US3524384A - Stroke control for ram type machine - Google Patents

Description

United States Patent [72] Inventor Rolland A. Richardson Alameda, Canada 1211 Appl. No. 720,053

[22] Filed April 10, 1968 [45] Patented Aug. 18, 1970 [73] Assignee Pacific Press & Shear Corp.

a Corp. of Delaware [54] STROKE CONTROL FOR RAM TYPE MACHINE 8 Claims, 4 Drawing Figs.

[52] U.S. Cl 91/35 [51] lnt.Cl. Fl5b2l/02 [50] Field ofSearch 9l/35,38

[56] References Cited UNITED STATES PATENTS 2,923,973 2/1960 Ninneman l/35X 3,183,790 5/1965 Raymond 9l/35X 3,256,778 6/1966 Fine 9l/35 Primary E.raminer Everette A. Powell, Jr. Almrney Edward Brosler ABSTRACT: A remote control for the ram of a ram type machine such as a press brake for example, wherein adjustable timing means is employed to determine (1) the extent of the return stroke, and (2) the point of change from fast approach to pressing speed in a work stroke when the machine is provided with a two speed work stroke feature.

' Patented Aug. 18, 1910 Sheet orz FIG.

INVENTOR. ROLLAND A. RICHARDSON ATTORNEY Y B 5 T 9 7 3 M B J j a 5 w mm 4 m 6 W I ll STROKE CONTROL FOR RAM TYPE MACHINE My invention relates to ram type machines and more particularly to means for controlling the stroke of the ram of such a machine.

In a press brake, which represents one example of a ram type machine to which the present invention is applicable, a depth stop adjustably installed on the ram, is adapted to engage and actuate a depth limit switch mounted on an adjacent fixed portion of the machine in the path of movement of the depth stop. On the return stroke, a back travel stop adjustably installed on the ram is adapted to engage a back travel limit switch similarly mounted on the fixed portion of the machine. Thus, both the depth of stroke and the extent of the back travel of the ram may be manually adjusted to conform to the work and the job to be accomplished.

Machines, however, have become so large that such adjustments are beyond the reach of an operator, and necessitate the use of a ladder to make necessary adjustments.

ln some machines, provision is also made for advancing the ram at a faster than normal or pressing speed until the ram approaches the work, at which time the speed is slowed to normal or pressing speed, if the machine be a press brake.

Among the objects of my invention are:

(1) To provide a ram type machine having a novel and improved stroke control means;

(2) To provide a novel and improved ram type machine in which the stroke of the ram may be controlled from a remote point which is readily accessible to an operator;

(3) To provide a novel and improved ram type machine in which the back or return stroke of the ram may be adjusted from a remote point conveniently accessible to an operator;

(4) To provide a novel and improved ram type machine in which a remote control enables additional back travel within a cycle, beyond the back travel limit otherwise provided for within that cycle;

(5) To provide a novel and improved ram type machine in which a two speed work stroke may be remotely controlled as to the point of speed change.

Additional objects of my invention will be brought out in the following description of preferred embodiment of the same, taken in conjunction with the accompanying drawings wherein,

FIGURE 1 is a view depicting the hydraulic system ofa ram type machine of the present invention;

FIGURE 2 is a view depicting the flow passages and manner of operation of a valve assembly employable in the system of FIGURE 1;

FIGURE 3 is a view depicting the electrical control system involved in cooperation with the hydraulic system of FIGURE l;and

FIGURE 4 is a graph depicting the various stroke control adjustments available with the present invention.

For the purpose of the present disclosure, the invention is depicted as incorporated in a ram type machine of the press brake type, in which the ram is operated hydraulically, and provision is made for initially advancing the ram at an increased rate of speed, and changing it to the normal pressing speed as the ram approached the work. Being that this type of machine is not basically new, only a brief description of the machine is necessary, and then only the pertinent portions thereof involved in the operation of the present invention.

