Press driven tool actuator module

REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of copending application Ser. No. 08/976,775 filed Nov. 24, 1997 entitled Press Driven Tool Actuator Module.

FIELD OF THE INVENTION

This invention relates generally to fluid actuated cylinders and more particularly to an actuator for fluid actuated cylinders.

BACKGROUND OF THE INVENTION

Press driven tool modules utilizing fluid actuated cylinders have found acceptance due to their adaptability to conventional presses wherein a vertical force input by a press ram to one fluid power cylinder actuates a second fluid work cylinder to provide a horizontal or otherwise directed force output to actuate a tool to form a portion of a workpiece inclined to the axis of the press ram. This design is flexible in that various tool modules can be used with the same press to provided a number of forming operations actuated by a single press. One such press driven fluid actuated tool module is disclosed in U.S. Pat. No. 5,606,910. In this system a press ram displaces a piston of a hydraulic power cylinder to pressurize the hydraulic fluid and thereby displace a piston of a work cylinder which has a tool mounted thereon to engage the tool with the workpiece. The power cylinder has an upper reservoir containing a reserve supply of hydraulic fluid which when the piston is retracted communicates with a lower portion of the cylinder, which contains the hydraulic fluid to be pressurized by displacement of the piston, after it engages with a high pressure seal to prohibit pressurized fluid from flowing into the upper reservoir. The power cylinder must be disposed in substantially vertically upright position to function properly. When the high pressure seal wears, there is, at the very least, a loss in pressure of the hydraulic fluid when the work cylinder piston is displaced which reduces the efficiency of the system and effects the performance of the work tool in use. Further, wear on the seal can lead to failure of the power cylinder requiring replacement of the entire power cylinder or at least the high pressure seal resulting in increased down time for the system.

SUMMARY OF THE INVENTION

For a hydraulically actuated device a hydraulic power cylinder with an actuator slidably received for reciprocation within the cylinder and a piston slidably received for reciprocation within the actuator and defining in part a gas chamber on one side of the piston and a hydraulic fluid chamber on the other side of the piston so that the maximum pressure in the hydraulic fluid chamber is limited as a function of the pressure of gas in the gas chamber acting on the piston. In this way, the maximum system pressure corresponds to the pressure of the gas within the gas chamber acting on the piston. Desirably, the pressure within the gas chamber can be readily changed to change the maximum hydraulic fluid pressure.

In one form, the hydraulic actuator is used to drive a work cylinder having a work tool to form a workpiece adjacent the work cylinder. Preferably, a press displaces the actuator to decrease the volume of the hydraulic chamber and force hydraulic fluid under pressure from the hydraulic actuator to the work cylinder to drive a piston and rod of the work cylinder to displace the associated work tool to form the workpiece. A biasing member in the work cylinder acting on its rod and piston returns the hydraulic actuator to its unloaded position when the press ram is retracted from the actuator. The biasing member may be one or more gas springs carried by the work cylinder.

Objects, features and advantages of this invention include providing a hydraulic actuator which limits the maximum pressure within the hydraulic actuator and within a device driven by the hydraulic actuator, is readily adaptable to many hydraulic cylinder applications, enables the maximum hydraulic fluid pressure to be readily varied, improves the in-service useful life of the high pressure seals, is reliable durable, of relatively simple design and economical manufacture, and has a long useful life in service.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of this invention will be apparent from the following detailed description of the preferred embodiment and best mode, appended claims and accompanying drawings in which:

FIG. 1

is a sectional view of a work cylinder and a hydraulic actuator according to the invention;

FIG. 2

is a sectional view of the hydraulic actuator of

FIG. 1

;

FIG. 3

is a sectional view of the work cylinder of

FIG. 1

;

FIG. 4

is a sectional view taken along line

4

—

4

of

FIG. 3

;

FIG. 5

is an end view of the work cylinder; and

FIG. 6

is a sectional view taken along line

6

—

6

of FIG.

