FR2590362A1 - SENSORS FOR CONTROLLING PROCESSES OR MACHINES - Google Patents

Abstract

A SENSOR 10 ACCORDING TO THE PRESENT INVENTION INCLUDES A TRANSDUCER 14 WHICH IS ACOUSTICALLY COUPLED TO A MACHINE 12 OR A PROCESS, ETC., AND WHICH DETECTS ACOUSTIC EMISSIONS OR SECONDARY ACOUSTIC EMISSIONS AND CONVERTS ACOUSTIC SIGNALING ACTIVITY INTO AN ACOUSTIC SIGNALING ACTIVITY ELECTRIC. THE ELECTRIC SIGNAL IS AMPLIFIED BY THE AMPLIFIER 16 AND THE LEVEL OF THE ACOUSTIC EMISSION GENERATING ACTIVITY IS DETECTED BY A LEVEL 18 DETECTOR. A COMPARATOR 20 COMPARES THE LEVEL OF THE ACOUSTIC EMISSION GENERATING ACTIVITY AS IT IS HAS BEEN DETECTED AT A PRESET LEVEL OF ACOUSTIC-GENERATING ACTIVITY, DETECTED CHANGES AROUND THE PRESET LEVEL AND SIGNALED. THE SIGNAL MAY BE USED TO CONTROL THE MACHINE 12 OR THE PROCESS, THAT IS, TO TURN IT ON OR OFF OR TO INDICATE A CHANGE IN THE LEVEL OF THE ACOUSTIC EMISSION GENERATING ACTIVITY. THE SENSOR IS SIMPLE, ITS ORIENTATION AND POSITIONING ARE NOT CRITICAL, AND REAL-TIME CONTROL OF AN APPRECIABLE ZONE OR VOLUME IS POSSIBLE.

Description

This invention relates to sensors for process control or

  machines, especially sensors that

  on or off a process or a machine.

  Switches are devices used to open and close an electrical circuit. The prior art includes many mechanical systems, such as for example lever switches, knife switches, rotary switches, switches and microswitches, all systems whose operation is linked to the movement of parts. The prior art also includes

  1 o electro-magnetic switches and pressure switches.

  The devices of the prior art generally include

  moving parts and are not simple.

  The subject of the present invention is a sensor which does not have moving parts, which is simple, and which can be used for

  1 5 controlling processes or machines.

  To achieve this object, the present invention provides a sensor comprising a transducer capable of providing an electrical output signal dependent on the intensity of the activity generating acoustic emission, a level detector capable of measuring the level of the electrical signal which corresponds to the level of activity generating acoustic emission, a comparator capable of comparing the level of activity generating acoustic emission with a preset level of activity generating acoustic emission, the comparator detecting changes in the level of the activity generating acoustic emission from a level lower or higher than said preset level of activity generating acoustic emission compared to a higher or lower level, respectively, at said preset level

  of activity generating acoustic emission, and producing a signal.

  The comparator can produce a change in signal level

  digital or a signal intended to change the state of a relay contact.

  The comparator can produce a signal which is either an on or off signal, or a signal which indicates that the level

  of the activity generating acoustic emission has changed.

  The transducer can be acoustically coupled to the housing of a device to detect changes in the level of activity

  generator of acoustic emission in said casing.

  The sensor can be mounted in a housing and be acoustically coupled to it, it detects changes in the level of the activity generating acoustic emission in the housing and produces a signal to control the device; it can be hermetically embedded in a mass of metal or other suitable material. The level detector can measure the mean square level or the peak level of the activity generating acoustic emission

detected by the transducer.

  The present invention further provides a 1o key keyboard comprising a housing adapted to receive a plurality of key pads, the housing forming an increased attenuation path for an activity generating acoustic emission, each key pad being acoustically coupled to a respective sensor, each sensor comprising a transducer adapted to supply an electrical output signal dependent on the intensity of the activity generating acoustic emission in the corresponding key pad, a level detector adapted to measure the level of the acoustic emission generating activity, a comparator adapted to compare the level of acoustic emission generating activity with a preset level of acoustic emission generating activity, the comparator detecting changes in the level of activity generating d emission from a level lower or higher than said preset level of activity generating acoustic emission compared to a higher or lower level, respectively, at said preset level

  of activity generating acoustic emission, and producing a signal.

  The present invention also provides a method of controlling a process or a machine comprising the steps of: - detecting the level of acoustic emission from a remarkable position of the process or the machine, - comparing the level of the acoustic emission generating activity from the remarkable position of the process or the machine at a preset level of acoustic emission generating activity, - detecting changes in the level of the acoustic emission generating activity at from the remarkable position of the process or the machine from a level lower or higher than said preset level of the activity generating acoustic emission compared to a 3- level higher or lower, respectively, at said preset level of acoustic emission generating activity, said changes

  producing a signal to control the process or the machine.

