Safe-To-Operate Hydraulic Drive

Abstract

A safe hydraulic drive system and process, comprising at least one first cylinder chamber and a second, separate cylinder chamber which are connected to one another via a connecting line to form a fluid-filled hydraulic circuit, and a hydraulic drive for conveying the fluid from one cylinder chamber, via the connecting line, into the other cylinder chamber in which the connecting line is arranged. The connecting line has at least one parallel system, between the hydraulic drive and one of the two cylinder chambers, including at least one first sub-connection with at least one first stop valve and a second sub-connection with a baffle arranged therein. The connecting line, excluding the second sub-connection, has a first flow resistance and the second sub-connection has a second flow resistance due to the baffle arranged therein, which is greater than the first flow resistance for the fluid, wherein the drive system is provided with at least one open first stop valve in normal mode and with a closed first stop valve in safe mode for conveying the fluid, and a suitably high second flow resistance has been selected so that a maximum permissible speed for a piston rod is not exceeded in safe mode, even when an external force acts on the drive system in the direction of movement of the piston rod.

Claims

1. A hydraulic drive system for moving a piston rod of at least one cylinder, the drive system comprising at least a first cylinder chamber and a second cylinder chamber separated from the same, which are connected to one another via a connecting line to form a fluid-filled hydraulic circuit, and a hydraulic drive for conveying the fluid from one cylinder chamber, via the connecting line, into the other cylinder chamber, is arranged in connecting line, wherein the connecting line has at least one parallel system of at least one first sub-connection with at least one first stop valve and a second sub-connection with a baffle arranged therein, between the hydraulic drive and one of the two cylinder chambers, wherein the connecting line, excluding the second sub-connection, has a first flow resistance and the second sub-connection has a second flow resistance due to the baffle arranged therein, which is greater than the first flow resistance for the fluid, wherein the drive system is provided with at least one open first stop valve in normal mode and with a closed first stop valve in safe mode for conveying the fluid, and a suitably high second flow resistance has been selected such that a maximum permissible speed for the piston rod is not exceeded in safe mode, even where an external force acts on the drive system in the direction of movement of the piston rod, and wherein the first stop valve can be operated electronically and the drive system includes a drive control for actuating the hydraulic drive for moving the piston rod and for electronic switching of at least the first stop valve for at least normal and safe mode.

2. (canceled)

3. The drive system according to claim 1, wherein the hydraulic drive incorporates a tachometer for monitoring the rotational speed of the hydraulic motor, wherein the tachometer is connected to the drive control for at least safe limiting of the rotational speed by the drive control.

4. The drive system according to claim 3, wherein the hydraulic drive is an electro-hydrostatic drive with an electric motor and a hydraulic pump driven by the electric motor via a motor shaft, wherein the tachometer is provided for measuring the rotational speed of the electric motor.

5. The drive system according to claim 1, wherein the drive control incorporates a safety logic circuit, which is provided in order at least to switch over at least the first stop valve from normal mode to safe mode, in response to the safety signals received.

6. The drive system according to claim 5, wherein the safety logic circuit is provided for the purposes of switching from normal mode to safe mode when the hydraulic drive is overloaded in order at least to throttle or preferably to stop the hydraulic drive.

7. The drive system according to claim 1, wherein a second stop valve is arranged in the connecting line outside of the first sub-connection in order to enable safe shutdown of the drive system.

8. The drive system according to claim 7, wherein the second stop valve is arranged in the second sub-connection in series with the baffle; preferably, the second stop valve is closed in normal mode.

9. The drive system according to claim 1, wherein the first sub-connection incorporates a third stop valve arranged in series with the first stop valve and which preferably has the same switch settings as the first stop valve in normal mode and in safe mode.

10. The drive system according to claim 1, wherein the second stop valve can also be switched electronically; preferably, the third stop valve and, if required, all other stop valves can also be switched electronically.

