DESC:FORM – 2

THE PATENTS ACT, 1970
(39 OF 1970)

COMPLETE SPECIFICATION
(Section 10, rule 13)

“IMPROVED TOGGLE CLAMP FOR INJECTION MOLDING MACHINE”

Milacron India Pvt. Ltd.
An Indian Company
93/2 and 94/1, Phase-1, GIDC Vatva,
Ahmedabad–382445, Gujarat, India

The following specification particularly describes the nature of the invention and the manner it is to be performed:
Field of Invention:
The Present invention relates to an improved toggle clamp for an injection molding machine. In particular, it relates to an invention that increases the productivity of an injection molding machine by providing enhanced control of speed and position to the toggle clamp in injection molding machine. It reduces the unwanted oscillations of the toggle clamp in an injection molding machine
Background of Invention:
A toggle clamping unit in an injection molding machine is used to clamp the mold tightly for molding plastic. The toggle clamp unit performs the following functions; Holding the mold; clamp closing movement; Keep the mold closed under force during injection; clamp opening movement to allow the parts to be ejected; and accommodates the ejector system which ejects the part out of the mold. Toggle clamps are actuated by hydraulic cylinders. These clamps utilize mechanical linkages to generate higher forces than a direct connection from a hydraulic cylinder of the same size. A toggle clamp provides high speed movements. It builds the required clamping force in shorter time and uses less volume of hydraulic oil to build the clamp force. Thus, a toggle clamp is preferred in application which needs high clamp speeds.
The conventional toggle opening and closing mechanism is high speed; however, there is less accurate control of speed during opening and closing of the toggle clamp. This result in early application of brakes during clamp closing and Opening; resulting in sluggish braking or failing to apply brakes at the specific time at Clamp opening and closing causing more oscillations in the hydromechanical system of the machine. The acceleration of the toggle clamping unit and the pressure or force and oil flow to the cylinder driving the said toggle clamping unit has a vital role in driving the toggle clamping unit efficiently. However, unwanted structural oscillations due to excess acceleration degrade the performance and at a longer time can cause fatigue. On the other hand, sluggish acceleration in pressure and flow makes the system respond slowly and hence affects the productivity of the injection molding machine. Usually the conventional toggle machines suffer with either of the two or with both issues due to a constant amount of acceleration to the toggle clamping unit and pressure or force and oil flow to the cylinder, across the whole speed span of the said toggle clamping unit.
In conventional toggle machines, this acceleration is mutually and compromisingly pre-fixed, which provides an average performance at all speed values. This has two adverse effects. Either it results in oscillation of the hydraulic system when it is accelerated for lower velocities or the system becomes sluggish enough to restrict the productivity of the machine while it has to accelerate for the higher velocities.
Also, in conventional toggle clamping units the user sets a pre-defined speed according to the product required. Normally when a user sets the speed command according to product application on the interfacing unit, the command for the said Flow Valve and the flow command to the hydraulic pump of the hydraulic drive are released by the said controller with a fixed ratio between them. It means, for a specific speed set by the user, a fixed flow command is released for the pump as well as a fixed command is released for the said Flow Valve across the clamp movement. So the ratio between these commands remains fixed across the whole travelling stroke of the Toggle clamping unit. Hence, the Conventional Toggle clamp has a limited speed gain with a static ratio between the oil flow output from the said Flow Valve and the oil flow output from the pump of the hydraulic drive.
The conventional toggle clamp struggles with unsmooth switching of the speed resulting in either uncontrolled over-stroking of position or early sluggish braking. Due to uneven spool profile in conventional toggle clamp, the breaking of the speed remains sluggish or in other words breaking is required to be set sluggish to avoid the overstroking or bangs in the machine. This produces early slowdowns or excess of position override beyond the tolerance which, either result in reduced productivity of the machine by means of increased cycle time of the machine or induces structural oscillations in machine; making the machine unstable. This behavior is often noted in conventional toggle clamps in an injection molding machine.