Such machine includes a ram 1 reciprocally mounted for cooperation with a suitable die (not shown). The ram is driven or powered by a pair of hydraulic motors 3 and 5, one at each end of the ram and including a cylinder 7 mounted on the frame of the machine, and a piston 9 coupled to the ram at a proximate point thereof.

The hydraulic motors are supplied hydraulically by a pair of pumps 11 and 13. In the particular hydraulic systems of the specific embodiment illustrated,and for purposes of explaining the present invention, a flow line 15 from each pump is divided into two flow line branches 17 and 19. One branch 17 extends to the upper end of the cylinder of one of the hydraulie motors, and includes a normally closed valve assembly 23 controlled by a normally closed pilot valve 24 which, in turn, is electrically actuated by a solenoid winding 25.

Down stream of the valve assembly, this flow line 17 is adapted to be flow connected to a tank 26 through a normally closed valve assembly 27 controlled by a normally open pilot valve 29 which in turn, is electrically actuated by a solenoid winding 31.

The other branch 19 which leads to the lower end of the cylinder of the other hydraulic motor, includes a normally closed valve assembly 33 controlled by a normally closed pilot valve 35 which is electrically actuated by a solenoid winding 36.

The valve assembly 33 just referred to, may be of a design enabling a two speed work stroke, namely a work stroke in which the initial portion may be at a greater than normal rate of speed, to be changed to normal or pressing speed as the ram approaches the work. When the valve assembly is of this type, it will have the hydraulic characteristics depicted schematically in FIGURE 2.

Such valve assembly, by reference to FIGURE 2, involves a main flow passageway 39 having a normal input end 41 and a normal discharge end 43,.this passageway being spanned by a main valve 47 which is continually being urged toward its seating position by a valve spring 49.

The main valve is formed with a valve stem 51 extending upwardly therefrom and connecting with a piston 53 outside of the main passageway. Likewise the main valve is also provided with a valve stem 55 extending downwardly therefrom and similarly connecting with a piston 57 outside of the main passageway.

The upper piston is slidable in a cylinder 59 which is hydraulically coupled to the input side of the main flow passageway by a flow connection 61.

Similarly, the piston at the lower end of the downwardly extending valve stem, is housed in a cylinder 63 which is flow coupled to the flow passageway, also at the normal input side of the main valve, by a pressure connection 65.

As thus far described, the pump pressure will be applied to both pistons simultaneously and if the pistons are of approximately the same area, the pressure against one will substantially nullify the pressure applied to the other, leaving the valve spring 49 free to maintain the main valve in its closed position upon the valve seat, aided by liquid pressure against the limited exposed area of the valve. If the calibration of the valve spring is sufficiently low, such that the pressure applied to the lower piston, is greater than the combined pressure of the spring and liquid pressure on the main valve, the valve will open up on removal of hydraulic pressure against the upper piston.

This is realized by flow coupling the upper cylinder by a flow passageway 69 to the main flow passageway on the discharge side of the main valve, through the normally closed pilot valve 35 which is controlled by the solenoid 36. Upon energization of the solenoid, the pilot valve will open and thereby remove the hydraulic pressure against the upper piston and permit the main valve to open.

Designed into this valve assembly, are features permitting reversal of flow therethrough, should pressure at the output side of the valve assembly develop to a value exceeding that of the pump pressure at the input side, a condition which can develop upon initiating a work stroke of the ram.

Accordingly, and with this in mind, the normal output side of the main flow passageway is flow coupled to a check valve assembly 71 involving a housing 73, an internal valve seat 75 and a check valve 77 biased to seating position by a valve spring 79 in the housing behind the check valve.

The check valve housing is included in and made a part of the pressure connection 65 to the lower piston. Also included in such pressure connection, is a restricted section 81 capable of causing a pressure drop, with flow of liquid therethrough.

With the aforementioned valve assembly completed as described, it will become apparent that with build up of pressure in the main passageway, on the output side of the main valve, to a value exceeding pump pressure, the check valve 77 will open, and a flow will occur through the check valve to the pump side of the main valve, while increasing pressure against the lower piston 57. Being that this pressure will exceed that of the pump, it will block pump flow to the main valve and bring about a build up of pressure against the upper piston, which because of the pressure drop across the restricted section 81, will be less than that against the lower piston.