11. A method of operating a drive system including at least one cylinder with at least one cylinder chamber and one second cylinder chamber separated from the same, which are connected to one another via a connecting line to form a fluid-filled hydraulic circuit with a hydraulic drive arranged therein, and the connecting line has at least one parallel system, between the hydraulic drive and one of the two cylinder chambers, of at least one first sub-connection with at least one first stop valve and a second sub-connection with a baffle arranged therein, wherein the connecting line, including the first sub-connection and excluding the second sub-connection, has a first flow resistance and the second sub-connection, has a second flow resistance determined by the baffle arranged therein, which is greater than the first flow resistance for the fluid, the method comprising the following steps: Opening at least the first stop valve for a normal mode of the drive system; Conveying the fluid by means of the hydraulic drive in normal mode from one cylinder chamber, via at least the first sub-connection, into the other cylinder chamber in order to move a piston rod of the cylinder; Closing the first stop valve in order to operate the drive system in a safe mode, wherein a maximum permissible speed of the piston rod is not exceeded in the safe mode, even where an external force acts on the drive system in the direction of movement of the piston rod, by having selected a suitably high second flow resistance.

12. The method according to claim 11, including the additional step of conveying the fluid by means of the hydraulic drive in safe mode from one cylinder chamber, via the second sub-connection, into the other cylinder chamber in order to move the piston rod of the cylinder.

13. The method according to claim 11, including the additional step of actuating the hydraulic drive in order to move the piston rod and at least the first stop valve by means of a drive control of the drive system for at least normal and safe mode, for which at least the first stop valve is designed to be able to be switched electronically.

14. The method according to claim 13, including the following additional steps: receiving safety signals by means of the drive control, which additionally incorporates a safety logic circuit and switching from normal mode to safe mode based on the safety signals received from the safety logic circuit (51).

15. The method according to claim 13, wherein the hydraulic drive (4) incorporates a tachometer (43) for monitoring the rotational speed (MD) of the hydraulic motor (4), wherein the tachometer (43) is connected to the drive control (5) for at least safe limiting of the rotational speed by the drive control, including the following additional steps: Transmitting a rotational speed of the hydraulic drive measured by the tachometer to the drive control; Controlling (SBK) the movement of the piston rod by the drive control, by means of the transmitted rotational speed and Switching from normal mode to safe mode by means of the drive control where the hydraulic drive is overloaded, in order at least to throttle the hydraulic drive; preferably, the hydraulic drive is stopped.

16. The process according to claim 11 including the additional step of closing a second stop valve, which is arranged outside of the first sub-connection, in order to enable a shutdown of the drive system.

Description

BRIEF DESCRIPTION OF THE FIGURES

[0044] These and other aspects of the invention are depicted in detail in the figures as follows:

[0045] FIG. 1 is a schematic representation of an embodiment of the drive system according to the invention;

[0046] FIG. 2 depicts examples of switch settings available in the stop valves for (a) the first stop valve, (b) the second stop valve, (c) the third stop valve, and (d) for alternative switch settings for the stop valves;

[0047] FIG. 3 is a schematic representation of the first (a) and second (b) cross-sectional areas in the connecting line, through which fluid flows as it is conveyed;