Thus, in the conventional toggle clamping unit the motion of the toggle clamp is more nonlinear in nature as it moves forward and in reverse direction for closing and opening the mold. During continuous operation of the injection molding machine, the toggle clamp opens and closes a number of times. During the operation, the positioning of the toggle clamp is compromised as it is compromisingly controlled. The high speed of the toggle clamp needs to be reduced when the clamp reaches near the mold closing end and near the mold opening end. During the slowing down of the speed, produces early slowdowns or excess of position override beyond the tolerance which, either result in reduced productivity of the machine. Thus, it needs accurate speed and position control. Increased machine cycle time and increased structural oscillations have a significant impact on overall productivity and life of the machine, finally accounted for affecting the business.
Prior Arts
A US patent number US5513115A discloses a control system utilizing a programmable controller for an injection molding machine in which the controller is periodically scanned in response to input signals to produce output control signals is provided with an impulse response filter arrangement. The impulse response filter senses a plurality of current and past sensor input signals to accurately predict the occurrence of a variable triggering event which will in fact be sensed by a sensor. A predictive sensor signal is then generated which is inputted to the controller in advance of the occurrence of the triggering event and at a time which corresponds to the processor scan time so that the controller generates the desired output at the precise time the triggering event occurs thus eliminating controller response latency from the control system.
However, the prior art fails to disclose accurate control of speed to avoid unsmooth switching of speed during the clamp closing movement; Resulting in either uncontrolled over-stroking of position or early sluggish braking. Hence it increases the oscillations in the machine; failing to provide stable machine.
A Chinese patent application number CN101758607A relates to a quick mould opening/closing control structure and a control method of a toggle type injection molding machine comprising an oil supply oil tank, a mould opening/closing hydraulic cylinder, a main oil pipeline, an oil return pipeline, a servo hydraulic driving device, a directional control valve and a proportional flow valve with feedback. By the device, the servo hydraulic driving device is utilized to provide pressure oil required by mould opening/closing, the pressure oil enters a mould opening/closing oil cylinder, then the set value of the mould opening/closing pressure is reasonably increased by utilizing the performance of the servo hydraulic driving device, and the speed tracing pressure of the pressure oil keeps high-speed running with large flow rate in the mould opening/closing process; the proportional flow valve with the feedback is reasonably regulated at a mould closing stop stage and a mould opening termination stage to control the magnitude of the oil return quantity, oil return resistance is provided to prohibit the movement of a movable template, the rigid impact of the template to a machine in the high-speed running process is reduced, the mould opening/closing running is stable, and the accuracy of a stop position is high; and the quick mould opening/closing control structure and the method realize the advantages of high speed, high accuracy, high efficiency, low energy consumption and the like.
However, the prior art controls the movement by controlling the oil in the return line to provide high speed of the toggle clamp. The prior art fails to provide smooth switching of speed during clamp opening and closing movement; making it unsure that it reduces oscillations or not.
A Japanese patent number JP4777232B2 discloses a mold clamping control apparatus comprises a controller 110 controlling the drive of a drive unit 107, a setting unit 111 setting advancing speed, a switching position, set mold clamping pressure, a strain sensor 114 measuring the strain generated in tie bars 104 by the mold clamping force, a calculating unit 115 calculating the mold clamping force from the strain of the tie bars 104 detected by the strain sensor 114, and a comparator 113 comparing a position of a cross-head 105 detected by a position detector 109 and the set value of the setting unit 111 to command shifting signals to the controller 110 in a mold closing step and comparing the mold clamping force calculated by the calculating unit 115 and the set mold clamping force set by the setting unit 111 to command shifting signals to the controller 110 in a mold clamping step. Further, the apparatus is constituted so as to compare the mold clamping force calculated by the calculating unit 115 and the value detected by the position detector 109, calculate mold thickness adjusting quantity by a mold adjusting calculator 116, and command a mold thickness controller 127.
However, the prior art is focused on the mold clamping closing force rather than controlling the speed and speed of the toggle clamp of the machine. Thus, the prior art fails to control the speed of the toggle clamp. Therefore, it also fails to provide smooth switching of speed to avoid position override or sluggish breaking; fails to remove the unwanted oscillations in the machine, in turn failing to provide a stable injection molding machine.
