DD246714A1

DD246714A1 - DEVICE FOR CONSTANT TO KEEP THE RETURN AND RETURN SPEED OF HYDRAULICALLY DRIVEN RIDING STOCKPINOLS

Info

Publication number: DD246714A1
Application number: DD28797186A
Authority: DD
Inventors: Lothar Schubert
Original assignee: Grossdrehmaschinenbau 8 Mai Ve
Priority date: 1986-03-17
Filing date: 1986-03-17
Publication date: 1987-06-17

Abstract

Die Erfindung bezieht sich auf eine Einrichtung zum Konstanthalten der Vor- und Ruecklaufgeschwindigkeit der hydraulisch angetriebenen Reitstockpinole, insbesondere von Drehmaschinen bei kleinem Arbeitsdruck. Aufgabe der Erfindung ist es, eine Einrichtung zu schaffen, mit welcher bei allen statischen Andrueckkraeften die gleiche Verschiebegeschwindigkeit der Pinole wirkt und kein Einrichteaufwand erforderlich ist. Erfindungsgemaess wird dies dadurch erreicht, dass die Kolbenstange des Schubkolbenantriebes der Pinole mittels einer Feder mit dem Gehaeuse in Wirkverbindung steht, wobei die Feder eine Vorspannkraft aufweist, die etwas groesser als die reibungsbedingte Verschiebekraft der Pinole ist, so dass die Kolbenstange waehrend der freien Bewegung der Pinole in Ruhelage bleibt und erst beim Antreffen der Zentrierspitze am Werkstueck eine Bewegung der Kolbenstange gegen die Feder einsetzt, so dass nach einer kleinen Verschiebung der Kolbenstange ein Schalter betaetigt wird, welcher den Verschiebedruck auf den Arbeitsdruck umschaltet, welcher die weitere Bewegung der Kolbenstange bis zu einem festen Anschlag am Gehaeuse bewirkt und nach Erreichen des Anschlages das Werkstueck spannt. FigurThe invention relates to a device for keeping constant the forward and backward speed of the hydraulically driven tailstock quill, in particular of lathes at low working pressure. The object of the invention is to provide a device with which acts in all static pressure forces the same displacement speed of the sleeve and no setup effort is required. This is achieved according to the invention in that the piston rod of the thrust piston drive of the quill is in operative connection with the housing by means of a spring, wherein the spring has a preload force which is somewhat greater than the frictional displacement force of the quill, so that the piston rod during the free movement of Quill remains in rest position and only when encountering the centering on the workpiece movement of the piston rod against the spring begins, so that after a small displacement of the piston rod a switch is actuated, which switches the displacement pressure to the working pressure, which further movement of the piston rod up to causes a fixed stop on the housing and tensioned after reaching the stop the workpiece. figure

