Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/24—Arrangements for observing, indicating or measuring on machine tools using optics or electromagnetic waves
  • B23Q17/2433—Detection of presence or absence
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/24—Arrangements for observing, indicating or measuring on machine tools using optics or electromagnetic waves
  • B23Q17/2433—Detection of presence or absence
  • B23Q17/2442—Detection of presence or absence of a tool
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Program-control systems
  • G05B19/02—Program-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form
  • G05B19/401—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form characterised by control arrangements for measuring, e.g. calibration and initialisation, measuring workpiece for machining purposes
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B19/00—Program-control systems
  • G05B19/02—Program-control systems electric
  • G05B19/18—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form
  • G05B19/406—Numerical control [NC], i.e. automatically operating machines, in particular machine tools, e.g. in a manufacturing environment, so as to execute positioning, movement or co-ordinated operations by means of program data in numerical form characterised by monitoring or safety
  • G05B19/4065—Monitoring tool breakage, life or condition
• • G—PHYSICS
  • G05—CONTROLLING; REGULATING
  • G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
  • G05B2219/00—Program-control systems
  • G05B2219/30—Nc systems
  • G05B2219/37—Measurements
  • G05B2219/37233—Breakage, wear of rotating tool with multident saw, mill, drill

Definitions

• This invention relates to a detection device and method of detection. More particularly, the invention concerns the detection of objects which rotate or are subjected to other cyclic or repetitive motion relative to the detection device. Particularly, but not exclusively, the object is a rotating tool for use with a machine tool. Additionally the invention relates to the detection of objects which come between the device and a rotating element.
• a problem with this arrangement is that the tool etc has to fit between the light transmitter and receiver in order to be detected. Vibrations can cause transmitter and receiver misalignment which affects the detection of the tool. Additionally the tool has to be positioned accurately which is not always possible if the exact size of the tool is not known. In this type of system a shadow is formed on the detector by the tool or other article which passes through the beam and when that shadow obscures the beam by a predetermined amount, a tool present signal is produced.
• the tool or the like can be used to reflect light and the transmitter and receiver can be mounted together.
• Such systems are described in US5,293,048, GB2200747A and DE 34 344 61.
• the amount of light reflected by the tool is limited because tools generally have poor reflectivity, so the light transmitter must be powerful in comparison to the power of the light transmitter of the aligned system described in the paragraph above.
• the light transmitter is a laser the output power required of the laser to produce a measurable reflection from the tool may exceed current safety limits.
• the invention provides a detection device for detecting the presence or absence of an object, the device comprising a light transmitter and a light receiver positioned relative to the light transmitter to receive light reflected by the object, characterised in that the transmitted light is transmitted with varying intensity.
• the invention provides a method of detecting the presence or absence of an object, comprising the steps of: transmitting light towards the object; and receiving light reflected by the object; wherein, the transmitted light is transmitted with varying intensity.
• the varying intensity is a variation between no light and full light transmitted by the light transmitter.
• the light is transmitted periodically.
• the "on" period is l-50 ⁇ S in every 2-100 ⁇ S, i.e. approximately 10- 50OkHz.
• the object is adjacent the device.
• the detection device does not detect light continuously but only at predetermined periods. This results in the periodic instantaneous power of the light transmitter being higher than the average output power because the light transmitter does not output light continuously. This higher periodic output power can be used to safely increase the amount of light received at the light receiver during the said periods without causing unsafe average levels of output light.
• the average output is preferably below current acceptable limits for unprotected viewing of the laser.
• the varying intensity of light produces an alternating signal at the light receiver which can be readily amplified separately from the signal produced by the generally constant ambient light.
• a problem with the prior art is that any reflection that is above the threshold is recorded as a tool present signal thus false triggers from the presence of coolant or swarf occur.
• the tool is provided with through tool coolant. In this case, in order to perform a tool check one has to wait until the coolant has drained away which results in a delay in the machining process.
• the invention provides a device for detecting the presence or absence of an object which has repetitive motion, the device comprising a receiver for receiving a signal from the object and circuitry for determining the presence or absence of the object to be detected, characterised in that the circuitry records the signal from the receiver as a pattern of data during at least part of the repetitive motion of the object, compares the data with a previously recorded data pattern and, produces an output signal based on the comparison.
• the circuitry produces an object detection output signal either when the pattern matches a previously recorded data pattern or when the pattern no longer matches a previously recorded data pattern.
