GB2039085A - Drive assembly for a pivotally mounted part, such as a machine tool head - Google Patents
Drive assembly for a pivotally mounted part, such as a machine tool head Download PDFInfo
- Publication number
- GB2039085A GB2039085A GB7940003A GB7940003A GB2039085A GB 2039085 A GB2039085 A GB 2039085A GB 7940003 A GB7940003 A GB 7940003A GB 7940003 A GB7940003 A GB 7940003A GB 2039085 A GB2039085 A GB 2039085A
- Authority
- GB
- United Kingdom
- Prior art keywords
- pivotally mounted
- machine tool
- tool head
- drive assembly
- mounted part
- 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.)
- Withdrawn
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
- G05B19/182—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 the machine tool function, e.g. thread cutting, cam making, tool direction control
-
- 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
- G05B19/33—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 analogue measuring device
- G05B19/35—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 analogue measuring device for point-to-point control
- G05B19/351—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 analogue measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude
- G05B19/353—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 analogue measuring device for point-to-point control the positional error is used to control continuously the servomotor according to its magnitude with speed feedback only
-
- 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
- G05B2219/37473—Resolver
-
- 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
- G05B2219/41—Servomotor, servo controller till figures
- G05B2219/41036—Position error in memory, lookup table for correction actual position
-
- 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
- G05B2219/41—Servomotor, servo controller till figures
- G05B2219/41047—Recirculating ballnut, ballscrew, preloaded bearing
-
- 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
- G05B2219/49277—Oscillating, swinging feed drive, for grinding
Landscapes
- Engineering & Computer Science (AREA)
- Human Computer Interaction (AREA)
- Manufacturing & Machinery (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- Control Of Position Or Direction (AREA)
Abstract
The invention is concerned with the angular positioning of a pivotally mounted part about its pivot axis. In the particular case of this part being a machine tool head a screw drive mechanism (5, 7) of the recirculating ball nut type is used for adjusting the angular position of the machine tool head by means of a servo motor 9. A control system generates (by means of a comparator) an error signal in dependence upon the difference between first and second values ( alpha c, alpha D), representing true and desired angular displacements, respectively, of the movable part (2), so as to control the operations of the drive motor (9) in such manner as to tend to reduce the magnitude of the error signal, the first value ???c being derived as a function of the angular rotation of the motor (by a resolver 21) from a datum position. The motor has velocity feedback from a tachogenerator 20. <IMAGE>
Description
SPECIFICATION
Drive assembly for a pivotally mounted
part, such as a machine tool head
This invention relates to a drive assembly for a pivotally mounted part such as a machine tool head.
It has been proposed for adjusting the an
gular position of a machine tool head about a
pivot axis thereof, that two gear drives can be employed, one for each direction of pivoting, to avoid backlash and inaccuracies due to translating movement from each gear to the
next. Such an arrangement is bulky, uses
many parts and may not always correctly orientate the tool head with the required accuracy.
According to the invention from one aspect there is provided a machine tool head drive assembly in which the machine tool head is
pivotally mounted and a screw drive mechanism of the recirculating ball nut type is connected to the machine tool head and is operable to displace the same about its pivot axis.
In a development, the invention from another aspect is concerned in particular with controlling rotation of the drive screw so that the machine tool head can be moved with precision into any desired new position of angular displacement although this aspect of the invention finds wider application to screw drive mechanism in general, whether or not they are used to orientate pivotally mounted machine tool heads.
According to the invention, then, from another aspect there is provided a drive assembly comprising a pivotally mounted part, a screw drive mechanism, including a drive motor, connected to the pivotally mounted part and operable to displace the same about its pivot axis, signal generating means arranged to produce a signal directly proportional to the angular displacement of the drive motor shaft from a first datum position, and processing means responsive to the signal generating means and arranged to produce an error signal in dependence upon the difference between first and second values, representing true and desired angular displacements, respectively, of the pivotally mounted part from a second datum position, so as to control the operation of the drive motor in such manner as to tend to reduce the magnitude of the error signal, the operation of the processing means being such that said first value is equal to a third value, directly proportional to the shaft angular displacement, as modified in accordance with a correction value determined by a preselected correction function.
Additionally, the drive assembly can incorporate a tacho-generator arranged to sense the instantaneous angular velocity of the motor shaft, and a feedback loop responsive to the output of the tacho-generator to provide velocity feedback control for the drive motor.
