EP0288719A2 - Control arrangement for pneumatic-hydraulic power drive - Google Patents

Abstract

The control arrangement has a pneumatic-hydraulic power drive (14) with an actuating rod (17). The actuating rod (17) can be actuated pneumatically with small force over large distances by means of a working piston (40) and hydraulically with large force over small distances by means of a displacing piston (63). The displacing piston (63) can in turn be actuated pneumatically via a pressure intensifier (62/63). So that workpieces with freely programmable force/displacement profiles set in a controlled manner can be manipulated or machined, the actuating rod (17) is coupled to a displacement-measuring unit (20). The actuating pressure of the working piston (40) can be set independently of the actuating pressure of the displacing piston (63) as a function of an output signal of the displacement-measuring unit (20) (Fig. 2).

Description

The invention relates to a control device for a pneumo-hydraulic power drive with an actuating rod which can be actuated pneumatically with low force over long distances by means of a working piston and hydraulically with great force over short distances by means of a displacement piston, the displacement piston in turn being pneumatically actuatable via the pressure intensifier .

Such a control device is known from DE-OS 28 18 337.

In the known control device, the power drive has a front, double-acting and pneumatically actuated working piston which runs in a cylinder bore with a relatively large diameter and can be pressurized with compressed air from both sides. The working piston carries an actuating rod, which can be used for riveting, for example. If compressed air is applied to the back of the working piston, it travels forward in rapid motion with relatively little force. When an end position is reached, the pressure on the back of the working piston increases. The compressed air now flows onto the back of an air piston of approximately the same cross-section, which in turn carries the displacement piston with a significantly smaller cross-sectional area. The displacer plunges into an oil reservoir which is arranged in the area of the rear of the actuating rod. As a result of the diameter ratio of the air piston and displacement piston, when the displacement piston is actuated pneumatically, there is an increase in force in the area of the oil reservoir and thus a high actuation force for the actuation rod with little deflection.

In the known device, the switch from rapid traverse with low force to slow speed (power stroke) with high force occurs automatically because, as mentioned, the compressed air from the rear of the working piston automatically reaches the rear of the air piston when a certain value is reached and the power stroke automatically starts.

For the control, switching valves can also be provided in the known device, the compressed air being passed on to the air piston by a pressure directional control valve which is switched over when the pressure at the inlet (rear side of the working piston) exceeds a predetermined amount. In the known device, there is also the possibility of using a path-dependent control, in which a limit switch is provided in the movement path of the actuating rod, which switches over from rapid traverse to slow speed (power stroke) when actuated. However, only switching valves are used in all of these controls, and the actuation of the air piston takes place via a forced sequence control depending on the actuation of the working piston.

The known device thus has the disadvantage that the transition from rapid to slow speed is always abrupt and the slow speed is uncontrolled, so that the known device cannot be used for a large number of applications when it comes down to the actuating force as a function of predetermined parameters meter or regulate depending on the respective application.

The invention is therefore based on the object of developing a device of the type mentioned at the outset such that the operating parameters of the device can be freely specified and in particular can be set in a controlled manner.

This object is achieved in that the actuating rod is coupled to a displacement measuring unit and that the actuating pressure of the working piston is adjustable independently of the actuating pressure of the displacement piston as a function of an output signal from the displacement measuring unit.

The object underlying the invention is completely achieved in this way.

Due to the position measuring unit, which can be used continuously over a longer distance, the rapid traverse can be freely programmed in contrast to the known limit switch. By separating the actuation of the displacement piston from the actuation of the working piston, the slow gear (power stroke) can also be freely programmed after passing through the rapid traverse, any force / displacement dependencies being specifiable.

These measures have the advantage that the control device according to the invention can be used for a variety of tasks, not only for relatively rough power work, such as the riveting mentioned above, but also for precise power work, for example when operating a hand of a handling device and the like more.

In a particularly preferred embodiment of the invention, the working piston is double-acting and the actuating pressure of the working piston is set by means of electro-pneumatic 2/2 servo valves.