[0048] FIG. 4 is a schematic representation of an embodiment of the method according to the invention for operating the drive system according to the invention.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0049] FIG. 1 is a schematic representation of an embodiment of the drive system 1 according to the invention, in which a piston rod 23 of a synchronized cylinder 2, with a first cylinder chamber 21 and a second, separate cylinder chamber 22, is moved. To this end, the cylinder chambers 21, 22 are connected to one another, via a connecting line 3, and, together with the connecting line 3, form a hydraulic circuit (a closed pressure circuit in this case), which is filled with a fluid F as the hydraulic fluid. The fluid F is conveyed UN, US from one cylinder chamber 21, 22 into the other cylinder chamber 21, 22 via the connecting line 3 in order to move the piston rod 23 with a hydraulic drive 4, which is arranged at a suitable position in the connecting line 3, which can be selected by an expert. In this embodiment, the connecting line 3 incorporates a parallel system consisting of a first sub-connection 31 and a second sub-connection 32 between the hydraulic drive 4 and the second cylinder chamber 22. The two sub-connections branch out from the hydraulic drive, when viewed at connecting point V2, and come back together again at connecting point V1. The two sub-connections 31, 32 depicted here have differing lengths between the connecting points V1 and V2, wherein the second sub-connection 32 is longer. The two sub-connections 31, 32 can, however, also have the same length between connecting points V1 and V2. In another embodiment, the two sub-connections 31, 32 can also be arranged between the hydraulic motor 4 and the first cylinder chamber 21, wherein here, the position of the sub-connections 31, 32 is independent of the type of cylinder 2. In other embodiments, more than two sub-connections can also be arranged in the connecting line 3, wherein, however, at least one of the sub-connections has a baffle 322 according to the present invention. Here, the first sub-connection 31 incorporates a first stop valve 311 and a third stop valve 313, arranged in series with it (behind one another in the direction of flow), so that the fluid F first flows through one and then through the other stop valve, depending on the direction of flow. In other embodiments not depicted here, there is no third stop valve 313. Preferably, the third stop valve 313 has the same switch settings as the first stop valve 311 in normal mode N and in safe mode S and thus represents a redundant component. The connecting line 3, including the first sub-connection 31, that is, the connection from the first cylinder chamber 21 to the second connection point V2, the first sub-connection 31 (not the second sub-connection 32) and the connecting line between first connection point V1 and the second cylinder chamber 22, represents a first flow resistance for the fluid F and, to that end, has a smallest first cross-sectional area Q3a, through which the fluid F flows, and the size of the cross-sectional area is measured so that the drive system 1 has no or only a slight loss of power in normal mode N and thus the force acting upon the piston rod 23 is determined by the power of the hydraulic drive 4. The first smallest cross-sectional area Q3a is thus smaller than or the same size as all of the other cross-sectional areas in the previously described connecting line. Here, the second sub-connection 32 incorporates a second stop valve 321 and a baffle 322 arranged in series with this, in order to provide a second flow resistance by means of the baffle 322, which, to this end, has a second cross-sectional area Q3b, reduced in comparison with the first cross-sectional area Q3a, through which the fluid F flows in at least safe mode S. The second cross-sectional area Q3b thus represents an additional flow resistance with respect to the rest of the connecting line with the smallest cross-sectional area Q3a for the fluid F and thus determines the second flow resistance through the second sub-connection 32. This additional flow resistance is not effective in normal mode N, however, since the drive system 1 is operated with an open first stop valve 311 and preferably, as shown here, with a closed second stop valve 321, in order to convey UN the fluid F in the normal mode N. In other embodiments not depicted here, there is no second stop valve 321, which means that the fluid F can also flow through the second sub-connection 32 with the second flow resistance in normal mode N. In another embodiment, the second stop valve 321 could also remain open in normal mode N as the flow resistance is determined by the remaining connecting line, including the first sub-connection 31, and thus the first flow resistance, the smallest first cross-sectional area Q3a of which is greater than the second cross-sectional area Q3b. In this case, the second sub-connection 32 would merely be a bypass.

[0050] In another embodiment not depicted here, the second stop valve 321 could also be arranged outside the second sub-connection 32, between the second cylinder chamber 22 and the first connection point V1 or between the first cylinder chamber 21 and the second connection point V2. The first and the second stop valves 311, 321 would then be open for the normal mode N. For the safe mode S, only the first stop valve 311 would be closed, while the second stop valve 321 would remain open. To shut the drive system down, only the second stop valve 321 would then need to be closed in this embodiment, which is not depicted here.

[0051] Here, the cross-sectional areas Q3a, Q3b denote the inner area of the respective connecting line 3, which is perpendicular to the direction of flow of the fluid F. At the same time, the cross-sectional areas Q3a, Q3b denote the smallest cross-sectional areas present in the respective connections 3, 31, 32 (connecting line) since the respectively smallest cross-sectional area determines the flow resistance in the respective connecting line. In safe mode S, then, the drive system 1 is operated with a closed first stop valve 311 and with an open second stop valve 321. Thus, the fluid F is forced to pass the baffle 322 when conveyed US. Because the second cross-sectional area Q3b is suitable (small) and thus a suitably high second flow resistance has been selected, a maximum permissible speed of the piston rod 23 in safe mode S is thus defined, even with an external force FG acting on the drive system 1 in the direction of movement B of the piston rod 23, which cannot be exceeded due to the flow resistance due to the baffle 322. When there is a shutdown ST of the drive system 1, on the other hand, at least the first and second stop valve 311, 321 are closed; preferably, all stop valves 311, 321, 313 are closed in this case. Here, in order to be able to operate the drive system easily, the stop valves 311, 321, 313 are designed to be able to be switched electronically and are connected to a drive control 5 in order to switch the stop valves 311, 321, 313 electronically. The same also applies to the hydraulic drive 4 in order to move the piston rod 23. The corresponding actuation signals are represented schematically as A311, A313, A321, and A4, using dashed lines. Here, the hydraulic drive 4 is an electro-hydrostatic drive, which comprises an electric motor 41 and a hydraulic pump 42 driven by the motor with a typical slippage of fluid F, regardless of the direction of the pump and the throughput rate of the pump. This slippage becomes irrelevant from a safety perspective, due to the arrangement according to the invention with the second sub-connection 32. The motor 41 is also connected to a tachometer 43 for measuring the motor speed MD; the measurement is transmitted to the drive control 5 (dashed arrow) and, based on this, the movement of the piston rod 23 is controlled by the drive control 5. In addition, the drive control 5 incorporates a safety logic circuit 51, which switches UM the stop valves 311, 321, 313 from normal mode N to safe mode S, for example, in response to safety signals SHS received by a safety unit 7. The safety unit 7 can represent, for example, an access monitoring mechanism 7 for the movement area of the machine operated with the drive system 1 according to the invention. If a person enters the movement area, the access monitoring mechanism transmits the safety signals SHS to the drive control 5, and, in response, its safety logic circuit 51 switches UM the drive system 1 to safe mode S. The safety logic circuit 51 can also be designed for the purposes of switching UM from normal mode N to safe mode S when the hydraulic drive 4 is overloaded in order at least to throttle, or preferably to stop, the hydraulic drive 4.