In a preferred arrangement the screw drive
mechanism and drive motor are supported together as an assembly by a pivotal mounting and the screw drive mechanism is connected by a pivotal connection to the pivotally mounted part so that is can displace the same between end angular positions about the said pivot axis of the pivotally mounted part, the respective positions of the pivot axis of the said pivotal connection in the two end angular positions and the said pivotal mounting being coplanar, the preselected correction function being a parabolic function relating the angular displacement of the drive motor shaft to said correction value.
For a better understanding of the invention and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying drawings in which:
Figure 1 illustrates diagrammatically in side view a screw drive mechanism for adjusting the orientation of the machine tool head,
Figure 2 is a diagram showing the reiative positions of the different parts of the mechanism,
Figure 3 is a graph showing an error curve, and
Figure 4 is a block diagram of a control system for operating the drive mechanism.
Referring to Fig. 1, a machine tool head assembly comprises a machine tool head (not shown), which is mounted on a supporting plate 2 pivotally mounted on a base plate 1 for limited rotational movement about a pivot axis 3, and also comprises a screw drive mechanism consisting of a ball re-circulating nut 5 in which is engaged a ball screw 7. The plate 2 is supported at one side by a guide plate 4. The ball re-circulating nut 5 is supported, at right angles to its screw axis, on a pair of taper roller bearings 6 located in the plate 2 in such a manner that the ball nut can pivot about an axis parallel to the pivot axis 3.
Similarly, a servo-motor 9 is mounted on a drive bracket 8 which can pivot about a pin 10 rigidly supported by the base plate 1. The ball screw 7 is connected to the servo-motor shaft via an anti-backlash coupling (not shown) and supported in the drive bracket 8 by a bearing assembly comprising radial ball bearings and axial front location bearings. The servo-motor 9 is provided with a tacho-feedback generator 20 to give velocity feedback and a resolver 21 to give positional feedback to a control unit whose circuitry is indicated at 23 in Fig. 4.
In operation, the servo-motor 9 rotates the ball screw 7 to cause the ball re-circulating nut 5 to travel in a selected direction along the screw 7. This angularly displaces the subplate 2 about the pivot axis 3. As the movement continues, the roller bearings 6 and drive bracket pin 10 accommodate the changing attitude of the ball screw 7 caused by the roller bearings 6 moving in an arc about pivot 3 whilst the pivot axis of pin 10 remains in a fixed relationship relative to axis 3.
The geometry of the pivot points is shown in Fig. 2. In this figure, a represents the angular displacement of the roller bearing pivot 6 from the central vertical datum. The relationship between angle CL and the spacing
D between the pivots 6 and 10 can be obtained from the cosine rule from which:
where B is the distance between the pivots 3 and 10, R is the distance between the pivots 6 and 3 and ss is a fixed angle.
B and R are given fixed lengths which would be arrived at by normal design requirements and would be influenced by the angle a0 which represents the limits of angular displacement of the sub-plate 2 from the central vertical datum.
Let the angle (p represent the angular displacement of the shaft of the servo-motor 9 from its datum position in which the pivot 6 is in the central vertical position. D and (p are functionally interrelated by a linear relationship and so D can be expressed in terms of: D=k++c (2) where k and c are constants. Thus, the exact mathematical relationship between CL and f is given by:
The change of CL with (p when the roller bearing 6 coincides with the central vertical datum can be calculated and can be expressed in terms of a finite angle per revolution of the ball screw.The control unit 23 operates on the assumption that this relationship between CL and (p is true for all angular positions of the plate 2 between the limits
+ aO and the drive would then operate on a purely linear basis. In view of the true relationship (3) this assumption gives rise to an error (lea) which, except for a smali range of values of (p near the curve minimum, increases with increasing values of +. The control unit 23 then uses a mathematical approximation to the error curve shown in Fig. 3 to apply a correction to an assumed value df a
derived from the assumed linear relationship
between a and + to arrive at a 'corrected'
value of a.The way in which this is achieved
will now be described with reference to Fig.
4. The operator feeds in a signal clod, representing the desired value of CL, to a comparator (error counter) 24 which compares ad with a signal cuc which represents the 'corrected' value of a. The output error signal from the comparator 24 is fed via an amplifier 25, which also has a velocity feedback signal input from the tacho-generator 20, to the servo-motor 9 which accordingly starts to rotate the ball screw 7.The resolver 21 gives an output positional signal which is compared in a comparator 26 with a datum signal stored in a memory 27, the comparator providing an output signal directly proportional to the angle f. A correction curve function generator 28 supplies a control signal to a comparator/processor 29 which applies a correction to the output signal from the comparator 26, which is processed in the comparator/ processor 29, thereby to provide the signal ac.