This measure has the advantage that the overdrive of the working piston can be adjusted particularly precisely from the starting position to the end position, because the use of electropneumatic servo valves allows an analog input variable to be converted precisely into a pneumatic output variable.

In a further preferred embodiment of the invention, the displacement piston with pressure intensifier has a single action, and the actuation pressure of the pressure intensifier is set by means of an electropneumatic 2/2-way valve with pilot valve.

This measure has the advantage that the high force of the actuating rod can be adjusted precisely.

In a further preferred embodiment of the invention, the working piston can be extended in rapid traverse with low force until a first output signal of the displacement measuring unit is reached, and then the displacement piston can be extended with high force in slow speed until a second signal is reached.

In a variant of this exemplary embodiment, the second signal is a second output signal of the displacement measuring unit.

This measure has the advantage that tasks can be carried out in which the actuating rod has to travel a certain distance with high force without the actuation pressure being important, as is the case e.g. is the case with joining work.

In this variant, it is preferred if, when the second signal is reached, the actuating pressure of the displacement piston is measured by means of a pressure sensor and compared with a predetermined actuating pressure interval.

This measure has the advantage that it can be monitored whether an actuating pressure had to be applied to measure the above-mentioned distance in the power stroke, which pressure was within one specified tolerance range. If, for example, a part is to be pressed into another part as part of a joining work, falling below the interval would mean that the parts to be joined were imprecise in the sense that they fit too loosely into one another and consequently only a slight actuation pressure was required, to measure the given distance, while exceeding the interval indicates that the parts were made too narrow and therefore too high an actuation pressure was required to achieve the desired joining. In both cases, this may be unacceptable for the intended use of the parts being joined, so that if the interval is exceeded or fallen short of, the parts joined can be declared as rejects.

In another variant of the exemplary embodiment, the second signal is an output signal from a pressure sensor that detects the actuating pressure of the displacement piston.

In this variant, instead of a distance to be measured in the power stroke, a pressure value to be achieved is specified if, for example, the joining force is specified in the course of joining work.

In this embodiment too, when the second signal is reached, the output signal of the displacement measuring unit can be compared with a predetermined displacement interval.

In this variant, a criterion for a reject part is thus formed by checking whether there is a path within a permissible range until the predetermined pressure value is reached Tolerance range was measured. In the case of parts that fit too loosely into one another, for example when the predetermined pressure (actuating force) is applied, a too large path would be measured, while conversely only a small path could be measured in the case of parts that were manufactured too closely.

Further advantages result from the description and the attached drawing.

It goes without saying that the features mentioned above and those explained below can be used not only in the respectively specified combination, but also in other combinations or on their own, without departing from the scope of the present invention.

This applies in particular to the interconnection by means of electropneumatic valves, which is explained below using an exemplary embodiment and which can also be implemented in other known ways within the scope of professional action.

• Fig. 1 eine schematisierte Gesamtansicht einer erfindungs­gemäßen Steuereinrichtung für den Einsatzfall eines Fügegerätes;
• Fig. 2 einen Hydraulik- und Stromlaufplan zur Erläuterung der Wirkungsweise eines Ausführungsbeispiels einer erfindungsgemäßen Steuereinrichtung;
• Fig. 3 einen weiter detaillierten Stromlaufplan zur Erläute­rung eines Ausführungsbeispiels einer erfindungsge­maßen Steuereinrichtung;
• Fig. 4 eine Stromlaufplan, ähnlich Fig. 3, jedoch für ein anderes Ausführungsbeispiel.

Embodiments of the invention are shown in the drawing and are explained in more detail in the following description. Show it:

• Figure 1 is a schematic overall view of a control device according to the invention for the application of a joining device.
• 2 shows a hydraulic and current flow diagram to explain the mode of operation of an exemplary embodiment of a control device according to the invention;
• 3 shows a further detailed circuit diagram to explain an exemplary embodiment of a control device according to the invention;
• Fig. 4 is a circuit diagram, similar to Fig. 3, but for another embodiment.

