceleration. The SAM will
process all data and interrupt the system controller should the actual shaft speed or acceleration falls out
of SAM pre-set threshold. This saves a lot of commissioning time and resources.
1.6 Conclusion
The new Speed-Acceleration Monitoring (SAM) inductive sensor is designed to simplify factory
automation process. With SAM inductive, the bandwidth consuming task of computing angular speed and
acceleration data can be offloaded by system PLC to this sensor. This results in a simpler control
system, which drives cost down. In addition, system commission and calibration is also made easier.
SICK is one of the world's leading manufacturers of sensors and sensor solutions for industrial
applications. Founded in 1946 by Dr.-Ing. e. h. Erwin Sick, the company is headquartered in the German
town of Waldkirch, in the Breisgau region near the city of Freiburg. It is a technology and market leader,
maintaining a global presence with more than 50 subsidiaries and equity investments as well as
numerous representative offices. In the 2014 fiscal year, SICK had around 7,000 employees worldwide
and generated Group revenues of €1,099.8 million.
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