[0052] FIG. 2 depicts examples of switch settings available in the stop valves for (a) the first stop valve 311, (b) the second stop valve 321, (c) the third stop valve 313, and (d) for alternative switch settings for the stop valves 311, 321, 313. Figures (a)-(c) each depict switch settings of 2/2-way valves, wherein S1, S2, S3 indicate the stop divisions of the first, second, and third stop valves 311, 321, 313. Accordingly, O1, O2, O3 indicate the settings of the stop valves 311, 321, and 313, in which the fluid can flow through the stop valves in both directions unimpeded. In an alternate embodiment, one or more stop valves 311, 321, 313 can also have more than just two switch settings, for example, a return setting R, in addition to a stop setting S and an open setting O. This can also be set in normal mode, for example, for the second switching valve 321.

[0053] FIG. 3 is a schematic representation of the first (a) and second (b) cross-sectional areas Q3a, Q3b in the connecting line 3, through which fluid flows as it is conveyed. The first and second cross-sectional areas Q3a and Q3b denote the inner area of the respective connecting line 3, 31, 32, through which fluid F can pass as it is conveyed and which is perpendicular to the direction of flow of the fluid F as it passes through. The second cross-sectional area Q3b is depicted as significantly smaller than the first cross-sectional area Q3a, so that the second cross-sectional area Q3b represents the significantly largest second flow resistance in the entire connecting line. In hydraulic drives 4, whose rotational speed is not monitored and controlled, the second cross-sectional area Q3b is designed to be smaller than it is in hydraulic drives 4 with rotational speed monitoring and rotational speed control for limiting the speed during safe mode S since, in the latter case, the baffle 322 with the second flow resistance provided in this manner must only compensate for the volume slippage through the hydraulic drive 4, while the baffle 322 in the first case must safely limit the volumetric flow independently of the hydraulic drive 4 with the correspondingly greater second flow resistance. The first cross-sectional area Q3a, on the other hand, does not determine the flow resistance of the connecting line 3 if the fluid F is only able to flow through the second sub-connection 32, as is the case in safe mode S. However, if the fluid can flow through the first sub-connection 31 in normal mode N, then the first flow resistance in the entire connecting line 3 is only determined by the first cross-sectional area Q3a since, on one hand, the first cross-sectional area Q3a represents the smallest cross-sectional area in the connecting line 3 through which fluid flows (in this case, there is no fluid F flowing through the second sub-connection 32 at all) when the second sub-connection is blocked, and, on the other hand, when the second sub-connection 32 is open, this only represents a bypass, which cannot negatively influence the flow resistance of the connecting line 3 since the second sub-connection 32 is a parallel connection with the rest of the connecting line 3.