Description

Die in der Figur dargestellte Lage entspricht dem entspannten Zustand des Werkstückes 14. In diesem Zustand drückt die Feder 6 die Kolbenstange 4 nach links an den Gehäuseanschlag 9. Dabei ist die Vorspannkraft der Feder 6 um einen kleinen Sicherheitsbetrag größer als die Reibkraft zwischen Pinole 2 und Reitstockgehäuse 1. Der Kraftüberschuß der Feder 6 gegenüber der Reibkraft muß immer die Anlage des Bundes 5 am Gehauseanschlag 9 beim Entspannen gewährleisten. Zum Spannen des Werkstückes 14 wird die Pinole 2 nach links verschoben, indem die Leitung 8 mit der Druckquelle und die Leitung 7 mit dem Rücklauf verbunden werden. Das druckbestimmende Ventil ist dabei auf einen relativ hohen, oberhalb des den Geschwindigkeitswechsel bestimmenden Druckschwellwertes liegenden Druckwert eingestellt. Die während der Pinolenbewegu ng zwischen Pinole 2 und Gehäuse 1 wirkende Reibkraft hat an der Kolbenstange 4 eine Reaktionskraft zur Folge, die über den Bund 5 und die Druckfeder 6 in das Gehäuse 1 eingeleitet wird. Die Vorspannkraft der Feder 6 hält den Bund 6 am Gehäuseanschlag 9 fest. Sobald die Zentrierspitze 13 in der Zentrierbohrung des Werkstückes 14 antrifft, steigt der Druck im linken Zylinderraum an. Die dabei ansteigende Kraft am Kolben 3 verschiebt nach Überschreiten der Vorspannkraft der Feder 6 die Kolbenstange 4 nach rechts. Nach einem kleinen Verschiebeweg bringt der Nocken 11 den Schalter 12 zum Umschalten. Dieser bewirktem Umschalten des druckbestimmenden Ventils auf einen kleineren Druckwert, dessen Größe nur durch die gewünschte Andrückkraft derZentrierspitze 13 in der Zentrierbohrung des Werkstückes 14 bestimmtwird, der aber noch so groß sein muß, daß die Kolbenstange 4 noch bis zur Anlage des Bundes 5 am Gehäuseanschlag 10 verschoben wird. In diesem Zustand ist das Werkstück 14 gespannt. Die Restverschiebung vom Zeitpunkt der Betätigung des Schalters 12 bis zum Erreichen des Anschlages 10 erfolgt mit der dem niedrigen Druck entsprechenden kleinen Geschwindigkeit, da ein Teil des Pumpenstromes über das Druckbegrenzungsventil zum Behälter abfließt. Demgegenüber erfolgt die Verschiebung bis zum Schalten des Schalters 12 mit hoher Geschwindigkeit, da auf Grund der hohen Ventileinstellung der gesamte Pumpenförderstrom in den Schubkolbenantrieb fließt. Noch vor Anschlagen des Bundes 5 am Gehäuseanschlag 10 muß die Druckänderung infolge von Ventilumschaltung im Zylinderraum beendet sein. Anderenfalls steigt die Andrückkraft der Zentrierspitze 13 kurzzeitig auf einen, dem höheren Verschiebedruck entsprechenden Wert.The position shown in the figure corresponds to the relaxed state of the workpiece 14. In this state, the spring 6 pushes the piston rod 4 to the left on the housing stop 9. Here, the biasing force of the spring 6 by a small amount of security is greater than the frictional force between sleeve 2 and Tailstock housing 1. The excess force of the spring 6 against the frictional force must always ensure the installation of the Federal 5 on Gehauseanschlag 9 when relaxing. To clamp the workpiece 14, the sleeve 2 is shifted to the left by the line 8 to the pressure source and the line 7 are connected to the return. The pressure-determining valve is set to a relatively high, above the speed change determining pressure threshold value lying pressure. The frictional force acting during the sleeve movement between sleeve 2 and housing 1 results in a reaction force on piston rod 4 which is introduced into housing 1 via collar 5 and pressure spring 6. The biasing force of the spring 6 holds the collar 6 fixed to the housing stop 9. As soon as the centering tip 13 encounters the centering bore of the workpiece 14, the pressure in the left cylinder chamber increases. The thereby increasing force on the piston 3 moves after exceeding the biasing force of the spring 6, the piston rod 4 to the right. After a small displacement, the cam 11 brings the switch 12 to switch. This effected switching the pressure-determining valve to a smaller pressure value whose size is determined only by the desired pressing force of the centering point 13 in the center hole of the workpiece 14, but still must be so large that the piston rod 4 until the installation of the Federal 5 on the housing stop 10th is moved. In this state, the workpiece 14 is tensioned. The residual shift from the time of actuation of the switch 12 until reaching the stop 10 takes place with the low pressure corresponding to the low speed, since a portion of the pump flow flows through the pressure relief valve to the container. In contrast, the shift takes place until the switching of the switch 12 at high speed, since due to the high valve setting, the entire pump delivery flow flows into the thrust piston drive. Even before hitting the collar 5 on the housing stop 10, the pressure change must be completed as a result of valve switching in the cylinder chamber. Otherwise, the pressing force of the centering tip 13 briefly increases to a value corresponding to the higher displacement pressure.

Zum Entspannen des Werkstückes 14 werden die Leitungen 7 und 8 durch ein Wegeventil umgeschaltet, so daß der rechte Zylinderraum mit der Druckquelle verbunden wird und der linke Zylinderraum mit dem Rücklauf. Der dabei am Druckventil einzustellende Druckwert entspricht dem Druck in der ersten Bewegungsphase des Spannvorganges. Die Pinole 2 bewegt sich dadurch mit großer Geschwindigkeit nach rechts, die Feder 6 verschiebt die Kolbenstange 4 bis zur Anlage des Bundes 5 am Gehäuseanschlag 9. Dabei bleibt der Schalter 12 wirkungslos. Die Bewegung wird entweder durch den Anschlag der Pinole 2 im Gehäuse 1 oder durch Absperren der Leitungen 7 und 8 durch ein Wegeventil beendet.To relax the workpiece 14, the lines 7 and 8 are switched by a directional control valve, so that the right cylinder chamber is connected to the pressure source and the left cylinder chamber with the return. The pressure value to be set at the pressure valve corresponds to the pressure in the first movement phase of the tensioning process. The quill 2 moves thereby at great speed to the right, the spring 6 moves the piston rod 4 until the federal government 5 on the housing stop 9. In this case, the switch 12 is ineffective. The movement is terminated either by the stop of the sleeve 2 in the housing 1 or by shutting off the lines 7 and 8 by a directional control valve.