Disadvantages of the Prior Art:
The prior arts described above suffer from one or more disadvantages as listed below:
• Most of the prior arts fail to provide an improved toggle clamp for an injection molding machine.
• Many of the prior arts fail to provide accurate speed control of the toggle clamp during clamp opening and closing movement.
• Many of the prior arts fail to provide acceleration control according to the set speed of the toggle clamp.
• Many of the prior arts have to deal with sudden jerks which decreases the stability of the toggle clamp due to switching of speed from high speed to low speed during the toggle clamp opening and closing movement.
• Many of the prior art fail to provide speed controlled braking that is smooth slowing down of the toggle clamp during clamp closing movement; thereby causing unwanted oscillations in the toggle clamp which decreases the stability of the toggle clamp.
• Many of the prior art fail to reduce unwanted oscillations in the toggle clamp of the injection molding machine; thereby reducing the efficiency and the productivity of the injection molding machine.
• Uncontrolled braking of the toggle clamp in many of the prior arts fails to prevent position override of the toggle clamp, while clamp closing movement making the toggle clamp unstable and ; thereby reduces the efficiency of the toggle clamp.
• In many of the prior arts, early brakes application during clamp opening and clamp closing movement results into very slow speed that it fails to complete the faster opening and closing movement of the toggle clamp. This reduces the efficiency and the productivity of the machine.
Objects of the Present Invention:
The main object of the present invention is to provide an improved toggle clamp for injection molding machine.
Another object of the present invention is to provide an improved toggle clamp for injection molding machine that has accurate speed control of the toggle clamp during clamp opening and clamp closing movement; thereby preventing excess position override while clamping movement making the toggle clamp stable and; thereby improves the efficiency of the toggle clamp.
Yet another object of the present invention is to provide an improved toggle clamp for injection molding machine that adjusts the acceleration according to the speed of the toggle clamp; thereby providing improved efficiency and productivity of the injection molding machine.
Yet another object of the present invention is to provide an improved toggle clamp for injection molding machine that has smooth switching with of speed from high speed to low speed during the toggle clamp opening and closing movement; eliminating jerks in the toggle ; thereby providing a mechanically stable toggle clamp.
Yet another object of the present invention is to provide an improved toggle clamp for injection molding machine that has speed controlled braking; providing smooth slowing down of the toggle clamp during clamp opening movement; thereby reducing the unwanted oscillations in the toggle clamp thereby providing the stability of the toggle clamp.
Yet another object of the present invention is to provide an improved toggle clamp for injection molding machine that is stable and has reduced oscillations in the toggle clamp of the injection molding machine; thereby improving the efficiency and the productivity of the injection molding machine.
Brief description of Drawings
Fig. 1 : Shows the perspective view of existing injection molding machine
Fig. 2 : Shows perspective view of existing injection molding machine
Fig. 3a : Shows the perspective view of the present improved toggle clamp
Fig. 3b : Shows the block diagram of the improved toggle clamping unit
Fig. 4 : Shows the Speed v/s acceleration curve for clamp closing graph
Fig. 5a : Shows the Effect of acceleration on hydraulic cylinder pressure graph
Fig. 5b : Shows the Effect of modulated acceleration on hydraulic in line pressure graph
Fig. 6a : Shows the effect of acceleration during high speed operation on pressure of hydraulic cylinder
Fig. 6b : Shows the effect of acceleration during high speed operation on in line hydraulic pressure
Fig. 7 : Shows the graph of pressure drop across the hydraulic cylinder during closing of toggle clamping unit
Fig. 8a : Shows the graph of utilization of pump flow v/s flow valve
Fig. 8b : Show the graph of utilization of speed
Fig. 9a : Shows the graph of speed deceleration at lower speed
Fig. 9b : Shows the graph of speed deceleration at higher speed
Fig. 10 : Shows the pressure deceleration profile during clamp opening
Fig. 11a : Shows the effect of modulating characteristics of flow valve on spool position,
Fig. 11b : Shows the effect of modulating characteristics of flow valve on clamp speed
Meaning of reference numerals
100 : Injection molding machine
1 : A toggle clamping unit
2 : Injection unit
3 : Machine base
4 : Moving platen
5 : Die height platen
6 : Stationary platen
7 : Toggle linkages
8 : Tie bar
9 : Hydraulic cylinder
10 : Crosshead
11 : Ejector Axis
12 : Barrel
13 : Hopper
14 : Feed screw
15 : Controller
17 : Flow Valve
18 : Driver
19 : Pressure Transducer
20 : Position transducer
21 : a motor
22 : hydraulic pump

Detailed Description of the Invention
In order to provide foregoing objects, the present invention provides an improved toggle clamp for an injection molding machine. In particular, the present invention increases the productivity of an injection molding machine by providing enhanced control of speed and position to the toggle clamp in injection molding machine. It reduces the unwanted oscillations of the toggle clamp in an injection molding machine.
