JPH06144795A - Hydraulically actuated load handling clamp - Google Patents

Abstract

PURPOSE: To provide a clamp force control device wherein a clamp arm is quickly moved when not engaged with a load while a clamp force is limited at engagement by providing a relief valve comprising a variable relief pressure setting which corresponds to a clamp arm closure speed. CONSTITUTION: A pair of clamp arms 32 and 33 and at least one fluid operation actuator 30 and 31 for moving the clamp arm are connected to a fluid operation actuator. Pressurizing fluid sources 22 and 24 which selectively move the actuator in the direction of a load, at least one pressure relief valves 64, 66, and 68 comprising a variable relief pressure setting for limiting a fluid supply pressure, and regulator devices 70, 72, and 73 which, automatically corresponding to the movement speed of the clamp arm, raise a relief pressure setting to a high set value at fast movement while lower it to a low set value at slow speed, are provided.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a controller for a fluid operated load handling clamp. In particular, the present invention has one or more pressure relief valves,
These relief valves relate to a fluid operated clamping force control device having a variable pressure setting that automatically responds to the closing speed of the clamp.

[0002]

2. Description of the Related Art In the physical distribution industry, it is common to use hydraulically or pneumatically actuated clamping devices mounted on lift trucks to grab loads in order to move or manipulate them. To prevent the clamp from collapsing or breaking a fragile load, such as a carton or paper roll, the clamp uses one or more pressure relief valves to create a fluid pressure that determines the clamping force. Thus, in a typical logistics system, when the fluid pressure sensed by the relief valve equals the relief pressure setting, the relief valve is opened, a portion of the fluid is bypassed to the clamp arm actuator, and the maximum clamp is reached. Limit power.
Selectors are used to determine different relief pressure settings and valves that control the pressure, allowing different maximum clamping forces to be selected for different types of cargo.

[0003]

However, in a system using such a relief valve, the relief valve is opened early when the clamp arm is rapidly moved toward the load to engage with the load. Therefore, a problem arises. In such control systems, there is considerable fluid resistance due to the presence of long, relatively thin walled fluid conduits, various fittings, bends and check valves. In order to move the clamp arm quickly, the volumetric flow rate of the fluid must be proportionately large, and thus the pressure differential required between the pressure source and the clamp arm actuator is also large. Therefore, rapid closing of the clamp arm requires a high pressure in the conduit, which prematurely exceeds the pressure setting of the relief valve, in particular the low setting value, long before the clamp arm actually engages the load. This opens the relief valve, bypassing the fluid flow to the clamp arm actuator and limiting the speed of the clamp arm. This slows down the entire load handling process, which tends to cause the operator to make selections beyond the proper pressure settings to increase the speed of movement of the clamp arm. However, this creates excessive clamping force and damages the load.

The preferred components of the present invention include Sun Hydraulics Corporation.
Dual pressure relief available from
It is an RHEA cartridge. Sun Hydrourix offers dual pressure relief valve cartridges in oscillating control valves to provide smooth deceleration of rotating devices, such as hydraulic cranes, but with automatic speed control of the fluid operated actuator. There is no teaching on the use of dual pressure relief valve cartridges to respond and detect positively.

It is an object of the present invention to prevent overclamping by limiting the fluid supply pressure to ensure a high clamp arm closing speed even at fluid clamp pressures above the required pressure limit and at high clamp arm speeds. To obtain the resulting fluid clamping force control device.

[0006]

To this end, the clamping force control device according to the invention comprises a regulator device for automatically selecting the relief pressure in response to the closing speed of at least one clamping arm. Provide one or more variable pressure relief valves.

[0007]

When the closing speed of the clamp arm is "fast", the relief valve regulator device sets the relief valve pressure to "high" pressure so that the fluid supply pressure does not open the relief valve. Also, when the clamp arm speed is "slow", the regulator device sets the relief pressure to a relatively "low" pressure so that the fluid supply pressure opens the relief valve to form the clamping force.