Claims

Invention claim:

1. means for keeping constant the speed of movement of the hydraulically controlled tailstock quill, in particular of lathes at low working pressure, being switched between a displacement pressure and a working pressure, characterized in that the piston rod (4) by means of a prestressed compression spring (6) with the housing (1 ) is in operative connection, the piston rod (4) in the housing (1) is slidably disposed and a collar (5) which can be in operative connection with the housing stops (9; 10) and a Druckumschaltu ng controlling Scha Lter (12) by a connected to the piston rod (4) cam (11) is in operative connection.

3. Device according to item 1, characterized in that the biasing force of the compression spring (6) is set to a security amount greater than the largest between sleeve (2) and housing (1) acting frictional force.

3. Device according to point T, characterized in that the cam (11) to the switch (12) is arranged so that the pressure change is completed before reaching the working stroke.

To this 1 page drawing '

Field of application of the invention

The invention relates to a device for keeping constant the forward and reverse speed of the hydraulically driven tailstock quill, in particular of lathes at low working pressure.

Characteristic of the known technical solutions

The speed of movement of the tailstock quill driven by means of hydraulic thrust pistons is uniquely determined by the delivery rate of the pump when pressure is generated by means of a constant-current pump only above a pressure threshold value. If the pressure-determining pressure limiting valve is set to a value below this threshold value, the pump delivery flow is divided into a flow flowing out via the pressure limiting valve and a flow flowing into the thrust piston drive. Only this current determines the piston speed. It is less than the speed at a pressure above the threshold. Responsible for this phenomenon are friction in the drive and flow losses during the movement phase. The lower the static pressure of the quill pressure is set, the smaller the movement speed of the quill is. With large Pinolenweg therefore the time becomes unreasonably large. To generate the same high speed of movement of the quill in all static pressure forces, a solution is known in which the thrust piston drive is successively acted upon by two different pressures, a displacement pressure and a static working pressure. To move the sleeve, a shift pressure lying above the pressure threshold is first switched on, which is switched by an adjustable cam and a switch shortly before reaching the clamping position to the static working pressure. The remaining distance to the clamping position is covered at low speed.
The disadvantage of this solution is that the cam must be set workpiece dependent.

Object of the invention

The invention is based on the object to eliminate the indicated disadvantage of the known solution.

Explanation of the essence of the invention

The object of the invention is to provide a device with which bej all static pressure forces the same displacement speed of the sleeve acts and no setup effort is required. According to the invention this is achieved in that the piston rod of the thrust piston drive of the quill is in operative connection by means of a spring, wherein the spring has a biasing force which is slightly larger than the frictional displacement force of the sleeve, so that the piston rod during the free movement of the Quill remains in rest position, and only when encountering the centering on the workpiece movement of the piston rod against the spring begins, so that after a small displacement of the piston rod, a switch is actuated, which switches the displacement pressure to the working pressure, which further movement of the piston rod to causes a firm stop on the housing and clamped after reaching the stop the workpiece.

embodiment

The invention will be explained in more detail below using an exemplary embodiment. The accompanying drawing shows a schematic longitudinal section through the overall arrangement.

In a tailstock housing 1 a quill 2 is slidably disposed. This forms together with a piston 3 and a piston rod 4 a hydraulic thrust piston drive. The inlet and outlet of the hydraulic fluid is carried by lines 7 and 8. The piston rod 4 has a collar 5, which serves as an abutment for a prestressed compression spring 6 and in conjunction with housing stops 9 and 10 as an abutment for the thrust piston drive. With the piston rod 4, a cam 11 is fixedly connected, which is in operative connection with a switch 12. The sleeve 2 has a centering tip 13 Dodge can be brought into operative connection with the center hole of a workpiece 14. The operation of the device will be described below.