As the pressure build up at the output side of the main valve increases, the flow through the check valve will increase and increase the prevailing pressure drop across the restricted portion 81. With such increase in pressure drop, a corresponding pressure will build up against the lower piston in the direction of unseating the main valve and accordingly, when the pressure drop reaches a predetermined value, the main valve will open and a reverse flow will occur through the main passageway of the valve assembly. The significance of this will develop in the subsequent discussion of the system as a whole.

Down stream of this valve assembly 33 as viewed from the pump, the branch flow line 19 is adapted to be flow connected to tank through a normally closed valve assembly 85 controlled by a normally open pilot valve 87 which is electrically actuated by a solenoid winding 89.

In addition to the foregoing, each pump is adapted to be directly flow connected to tank through a normally closed overload relief valve assembly 93 adapted to be opened by a normally open pilot valve 95 which is electrically actuated by a solenoid winding 97.

The pilot valve associated with each overload relief valve assembly, being a normally open valve, both pumps will be flow connected to tank, thus shunting the hydraulic motors, and the machine under these conditions will be idle.

All of the valve assemblies described above, as indicated, are controlled through solenoid windings, and the electrical circuitry controlling the operation of these valve assemblies, and including the stroke control feature of the present invention, is depicted in FIGURE 3 of the drawings, to which reference will now be made.

Power is derived from main lines 101, 103 by means of a multiple switch 105, preferably foot operated and involving a pair of switches 107 and 109 sequentially operated through depression ofa foot pedal 1 l].

The first switch has a pair of normally closed contacts 113 adapted to open a circuit including a manual switch 115, a normally closed back travel limit switch 117, a pair of normally closed contacts 119, and the coil of a time delay relay 121.

Shunting the time delay relay coil, are the normally open slow acting contacts 123 of the time delay relay, and the winding 125 ofan "up relay.

ln parallel with the winding of the up relay, is a timing mechanism 127, the time adjustment of which is controlled by a manually adjustable rheostat 129. While any suitable timing mechanism may be employed, that which is the subject of patent No.3,ll54,725 has proven quite satisfactory.

Associated with the normally closed contacts of the first switch, is a pair of normally open contacts 135 which will automatically close following opening of the first pair of contacts, and these normally open contacts are in circuit with a pair of normally closed contacts 137 associated with the "up relay winding 125, and a relay winding 139.

The second switch 109, like the first, also includes a pair of normally closed contacts 141, and a pair of normally open contacts 143 to be engaged following opening of the normally closed contacts.

The normally closed contacts 141 are connected in circuit with the solenoid winding 89 associated with the valve assembly coupling the return line 19 to tank, while the normally open contacts of this second switch connect through the normally open contacts 147 of a depth limit switch 149 to the back travel limit switch 117. Normally open contacts 143 also control a circuit through a set of normally closed contacts 151 of depth limit switch 149, a pair of normally closed contacts 153 associated with time delay relay 121, to parallel circuits controlling the operation of the solenoid windings 25 which initiate a down work stroke of the ram, and the solenoid windings 97 controlling the operation of the overload relief valve assemblies 93. The down solenoids are connected in circuit through normally closed contacts 155 associated with the time delay relay 121 while the overload relief valve solenoid windings are each connected in circuit'through a normally closed microswitch 157 to open the circuit at either of these points should the ram tilt too far in one direction or the other.

The manual switch 115, unless it is desired that the ram shall cycle, will remain open normally. Therefore, the normally closed contacts 113 of the foot switch, will be ineffective.

Normally closed contacts 141 of the foot switch maintain solenoids 89 energized, which in turn block valve assemblies to return flow to tank from return lines 19, thus supporting the ram in position for a down stroke.