[0054] FIG. 4 is a schematic representation of an embodiment of the process according to the invention for operating the drive system 1 according to the invention as depicted in FIG. 1. Here, the drive system 1 starts with opening O1 the first stop valve 311 and, additionally, with closing S2 the second stop valve 321 for a normal mode N of the drive system 1 (in an alternate embodiment, the latter can also be omitted, whereby the second stop valve 321 can remain in an open state). To this end, the stop valves 311 and 321, which can be actuated electronically, are accordingly actuated A311, A321 by the drive control 5. Subsequently, the piston rod 23 of the cylinder 2 is moved in a controlled manner SBK, as desired in the respective application, from one cylinder chamber 21, 22, via the first sub-connection 31, into the other cylinder chamber 21, 22, by conveying UN the fluid F by means of the hydraulic drive 4. To this end, the hydraulic drive 4 is actuated A4 accordingly by the drive control 5 in order to move the piston rod 23. During operation, the drive control 5 receives EF safety signals SHS, which are evaluated in the additional safety logic circuit 51. If necessary, the safety logic circuit 51 initiates switchover UM from normal mode N to safe mode S, based on the safety signals SHS received. In addition, in this embodiment, the motor speed MD of the motor 41 measured by means of a tachometer 43 is transmitted to the drive control 1. In addition to the control SBK of the movement of the piston rod 23 by means of the motor speed MD transmitted by the drive control 1, the safety logic circuit 51 can initiate a switchover UM from normal mode N to safe mode when the hydraulic drive 4 is overloaded, which will result in at least throttling the hydraulic drive 4 or preferably stopping the hydraulic drive 4. To this end, the drive control 5 controls A311, A321 the closing S1 of the first stop valve 311 and the opening O2 of the second stop valve 321, whereby a maximum permissible speed of the piston rod 23 is not exceeded in the safe mode S, even where an external force FG (for example gravity or gravitational force) acts upon the drive system 1 in the direction of movement B of the piston rod 23, by the second cross-sectional area Q3b having been selected as suitable to provide an additional second flow resistance for the fluid F through the baffle 322. Subsequently, in safe mode S, the fluid F is conveyed US by means of the hydraulic drive 4 from one cylinder chamber 21, 22, via the second sub-connection 32, into the other cylinder chamber 21, 22 in order to move the piston rod 23 of the cylinder 2. Alternately or subsequently to this, the process can include the additional step of closing SI, S2 at least the first and second stop valves 311, 321 to stop ST the drive system 1. If it is determined that the maximum safe rotational speed has been exceeded in safe mode S, then the motor can be stopped (power switched off), and the second stop valve 321 can be closed. These measures would then lead to a shutdown of the drive system 1.

[0055] The embodiments depicted here only represent examples of the present invention and are therefore not to be understood as limiting. Alternate embodiments considered by the expert are similarly encompassed by the protective scope of the present invention.

LIST OF REFERENCE CHARACTERS

[0056] 1 Drive system according to the invention [0057] 2 Cylinder [0058] 21 First cylinder chamber [0059] 22 Second cylinder chamber [0060] 23 Piston rod [0061] 3 Connecting line [0062] 31 First sub-connection [0063] 311 First stop valve [0064] 313 Third stop valve [0065] 32 Second sub-connection [0066] 321 Second stop valve [0067] 322 Baffle (flow resistance) [0068] 4 Hydraulic drive [0069] 41 Electric motor [0070] 42 Pump [0071] 43 Tachometer [0072] 5 Drive control (including converter and driver) [0073] 51 Safety logic circuit [0074] 6 Driven object [0075] 7 Safety unit [0076] A311 Actuation of first stop valve [0077] A313 Actuation of third stop valve [0078] A321 Actuation of second stop valve [0079] A4 Actuation of hydraulic drive [0080] B Movement of the piston rod [0081] EF Reception of safety signals [0082] F Fluid [0083] FG External force, for example force of gravity [0084] MD Rotational speed of hydraulic drive (motor speed) [0085] N Normal mode [0086] O1 Opening of the first stop valve (open position) [0087] O2 Opening of the second stop valve (open position) [0088] O3 Opening of the third stop valve (open position) [0089] Q3a First cross-section of the connecting line [0090] Q3b Second cross-section of the connecting line [0091] SI Closing of the first stop valve [0092] S2 Closing of the second stop valve [0093] S3 Closing of the third stop valve [0094] S Safe mode [0095] SBK Control of the movement of the piston rod [0096] SHS Safety signal [0097] ST Shutdown of the drive system [0098] UM Switchover from normal mode to safe mode [0099] UN Conveyance of fluid in normal mode [0100] US Conveyance of fluid in safe mode [0101] V1 First connection point [0102] V2 Second connection point