• the invention provides, a method for detecting the presence or absence of an object which has repetitive motion, the method comprising the steps of: receiving a signal from the object at a receiver; recording the signal from the receiver as a pattern of data during at least part of the repetitive motion of the object; comparing the data with a previously recorded data pattern; and producing an output signal based on the comparison.
• the art of tool breakage detection has been moved from identifying a beam obscuration or breakage or, registering that a reflected beam has an intensity which is above a threshold, i.e. a choice of on/off systems to the positive identification of a tool being present by pattern recognition i.e. the change in the beam is identified as being characteristic of a tool.
• the repetitive motion can be a rotation or any other repeating motion.
• the signal is light.
• the light is from a transmitter and the receiver receives light from the transmitter in order to produce the said signal.
• the transmitted light is transmitted with varying intensity.
• the circuitry of the device is able to find patterns of data which match, thus confirming the presence of the rotating object.
• the patterns of data may be selected or downloaded from historical data of drill bit patterns which are then compared to the current data or, in a preferred embodiment, current data is compared to previously recorded data received during at least one earlier rotation.
• previously recorded data in this specification includes both data recorded during an earlier rotation of the tool during the same inspection cycle and historical data.
• An advantage of using historical data occurs when a tool having more than one cutting edge is being used.
• the absence of one or more of the cutting edges can be identified as the pattern produced will differ from the historical data.
• a mixture of the two types of data could be employed to flag that a tool should be changed soon as surface finish will be affected and the tool is more prone to breaking which increases the risk of creating scrap. Any geometrical change can be identified for example, that the wrong tool is in the chuck, which is flagged to an operator.
• the object may be a cutting tool, the presence of which is to be confirmed, or a moving part of a machine, the tool being brought between the device and the moving part to prevent the object detection signal and thus to confirm its presence as a result of the discontinuation of an object found signal.
• the circuitry determines the amount of signal received at the receiver during discrete time intervals and produces a value for each interval.
• the circuitry either converts the value of signal (such as light) received into digitised form such as a binary value or an analogue signal is used.
• Binary is preferred as it enables simple processing that can be done real time.
• a tool found signal is issued by the circuit.
• a rotating tool or similar moving object will be detected when the patterns of two or more sets of data are compared and matched.
• the amount of signal received at the receiver is monitored and if a threshold is exceeded during any one interval then the binary value of the data is recorded as a 1. Alternatively, if the value of the signal does not reach the threshold during the interval then a binary 0 is recorded.
• Fig 1 shows a detection device according to the invention in use as a cutting tool detector
• Fig 2 shows a schematic diagram of the device shown in Fig 1;
• Fig 3 shows a block circuit diagram of circuitry for use in the detection device shown in Figs 1 and 2;
• Figs 4a,b and c show diagrammatic representations of the operation of the circuitry shown in Fig 3;
• Fig 5 shows the invention used in a different way
• Fig ⁇ shows a diagrammatic representation of an alternative operation of the circuitry shown in Fig 3.
• Figs 7a and b show alternative configurations of a device according to the invention.
• Fig 1 shows a pictorial view of a detection device 10 and a mounting bracket 80 for fixing the device to a machine or the like. Shown also is a portion of a tool 30 which is to be detected by the detector 10.
• Fig 2 shows the same device 10 in section. Shown are a laser diode light transmitter 12, a transmitter focusing lens 14, an output light path 52, a reflected light path 54, a receiver lens 16 and a photodiode light receiver 18. The light is transmitted nominally normally to the tool 30.
• Light issued from the laser 12 is focused approximately at the point where the tool 30 is expected, along path 52.
• the transmitted light is reflected, at least along reflected light path 54.
• Reflected light 54 is then focused by lens 16 onto the photodetector 18.
• the transmitter lens 14 is provided with an air supply 22 which flows out into the machine environment via an aperture in housing 24 and the receiver lens 16 is larger than required so if any particles do stick to the surface or an oil film partially coats the surface, there is sufficient surface area remaining to enable the signal to be received.
• the system has in built redundancy so, the reflected signal can deviate from the optimal path and still be received.
• the detector device 10 includes circuitry 20, in this instance mounted inside the device 10.
• the circuitry 20 is shown in detail in Fig 3.
• the controller 50 which controls operations of the tool 30.
