GB2047430A - Machine tool - Google Patents
Machine tool Download PDFInfo
- Publication number
- GB2047430A GB2047430A GB8009044A GB8009044A GB2047430A GB 2047430 A GB2047430 A GB 2047430A GB 8009044 A GB8009044 A GB 8009044A GB 8009044 A GB8009044 A GB 8009044A GB 2047430 A GB2047430 A GB 2047430A
- Authority
- GB
- United Kingdom
- Prior art keywords
- machine tool
- signals
- machine
- transducers
- supplied
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
Links
Classifications
-
- 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—Programme-control systems
- G05B19/02—Programme-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 programme data in numerical form
- G05B19/19—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 programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path
- G05B19/21—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 programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device
- G05B19/23—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 programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control
- G05B19/231—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 programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude
- G05B19/237—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 programme data in numerical form characterised by positioning or contouring control systems, e.g. to control position from one programmed point to another or to control movement along a programmed continuous path using an incremental digital measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude with a combination of feedback covered by G05B19/232 - G05B19/235
-
- 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—Programme-control systems
- G05B19/02—Programme-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 programme data in numerical form
- G05B19/416—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 programme data in numerical form characterised by control of velocity, acceleration or deceleration
- G05B19/4163—Adaptive control of feed or cutting velocity
-
- 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
- G05B2219/37285—Load, current taken by motor
-
- 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
- G05B2219/49—Nc machine tool, till multiple
- G05B2219/49206—Compensation temperature, thermal displacement, use measured temperature
Landscapes
- Engineering & Computer Science (AREA)
- Human Computer Interaction (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Automatic Control Of Machine Tools (AREA)
Abstract
A machine tool includes a numeric control unit which controls the operation of a drive motor 17 which effects relative movement of two parts of the machine tool. The control unit includes a store 27 which provides control signals to a comparator 26 which also receive feedback signals from a transducer 28. The signal provided by the transducer is modified by an electronic circuit 31 which is supplied with correction signals by an error calculation unit 30. A memory 32 is provided in which is stored information relative to machine tool errors and also machine operating conditions. Based on the signals from the transducer and the information in the memory the error calculation unit adjusts the signal provided by the transducer to effect correction for machine errors and the operating conditions of the machine tool. <IMAGE>
Description
SPECIFICATION
Machine tool
This invention relates to machine tools of the
kind comprising at least two movable members which in use provide support for a tool relative to a workpiece supporting device of the machine, motors operable to effect movement of said members respectively and transducers for providing signals indicative of the positions of said members respectively, the motors in use, being controlled by a numeric control system to which the signals from said transducers are supplied.
An example of a machine tool of the above kind is a lathe in which the two members are the saddle and the cross-slide. The cross-slide mounts the tool post and the bed of the machine through the head stock and the chuck, carries a workpiece. The saddle and the cross-slide are driven by motors which conveniently are of the reversible electric type, through the intermediary of lead screws and nuts. The transducers may be encoders having rotary parts connected to and driven by the lead screws or they may be of the linear displacement type.
The accuracy of machining of a workpiece by a programme of instructions supplied to the numeric control system depends amongst other things on the control system being supplied with information as to the exact location of the tool relative to the work piece. In known machines information regarding the tool offset that is to say the position of the tool tip relative to the holding device, is determined and supplied to the control system. This offset can be regarded as a variable offset in that it will change each time the tool is changed. There are however other offsets to be considered which can be said to be due to the machine tool itself. For example there may be non-linearities in the lead screws and backlash in the nuts and screws. This latter nonlinearity is particularly important where the transducers are encoders.In known machines these fixed errors have been measured and the error information used to vary the demanded position signals of the movable members respectively.
There are however other offsets due to the machine. For example, in the case of a lathe if the vertical plane containing the axis of rotation of the chuck is not parallel to the vertical planes containing the slides which support the saddle, then for a fixed position of the crossslide, when the turning operation is being carried out a taper will be produced on the workpiece. This of course is a well known effect and in order to provide a right cylindrical surface on the work piece it is necessary to alter the position of the cross-slide as the saddle is moved. Thus an error in one plane can produce an offset in another plane.
Variable errors can arise due to the way in which the machine is operated. For example,
if a heavy cut is taken than a considerable
load will be imposed on the tool, the tool
post, the cross-slide and the saddle which
may lead to the tool tip being deflected away from its correct position. Similarly the work piece itself may be locally distorted. Errors can also arise due to temperature variations which occur during the use of the machine.