In Fig. 1, 10 designates a force unit as a whole, such as e.g. for pressing, embossing and Like. Can be used. A U-shaped portal 11 is placed on a work table 12 which carries a workpiece 13 to be joined. A power drive 14, the details of which will be explained further below in relation to FIG. 4, is provided with valve packs 15 and 16 attached to the side. An actuating rod 17 protrudes from the bottom of the power drive 14 and can be moved vertically depending on the actuation of the valve packages 15, 16. The actuating rod 17 can carry a tool 18, for example an embossing stamp or the like, at its lower axial end.

The actuating rod 17 is laterally coupled to an arm 19 which interacts with a displacement measuring unit 20 for the vertical deflection of the actuating rod 17.

The distance measuring unit 20 and the valve packages 15, 16 are connected to a control unit 25 via connecting cables 21, 22, 23, 24.

The control unit 25 has, for example, a first keyboard 26 for specifying one or more extension paths of the actuating rod 17 and a second keyboard 27, which can be used, for example, for specifying certain actuating forces or path / force profiles. A schematically indicated display unit 28 serves to display operating states, operating parameters and. the like

With the force unit shown in Fig. 1 one wants e.g. can specify that the actuating rod 17 first traverses a large distance in rapid traverse by which it was previously lifted from the workpiece 13 in order to be able to handle it in the region of the work table 12. The actuating rod 17, possibly with a tool 18, is then to travel a certain distance under low force at high speed (typically in the range between 10 and 500 kN). The power unit 10 should be able to be controlled so that the actuating rod 17 either measures a predetermined power stroke, i.e. without influencing the actuating force, provided it does not, of course, exceed a certain limit value, or a certain final force value is to be achieved, without taking into account the stroke required for this.

In the case of the specified stroke, however, one wants to be able to determine whether the force required for this lies within a certain tolerance range, and conversely, for a given actuating force, one would like to know whether the stroke with this diameter lies within a specific tolerance range, in order to have a scrap part if the tolerance range is exceeded to be able to define.

2 shows further details of the power drive 14 including the associated control.

The power drive 14, which is known per se, has a working piston 40 in the front part, which runs in a first cylinder bore 41 of relatively large diameter. Means a front channel 42 and a rear channel 43, the working piston 40 can be acted upon from both sides with compressed air. For this purpose, a first line 44 is used, which is connected to the front channel 42 and leads to a first electropneumatic 2/2-servo valve 45. A second pneumatic line 46 is connected to the rear channel 43 and leads to a second electropneumatic 2/2 servo valve 47. The servo valves 45, 47 are connected via a third line 48 and a fourth line 49 to a common compressed air connection 50, which is typically is supplied with a supply pressure of 5 bar.

The actuating rod 17, which separates the working piston 40, is provided with a second cylindrical bore 56. In a third cylindrical bore 57, the diameter of which corresponds approximately to that of the first cylindrical bore 41, an oil piston 58 runs, which defines in front of it an oil space (storage space) 60 which extends into the second cylindrical bore 56. The oil piston 58, which runs freely in the third cylindrical bore 57, is connected via a helical spring 61 to an air piston 62 which also runs freely in the third cylindrical bore 57. The air piston 62 runs forward into a displacement piston 63, the cross-sectional area of which is substantially smaller than the cross-sectional area of the air piston 62, the oil piston 58 and the working piston 40. The diameter of the displacement piston 63 is slightly smaller than the diameter of the second cylindrical bore 56.

The rear side of the air piston 62 can be acted upon by compressed air via a fifth line 65 by means of a channel 64. The fifth line 65 leads to a 2/2 switching valve 66 which is provided with a pilot valve in the illustrated embodiment.

A sixth line 67 is connected to the rear channel 43 and is used to supply compressed air to the 2/2-way switching valve 66.

With 68 a seventh line is indicated, which opens into the space between the oil piston 58 and air piston 62. The seventh line 68 is intended to indicate that the air piston 62 can of course also be double-acting and can be pressurized with compressed air from both sides if this should be cheaper in individual cases.

