GB2075389A - Lathe with hydraulic slide - Google Patents

Abstract

The invention relates to a lathe for metal-spinning, comprising a hydraulic slide for controlling movement of a metal-spinning tool 9, a hydraulic system, and a two-way valve 11 in the system, controlled by a joystick 8, for controlling movement of the slide in a metal spinning operation. A record and playback system is described which bypasses the joystick 8 in the playback mode. <IMAGE>

Description

SPECIFICATION Lathe with hydraulic slide Technical Field of the Invention The invention relates to a lathe with a hydraulic slide.

Background Art Lathes, particularly metal-spinning lathes, have been proposed in which there is a spinning tool such as a roller. The movement of the tool with reference to a workpiece and a. former on which it is mounted is controlled by a steering system including a hydraulic slide and a turntable platform which is clamped to a bed which is slidable. The hydraulic slide incorporates two cross-motion slides which are operated by a four-way valve. The four-way valve is complex and expensive and is not able to provide the precision required.

Disclosure of the Invention It is an object of the invention to provide a lathe which seeks to mitigate the disadvantages of the prior art.

According to the invention there is provided a lathe comprising a hydraulic slide for controlling the movement of a metal-tool, a hydraulic system, and a two-way valve of the hydraulic system for controlling movement of the slide in a metalspinning operation.

Using the invention it is possible to provide for direct numerical control of the hydraulic slide.

Metal spinning lathes embodying the invention are hereinafter described, by way of example, with reference to the accompanying drawings.

Brief Description of the Drawings Figure 1 is a schematic perspective view of a lathe with a hydraulic slide; Figure 2 shows a hydraulic system for a lathe such as the lathe of Figure 1; Figure 3 shows a modification of Figure 2 in the form of an electro-hydraulic system; Figure 4 shows a modification of Figure 2 including a digital position transducer; Figures 5 and 6 show a digital numerical control system; Figure 7 shows a modification of control system; Figure 8 shows another operating system; and Figure 9 shows yet another system.

Best Modes for Carrying Out the Invention Referring to the drawings in which like parts are indicated by like reference numerals, the metalspinning lathe 1 shown has a headstock 2, a hydraulic slide 3, a hydraulic tailstock 4, a hydraulic unit 5, a sliding bed 6, and a base 7. The hydraulic slide 3 is mounted on a rotatable platform. The hydraulic slide has two transversely movable slides which are hydraulically operated by a joystick 8 controlling a two-way valve (not shown).

The hydraulic slide 3 carries a spinning tool 9 on a post 10, which tool 9 in use leaves on a metal sheet which is to be spun to a desired shape about a former carrier by the headstock or tailstock.

The hydraulic slide 3 can be moved in both the longitudinal direction, and in mutually perpendicular directions to carry out spinning operations on both x- and y- axis or co-ordinates to produce a desired shape during spinning.

Figure 2 shows one, open-loop, hydraulic system where the joystick 8, one of the x- or yaxes controlled by the joystick 8 being shown. The joystick 8 controls flow through the two-way valve 1 1 to control movement of the toolpost 10 and hence of the tool 9 mounted thereon, the post being moved by a ram 1 Oa.

Referring now to Figure 3, the electro-hydraulic servo system shown includes potentiometers 12 and 13 respectively actuating (transmitting) and sensing (feedback) of position. Differencing and amplifying functions 14 and 1 5 of the analogue electronics are shown separated, though in practice they would be performed by the same module.

Figure 4 indicates a modification of the system of Figure 3 to incorporate a digital position transducer, the output from which is converted from Digital to Analogue at 17 in order to feed the electro-hydraulic servo system as before. A directreading digital display (not shown) could be driven by the position transducer (this applies to the embodiments of Figure 5 to 9 as well).

Figure 5 shows a modification in which the differencing function 14 is replaced by a digital system in other words a computer 18 performing numerical subtraction. As a result, the D-A converter from the position transducer is no longer required. The joystick potentiometer 12 is converted from Analogue to Digital, at 19 and the computer 18 output needs converting back to analogue at 20 to preserve the proportional characteristic of the electro-hydraulic valve 11.

The amplifying function of the servo system is performed by applying a numerical scaling factor either to the subtractor 21 or to the D to A converter 20 (or both) but preferably to the subtractor 21 as it will then be under control of the software (program).

Figure 5 also shows a memory 22 which is continuously and serially storing the changing position of the toolpost 10, and is thus in the "recording" mode (Figure 5). In Figure 6 the same system is shown in the "playback" mode; there is no change in the external connections of the system, but the computer 18 is now taking 8 a desired position of the post 10 from the memory 22 instead of the joystick 8, which is effectively by-passed.

It will be understood that the resolution requirements of D to A 17, Figure 4, must be as good as the resolution of the ordinary feedback potentiometer 13 of Figure 3 merely for Figure 4 to duplicate its performance; in practice this would not do justice to the inherently high resolution of the digital position transducer, to which the D to A should ideally be matched. However the configurations of Figures 5 to 9 do not require this potentially expensive item. The D to A converter 20 is "inside" the feedback loop and is not so critical: this, plus a simple current amplifier to provide sufficient drive for the electromagnets in the valve 11 will suffice.

The A to D 19 should provide as high a resolution as the digital position transducer 16.

This requirement is met by a dual coarse and fine (or fast and slow) control shown in Figures 7 and 8 which respectively show a coarse positioning and a fine positioning 23 and 24 where the digital information is split into high-order "H" and low- order "L" bits (or digits). The joystick 8 controls the most significant (high-order) bits H only, and the least significant bits are left at zero. A register 25 is continuously updated with the high-order bit H of the toolpost 10 position (the memory 22 also gathers data on position, but for simplicity is not shown). In Figure 8 the system 24 is on fine control: the high-order H data comes from the last recorded coarse position as held in the register 25, and the joystick 8 is now supplying the low-order L data (for fine position).

The resolution requirements upon the joystick 8 and its potentiometer 12 are well within their capabilities. The change-over from fine to coarse could be initiated by (for example) a push button (not shown) on the joystick 8; but the actual "switch-over" is done (by software) entirely within the computer 18. The systems 23 and 24 are closed-loop servos but this need not be the case.

In Figure 9 an extra joystick 8 operating override switch 26 is shown which, when operated, loads maximum forward or reverse into the high order end of the control data word, and thus initiates fast movement of the toolpost 10 under open-loop conditions with the register 25 monitoring the (coarse) position (Figure 7) that the toolpost 10 is actually at instantaneously. When the over-ride joystick 8 is released (to its central off position) the system reverts to "fine" (or "slow") closed-loop mode, as in Figure 8. Using these systems a resolution of 1 in 30,000 is achievable, equivalent to 1 5 bits in binary digital which is achievable within the computer 18.

Claims (7)

1. A lathe comprising a hydraulic slide for controlling the movement of a metal-spinning tool, a hydraulic system, and a two-way valve of the hydraulic system for controlling movement of the slide in a metal-spinning operation.

2. A lathe according to Claim 1 , the hydraulic system comprising an electro-hydraulic servo system.

3. A lathe according to Claim 2, in which there is a digital position transducer.

4. A lathe according to Claim 3, including a digital display.

5. A lathe according to Claim 1, comprising a numerical control device.

6. A lathe according to Claim 5, the numerical control device comprising a computer.

7. A lathe, substantially as hereinbefore described with reference to and as shown in the accompanying drawings.