It is proposed that the aforesaid errors and others measure where possible, by operating the machine and storing the information. The information appropriate for a particular machining operation or a particular setting of the various parts of the machine can then be taken out of the store and utilised in the control system to effect the necessary connection.
The object of the present invention is to provide a machine tool of the kind specified in a simple and convenient form.
According to the invention a machine tool of the kind specified includes an information store in which is stored information relative to fixed machine errors, an error calculation unit to which is supplied information from said store and signals from said transducers, said error calculation unit providing two correction signals which influence the control signals supplied by the numeric control unit to said motors respectively.
In the accompanying drawings:
Figure 1 is a diagrammatic plan view of an example of a machine tool;
Figure 2 shows a modification to part of the tool of Fig. 1; and
Figures 3-5 show block diagrams of an electronic control system associated with the machine tool.
With reference to Fig. 1, the machine tool to be considered is a simple lathe having a bed 10, a saddle 11 slidably mounted on the bed, a cross-slide 1 2 carried by the saddle, the cross-slide mounting a tool post 1 3 which carries the tool. In addition the bed of the machine mounts a head stock 14 which carries a chuck 1 5.
The saddle is moved along the slides on the bed by means of a lead screw 1 6 which is driven by a reversible electric motor indicated at 1 7 in the diagram. The lead screw is engaged by a nut which is mounted on the saddle. A further lead screw and nut are mounted on the saddle and cross-side for moving the cross-slide relative to the saddle, the further lead screw being driven by an electric motor 1 8 in order to effect movement of the cross-slide.
Signals representing the position of the saddle on the bed of the machine and the crossslide on the saddle are provided by a pair of transducers. The transducers may be rotary encoders associated with the lead screws or they may be linear displacement transducers.
An example of a rotary encoder is seen in Fig.
2. In this case the encoder includes a housing 1 9 and a rotary part 20 which is coupled by means of a coupling 21 to the drive shaft of the motor 1 7 so that the rotary part 20 is effectively coupled to the lead screw 16. The housing 1 9 is carried in bearings which permit the housing to be moved angularly and the housing is connected by gearing 22 to a stepper motor 23. For a given position of the rotary part 20 of the encoder the angular position signal provided by the encoder can be altered by moving the housing angularly by means of the stepper motor.
A linear displacement transducer is not illustrated but can have its housing secured to the bed 10 of the lathe and its moving component to the saddle 11 or to the saddle 11 and the cross-slide 1 2.
Turning now to Fig. 3, the numeric control unit for the machine tool includes a drive circuit for the motor 1 7 these being indicated at 23. The drive circuits are supplied with analogue signals by means of a digital to analogue converter 24 which receives an input signal from an error store 25. The error store stores the output of a comparator 26 to which is supplied a demanded position signal from a machining instruction unit 27 the machining instruction unit may store the machining instruction on tape or some other medium.
The other signal which is fed to the comparator 26 is the signal derived from the transducer indicated at 28 and this signal is supplied to the comparator by interface circuitry indicated by the block 29. Ignoring for the moment the block shown between the block 29 and the transducer 28, the system is a simple closed loop servo system which when in operation, strives to ensure that the position of the saddle represented by the signal obtained from the transducer 28 is the derived position as represented by the signal supplied by the instrumentation unit 27. It will be understood that in Fig. 3 only the control for the motor 1 7 is shown. The machine instruction unit 27 will have a further output to supply a similar circuit associated with the motor 1 8.
As mentioned above it is desired to correct for inaccuracies in the construction of the machine as well as for various operating conditions of the machine which can have an influence on the position of the tool tip relative to the workpiece. An error calculation unit 30 is provided and which supplies a correction signal which is utilised in the block 31 disposed intermediate the transducer 28 and the block 29 interface, to modify the output signal provided by the transducer 11. In this case the transducer 28 is a linear displacement transducer. The block 31 is not regarded as being part of the numeric control unit neither is the error calculation unit 30.
The error calculation unit does in fact provide a second correction signal which is supplied to a block equivalent to the block 31 to modify the output of the transducer which is associated with the cross-slide. In this arrangement the block 1 8 provides electrical modification of the signal provided by the transducer.
In the case where the rotary encoder is used the signal obtained from the error calculation unit is used to control the stepper motor 23 and it would be possible to adjustably mount the fixed part of a linear displacement transducer and to vary its position in a similar fashion.