An eighth line 70 leads as a branch line from the sixth line 67 to a pressure sensor 71. The pressure sensor 71 is in turn connected to a controller 72 which receives a further input signal via a signal line 73 from the displacement measuring unit 20. In addition, the controller 72 is connected to the keyboards 26, 27 and it has output terminals 74 which lead via the connecting cables 22, 23 to the valve packages 15, 16 or the servo valves 45, 47 and the switching valve 66 contained therein.

The mode of operation of the arrangement according to FIG. 2 will now be explained in more detail with reference to the circuit diagram of FIG. 3.

In the variant described below, the user of the force unit 10 prescribes a first path s _a , which the actuating rod 17 is to travel through at high speed. After measuring this path s _a , a second, smaller path s _{e should be} measured in the power stroke. During the power stroke, the pressure p, which acts on the air piston 62 and above the force amplifier 62/63 can be converted into the force of the actuating rod 17, determined, and a statement is to be made as to whether the pressure p required for measuring the power stroke s _e is within a predetermined tolerance between a lower pressure value p _u and a upper pressure value p _o .

To achieve this, the values s _a , S _e , p _u and p _{o are} first entered into the control unit 25 using the keyboards 26, 27.

In order to put the power unit 10 into operation, a start signal is first given to a flip-flop 76 via a terminal 75 and the flip-flop 76 is thus set. The flip-flop 76 in turn actuates the second electropneumatic 2/2-servo valve 47, so that compressed air can reach the working piston 40, namely from the right in FIG. 2.

The displacement measuring unit 20 is connected to a first comparator 81, the output of which is connected to a first zero detector 82. The zero detector 82 in turn controls the set input of a second flip-flop 83, the output of which in turn actuates the 2/2 switching valve 66. A second comparator 84 is connected on the output side to a second zero detector 85, the output of which is connected to the reset input of the second flip-flop 83.

The further inputs of the comparators 81, 82 are formed by terminals 86, 87, to which setpoints, namely a value s _a for the end of the rapid traverse and a value s _e for the end of the slow traverse, are applied.

The pressure sensor 71 is connected to a third comparator 88, the output of which is connected to a first threshold value stage 89. The output of the threshold stage 89 is in turn at the input of an AND gate 90.

The pressure sensor 71 is also connected to an input of a fourth comparator 91, the output of which is connected to a second threshold value stage 92. Its output is in turn connected to a second input of the AND gate 90. The further inputs of the comparators 88, 91 are connected to terminals 93, 94, to which setpoints can be applied, namely the lower threshold value P _u and the upper threshold value p _{u of} the pressure p. The threshold values of the threshold value stages 89, 92 define a printing interval 95. The output of the AND gate 90 is led to a display 96.

The mechanism works as follows:

As soon as the working piston 40 moves to the left by setting the first flip-flop 76 in FIG. 2, the arm 19 emits a signal s with the displacement measuring unit 20, which is fed to the controller 72 via the signal line 73. In the controller 72, the signal s is compared in the comparators 81 and 84 with the kort predetermined target values s _a and s _e . As soon as the target value s _{a has been} reached, ie at the end of the overdrive range, the zero detector 82 responds and sets the second flip-flop 83, which in turn actuates the 2/2 switching valve 66. Since the second electropneumatic 2/2 servo valve 47 still remains switched on, air pressure can be taken from the right channel 43 via the sixth line 67 and can be conducted into the channel 64 via the lines 67, 65 by means of the 2/2 switching valve 66 that the air piston 62 moves to the left and the displacement piston 63 with appropriate power amplification ensures a pressure build-up in the oil space 60. The actuating rod 17 thus continues its path to the left in FIG. 2, the same pressure being able to be set on both sides of the drive piston 40 by switching over the first electropneumatic 2/2 servo valve 45 in order to prevent the further movement of the actuating rod 17 to make the deflection of the displacer 63 dependent.