3

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring in more detail to the drawings,

FIG. 1

illustrates a hydraulic actuator

10

for a hydraulically driven work tool

12

and having an actuator

14

displaceable by a ram

16

of a press

17

to pressurize hydraulic fluid in the actuator

10

and deliver it to a work cylinder

18

to drive a work cylinder piston

20

to advance the work tool

12

along its axis to punch a hole in or form a workpiece

22

received on a carrier

24

. After the forming operation is complete, the press ram

16

is retracted or withdrawn and the actuator

14

is returned to its retracted position by a biasing means, such as a spring or a gas spring carried by the work cylinder

18

and constructed and arranged to cause the work cylinder piston

20

to return it to its retracted position and displace the hydraulic fluid back into the actuator

10

thereby displacing the actuator

14

to its retracted position. With the system reset in its starting position, a subsequent cycle of the hydraulic actuator

10

and the work tool

12

can be performed to form another workpiece

22

.

As best shown in

FIGS. 1 and 2

, the hydraulic actuator

10

has a cylinder body

30

with a stepped, generally cylindrical bore

32

in which the actuator

14

is slidably received for reciprocation between advanced and retracted positions. An annular bearing retainer

34

is threadably received in the bore

32

and has a first annular groove

36

in which an annular bearing

38

is received and a second annular groove

40

in which a seal ring

42

is received. A wiper

44

may also be carried by the retainer

34

. An outlet

46

through the cylinder body

30

communicates a hydraulic fluid chamber

48

with the work cylinder

18

. An opening

50

through the cylinder body

30

may be used to add hydraulic fluid to or remove hydraulic fluid from the chamber

48

and in use is closed by a plug

52

.

The actuator

14

has a cylindrical sleeve

54

threadably attached to an annular retainer

56

with one or more set screws

58

received through openings in the retainer

56

to fix its position relative to the sleeve

54

. A cap

62

closes the upper end of the sleeve

54

and is preferably welded or otherwise attached and sealed to the sleeve

54

and preferably has a gas filler valve

64

extending therethrough to permit pressurized gas to be added to or removed from a gas chamber

66

. The gas chamber

66

is defined in part by a piston

68

slidably received within the sleeve

54

and retained therein by an inwardly extending edge

70

of the retainer

56

. The piston

68

has a first annular groove

72

which receives an annular bearing

74

and a second annular groove

76

which receives a seal ring

78

to prevent fluid transfer between the gas chamber

66

and the hydraulic fluid chamber

48

. The movement of the actuator

14

toward its retracted position is limited by engagement of an overhanging edge

80

of the retainer

56

with an end or inwardly extending rim

82

of the bearing retainer

34

.

As best shown in

FIGS. 1 and 3

, the work cylinder

18

has a body

84

constructed to be bolted to a base through mounting holes

86

extending through feet

88

of the body

84

. The body

84

has a generally cylindrical bore

90

in which a piston rod

92

is slidably received for reciprocation and a counterbore

94

providing a shoulder

96

engageable by the piston

20

which is operably connected to the piston rod

92

to limit the travel of the piston

20

and rod

92

.

The piston

20

preferably comprises a split ring having a throughbore and a counterbore providing a rib

98

received in an annular groove

100

in the end of the piston rod

92

. The piston

20

is slidably received in a generally cylindrically bore of a cup shaped end cap

102

threadably received in the counterbore

94

of the body

84

. The piston

20

preferably carries an annular bearing

104

which guides the piston

20

for reciprocation within the end cap

102

. A hydraulic fluid chamber

106

is defined between the piston

20

and end cap

102

and communicates with the hydraulic fluid chamber

48

of the hydraulic actuator

10

through an opening

108

in the end cap

102

and an interconnecting conduit

110

.

The work cylinder body

84

carries one or more annular seals

112

which prevent any fluid in a chamber

114

defined between the piston rod

92

and the body

84

from leaking out of the body. Any air or gas in the chamber

114

may be communicated with the atmosphere through a small bleed hole (not shown) which is normally closed.