  The present invention further provides a method for controlling a process or a machine comprising the steps of: - detecting the level of the activity generating acoustic emission from a remarkable position of a first process or of a first machine, - compare the level of acoustic emission generating activity from the remarkable position of the first process or the first machine to a preset level of acoustic emission generating activity, detect changes in the level of the activity generating acoustic emission from the remarkable position of the first process or the first machine, from a level lower or higher than said preset level of activity generating acoustic emission compared to a higher level or below, respectively, said preset level of acoustic emlsslon-generating activity, said changes producing a signal to control

  a second process or a second machine.

  The process or machine control signal can be a

  signal for activation or deactivation.

  The present invention will now be described in detail, with reference to the accompanying drawing, in which FIG. 1 represents

  schematically a sensor according to the present invention.

  The sensor I 0, represented in FIG. 1, comprises a transducer 14, an amplifier 16, a level detector 18 and a comparator 20. The transducer is acoustically coupled to a machine 12, for example, and it detects shock waves , also known as acoustic emission or secondary acoustic emission, and converts these acoustic emissions into electrical signals. The electrical signals produced by the transducers are then amplified by the amplifier and are supplied to the level detector. The level detector analyzes the amplified signal to detect or measure the level of the acoustic emission generating activity detected by the transducer. The detector can be a quadratic level detector or a

peak level detector.

  The comparator then compares the level of acoustic emission generating activity as detected by the level detector to a preset level of acoustic emission generating activity, the comparator detects changes in the level of activity generating acoustic emission from a value lower or higher than the present level compared to a value higher or lower, respectively, at the predetermined level, and sends a signal

  to a control member 22 for the machine 12.

  The activity generating acoustic emission detected is not of the type that is generated by the propagation of cracks and by plastic deformations, but is of the type generated by Impacts, friction and turbulence, in fact by any process

  which generates transient broadband shock waves.

  The invention will now be illustrated by means of the examples

  below, which are examples of possible use of the sensor.

  A shock between two objects generates a transient phenomenon of wideband shock waves; the frequency band and the amplitude of the shock wave depend on the physical properties of the objects. These waves

  shock are detectable in very many structures.

  Example I The shock of two objects coming into contact can be detected by the resulting shock wave. The sensor can be used to provide a signal confirming that a mechanism has blocked or stopped completely or can be used to establish the coordinates of a

  object by recording the shock of a probe.

Example 2

  The projection of sand, shot, drops or steam, for example, which is used to clean objects, consists of a rapid succession of violent shocks. Although these shocks are intentional, the sensor could be useful to detect the absence of projection material or the absence of a workpiece and would send

a corresponding signal.

Example 3

  Parts or pieces of parts often produce shocks due to a fall due to gravity, such as, for example, fasteners falling from machines or structures. The sensor can be used to indicate that a fastener has fallen or to put

machine out of service.

Example 4

  Pieces of parts of engines, machines, are often entrained in a flow of liquid, such as, for example pieces of bearing in the oil of a lubrication system, and the shocks of these pieces in the casing of the system lubricants generate shock waves. The sensor could be used to indicate bearing wear or to shut down the machine if wave levels of

  1 o excessive shock were detected.

  Disturbances occurring inside a fluid can generate broadband shock waves which propagate through the fluid and inside the walls of the container. Broadband shock waves can be detected through the use of a submerged transducer or, more appropriately, through the use of a transducer

  mounted on a dry surface of the container.

Example 5

  Turbulence is generally generated inside a flow of liquid and it produces shock waves, the level of activity generating shock waves depending on each particular arrangement. The sensor can be used to detect excessive turbulence, shock wave generating activity, due to excessive flow rate caused by a leak located downstream or by the failure of a valve, in order to close and d 'to stop the system. Similarly, the sensor could be used to detect an insufficient flow rate in a refrigeration or lubrication system, due to loss of coolant or lubricant, and to prohibit operation. This would be useful for internal combustion engines or turbines, etc. Example 6 Transient shock waves are generated by the crushing of the bubbles inside a fluid, whether the bubbles are due to cavitation, boiling or effervescence, and the level of activity generator of acoustic emission depends on each particular situation. A sensor could be used to generate a signal when bubbles caused by the above mentioned processes form, or when they cease to form. This could be applicable to pumps where cavitation occurs, and

  also in chemical and food processing methods.

  In addition to the production of heat due to friction, broadband shock waves are also generated, which represent a part of the energy losses. The sliding contact between two solid surfaces is characterized by slip-stick processes, macroscopic or microcospic, which each act as a source of transient shock wave phenomena

Example 7

  The unintentional sliding of stapled, welded, linked, slinged or bolted objects is accompanied by a broadband shock wave generating activity. A sensor could be used as a detector

  of sliding for a robot hand.