Referring to Fig. 1 and 2, the present improved toggle clamp for injection moulding machine utilizes an existing injection moulding machine (100) with:
• A toggle clamping unit (1),
• Injection unit (2)
Wherein, said existing injection moulding (100) machine comprises of:
• Machine base (3)
• Moving platen (4)
• Die height platen (5)
• Stationary platen (6)
• Toggle linkages (7)
• Tie bar (8)
• Hydraulic cylinder (9)
• Crosshead (10)
• Ejector Axis (11)
• Barrel (12)
• Hopper (13)
• Feed screw (14)
• Controller (15)
Wherein,
Said toggle clamping unit (1) and the injection unit (2) are based upon the machine base (3). The Moving Platen (4) and said Die Height Platen (5) connected through the Toggle Linkages (7). Further these Moving Platen (4) and Die Height Platen (5) along with the stationary Platen (6) are connected through Tie bar (8). The mold of the plastic product is mounted on the Stationary Platen (6) and the Moving Platen (4). The Moving Platen (4) guides over the Tie bar(8) and over the linear motion guideways or strip wear plates. The hydraulic Cylinder (9) is directly connected with the Crosshead (10) is further connected with the Toggle link (7).
Said Material Hopper (13) is connected to feedscrew(14); wherein the plastic raw material is fed in through the machine hopper. The barrel (12) melts the plastic material with the help of heaters mounted over it. The Feed Screw plasticize the plastic material by radially rotating at a defined angular velocity
Referring to fig. 3a and 3b, the present improved toggle clamp for injection molding machine (1) comprises of:
• Controller (15),
• Motor(21)
• Hydraulic Pump(22)
• Flow Valve (17),
• Driver (18)
• Pressure Transducer (19)
• Position transducer (20)
Wherein,
Said controller (15) controls the operation of the injection molding machine including the toggle clamping unit (1).
The pressure transducer (19) is connected in the line connecting delivery of pump (22) to the flow valve (17); A position transducer (20) is connected to the hydraulic cylinder (9); wherein the position transducer (20) senses the position of the toggle clamping unit (1). The position sensed is in the range of 0 to 2000mm and the pressure transducer (19) senses the pressure of the Pump (22); wherein the pressure sensed is in the range of 0 to 250bar. The feedback of pressure transducer (19) and position transducer (20) is given to the said controller (15). The data of both pressure of the pump(22) and position of said Toggle Clamping unit (1) provides feedback to the Controller (15) through Signals; Based on the feedback of the position of the toggle clamp and the pressure, the controller(15) modulates the pressure of the oil flow in the range of 0 to 250bar and the oil flow from pump in the range of 0 to 1000 lpm to provide accurate speed and position control of the toggle clamp; wherein the speed and position is in the range of 0 to 2000mm/sec and 0 to 2000mm respectively according to the input that is provided by the user. By providing the accurate speed control of the toggle clamping unit (1), it provides accurate position control of the toggle clamping unit (1) by preventing position override and preventing early slowdown of the toggle clamping unit (1), making the toggle clamp more stable by reducing the unwanted oscillations and; thereby improves the productivity of the toggle clamping unit(1) by 15-20% and reduces the oscillation in hydraulic pressures across the Flow valve(17) by 20-25%.