• Figs 7a and 7b show alternative arrangements of a device according to the invention.
• the transmitter 112 and receiver 118 are displaced vertically from each other and provided in separate housings 100 and 102 respectively.
• Fig 7b two sets of transmitters and receivers 212/218 and 212' /218' respectively are shown.
• the transmitter / receiver pair lies in substantially the same vertical plane but, they are radially displaced about the rotating axis of the tool 30.
• the angle of displacement is less than 90°.
• 212' /218' the angle of displacement is between 90° and 180°.
• the divider 22 produces two synchronised outputs.
• the first output is a signal to trigger the laser and the second output is a signal to a sample and hold circuit 23.
• the signal from the divider circuit operates at about 15OkHz.
• the laser diode 12 is constantly flashing on and off at a rate which, to a machine operator or observer appears as a weak laser output.
• the average light output 52 of the laser 12 will be below currently acceptable limits for unprotected viewing of the laser. Consequently the output 52 from the laser is safe for the operator.
• Reflected light 54 returning to the lens 16 and ambient light is detected by the photodiode 18 and its analogue signal is amplified in a two-stage amplifier 24/25.
• a DC restorer 26 holds the alternating signal about a suitable voltage to stop it wandering due to changes e.g. in ambient light levels.
• the sample and hold circuit 23 is triggered at approximately the same time as the laser by the synchronised signal from the clock divider circuit 22.
• the signal produced by the amplifier 24/25 will represent one flash of the laser light 52.
• a signal 37 from the sample and hold circuit is so frequent (15OkHz) that it appears continuous as shown in Fig 4a although in practice one sample is taken approximately every 6 ⁇ Sec.
• the sampled signal is then filtered in a low pass filter 27 to remove unwanted high frequency noise.
• the periodic analogue signal from the filter is then split and fed to a signal comparator and reference voltage producing circuitry 29 comprising a peak signal strength detector and a percentage dividing circuit.
• the output from the reference voltage circuit 29 Vref is thus a percentage of the peak analogue signal strength from the low pass filter 27.
• This reference voltage Vref is compared with the analogue signal 37 and the comparator 28 produces an output only when the analogue signal exceeds the reference voltage. This will happen only when the amount of light at the photodetector is abnormally high i.e. when the laser light 54 is reflected onto the photodetector 18.
• the -output 38 from the comparator 28 is shown in Fig 4b.
• the amount of light detected by the photodetector will peak regularly as the teeth etc move into the pulses of light 52 and cause reflections 54 which are detected by the detector 18. The pulses occur so frequently that rotating teeth etc are not missed by the detection circuitry.
• the output from the comparator 28 is fed into a microcontroller 32.
• the microcontroller is programmed via a programming input and has a clock to keep it synchronous with the sampling rate.
• the microcontroller monitors the digital input signal over a period of time and if the signal is obtained from the comparator then the microcontroller records this event as a binary "1". Otherwise a binary "0" is recorded.
• the period is 3.75mS. Put another way the period is one 16th of a revolution of a tool which rotates at lOOOrpm. Other periods are possible.
• the recordings are entered into a 32 bit register 40 shown in Fig 4c in a scrolling manner, new data constantly displacing the old data by one place.
• Line 1 of Fig 4c shows recordings of the microcontroller for one revolution of the tool 30 which corresponds to the signals shown in Figs 4a and b.
• Line 2 represents data which was recorded during the revolution of a tool prior to the revolution of the tool recorded in line 1.
• the data in line 2 has been displaced from line 1.
• the register is long enough to hold data which is 12OmS old, i.e. two revolutions of the tool rotating at lOOOrpm.
• lines 1 and 2 are one register.
• Line 3 will only be all Os when lines 1 and 2 match, lines 1 and 2 will match only when they have the same pattern of data. Lines 1 and 2 will have the same pattern of data when a rotating tool or the like reflects light onto the photodetector 18 at the same point in time during each revolution of the tool. Thus line 3 will contain all Os when the tool is rotating at the detector 10.
• line 3 will contain all Os when lines 1 and 2 contain all Is or all Os. This is possible when no tool is present, when light beam 52 is constantly reflected onto the detector 10, or when excessive light reaches the detector. To prevent any of the above events causing the tool detector to false trigger, logic is used. If lines 1 and 2 contain all Is or all Os then a logical 0 is entered at AND gate 42. Only when lines 1 and 2 are not all Is or not all 0s ⁇ and line 3 is all Os does the AND gate trigger an output. It can be seen from the foregoing that a rotating object is required to produce an output from the circuitry 20. In general this output is fed to machine tool controller 50 via what is known as a skip line comprising a simple 24 volt on/off signal.