In the preferred embodiment of the present invention, "high".
Use a dual pressure relief valve with a relief pressure and a "low" relief pressure. The regulator device is
The choice between "high" and "low" relief pressure is made in response to fluid flow, which is representative of the closing speed of the clamp arm. Suitably, the regulator is in fluid communication with an output conduit carrying fluid exiting the clamp arm actuator during closure of the clamp arm. When the fluid actuator moves rapidly before the clamp arm engages the load, the fluid flow exiting the actuator creates a pressure in the output conduit that is non-linearly proportional to the fluid flow rate, and this pressure is relieved. The device senses and selects the "high" relief pressure setting. On the contrary, when the fluid actuator does not move or moves very slowly due to the clamp arm engaging the load, the pressure in the output conduit becomes “low” and the relief valve regulator device that senses this low pressure is ,
Select the relief valve's relief pressure setting to the "low" setting. In this way, the relief valve opens with a "high" relief pressure when the fluid actuator moves rapidly, thus allowing a rapid movement with the "high" fluid pressure. On the other hand, when the fluid actuator does not move, or moves very slowly, the relief valve opens at "low" pressure, limiting the maximum clamping force.

[0009]

The preferred embodiments of the present invention will now be described with reference to the drawings.

Prior to a detailed description of the preferred embodiment of the present invention, a typical conventional fluid clamping force control system will be described. A circuit diagram of a conventional force control device for a carton clamp of a fluid operated lift truck is shown in FIG. A fluid pump 22 delivers pressurized fluid from a fluid reservoir 24 to a manual clamp arm directional control valve 26 (shown in the central deactivated state in the drawing). Adjustable relief valve 28
Opens in response to excess fluid pressure determined by the adjustable setting of relief valve 28 and sets an upper limit on the fluid pressure delivered by pump 22 by returning fluid to reservoir 24.

A pair of double acting fluid actuated actuators 30, 31
Are connected to the clamp arms 32 and 33, respectively. The clamp arms 32, 33 are closed by the lift truck driver operating the directional control valve 26 to move the spool downwards as viewed in FIG. This allows the pressurized fluid to
And the fluid is delivered to the first chamber 38 of the actuator 30 via the pilot operated check valve 36 and to the first chamber 39 of the fluid actuator 31 via the interconnecting conduit 40. As the clamp arms 32, 33 move toward each other and engage the load, fluid flows from the second chamber 44, 45 of the actuator into the reservoir 24 via the conduit 42 and the return port of the directional control valve 26.

On the contrary, the spool of the directional control valve 26 is shown in FIG.
Moving above, the pressurized fluid is delivered to the conduit 42, which causes the pressurized fluid to flow into the second chambers 44, 45, respectively. Pilot operated check valve 36
To the reservoir 24 via the conduit 34 and the direction control valve 26 from the first chambers 38, 39 of the actuators 30, 31 to open the clamp arm.

The maximum closing force of the clamp arms 32, 33 is limited by the clamp force control 48 which includes a manual clamp force selector valve 52 having a four position spool in fluid communication with the conduit 34 via the conduit 50. This clamping force control device 48 has three adjustable relief valves 54, 56, 58.
These relief valves have different relief pressure settings P1, P2, P3 (all lower than the valve 28 setting) corresponding to a predetermined maximum clamping force for a particular load. The relief valve is normally closed, but the relief valve is conduit 50 and selector valve.
Upon receiving a fluid pressure via 52 that is higher than the relief pressure of the valve, the valve opens and allows fluid to escape from conduit 34 to conduit 42. In this way, when the selector valve 52 is set as shown in FIG. 1, the fluid pressure from the conduit 34 communicates with the relief valve 58, and the pressure in the conduit 34 becomes the relief pressure P3.
Open when equal to, limiting the fluid pressure and thus the clamping force. The driver changes the maximum clamping force by moving the selector valve 52 so that the input conduit 34 communicates with relief valves 54, 56 having different relief pressure settings or moves the selector valve 52 to the closed position. This deactivates the clamping force controller 48.