A guide plate

120

is fixed to the end of the piston rod extending from the body

84

by a pair of cap screws

122

(

FIG. 4

) threaded into the piston rod

92

. To guide the piston rod

92

for reciprocation, a pair of generally cylindrical rods

124

are connected to the guide plate

120

by cap screws

125

threadably received in the rods

124

and are slidably received in bushings

127

through bores

126

in the body

84

. The work tool

12

is preferably threadably received in aligned openings

128

,

130

in the guide plate

120

and piston rod

92

for comovement in unison therewith.

To yieldably bias the rod

92

and piston

20

, as best shown in

FIG. 6

, gas springs

132

are each received in separate pockets

134

in the body

84

and fixed therein by a cap screw

136

received in a threaded bore in an end cap

138

of each gas spring

132

. Each gas spring

132

has a plunger

140

extending out of its pocket

134

and engageable with a bar

142

connected to each leg

124

by a cap screw

144

to yieldably bias the bar

142

and hence, the guide plate

120

, piston rod

92

and piston

20

to their retracted positions to minimize the volume of the hydraulic fluid chamber

106

to return the hydraulic fluid to the hydraulic actuator

10

when the actuator

14

is not engaged by the press ram

16

. The gas springs

132

may be of substantially any type, such as that disclosed in U.S. Pat. No. 5,303,906, the disclosure of which is incorporated herein by reference in its entirety. Optionally, some other biasing mechanism, such as a coil spring or other mechanical device, may be provided in the pockets to yieldably bias the bar

142

and connected components.

OPERATION

In use, the press ram

16

is advanced to move the actuator

14

from its retracted position to its advanced position to displace the hydraulic fluid from the chamber

48

of the hydraulic actuator

10

to the chamber

106

of the work cylinder

18

. The hydraulic fluid in the work cylinder chamber

106

displaces the piston

20

to axially advance the work tool

12

. As the piston

20

is advanced, the guide plate

120

is moved away from the body

84

and the bar

142

is moved toward the body

84

and thus bears on and displaces the plungers

140

of the gas springs

132

thereby increasing the pressure of the gas in the gas springs

132

. As the press ram

16

is retracted, the plungers

140

of the gas springs

132

displace the bar

142

which, through the rods

124

, displaces the guide plate

120

and hence, the rod

92

and piston

20

to decrease the volume of the hydraulic fluid chamber

106

to return hydraulic fluid from the work cylinder

18

to the hydraulic actuator

10

. This resets the actuator

14

to its retracted position so that the system is ready for a subsequent cycle.

The piston

68

of the hydraulic actuator

10

is acted on by hydraulic fluid in the chamber

48

on one face and gas in the gas chamber

66

on its other face. Desirably, this permits the system operating pressure to be controlled according to the pressure of the gas in the gas chamber

66

. Should the force of the hydraulic fluid acting on the lower face of the piston

68

exceed the force of the gas acting on the upper face of the piston

68

, the piston

68

will be slidably displaced within the sleeve

54

thereby relatively increasing the volume of the hydraulic fluid chamber

48

to limit the pressure therein. In one embodiment, the gas chamber

66

may contain a compressed gas, such as nitrogen, at a pressure of 10 to 200 bars (150 to 3000 psi) or more. While the pressure in the gas chamber

66

may increase slightly as the piston

68

is displaced, the system pressure will still be controlled as a function of the gas chamber pressure. In this way, the system operating pressure can be controlled as a direct function of the pressure of the gas in the gas chamber

66

. Desirably, the gas chamber pressure can be readily changed as desired for a particular application.

As an alternative, another biasing member, such as a spring, may be provided in chamber

66

and acting on the piston

68

. A compression coil spring or belleville spring washers may be utilized. The force of the spring would set the maximum hydraulic fluid pressure in the same manner as the compressed gas described earlier would.