The controller (15) is connected to interfacing unit (16); wherein The user inputs the set points of pressure, speed and position in the Controller(15) through the interfacing unit (16); wherein the pressure set is in the range of 0 to 250bar, speed set is in the range of 0 to 2000mm/sec and position that is set is in the range of 0 to 2000mm. On turning ON the injection molding machine, these set points are provided, to run the injection molding machine according to end product requirements.
Said Controller (15) and interfacing unit (16) provides an interface between the user and the injection moulding machine. Said Controller (15) sends the value of pressure and speed that is set by the machine user based on his/her requirement for producing the final product in the interfacing unit (16) to the motor (21), hydraulic pump(22) and to the flow valve(17). through signals.
The controller (15) is connected to the motor(21) and hydraulic pump(22) and to the Driver (18) of the flow valve(17). Said motor(21) and hydraulic pump(22) is connected to the hydraulic cylinder (9) through a flow valve(17); wherein said hydraulic pump(22) delivers the power in terms of hydraulic oil flow to the toggle clamping unit (1); wherein the hydraulic oil flow is in the range of 0 to 1000 lpm and the pressure is in the range of 0 to 250bar.
The motor (21) rotates the hydraulic pump (22). The motor (21) not limited to its size and/or its type which means synchronous or asynchronous, variable speed or fixed speed. Similarly, the hydraulic pump (22) is not limited to its size or its internal designs, are but not limited to Axial piston pumps, Internal gear pumps, External gear pumps and Vane pumps. The oil flow from the pump is controlled by two ways: one by alternating the speed of the motor(21); or the second by the hydraulic pump(22) itself; wherein the oil flow from the pump is in the range of 0 to 1000 lpm and the speed of the motor is in the range of 0 to 3500rpm.
The oil flow from the pump controlled by the speed of the motor, the flow from the hydraulic pump remains constant. And if the oil flow from the pump is controlled by the hydraulic pump (22) itself, in such case the speed of the motor remains constant.
For the control over position of the said Toggle Clamping unit (1), based on the feedback of the pressure and position values received that is the pressure and position 0 to 2000mm respectively, the command of pressure which is in the range of 0 to 250bar and command of speed of the motor (21) which is in the range of 0 to 3500rpm or oil flow from the hydraulic pump (22) is in the range of 0 to 1000 lpm are controlled by the said controller(15). The acceleration of the pressure at the hydraulic cylinder (9) is modulated by the said controller (15) proportional to the speed value set by the user at which the said Toggle clamp axis(1) has to move. It means higher the speed value set by the user, smaller will be the acceleration time for the pressure at which the said Toggle clamp axis(1) is supposed to move. This provides faster speed gains and increases the productivity of the machine.
On the other hand, when the speed at which said Toggle clamp axis(1) has to move is required to be kept low due to limitations of the application or mold design, the said controller(15) reduces the acceleration for the pressure in order to gain the speed smoothly without any unwanted oscillation in the pressures across the said flow valve(17) and hence providing least oscillation in the machine structure. The increase in the speed of the toggle clamping unit is measured by the position feedback values from the said position transducer(20) to the controller (15).
The Controller(15) controls the oil flow to the said hydraulic cylinder(9) by controlling the flow valve(17) and oil flow coming out from the hydraulic pump(22). It controls the acceleration, deceleration and speed of the said Toggle clamping unit(1) based on the feedback of the position of the Toggle clamp unit(1) from the position transducer(20). While the said controller(15) changes the amount of pressure acceleration for closing movement in proportional to the set point of closing speed, the said controller(15) also changes the amount of deceleration of the said Toggle clamping unit(1) based on the setpoint of the opening speed and the opening position at which the said Toggle clamping unit(1) has to stop or reduce the speed. The said controller(15) adjusts the rate of deceleration for the flow valve(17) and the oil flow to the hydraulic cylinder(9) depending on the set point of the speed and position for the said Toggle clamping unit(1) by the user in the controller(15).
thereby eliminating the excess position override or bangs and early slowing down of the said Toggle clamping unit(1). This improves the stability and clamping cycle of the said toggle clamping unit (1). Therefore, the efficiency and the productivity of the injection molding machine (100) is enhanced significantly.