Upon depressing the foot switch, closing of contacts 135, energizes the relay 139 through the normally closed contacts 137 of the up relay. The relay I39 closes a pair of normally open contacts 161 shunting the switch contacts 135, to effect a holding circuit. Relay 139 has a second pair of normally open contacts 163, which are in circuit with a pair of normally closed contacts 167 of the "up" relay and a timer 169 similar to timer 127. The timer 169 thus becomes energized.

Upon opening of the normally closed contacts 141 of the lower switch, each solenoid winding 89 would normally become de-energized to open the proximate valve assembly 85 connecting the lower end of the associated hydraulic motor to tank. Upon closing of contacts 143, the overload relief valve assemblies 93, each will function to block direct flow from the proximate pump to tank. The down' solenoids 25 each will become energized to unblock its associated line 17 to the upper end ofa hydraulic motor. Thus, in the absence of other provisions, the machine would be conditioned for a normal down or work stroke at a uniform rate of advance, or what may be termed as normal press speed if the machine be a press brake.

However, to convert to two speed operation, with an initial fast rate of advance followed by conversion to normal pressing speed, the normally closed contacts 141 of this lower switch are shunted by a circuit including a manual switch in series with a pair of normally closed contacts 177 associated with the rapid advance timer 169. With the manual switch 175 closed, opening of the normally closed contacts of the lower switch 109 will be ineffective to de-energize the solenoid windings 89, and accordingly, the valve assembly 85 controlled thereby, will remain closed, while the solenoid windings 97 and 25 will become energized upon closing ofthe lower contacts 143, to respectively close the valve assemblies 93 while opening the valve assemblies 23, to connect each pump to the upper end of one of the hydraulic motors, to initiate a work stroke.

With the solenoid windings in their energized condition and causing valve assemblies 85 to block discharge to tank from the lower ends of the hydraulic motors, normal advance of the ram cannot be expected. However, were the valve assemblies 33 open to reverse flow therethrough, hydraulic fluid discharging from a hydraulic motor, could join the output from the proximate pump to supply the upper end of the hydraulic motor being supplied by that pump, and with the pump supply thus supplemented by discharge from such hydraulic motor, a rapid advance of the ram would result, which at some point in the work stroke, could be converted to the normal pressing speed, by opening of the normally closed contacts 177 in the shunt circuit.

To properly condition each valve assembly 33 for such reverse operation, its solenoid winding 36 is connected across the supply lines through normally open contacts 179 associated with the "up relay 125, such "up" relay at this stage,

being unenergized. in this condition of the up relay, the pilot valve passageway 169 is blocked, and reverse flow through the valve in the manner previously described, becomes possible. Thus conditions are right for a down or work stroke of the ram, although no movement takes place until reverse pressure on the valve assembly 33 builds up to a value exceeding the pump pressure, at which time, each hydraulic motor can discharge through its associated valve assembly 33 in reverse, the liquid thus discharged, augmenting the supply to the other hydraulic motor from one of the pumps, thus causing a rapid advance of the ram towards the work.

At a point in the work stroke, determined by the timer 169, the normally closed contacts 177, associated with the timer, will open, with the result that the solenoid windings 89 will become de-energized and cause valve assemblies 85 to open and flow connect the lines 19 to tank, which immediately converts the rapid advance speed of the ram to normal pressing speed, for the power liquid to the hydraulic motors no longer includes liquid discharged from such motors. By adjusting the rheostat of the timer, the timing of the speed change point in the work stroke, may be correspondingly altered.

When the ram reaches the lower limit of its work stroke, it engages the depth limit switch 149, in the course of which it opens the normally closed contacts 151 thereof, and closes its normally open contacts 147.

Opening of the normally closed contacts 151 of this depth limit switch, immediately opens the circuit to the solenoid windings 25 as well as the solenoid windings 97, the former causing the flow lines 17 to the upper end of each hydraulic motor to become blocked, while the latter causes the pumps to be connected through the valve assemblies 93 directly to tank.