The function signal produced in the generator 28 can be suitably chosen to provide the required accuracy from the control unit. Any residual errors resulting from minor mechanical imperfections and/or differences between the true error function and the generated error function can be removed by standard correction compensations after axis calibration.
In a preferred arrangement, as shown in
Fig. 2 the two positions of the pivot axis of the pivot 6 at the angles + aO and the pivot axis of pivot 10 are coplanar. Then, the error curve shown in Fig. 3 can be very closely approximated to by a parabolic function.
Claims (8)
1. A drive assembly comprising a pivotally mounted part, a screw drive mechanism, including a drive motor, connected to the pivotally mounted part and operable to displace the same about its pivot axis, signal generating means arranged to produce a signal directly proportional to the angular displacement of the drive motor shaft from a first datum position, and processing means responsive to the signal generating means and arranged to produce an error signal in dependence upon the difference between first and second values, representing true and desired angular displacements, respectively, of the pivotally mounted part from a second datum position, so as to control the operation of the drive motor in such manner as to tend to reduce the magnitude of the error signal, the operation of the processing means being such that said first value is equal to a third value, directly proportional to the shaft angular displacement, as modified in accordance with a correction value determined by a preselected correction function.
2. A drive assembly according to claim 1, wherein the processing means includes comparator means arranged to receive respective signals representing said first and second values and to generate said signal accordingly.
3. A drive assembly according to claim 1 or 2, further comprising a tacho-generator, arranged to sense the instantaneous angular velocity of the motor shaft, and a feedback loop responsive to the output of the tachogenerator to provide velocity feedback control for the drive motor.
4. A drive assembly according to any preceding claim, wherein the screw drive mechanism and drive motor are supported together as an assembly by a pivotal mounting and the screw drive mechanism is connected by a pivotally mounted part so that it can displace the same between end angular positions about the said pivot of the pivotally mounted part, the responsive positions of the pivot axis of the said pivotal connection in the two end angular positions and the said pivotal mounting being coplanar, the preselected correction function being a parabolic function relating the angular displacement of the drive motor shaft to said correction value.
5. A drive assembly according to any preceding claim, wherein said pivotally mounted part is a machine tool head and the screw drive mechanism is of the recirculating ball nut type.
6. A drive assembly substantially as here it before described with reference to Figs. 2, 3 and 4.
7. A machine tool head drive assembly in which the machine tool head is pivotally mounted and a screw drive mechanism of the recirculating ball nut type is connected to the machine tool head and is operable to displace the same about its pivot axis.
8. A machine tool head drive assembly substantially as hereinbefore described with reference to Figs. 1 to 4 of the accompanying drawings.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7940003A GB2039085A (en) | 1978-11-20 | 1979-11-20 | Drive assembly for a pivotally mounted part, such as a machine tool head |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB7845202 | 1978-11-20 | ||
| GB7940003A GB2039085A (en) | 1978-11-20 | 1979-11-20 | Drive assembly for a pivotally mounted part, such as a machine tool head |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| GB2039085A true GB2039085A (en) | 1980-07-30 |
Family
ID=26269658
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB7940003A Withdrawn GB2039085A (en) | 1978-11-20 | 1979-11-20 | Drive assembly for a pivotally mounted part, such as a machine tool head |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2039085A (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2208947A (en) * | 1987-08-19 | 1989-04-19 | Mcconnel F W Ltd | System for controlling the angular position of an implement |
| EP1171808A1 (en) * | 1999-03-22 | 2002-01-16 | Unova IP Corp. | Method for controlling pivoting machine member |
-
1979
- 1979-11-20 GB GB7940003A patent/GB2039085A/en not_active Withdrawn
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB2208947A (en) * | 1987-08-19 | 1989-04-19 | Mcconnel F W Ltd | System for controlling the angular position of an implement |
| EP1171808A1 (en) * | 1999-03-22 | 2002-01-16 | Unova IP Corp. | Method for controlling pivoting machine member |
| EP1171808A4 (en) * | 1999-03-22 | 2003-03-26 | Unova Ind Automation Sys Inc | Method for controlling pivoting machine member |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| WAP | Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1) |