In practice, device 48 and actuators 30, 31
The conduits 34, 42 between the interconnections with and are extremely long,
It includes a multiple joint and a check valve. The diameter of these conduits is limited by the space available. All of these factors contribute to the increased resistance to fluid flow as the flow velocity increases, even if the clamp arms do not load. Therefore, if it is desirable to increase the clamp arm closing speed, the pressure in conduit 34 should be relatively high. However, problems arise when attempting to bring the fluid pressure in conduit 34 above the predetermined relief pressure (P1, P2, P3) when closing the clamp arm. That is, the reservoir opens to limit pressure,
Therefore, the flow rate is reduced and the movement of the clamp arm is slowed down. This leads to driver frustration, moving selector valve 52 to deactivate all reservoirs,
Alternatively, there is the risk of choosing a reservoir with a high pressure setting and creating an overclamping force that damages the load being handled.

The present invention is described above by incorporating a flow sensitive clamping force controller 60 as shown in FIG. 2 using a pressure reservoir with a variable pressure setting pressure that automatically responds to clamp arm closure flow conditions. Solve a problem. The fluid control method shown in FIG. 2 is substantially similar in structure and operation to the conventional device of FIG. 1, except that the flow sensing clamp force control device 60 is used in place of the control device 48. Therefore, all the fluid control devices in FIGS. 1 and 2 are described with the same reference numerals.

The flow sensing clamp force controller 60 is arranged in the same manner as the 4-position spool of the conventional selector valve 52.
Manual clamping force selector valve 62 with position spool
To provide. Selector valve 60 communicates with three pressure relief valves 64, 66 and 68, which are valves.
It is selected according to the spool position of 62. All three relief valves 64, 66, 68 operate in the same manner, but are adjusted to operate at different relief pressure settings (all lower than the valve 28 setting) in response to different maximum clamping forces. The purpose of providing three relief valves is the same as in the device of Figure 1 and gives the driver a range in which different maximum clamping forces for different types of loads can be easily selected.

For the following description, only the case where the selected relief valve when the clamping force selector valve 62 is in the position shown in FIG. 2 is the relief valve 68 will be described. At this time, the relief valve 68 is connected to the conduit 34.
Is in fluid communication with the relief valve and is normally closed to prevent fluid flow. Valve 68 is namely two relief pressure setting, with a high relief pressure P _H and a low relief pressure P _L. The setting of the low relief pressure P _L is set so that the spring responds to the required maximum clamping pressure.
It can be adjusted by mechanically adjusting the degree of compression of 68a. High relief pressure setting is controlled by the piston of regulator 70 in the relief valve,
This piston has an area which is considerably larger than the valve seat area of the relief valve, and when subjected to a certain pilot pressure it begins to compress the spring 68a more than the mechanically adjusted setting, increasing the setting proportionally higher. To do. The regulator piston selects the relief pressure setting of the relief valve 68 to P _H or P _L by sensing the pressure of the regulator pilot line 72. Store fluid flow in reservoir 24 while closing clamps.
Upon discharge via conduit 42, the fluid pressure at connection 73 in conduit 42 is non-linearly proportional to the volumetric flow rate and clamp closure rate. This pressure is the pilot line
Added to regulator piston via 72. Conduit 42
When there is no or very low flow rate in the piston, the piston in regulator 70 receives little or no pressure and the regulator reduces the compression of spring 68a to a mechanically adjusted setting to reduce the low pressure setting. Select P _L. Conversely, when the flow velocity is high, the corresponding high pressure further compresses the spring, increasing the relief pressure to the high pressure setting P _H.

By incorporating a flow-sensing and therefore velocity-sensitive clamping force controller 60 as shown in FIG. 2, the fluid controller operates as follows. Fluid pump 22 delivers pressurized fluid from fluid reservoir 24 to manual clamp arm directional control valve 26. Pressurized fluid is delivered from the conduit 34 to the first chamber 38, 39 of the actuator 30, 31 as the spool of the clamp arm control valve is moved downward to move the clamp arms closer together. As the clamp arms 32, 33 close, they are forced out of the fluid actuator into the conduit 42, increasing the volumetric flow rate and thus the pressure at the junction 73, which is indicative of the closure rate. The closing speed and thus the fluid pressure at the joint 73 is high when the clamp arm is not yet loaded, at which time the relief valve 68 is operated at the high pressure setting P _H , which causes the ratio of piston to valve seat. This keeps the relief valve 68 closed.