Example 8

  A lubrication system is provided to minimize damage and frictional loss. The effectiveness of lubrication conditions the activity generating shock waves generated. A sensor could be used in all types of machines and engines to detect the activity generating excessive shock waves caused by

  a lack of lubrication and to stop the machine or the engine.

Example 9

  Many static objects have a level of generating activity

  weak shock waves, except when physically handled.

  Furniture, for example, in an unoccupied office building and in houses has a very weak environment generating shock waves. A sensor could be used to detect the manipulation of doors, desks, secretaries,

  etc. and to produce a warning signal.

  A sensor according to the invention could be used as a switch, the transducer could be fixed to the casing of an object or of a domestic or industrial appliance. The entire casing of the object would act as a switch, touching the casing would create a shock wave which could be detected by the sensor and, if the level of the shock wave generating activity changed around the preset level, could be used to activate or deactivate the domestic or industrial object, or be used to detect

manipulation of the object.

  A manually operated sensor could be mounted inside a very robust casing which would be proof of acts of

vandalism and break-ins.

  If necessary, the sensor could be hermetically sealed in a mass of metal, for example. Such a switch would have no moving parts, and could put a device into service as a result of simple friction or a simple shock. It would be possible to form a key keyboard comprising a plurality of key pads, each of which is connected to a respective sensor. The key pads could be mounted in a robust housing, in which increased attenuation would be provided between the key pads, by the use of an impedance mismatch or a damping material intended to reduce the transmission of shock waves between key pads. When a key pad is subjected to friction or shock, a shock wave is transmitted to the respective sensor, which may have a level sufficient to produce a switching action, but the shock wave transmitted through the housing to adjacent key buffers and sensors is not sufficient to cause a switching action. Such a device could be used as a typewriter or, for example, as a keypad for

  automatic banknote dispenser.

  The sensors could be mounted in their respective key pads and be acoustically coupled to them, and they could be hermetically sealed in a metal key pad or made

any other suitable material.

  All mechanical means of metal machining, that is to say the.

  milling, drilling, turning, grinding, broaching and polishing generate a broadband shock wave generating activity. The sensor can be mounted on the tool or on the workpiece, or on the fixing support which holds the workpiece or the tool so that the workpiece or the tool can be changed without the sensor

is not affected.

Example 10

  When the metal machining process begins, there is a sudden increase in the wave-generating activity of this shock. The sensor can be used to recognize this change, and to generate a signal to confirm that the workpiece is

  within start tolerances.

Example l I

  The level of shock wave generating activity is related to the rate of metal machining and excessive cutting demand would cause an abnormally high level of shock wave generating activity. The sensor could be used to recognize this phenomenon and to produce a signal intended to stop the process and thus to prevent damage to the machine,

the tool and the workpiece.

Example 12

  Excessive tool wear such as that which produces aggregation and a clearly audible signal also results in increased spike shock activity with increased broadband. The sensor could be used to recognize this situation, to stop the machine and to prevent the workpiece from being damaged further.

Example 13

  The break of a cutting edge is characterized by a very brittle fracture which is associated with a transient phenomenon of shock waves of very large amplitude. The sensor could be used to detect this phenomenon or to detect the transition between levels of activity generating shock waves before break and after break, and

to stop the machine.

  A wide range of industrial processes, industrial plants, machines and equipment generate an activity that generates acoustic emissions during their operation. A signal shaping sensor can be used to start or stop a machine, apparatus, process in order to ensure that the machine or process

  operates within a desired operating range.

  A sensor can also be used to commission a second process or a second machine when the acoustic emission generating activity of the first process or of the first machine changes from a level lower or higher than a level preset relative to at a higher or lower level, respectively, at

  the preset acoustic emission generating activity.

  The invention is not limited to the examples which have just been given, and it can be applied to all situations where there is a change in the level of an activity generating acoustic emission. The sensor can be used to generate a signal when the comparator detects a change in the level of the activity generating acoustic emission from a level lower or higher than a preset level compared to a level

  higher or lower, respectively, at the preset level.

  The signal from the sensor can be used to activate, or to deactivate, a machine, apparatus, process or to otherwise control a machine or process or to indicate that a particular point 'a process o of a

  machining process has been reached.

  Broadband shock waves generated by processes are still present and in many cases are indicators

  very sensitive to variations in the process.

  A single sensor according to the invention provides real-time control of an appreciable area or volume. The positioning of the sensor is not critical since the shock waves propagate from their source towards the sensor. Therefore, the installation of the sensor is easy and, in most cases, does not take up space, since the sensor can be mounted outside and control the Interior of the machine. The orientation of the sensor is not important. The sensor is

  generally simple and has no expensive components.