Turning now to the error calculation unit. In the example above we quoted the case where the vertical plane containing the axis of rotation of the chuck was not parallel to the vertical planes containing the slides supporting the saddle on the bed. It was explained that as a result when moving the saddle and machining a component, the resulting surface would be tapered and that in order to correct this it would be necessary to adjust the crossslide. If in addition the slides were not straight then the angle between the cross-slide and the axis of rotation would change as the saddle moves. Thus the amount of taper would be dependent upon the position of both the saddle and the cross-slide. The discrepancy in the machine therefore would be measured at sometime during or after construction of the machine and stored in a store which is indicated at 32.In use in order to provide the desired correction, the error calculation unit needs to be supplied with signals indicative of the position of the saddle and of the crossslide and as will be seen from Fig. 3 such a signal is provided by the transducer 28, a further signal being obtained from the transducer associated with the cross-slide. The correction signal to the circuit associated with the motor 1 8 provided by the error calculation unit will take into account the information regarding the machine inaccuracy contained in the store 32 and a continuous adjustment of the cross-slide will be effected as the saddle is moved.
In order to take care of variation in the depth of cut, the current consumption of the drive motor 1 7 can be monitored. Alternatively the current consumption of the motor driving the chuck 1 5 can be monitored. It must be remembered that when a heavy cut is being taken then the amount of power required to drive the lead screw will be increased. In similar fashion the error calculation unit may be supplied with signals representing the temperature of various parts of the machine tool and the temperature of the workpiece itself. Particularly where linear transducers are utilised, it will be important to take into account variations in the temperature of the transducers.The three blocks indicated at
33, 34 and 35 represent the temperature sensing devices for the various parts of the
machine tool together with the component being machined. The blocks 36 and 37 indicate the circuits which provide the current signal from the motor 1 7 and the temperature signal of the transducer 28 respectively it being understood that similar circuits are provided for the motor 1 8 and the transducer associated with the cross-slide.
It will be appreciated that there must be contained in the store 32 all the information which will be required by the error calculation unit to provide the required correction signal.
As explained some of the information may be inserted into the store as a result of measurements on the machine tool. Other information such as component distortion, component expansion due to temperature variations etc., must be inserted into the store either as a result of measurement on workpieces machined by the machine tool or as a result of experience gained as a result of machining workpieces of comparable form and material.
The error calculation unit 30 is shown in detail in Fig. 4 and also shown in this figure is the memory 32. The error calculation unit comprises a microprocessor 38 with which the memory 32 is associated together with two further memories 39, 40. Memory 39 contains the programme instructions whilst memory 40 contains information relative to corrections to be discussed later. Associated with the microprocessor 38 is an interface unit 41 from which are obtained the outputs for application to the circuits 31 or for control of the stepper motor 23. Inputs referenced
A-l inclusive are provided.Inputs A and I are the saddle and cross-slide transducer signals whilst inputs B-H are identified as follows:
B-the current of motor 1 7 C-the saddle transducer temperature
D-the machine bed temperature
E-the saddle temperature F-the component temperature
G-the cross-slide transducer temperature
H-the current of motor 1 8 The inputs B-H inclusive are fed to a multiplexed analogue to digital converter 42 which provides signal to the interface unit 41 and also receives a control signal from the interface unit. The transducer signals A, I are supplied to phase comparators 43, 44 respectively which are connected to stores 45, 46.
The transducer signals are compared in the comparators with a reference signal to provide position signals which are stored in the stores 45, 46. The outputs from the stores are applied to the interface unit 41. On the basis of the information stored in the memory 32 the signals A-l are utilised to determine the signals supplied to the circuit 31.
An example of the circuit 31 is seen in Fig.
5 and it includes a shift register 47 the output of which is connected to the interface circuit
29 by way of a low pass filter 48. The signal from the respective transducer is supplied to the shift register by way of a zero crossing detector 49 and connected to the clock input of the shift register is the output of a binary multiplier 50. This is provided with an input from a crystal oscillator 51 and also receives an input from the interface unit 41.
In known machines correction for tool offsets may be effected by manual entry of data to the machining instruction unit. It is however possible for the correction for tool offset to be made by adjusting the signal provided by the transducer to the numeric control unit.
The determination of the tool offsets in various planes may be effected in a controlled sequence whereby the tool is offset progressively in each plane until a detection device is actuated and the resultant offset stored in a memory, for example the memory 40. Clearly several tools may be required for machining a component and the machine operator can measure the offsets of the tools in turn, these offsets being stored in the memory and being retrieved from the memory automatically when a particular tool is in use. There is therefore no need once the offsets have been determined, for the operator of the machine to determine the offset for the new tool which is brought into use.