When the clamp arms 32, 33 contact the load, the clamp arms stop abruptly and the pressure in the chambers 38, 39 increases in response to the resistance from the load. When the clamp arm is stopped, there is no fluid flow out of the fluid actuators 30, 31 and therefore no fluid flow in conduit 42. conduit
Since 42 is open to the reservoir 24, the pressure in conduit 42 at junction 73 decreases sharply. Regulator 70 senses the reduced pressure of the regulator pilot line 72, to reduce the degree of compression of the spring 68a, thus, selects the low pressure relief setting P _L. The relief valve 68 is
Fluid pressure in conduit 34 is opened when exceeding the P _L, thus limiting the clamping arm force.

The clamping force selector valve 62 can be arranged to communicate the conduit 34 with a relief valve 64 or 66, which valves have different low pressures which allow the maximum clamping force to be selected in three sizes. Relief pressure P _L
Set to. Regardless of the relief valve selected, it functions exactly as described for relief valve 68, only the magnitude of low relief pressure P _L differs.

Fluid passing through relief valves 64, 66 and 68 enters relief valve discharge conduit 74, which
74 communicates directly with fluid reservoir 24, bypassing conduit 42 and clamp arm directional control valve 26. The drain conduit 74 is disconnected from the conduit 42 so that fluid flow exiting the relief valve is not sensed by the regulator 70. If this is not done, the relief valve will be set to a high relief pressure P _H in response to such a flow, adversely affecting the clamping arm force limiting function.

Although described primarily for lift truck load clamps having one or more fluid-operated clamp arms, the present invention is applicable to other applications, including fluid-operated systems for grasping loads. The present invention can be applied to a robot system, an assembly line work, and an automatic physical distribution system.

The terms and expressions used in the present specification are used for the convenience of description and are not limited to them. It goes without saying that various modifications can be made in the claims.

[Brief description of drawings]

FIG. 1 is a fluid circuit diagram of a prior art fluid clamping force control device.

FIG. 2 is a fluid circuit diagram of a preferred embodiment of a device according to the present invention.

[Explanation of symbols]

 22 Fluid pump 24 Fluid reservoir 26 Manual clamp arm directional control valve 28,54,56,58,64,66,68 Relief valve 30,31 Double acting fluid actuated actuator 32,33 Clamp arm 34,50,42 Conduit 36 Pilot check Valve 38,39 First chamber 40 Interconnecting conduit 44,45 Second chamber 46 Pilot line 48 Clamping force controller 52,62 Manual clamping force selector valve 60 Flow sensing clamping force controller 70 Regulator 72 Regulator pilot line 73 Connection 74 Discharge conduit

Claims (6)

[Claims] 1. A fluid-operated cargo handling clamp comprising: (a)
A pair of clamp arms that can be selectively opened and closed; and (b) at least one fluid movement that selectively moves at least one of the clamp arms toward or away from a load. An actuator, (c) a source of pressurized fluid connected to the fluid-operated actuator and supplying fluid to the actuator to selectively move the actuator in the direction of the load, (d)
At least one having a variable relief pressure setting for limiting the pressure of fluid supply to said actuator
Pressure relief valves, (e) automatically responding to the speed of movement of the clamp arm in the direction and increasing the relief pressure setting to a high pressure setting in response to the high speed. Or a relief valve regulator device that automatically responds to the low speed to reduce the relief pressure setting to a low pressure setting. 2. The regulator device is configured to reduce the relief pressure setting in response to a decrease in speed due to contact between the load and one of the clamp arms. Fluid operated cargo handling clamp. 3. Providing different pressure relief valves with different low pressure settings when the speed is low, and only one of these relief valves at a time limits the fluid supply pressure. A fluid-operated cargo handling clamp according to claim 1, further comprising a selector. 4. The relief valve regulator device comprises:
A configuration that automatically responds to the velocity by responding to a fluid flow rate passing through the actuator.
The fluid-operated cargo handling clamp described. 5. The relief valve regulator device comprises:
The fluid operated load handling clamp of claim 4, wherein the clamp is responsive to the flow rate of fluid expelled from the actuator. 6. The relief valve limits fluid supply pressure by discharging fluid from the relief valve to a first conduit, and wherein the actuator is actuated when one of the clamp arms towards the load moves. 6. The fluid-operated cargo handling clamp according to claim 5, wherein the fluid is discharged to a second conduit separate from the first conduit.