When it is finally recognized via the second comparator 84 that the actuating rod 17 has reached the end value s _{e of} the slow power stroke, the second flip-flop 83 is reset via the zero detector 85 and the switching valve 66 is switched over again.

By venting the right side of the working piston 40 while simultaneously applying compressed air via the left channel 42, the working piston 40 can now be moved back to the starting position at high speed.

During the operation described above, in particular during the slow power stroke, the pressure p on the rear of the air piston 62 was monitored via the pressure sensor 71. If the pressure in this range lies within the interval 95, the display 96 responds because only in this interval the outputs of both threshold value stages 89 and 92 show a positive logic signal, while outside of the interval 95 one of the two threshold value stages shows a negative logic signal leads. This means that when the display 96 was actuated, a workpiece was machined in the target area, while when the display 96 went out, a scrap part was produced.

The circuit diagram recognizable in FIG. 4 largely corresponds to the circuit diagram of FIG. 3, and corresponding elements are provided with the same reference symbols. Only by adding an "a" are comparable components designated in their function.

In the embodiment shown in Fig. 4 variant, the driving through the quick passage through the element 81 to 83 by reaching the final value S _A is monitored in the manner already described. In the slow power stroke, however, the reaching of the final value of the power stroke is not monitored via the path but rather via the pressure, specifically in the second comparator 84a, which is connected to a corresponding setpoint p _a . When this end value is reached, the 2/2 switching valve 66 switches over and the slow power stroke is ended.

In order to make a statement about a correctly manufactured part or a reject part in this case as well, an interval 95a is defined with comparators 88a, 91a and threshold value stages 89a, 92a, in this case, however, an interval of the path which lies between a lower limit value s _u and an upper limit s _o . Otherwise, the logic corresponds to the elements in the lower half of FIG. 3.

Thus, while it was recognized in the variant according to FIG. 3 whether more or less than a predetermined pressure range was required to measure a predetermined path in the slow force stroke, the reverse is true in the variant in accordance with FIG. 4 because there it is in the slow force stroke reaching an end pressure value is stopped and only then is it checked whether a path has been measured to reach this pressure value, which lies within a certain tolerance.

Claims (8)

1. Control device for a pneumo-hydraulic power drive (14) with an actuating rod (17) which can be actuated pneumatically with low force over long distances by means of a working piston (40) and hydraulically with great force over short distances by means of a displacement piston (63), the displacer piston (93) in turn being pneumatically operable via a pressure intensifier (62/63), characterized in that the actuating rod (17) is coupled to a displacement measuring unit (20) and in that the actuating pressure of the working piston (40) is independent of the actuating pressure of the displacer piston (63) can be set as a function of an output signal from the displacement measuring unit (20). 2. Control device according to claim 1, characterized in that the working piston (40) is double-acting and that the actuating pressure of the working piston (40) is set by means of electropneumatic 2/2-servo valves (45, 47). 3. Control device according to claim 1 or 2, characterized in that the displacement piston (63) with pressure intensifier (62/63) is single-acting and that the actuating pressure of the pressure intensifier (62/63) by means of an electropneumatic 2/2 switching valve (66) is set with pilot valve. 4. Control device according to one of claims 1 to 3, characterized in that the working piston (40) until reaching a first output signal (s _a ) of the displacement measuring unit (20) in rapid traverse with low force and then the displacement piston (63) until it is reached a second signal (s _e , p _a ) can be extended in slow motion with high force. 5. Control device according to claim 4, characterized in that the second signal is a second output signal (s _e ) of the displacement measuring unit (20). 6. Control device according to claim 5, characterized in that when the second signal (s _e ) is reached, the actuating pressure (p) of the displacer (63) is measured by means of a pressure sensor (71) and compared with a predetermined actuating pressure interval (95). 7. Control device according to claim 4, characterized in that the second signal is an output signal (p _a ) of the actuating pressure (p) of the displacer (63) detecting pressure sensor (71). 8. Control device according to claim 7, characterized in that when the second signal (p _a ) is reached, the output signal (s) of the displacement measuring unit (20) is compared with a predetermined displacement interval (95a).

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