The machine tool described does not have to be built to the accuracy which is required of machine tools of the known type which incorporate numeric control. The reason for this is that errors in the machine tool can be compensated for during use and this compensation can take into account the operating conditions of the machine tool. In the known type of machine tool incorporating numeric control the machine tool must be built to an accuracy such that it can execute the programme of instructions.
Claims (8)
1. A machine tool comprising at least two movable members which in use provide support for a tool relative to a workpiece supporting device of the machine, motors operable to effect movement of said members respectively, transducers for providing signals indicative of the portions of said members respectively, a numeric control system for controlling the motors, said numeric control system being supplied with the signals from said transducers, an information store in which is stored information relative to fixed machine errors, an error calculation unit to which is supplied information from said store and signals from said transducers, said error calculation unit providing two correction signals which influence the control signals supplied by the numeric control unit to said motors respectively.
2. A machine tool according to claim 1 including means for supplying a signal or signals to said error calculation unit indicating an operating condition of the tool, said memory also containing information relative to variable machine errors.
3. A machine tool according to claim 1 or claim 2 including means responsive to said correction signals for modifying the signals supplied by said transducers to the numeric control unit.
4. A machine tool according to claim 3 in which said means comprises electronic circuits which modify the signals from the transducers.
5. A machine tool according to claim 3 in which said means comprises a pair of electromagnetic devices for varying the positions of parts of the transducers.
6. A machine tool according to claim 5 in which said transducers are rotary encoders having their rotary parts coupled to said motors respectively and said pair of electromagnetic devices comprise stepper motors operable to adjust the angular setting of the stators of said encoders.
7. A machine tool according to claim 1 including means for supplying temperature signals indicative of the temperatures of parts of the machine tool to said error correction unit.
8. A machine tool comprising the combination and arrangement of parts substantially as hereinbefore described with reference to the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8009044A GB2047430B (en) | 1979-04-07 | 1980-03-18 | Machine tool |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7912310 | 1979-04-07 | ||
| GB8009044A GB2047430B (en) | 1979-04-07 | 1980-03-18 | Machine tool |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2047430A true GB2047430A (en) | 1980-11-26 |
| GB2047430B GB2047430B (en) | 1983-02-02 |
Family
ID=26271178
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8009044A Expired GB2047430B (en) | 1979-04-07 | 1980-03-18 | Machine tool |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2047430B (en) |
Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0062076A1 (en) * | 1980-10-13 | 1982-10-13 | Fanuc Ltd. | Method and apparatus for controlling industrial robot |
| US20210178454A1 (en) * | 2019-12-17 | 2021-06-17 | Makita Corporation | Rebar tying tool and electric work machine |
| CN112983005A (en) * | 2019-12-17 | 2021-06-18 | 株式会社牧田 | Reinforcing bar binding machine and electric working machine |
| CN112977927A (en) * | 2019-12-17 | 2021-06-18 | 株式会社牧田 | Reinforcing bar binding machine |
-
1980
- 1980-03-18 GB GB8009044A patent/GB2047430B/en not_active Expired
Cited By (9)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| EP0062076A1 (en) * | 1980-10-13 | 1982-10-13 | Fanuc Ltd. | Method and apparatus for controlling industrial robot |
| EP0062076A4 (en) * | 1980-10-13 | 1985-06-06 | Fanuc Ltd | Method and apparatus for controlling industrial robot. |
| US20210178454A1 (en) * | 2019-12-17 | 2021-06-17 | Makita Corporation | Rebar tying tool and electric work machine |
| CN112983005A (en) * | 2019-12-17 | 2021-06-18 | 株式会社牧田 | Reinforcing bar binding machine and electric working machine |
| CN112977927A (en) * | 2019-12-17 | 2021-06-18 | 株式会社牧田 | Reinforcing bar binding machine |
| US11529669B2 (en) | 2019-12-17 | 2022-12-20 | Makita Corporation | Rebar tying tool |
| US11554409B2 (en) * | 2019-12-17 | 2023-01-17 | Makita Corporation | Rebar tying tool and electric work machine |
| CN112977927B (en) * | 2019-12-17 | 2023-05-09 | 株式会社牧田 | Reinforcing bar binding machine |
| CN112983005B (en) * | 2019-12-17 | 2024-06-18 | 株式会社牧田 | Reinforcing bar binding machine and electric working machine |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2047430B (en) | 1983-02-02 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |