GB2035464A - Actuator protection assemblies - Google Patents

Actuator protection assemblies Download PDF

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Publication number
GB2035464A
GB2035464A GB7909609A GB7909609A GB2035464A GB 2035464 A GB2035464 A GB 2035464A GB 7909609 A GB7909609 A GB 7909609A GB 7909609 A GB7909609 A GB 7909609A GB 2035464 A GB2035464 A GB 2035464A
Authority
GB
United Kingdom
Prior art keywords
piston
actuator
valve
current
cylinder
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.)
Granted
Application number
GB7909609A
Other versions
GB2035464B (en
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
DARTEC Ltd
Original Assignee
DARTEC Ltd
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by DARTEC Ltd filed Critical DARTEC Ltd
Priority to GB7909609A priority Critical patent/GB2035464B/en
Publication of GB2035464A publication Critical patent/GB2035464A/en
Application granted granted Critical
Publication of GB2035464B publication Critical patent/GB2035464B/en
Expired legal-status Critical Current

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Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B11/00—Servomotor systems without provision for follow-up action; Circuits therefor
    • F15B11/02—Systems essentially incorporating special features for controlling the speed or actuating force of an output member
    • F15B11/04—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed
    • F15B11/046—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed depending on the position of the working member
    • F15B11/048—Systems essentially incorporating special features for controlling the speed or actuating force of an output member for controlling the speed depending on the position of the working member with deceleration control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/305—Directional control characterised by the type of valves
    • F15B2211/30525—Directional control valves, e.g. 4/3-directional control valve
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/31—Directional control characterised by the positions of the valve element
    • F15B2211/3144—Directional control characterised by the positions of the valve element the positions being continuously variable, e.g. as realised by proportional valves
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/321—Directional control characterised by the type of actuation mechanically
    • F15B2211/325—Directional control characterised by the type of actuation mechanically actuated by an output member of the circuit
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/32—Directional control characterised by the type of actuation
    • F15B2211/327—Directional control characterised by the type of actuation electrically or electronically
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/30—Directional control
    • F15B2211/35—Directional control combined with flow control
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/705—Output members, e.g. hydraulic motors or cylinders or control therefor characterised by the type of output members or actuators
    • F15B2211/7051—Linear output members
    • F15B2211/7053—Double-acting output members
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F15—FLUID-PRESSURE ACTUATORS; HYDRAULICS OR PNEUMATICS IN GENERAL
    • F15B—SYSTEMS ACTING BY MEANS OF FLUIDS IN GENERAL; FLUID-PRESSURE ACTUATORS, e.g. SERVOMOTORS; DETAILS OF FLUID-PRESSURE SYSTEMS, NOT OTHERWISE PROVIDED FOR
    • F15B2211/00—Circuits for servomotor systems
    • F15B2211/70—Output members, e.g. hydraulic motors or cylinders or control therefor
    • F15B2211/755—Control of acceleration or deceleration of the output member

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Fluid Mechanics (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Actuator (AREA)

Abstract

Existing actuator protection assemblies prevent piston damage by using a relief valve to provide a constant resistive force at the end of the piston's travel. This tends to lead to a complicated and expensive design. In the present invention a change in the fluid supply is used to decelerate the piston at the end of its stroke. In the illustrated embodiment, a servovalve 5 for piston 1 is controlled by a control system 15 actuated by two sensors 7, 8 which are arranged to sense when the piston is nearing the end of its stroke. <IMAGE>

Description

SPECIFICATION Actuator protection assemblies The present invention relates to actuator protection assemblies and in particular, but not exclusively, to protection assemblies for hydraulic linear actuators.
Hydraulic linear actuators controlled by servo valves can have a combination of valve size and capacity so that the velocity of the actuator piston is of the order of 1-2 m/s or more. The actuator piston may strike the end stops at this velocity and the impact can cause damage to the end stops, bearings or piston.
The conventional method of preventing such damage is to arrange hydraulic "cushions" whereby the actuator piston enters at the end of its stroke a zone which is not connected to the control valve but which is connected to a relief valve so that the kinetic energy of the piston is reduced by a virtually constant resistive force created by passing the oil trapped in the cushion through the relief valve. This method is complicated and expensive and necessitates the inclusion in the design of actuator features which are undesirable from the aspect of a servo controlled actuator.
It is an object of the present invention to provide an actuator protection assembly in which these disadvantages are reduced or avoided.
According to the present invention, an actuator protection assembly comprises a cylinder, supply means operative to supply fluid to alternate sides of an actuator piston mounted for reciprocal movement between two stop surfaces between the cylinder, and control means operative to vary the fluid supply in such a way as to decelerate the piston during the latter part of its approach movement towards each stop surface.
The actuator fluid is conveniently a liquid for example, oil but as an alternative, a gas, for example, air could be used.
Conveniently the control means includes detectors arranged to sense the presence of the piston as it begins the latter part of its approach movement towards the stop surfaces. In preferred embodiments in which these detectors are present, the supply means include a servovalve and the control means includes a control circuit for these valves, the detectors being operable on sensing the presence of the piston as above described to increase the resistive load in the circuit thereby to reduce the supply flow through the servovalve and decelerate the piston.
Conveniently, the control circuit comprises an electric or electronic circuit although if desired pneumatic or hydraulic control circuits may be used instead.
An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing, in which the single figure illustrates a preferred embodiment in diagramatic form.
In the drawing, a linear hydraulic actuator 14 has a piston 1 on piston rods 2. The piston is enclosed by a cylinder 3 and the piston rods 2 run in bearings fitted to end blocks 4. The piston 1 is free to move the length of the cylinder 3 between the end blocks 4.
The flow of oil to the annular space between cylinder 3 and piston rod 2 on either side of the piston 1 is controlled by an electro-hydraulic servo valve 5. The servo valve 5 is connected to a high pressure oil supply and to a return line as indicated in the drawing and it gives a flow of oil proportional to an electrical control current in lead 6. This control current may be derived from a closed loop control system or from an open loop control system 1 5.
Two sensors 7 and 8 are mounted on the cylinder 3 in such a manner that one or other is activated as the piston 1 comes within a suitable distance of either end of its limits of travel.
Activation of either sensor 7 or 8 produces a change in the servo valve current in lead. In the version illustrated, the valve current is reduced by electronic means to a proportion of its original value. Before the sensors 7 or 8 are activated the current flows directly from the servo valve amplifier 9 to the servo valve 5. When either sensor is activated the current is switched by switches 10 or 11 through a resistance network represented by resistor 1 3.
The two switches are permanently shunted by a second resistor 1 2 and the values of the resistors 1 2 and 1 3 are selected so that the resistive load on the amplifier 9 remains essentially constant irrespective of the operation of the two switches and the current through the servo valve is reduced by the desired proportion. The reductions is servo valve current 6 thus achieved reduces the flow of oil to the actuator and thus the velocity of the piston 1.
The electronic circuit modifying valve current 6 can be arranged to produce some change other than direct proportional reduction of current if desired.
It will be appreciated that the invention is not restricted to the particular details disclosed above but that numerous modifications and variations can be made without departing from the scope of the invention as defined in the following Claims.
1. An actuator protection assembly comprising a cylinder, supply means operative to supply fluid to alternate sides of an actuator piston mounted for reciprocal movement between two stop surfaces in the cylinder, the
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Actuator protection assemblies The present invention relates to actuator protection assemblies and in particular, but not exclusively, to protection assemblies for hydraulic linear actuators. Hydraulic linear actuators controlled by servo valves can have a combination of valve size and capacity so that the velocity of the actuator piston is of the order of 1-2 m/s or more. The actuator piston may strike the end stops at this velocity and the impact can cause damage to the end stops, bearings or piston. The conventional method of preventing such damage is to arrange hydraulic "cushions" whereby the actuator piston enters at the end of its stroke a zone which is not connected to the control valve but which is connected to a relief valve so that the kinetic energy of the piston is reduced by a virtually constant resistive force created by passing the oil trapped in the cushion through the relief valve. This method is complicated and expensive and necessitates the inclusion in the design of actuator features which are undesirable from the aspect of a servo controlled actuator. It is an object of the present invention to provide an actuator protection assembly in which these disadvantages are reduced or avoided. According to the present invention, an actuator protection assembly comprises a cylinder, supply means operative to supply fluid to alternate sides of an actuator piston mounted for reciprocal movement between two stop surfaces between the cylinder, and control means operative to vary the fluid supply in such a way as to decelerate the piston during the latter part of its approach movement towards each stop surface. The actuator fluid is conveniently a liquid for example, oil but as an alternative, a gas, for example, air could be used. Conveniently the control means includes detectors arranged to sense the presence of the piston as it begins the latter part of its approach movement towards the stop surfaces. In preferred embodiments in which these detectors are present, the supply means include a servovalve and the control means includes a control circuit for these valves, the detectors being operable on sensing the presence of the piston as above described to increase the resistive load in the circuit thereby to reduce the supply flow through the servovalve and decelerate the piston. Conveniently, the control circuit comprises an electric or electronic circuit although if desired pneumatic or hydraulic control circuits may be used instead. An embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing, in which the single figure illustrates a preferred embodiment in diagramatic form. In the drawing, a linear hydraulic actuator 14 has a piston 1 on piston rods 2. The piston is enclosed by a cylinder 3 and the piston rods 2 run in bearings fitted to end blocks 4. The piston 1 is free to move the length of the cylinder 3 between the end blocks 4. The flow of oil to the annular space between cylinder 3 and piston rod 2 on either side of the piston 1 is controlled by an electro-hydraulic servo valve 5. The servo valve 5 is connected to a high pressure oil supply and to a return line as indicated in the drawing and it gives a flow of oil proportional to an electrical control current in lead 6. This control current may be derived from a closed loop control system or from an open loop control system 1 5. Two sensors 7 and 8 are mounted on the cylinder 3 in such a manner that one or other is activated as the piston 1 comes within a suitable distance of either end of its limits of travel. Activation of either sensor 7 or 8 produces a change in the servo valve current in lead. In the version illustrated, the valve current is reduced by electronic means to a proportion of its original value. Before the sensors 7 or 8 are activated the current flows directly from the servo valve amplifier 9 to the servo valve 5. When either sensor is activated the current is switched by switches 10 or 11 through a resistance network represented by resistor 1 3. The two switches are permanently shunted by a second resistor 1 2 and the values of the resistors 1 2 and 1 3 are selected so that the resistive load on the amplifier 9 remains essentially constant irrespective of the operation of the two switches and the current through the servo valve is reduced by the desired proportion. The reductions is servo valve current 6 thus achieved reduces the flow of oil to the actuator and thus the velocity of the piston 1. The electronic circuit modifying valve current 6 can be arranged to produce some change other than direct proportional reduction of current if desired. It will be appreciated that the invention is not restricted to the particular details disclosed above but that numerous modifications and variations can be made without departing from the scope of the invention as defined in the following Claims. CLAIMS
1. An actuator protection assembly comprising a cylinder, supply means operative to supply fluid to alternate sides of an actuator piston mounted for reciprocal movement between two stop surfaces in the cylinder, the control means operative to vary the fluid supply in such a way as to decelerate the piston during the latter part of its approach movement towards each stop surface.
2. An assembly as claimed in Claim 1 in which the actuator fluid is a liquid.
3. An assembly as claimed in Claim 1 or Claim 2 in which the control means includes detectors arranged to sense the presence of the piston as it begins the latter part of its approach movement towards the stop surfaces.
4. An assembly as claimed in Claim 3 in which the supply means includes a servovalve and the control means includes a control circuit for the valve, the detectors being operable on sensing the presence of the piston as it begins said latter part of its approach movement to increase the resistive load in the circuit thereby to reduce the supply flow through the valve and decelerate the piston.
5. An assembly as claimed in Claim 4 in which the control circuit comprises an electric or electronic circuit.
6. An assembly as claimed in Claim 1 and substantially as hereinbefore described with reference to, and as illustrated in, the accompanying drawing.
GB7909609A 1978-11-28 1979-03-19 Actuator protection assemblies Expired GB2035464B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7909609A GB2035464B (en) 1978-11-28 1979-03-19 Actuator protection assemblies