The simultaneous closing of the normally open contacts 147 of the depth limit switch 149, brings about energization of the time delay relay 121, which, in addition to its slow acting normally open contacts 123 and its normally closed fast acting contacts 153, and 155, is also provided with a normally open pair of fast acting contacts 185 paralleling the normally open contacts 143 of the foot switch in series with the normally open contacts 147 of the depth limit switch, whereby, upon energization of the time delay relay, a holding circuit will be established, for it will be apparent that the engagement of the depth limit switch by the ram will only be temporary until the ram begins its return stroke.

In view of this, it further becomes necessary to assure that solenoid windings 97 and 25 remain de-energized for a period longer than that measured by engagement of the depth limit switch by the ram. In the case of the solenoid windings 25, such period of de-energization should last throughout the return stroke. This is accomplished through the prior energization of the time delay relay, which immediately opens its fast acting normally closed contacts 153 and 155.

Following the delay built into the time delay relay, its slow acting normally open contacts 123 will close, to energize the up relay 125.

' The up" relay, upon becoming energized, opens the normally closed contacts 137 to break the circuit to the relay 139, which in turn will release holding contacts 161, and contacts 163 in the circuit of the timer 169. Further, normally closed contacts 167 associated with the up" relay will open.

Aside from the aforementioned contacts associated with the up relay, this relay includes a pair of normally closed contacts 189 adapted to open upon energization of the relay, to de-energize the solenoid windings 31 and open valve assemblies 27, to permit discharge to tank from the upper ends of the hydraulic motors during a return stroke.

To complete conditions necessary to effect a return stroke, the overload relief valve assemblies 93 must be closed through energization of the solenoid windings 97, and to accomplish this, the up relay is provided with another pair of normally open contacts 191, which, upon closing in response to energization of the up relay, will connect these solenoid windings 97 across the power supply source.

Thus, upon closing of the slow acting contacts of the time delay relay and the resulting energization of the "up relay, the ram will begin its return stroke.

The back travel timer 127 which is connected in parallel with the up relay, will become energized simultaneously with the up relay, and accordingly, will begin tolling its time period at the instant the ram begins its return stroke. The normally closed contacts 119 in circuit with the time delay relay, the up" relay and the timer 127 itself, are associated with and controlled by the timer 127. Accordingly, upon termination of the period for which this timer may be set, these contacts will be opened to de-energize the time delay relay and the up" relay, and bring the up stroke of the ram to a halt, and before the ram will have an opportunity to engage the normal back travel limit switch 117. By adjusting the rheostat of the timer 127, the return stroke may be correspondingly adjusted.

In the case where a machine may not be provided with a two speed work stroke, the rapid advance timer 169 and circuitry associated therewith, may be eliminated, and only the feature involving the back travel timer 127 and its function in controlling the back travel of the ram will be retained.

Where a two speed work stroke is a feature of the machine,

it becomes desirable to provide for simultaneous adjustment of both timers, while reserving the ability to effect an individual adjustment of the rheostat associated with the rapid advance timer. This is explainable by the fact that, if the return stroke is increased, the time it takes for the ram to reach the point in the work stroke where speed change is desired, will also increase. Likewise, in the eventthe return stroke is shortened, the time required for the ram to reach the point of speed change will also be shortened. Therefore, it would be advantageous if both rheostats could be adjusted simultaneously in the same direction.

On the other hand, should the nature of the work change, such as a change in thickness, and it becomes desirable to merely change the point in the work stroke where the change from rapid advance to normal pressing speed occurs, an adjustment ofthe pertinent rheostat in either direction should be available to the operator.

Accordingly, to permit of such simultaneous and individual adjustments, the sliding contacts 191 and 193 of the rheostats will be fixed to a common shaft 195 controlled by a knob 196, while the resistance element 197 of the rheostat associated with the back travel timer, will be fixed as to position, while the resistance element 199 of the rheostat associated with the speed change timer may be rotatably mounted on the shaft, and controlled as to rotatable adjustment on such shaft, by a belt drive from a drive pulley 201 fixed to a shaft 203 carrying a control knob 205. A scale associated with each knob, will enable precise adjustments as desired and inasmuch as such adjustments are linear, the scale calibration may be in inches.