Said Flow Valve (17) has an electronic Driver(18); wherein the Driver (18) is connected to the controller (15) to receive signals to actuate the flow valve (17).
The said Flow valve(17) directs the amount of oil from the hydraulic pump(22) to the hydraulic cylinder(9).
The opening and closing of the said flow valve(17) is controlled by the controller(15) which communicates with the Driver(18) for opening and closing of the said flow valve(17) based on the speed and position of the said Toggle clamping unit(1)
The internal characteristics of the valve in the said Flow Valve(17) are modulated to make it more suitable for enhancing the performance of said Toggle Clamping unit in an injection molding machine. The minimum opening of the valve and the deceleration time for the valve closing has been modulated to provide the enhanced control over the speed of the said Toggle clamping unit(1). Modulating the minimum opening of the valve provides the high gain in the speed along with the optimum breaking. Modulating the deceleration time for the valve closing provides the smoother breaking without earlier slow down. The modulation of the internal characteristics of the flow valve (17) provides enhanced control of speed and position to the toggle clamp in injection molding machine; thereby reducing the unwanted oscillations of the toggle clamp in an injection molding machine; thereby making the Injection molding machine more stable, increases the productivity of the machine. So modulating the internal characteristics of the flow valve (17) improves the efficiency of the toggle clamp and thereby increases the efficiency of the injection molding machine.
The said Flow Valve (17) is a hydraulic flow direction control valve which is not limited to the size or capacity of its own which includes both direct operated single stage valve and pilot operated double stage valve and also not limited to the type of the valve characterized by number of ports, number of positions of the spools, construction of the spools for controlling the oil flow supplied from hydraulic pump to the cylinder driving the said Toggle Clamping unit (1).
The controller (15) actuates the said Flow Valve(17); wherein the flow valve (17) is controlled by the controller (15) for the oil flow remains constant according to speed set point in the Controller(15) The ratio of oil flow from the hydraulic pump(22) to the oil flow coming out of the flow valve(17) for supplying to hydraulic cylinder(9) changes dynamically with respect to the gain in the speed of the said Toggle clamping unit(1). As the speed starts to gain, this ratio starts increasing and at the max speed it is already double than it is at the start of the movement of the said Toggle clamping unit(1). Hence the speed of the said Toggle clamping unit(1) is accelerated at much faster rate with increasing the ratio between the oil flow from hydraulic pump(22) to the oil going to the said hydraulic cylinder(9) from the said flow valve(17). This increases the productivity of the said Toggle clamping unit and so is the productivity of the injection molding machine having the said Toggle clamping unit(1).
Working
1. At the start of the injection molding machine (100), according to end product requirements, the user inputs the set points for the required pressure, position and speed; wherein the pressure is in the range of 0 to 250bar, position is in the range of 0 to 2000mm and speed is in the range of 0 to 2000mm/sec respectively for which the improved toggle clamp (101) of an injection molding machine is to be run.
2. Said Controller (15) sends the set points of pressure and speed to the motor(21) and/or to the hydraulic pump(22) through the signals according to their set points input on the controller(15) set by the machine user based on his/her requirement for producing the final product.
3. The actual pressure at the hydraulic pump(22) is sensed by a pressure transducer (19). The actual position of the said toggle clamping unit (1) is sensed by the position transducer (20). The data of both pressure at the hydraulic pump(22) and position of the said toggle clamping unit (1); wherein the pressure is in the range of 0 to 250bar and position 0 to 2000mm are sent as a feedback to said Controller (15). To control the position of the said toggle clamping unit (1), based on the feedback values received from the pressure transducer (19) and position transducer (20), the command for the pressure and speed of the motor and/or flow from the pump are modulated according to set values of speed, position, pressure by the user in the said Controller(15) simultaneously and in synchronization with this, the Controller (15) sends a command to said Flow Valve (17).