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB7846427 1978-11-28
GB7909609A GB2035464B (en) 1978-11-28 1979-03-19 Actuator protection assemblies

Publications (2)

Publication Number Publication Date
GB2035464A true GB2035464A (en) 1980-06-18
GB2035464B GB2035464B (en) 1982-12-15

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Family Applications (1)

Application Number Title Priority Date Filing Date
GB7909609A Expired GB2035464B (en) 1978-11-28 1979-03-19 Actuator protection assemblies

Country Status (1)

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GB (1) GB2035464B (en)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0022105A1 (en) * 1979-06-20 1981-01-07 Akermans Verkstad AB A device for reducing piston velocity in a cylinder
EP0053370A2 (en) * 1980-11-27 1982-06-09 Leybold-Heraeus GmbH Method to control a hydraulic mechanism, and hydraulic mechanism suited to carry out said method
WO1996002707A1 (en) * 1994-07-13 1996-02-01 O & K Orenstein & Koppel Ag Process for exactly positioning the tilting outfit mounted on the descending lift frame of movable construction machines
CN108915945A (en) * 2018-06-26 2018-11-30 深圳市名业精密机电设备有限公司 Piston cylinder passes through electrodeless or segmentation speed regulation accurate positioning method

Cited By (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0022105A1 (en) * 1979-06-20 1981-01-07 Akermans Verkstad AB A device for reducing piston velocity in a cylinder
EP0053370A2 (en) * 1980-11-27 1982-06-09 Leybold-Heraeus GmbH Method to control a hydraulic mechanism, and hydraulic mechanism suited to carry out said method
EP0053370A3 (en) * 1980-11-27 1983-05-04 Leybold-Heraeus Gmbh Method to control a hydraulic mechanism, and hydraulic mechanism suited to carry out said method
WO1996002707A1 (en) * 1994-07-13 1996-02-01 O & K Orenstein & Koppel Ag Process for exactly positioning the tilting outfit mounted on the descending lift frame of movable construction machines
US5784812A (en) * 1994-07-13 1998-07-28 O&K Orenstein & Koppel Ag Method of controlling the positioning of an outfit tilting cylinder mounted on the descending lift frame of movable construction machines
CN108915945A (en) * 2018-06-26 2018-11-30 深圳市名业精密机电设备有限公司 Piston cylinder passes through electrodeless or segmentation speed regulation accurate positioning method

Also Published As

Publication number Publication date
GB2035464B (en) 1982-12-15

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PCNP Patent ceased through non-payment of renewal fee