Pictorially represented in FIGURE 4 are the various stroke adjustments available under the present invention. The vertical axis represents stroke distance in terms of inches, while the horizontal axis is marked off in terms of seconds involved in ram travel.

Assuming a full stroke of five inches with a change from rapid advance to normal press speed at one inch from the termination of the work stroke, and that the total time involved for a complete cycle is a fraction over eleven seconds, such cycle would be represented by the heavy line 209 wherein the portion 211 representing back travel of the ram would be at a uniform rapid rate of speed comparable to the rapid advance portion 213 of the work stroke of the machine if the machine included a two speed advance stroke, wherein the terminal portion 215 of the work stroke would be at normal press speed.

if the thickness of the work to be operated on by the ram is such as who require the full return travel of the ram, and additional savings in time may be realized by shortening the return distance to four inches instead of five inches, the change can be effected by adjustment of the knob 196 which provides simultaneous adjustment of both rheostats, The magnitude of the resistance 199 in the rheostat associated with the advance stroke timer, may be such as to cause the point of change over to occur earlier or later in the stroke or approximately remain as it was. The new work stroke will accordingly start one inch closer to the work and follow the broken line 217 of FIGURE 4.

An adjustment of the other control knob 205 which serves to adjust but the one rheostat, may shift the point of speed change up or down with respect to the work, depending on the direction of adjustment. If the adjustment is made to accommodate work of a thicker character, the point of change over from one speed to another should occur earlier in the stroke as depicted by the line 219 with respect to the line 221 representing a prior setting.

Once an adjustment has been made for work of a particular thickness, it need not be changed for repeat operations on work of like thickness. However, an operator, in between work strokes, may require additional space above the work to permit of inspection or measurement, and the present invention makes provision for just such a contingency.

Referring back to the circuit diagram of FIGURE 3, this can be accomplished in a very simple manner by providing a push button switch 225 in parallel with the manual switch 115 illustrated. A momentary closing of this switch 225 will serve to energize the time delay relay 121 which in turn will, after the time delay, close its contacts 123 to energize the up" relay 125 and the back travel timer 127, causing the machine to follow the sequence of events previously traced, resulting in an additional increment of back travel of the ram, to provide the desired additional space above the work. Thereafter, upon depressing the foot switch 105, the machine will revert back to its prior schedule, as if the push button 225 had never been actuated.

lclaim:

1. A machine having a reciprocal ram, means for reciprocating said ram to produce a work stroke for operating on work and a return stroke, means for predetermining the end of travel of said ram on a work stroke, and timing means responsive to the arrival of said ram at the end of its work stroke for determining the duration of its travel on its return stroke.

2. A machine in accordance with Claim 1 characterized by said timing means being adjustable to alter the length of the return stroke.

3. A machine having a reciprocal ram, means for reciprocating said ram to produce a work stroke for operation on work and a return stroke, means for predetermining the end of travel of said ram during a Work stroke, means, during a work stroke, for driving said rarn at a rapid rate during an initial portion of said stroke and the final portion ofsaid stroke at slower rate, and means for adjusting the time of change from said rapid rate to said slower rate.

4. A machine in accordance with Claim 3, characterized by said means for adjusting the point of change as including adjustable timing means energized at the start of a work stroke for determining the time of change in the rate of travel of said ram during a work stroke.

5. A machine in accordance with Claim 1, characterized by means for adjustably dividing the work stroke into an initial portion at a fast rate of speed and a final portion at a slower speed.

6. A machine in accordance with Claim 5 characterized by said return stroke timing means including an adjustable rheostat, and said work stroke dividing means as including a timing means energized at the start of a work stroke for determining the point of change in the work stroke with said latter timing means including an adjustable rheostat.

7. A machine in accordance with Claim 6, characterized by both said rheostats being simultaneously adjustable, and means for also adjusting one of said rheostats to the exclusion of the other.

8. A machine in accordance with Claim 2, characterized by means for preadjusting the end of travel of said ram on a work stroke, and said timing means being responsive to arrival of said ram at the end of its work stroke, regardless of such preadjustment.

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