  It may be necessary to position the sensor as acoustically close as possible to the source of the shock waves which are of interest in the case where these shock waves are masked by another dominant shock wave source, because the use of 'an acoustic emission as a sensor is only effective if the source which is of interest is dominant. Another method would consist in analyzing the output of the sensor in a differential manner compared to that of a second sensor positioned near the source of competing shock waves.

Claims (14)

CLAIMS I. Sensor comprising a transducer (14) capable of providing an electrical output signal dependent on the intensity of the activity generating acoustic emission, a level detector capable of measuring the level of the electrical signal which corresponds to the level of the acoustic emission generating activity, a comparator (20) capable of comparing the level of the acoustic emission generating activity with a preset level of acoustic emission generating activity, the comparator (20) detecting changes in the level of the acoustic emission generating activity from a level lower or higher than said preset level of acoustic emission generating activity compared to a higher or lower level, respectively, at said preset level of generating activity d acoustic emission, and producing a signal.   2. Sensor according to claim 1, characterized in that the   comparator (20) produces a change in digital signal level.   3. Sensor according to claim 1, characterized in that the comparator (20) produces a signal intended to change the state of a contact relay.   4. Sensor according to one of claims 1 to 3, characterized in that   the comparator (20) produces a signal which is an activation signal service or deactivation.   5. Sensor according to one of claims I to 4, characterized in that   the transducer (14) is acoustically coupled to the housing of an apparatus to detect changes in the level of generating activity   acoustic emission in said casing.   6. Sensor according to one of claims I to 4, characterized in that   the sensor is mounted in a housing to which it is acoustically coupled, the sensor detecting changes in the level of the activity generating acoustic emission in the housing and producing a signal to control the device.   7. Sensor according to claim 6, characterized in that the sensor is hermetically included in a mass of metal or of a other suitable material.   8. Sensor according to one of claims I to 3, characterized in that   the comparator (20) produces a signal indicating that the activity level   acoustic emission generator has changed.   9. Sensor according to one of claims I to 7, characterized in that   the level detector measures the mean square level of the activity   acoustic emission generator detected by the transducer (14).   10. Sensor according to one of claims I to 7, characterized in that   that the level detector measures the peak level of the activity   acoustic emission generator detected by the transducer (14).   1 0 1. Keypad comprising a casing adapted to receive a plurality of key pads, the casing forming an increased attenuation path for an activity generating acoustic emission, each key pad being acoustically coupled to a respective sensor, each sensor comprising a transducer (14) adapted to supply an electrical output signal dependent on the intensity of the activity generating acoustic emission in the corresponding key buffer, a level detector adapted to measure the level of activity acoustic emission generator, a comparator (20) adapted to compare the level of acoustic emission generating activity with a preset level of acoustic emission generating activity, the comparator (20) detecting changes in the level of the activity generating acoustic emission from a level lower or higher than said preset level of activity generating acoustic emisslon relative to a ni higher or lower calf, respectively, at said preset level   of activity generating acoustic emission, and producing a signal.   12. Keypad according to claim 11, characterized in that each sensor is mounted in its respective key buffer   to which it is acoustically coupled.   13. Keypad according to claim 12, characterized in that each sensor is hermetically included in a buffer of   keys made of a mass of metal or other suitable material.   14. Method for controlling a process or a machine (12) comprising the steps of: - detecting the level of acoustic emission from a remarkable position of the process or the machine (12), - comparing the level of acoustic emission generating activity from the remarkable position of the process or machine (12) at a preset level of acoustic emission generating activity, - detecting changes in the level of generating activity acoustic emission from the remarkable position of the process or the machine (12) from a level lower or higher than said preset level of the activity generating acoustic emission compared to a higher or lower level, respectively , at said preset level of activity generating acoustic emission, said changes producing a signal to control the process or the machine (12).   15. A method of controlling a process or a machine (12) comprising the steps of: - detecting the level of the activity generating acoustic emission from a remarkable position of a first process or a first machine (12), - comparing the level of the acoustic emission generating activity from the remarkable position of the first process or of the first machine (12) to a preset level of acoustic emission generating activity, - detecting changes in the level of the acoustic emission-generating activity from the remarkable position of the first process or the first machine (12), from a level lower or higher than said preset level of generating activity of acoustic emission with respect to a higher or lower level, respectively, at said preset level of activity generating acoustic emission, said changes producing a signal to control   a second process or a second machine (12).   16. A method of controlling a process or a machine (12) according to claim 14, characterized in that the signal intended to control the process or the machine (12) is a start-up signal. service or deactivation.