• line 1 shows previously recorded data which has been selected or downloaded from a historical data source.
• lines 1 and 2 comprise two registers which are compared in the manner previously described.
• Fig 6 matching patterns of data are sought over three (a,b and c) revolutions of the tool.
• Logic circuits are used as shown in Fig 4c to produce a tool found signal if correlating data is found in the three parts a',b' and c' of the data in a register 41 i.e. matching Is or 0s. More than three revolutions could be used.
• the determination of correlation data is made once every revolution (6OmS in this instance) .
• the register 41 may be any length but 36 bits of information are required to be stored.
• register a',b' and c' all have matching data despite the tool rotating at only 980rpm because the recordings in the register are delayed slightly by an amount d at each thirteenth recording.
• the same concept can be used for a tool rotating too quickly. In such an instance the duration of the first sample after each twelfth sample will be cut so that the next sample starts 2.5mS later.
• Detector 10 is shown in plan view, fixed to the headstock 51 on the lathe and directed toward lathe chuck 56.
• Lathe chuck 56 rotates in the direction of arrow A.
• reflected features on the chuck will produce an output signal from the circuitry in the detector 10 when the chuck rotates.
• the output signal will stop. Consequently the presence or absence of lathe tool 30' can be determined from the state of the output signal from the circuitry 20. Greater accuracy can be obtained if the light beam 52 is focused to the point where a lathe tool is expected to enter that beam.
• the production of the pattern means that the tool is present, it is the inverse situation. It is the absence of the pattern produced by the chuck which is indicative of a tool being present. In either case, a change in the data stream either producing the pattern or obscuring the pattern indicates that a tool is present.
• light which has been reflected off an object - either a tool or a chuck - is directed to the receiver.
• the object is provided with LEDs.
• LEDs are inset at the points 58 and are angled to transmit light in approximately the same direction.
• rotation of the chuck 56 moves the LEDs with respect to the detector 10 producing a pattern which is obscured when a tool 30' is brought into the beam path.
• the pattern of data produced by rotation of the chuck may vary both in intensity and frequency/wavelength. This can be used to ascertain actual chuck/spindle speed (rather than merely knowing the demanded speed) and, use of different colours can show when one of the LEDs has blown.
• Software in the machine tool controller 50 can be used to inform the machine cutting program to carry on the machining process when a tool has been detected (either a rotating tool or a non-rotating lathe type tool) .
• any number of bits can be used in place of the single bit described above. In such instances it will then be possible to record the amount of light present at the receiver, not just an on/off value as described above.
• a unit can be provided to send a signal which corresponds to the light which would be reflected from a tool.
• the tool detector can be installed and checked on a machine tool without the need to bring a tool adjacent the detector.
• the unit could comprise a simple rotating mirror or other reflective surface, but is preferably a solid state arrangement which produces a pulse of laser light in response to a similar pulse sent by the tool detector.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Mechanical Engineering (AREA)
• Human Computer Interaction (AREA)
• Manufacturing & Machinery (AREA)
• General Physics & Mathematics (AREA)
• Automation & Control Theory (AREA)
• Length Measuring Devices By Optical Means (AREA)
• Machine Tool Sensing Apparatuses (AREA)
• Geophysics And Detection Of Objects (AREA)
• Switches Operated By Changes In Physical Conditions (AREA)

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• 2005
  • 2005-09-07 JP JP2007530759A patent/JP4764427B2/ja not_active Expired - Fee Related
  • 2005-09-07 EP EP05788909A patent/EP1799398B1/en not_active Expired - Lifetime
  • 2005-09-07 WO PCT/GB2005/003449 patent/WO2006027577A1/en not_active Ceased
  • 2005-09-07 AT AT05788909T patent/ATE426484T1/de not_active IP Right Cessation
  • 2005-09-07 US US11/659,848 patent/US7732797B2/en active Active
  • 2005-09-07 KR KR1020077007981A patent/KR20070053319A/ko not_active Ceased
  • 2005-09-07 DE DE602005013551T patent/DE602005013551D1/de not_active Expired - Lifetime

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