The command to said Flow Valve (17) is controlled by the said controller (15) based on the speed values for the said toggle clamping unit (16) set by the user in interfacing unit (16) of the said Controller (15). The Driver(18) of said Flow Valve (17) receives this command from said controller (15) and sends the signal to actuate the spool of the said Flow Valve (17) for delivering the flow to the hydraulic Cylinder (9) which in turn is driving the said toggle clamping unit (1)
The present invention lies in controlling the toggle clamping unit (1) by controlling its clamp opening and clamp closing movements of the toggle clamping unit (1); and the controlling of the flow valve (17) to enhance the performance of the improved Toggle Clamp (101) in an injection molding machine by means of faster movements and accurate position control of the said toggle clamping unit (1) with the least unwanted oscillation providing significantly enhanced stability to the machine.
4. Clamp closing movement control
During the starting of clamp closing movement, on receiving the command from said controller (15), the hydraulic Cylinder (9) drives the toggle clamping unit (1); wherein the moving platen (4), which has one half of the mold, is moved forward and clamps the mold mounted over the stationary platen (6) when it completes the clamp closing movement. Once the clamp force is built, the Feed Screw (14) injects the melted plastic into the mold halves mounted over the Stationary Platen (6) and the Moving Platen(4).
During the clamp closing movement, according to the set points of the speed of the toggle clamping unit (1) set by the user in the interfacing unit (16), the controller (15), it modulates the acceleration in the pressure automatically based on the speed value at which the said Toggle clamping unit(1) has to move; wherein the acceleration is in the range of 0 to 10meter/sec2 wherein the acceleration in the pressure of the oil flow to the hydraulic cylinder (9) driving the said toggle clamping unit has a vital role in driving the toggle clamping unit (1) efficiently which means when the said Toggle clamping unit(1) has to move at a higher speed it means the productivity expected from an injection molding machine is high, the acceleration to the pressure is more to gain the speed quickly avoiding the sluggish start of the movement. On the other hand when the said Toggle clamping unit(1) has to move at slower speed, the acceleration to the pressure is less hence the said Toggle clamping unit(1) reach to the speed value without any unwanted oscillation in the pressures across the hydraulic cylinder(9) driving the said Toggle clamping unit(1).
Therefore when the toggle clamping unit (1) moves at slower speed, the acceleration to the pressure of the oil flow to the hydraulic cylinder (9) is less so that the toggle clamping unit remains well balanced and eliminates the unwanted pressure peaks which induces structural oscillations in the toggle clamping unit (1). When the toggle clamping unit runs at higher speed, it requires higher acceleration ; therefore requiring higher oil flow to achieve the speed quickly, the present invention does the same by releasing higher acceleration for the pressure at which the hydraulic cylinder(9) is required to move; thereby said Toggle Clamping unit (1) avoids a sluggish start and hence ensures an enhancement in productivity.
During working of the toggle clamping unit (1), the controller (15) controls the oil flow from the hydraulic pump (22) according to the speed set by the user in the said controller(15)for the said toggle clamping unit(1) wherein the oil flow is dynamically increased in proportion to the increase in the speed of the toggle clamping unit (1). As the toggle clamping unit (1) moves, the command from the controller (15) to the said Flow Valve(17) remains constant according to speed set by the user in the controller (15) however the ratio between the oil flow from the hydraulic pump(22) to the said Flow Valve(17) and the opening(or utilization) of the flow valve(17) starts increasing as the speed increases. For achieving target speed of the said Toggle clamping unit(1), set by the user in Controller(15) in the range of 0 to 2000mm/sec, value of this ratio may be 2 or a value which results in drawing maximum oil flow from the hydraulic pump(22) ; wherein the oil flow is in the range of 50 lpm to 1000 lpm; whichever is less among these two values of ratio. Hence, with the present invention, the ratio of utilization of the Pump Flow to the utilization of the flow valve (17) increases with the movement of the toggle clamping unit (1).
5. Clamp opening movement control
After the adequate cooling of the injected melt plastic in the mold, the clamp force from the hydraulic cylinder (9) is released through the Crosshead (10) and the toggle clamp unit completes the clamp opening movement. Once the clamp force is released, the mold half mounted on the Moving Platen (4) separates from the other mold half mounted over Stationary Platen(6). Once the product is molded, it is ejected out of the mold by the Ejector Axis(11).
During opening movement, said controller (15) reads the position of said Toggle clamping unit (1) through the position transducer (19) mounted on the hydraulic cylinder (9). The controller (15) also reads the set values of speed in the range of 0 to 2000mm/sec by the user in the controller(15). Based on the set point of speed and position, the controller (15) when the said Toggle clamping unit(1) has to stop at the opening position limit defined by the user in the controller(15), applies brake to the said Flow Valve (17) and to the oil flow from the hydraulic pump(22). The deceleration in speed with respect to the set point of speed is mentioned but not limited to the values mentioned in below table 2.
Set point of Speed Deceleration (meter/s2)
100% 6.8
40% 3.2
13% 2.6
Table 1
The present invention modulates the speed deceleration based on these setpoints of speed and position to provide the adequate amount of breaking without any sluggish speed profile or any additional position override for said Toggle Clamping Unit (1); thereby the deceleration is automatically modulated by the controller (15) on the basis of the speed and position of the said toggle clamping unit(1) set by the user in the controller(15). It means for an opening stroke if the speed at which the said Toggle clamping unit moves is higher then the deceleration rate of the speed is also more. On the other hand when the speed at which the toggle clamping unit(1) moves is slower then the deceleration of the speed is also slower to avoid the unpleasant or harsh stopping of the toggle clamping unit(1). This ensures the smoother stopping of the Toggle clamping unit(1) with speed range for closing and opening movement between 0 to 2000mm/sec and the clamping stroke between the range of 0 to 2000mm. This provides steadiness to the toggle clamping unit and hence to the injection molding machine.
The pattern of deceleration for the hydraulic pressure at the delivery of the hydraulic pump (22) also plays an important role while applying brakes to the running Toggle Clamp, particularly at higher speed. More particularly, while braking, the synchronization of pressure deceleration trajectory with the same of flow to the hydraulic pump (22) in hydraulic drive (22) plays a key role when the toggle clamping unit has to stop smoothly without losing on productivity.
The internal characteristics of spool like the minimum opening of the spool, the deceleration time for the valve closing, in the said Flow Valve (17) are modulated to make it more suitable for enhancing the performance of said Toggle Clamping unit (1) in an injection molding machine, wherein these internal characteristics of the valve are adjusted to 00provide the smoother braking to the said Toggle clamping unit(1) without losing on the productivity,
This modulation of the internal parameters of the valve helps to achieve the enhanced position control of its spool and hence provides the superior position control and enhanced speeds to the closing and opening movements of said toggle clamping unit (1).
COMPARISON WITH CONVENTIONAL TECHNOLOGY
1. Referring to Figure 4, the hydraulic cylinder drives said Toggle Clamping unit (1) with a proportional acceleration with respect to the set speed at which the said Toggle Clamping unit (1) is moving. While on other hand as seen in Fig. 4, the conventional toggle perceives a fixed amount of acceleration for the whole range of speed which restricts the machine efficiency with unwanted oscillations of pressures in hydraulic system and compromised productivity.
The result of this is elaborated in Figure 5(a) and (b) which represents the effect on hydraulic pressures of the system at lower clamp speeds in a conventional Toggle Clamping unit and the present toggle clamping unit. The conventional Toggle Clamp which runs on a fixed amount of acceleration to oil flow sees a pressure peak at hydraulic cylinder as shown in Figure 5(a) as well as at the tank line of the machine as shown in Figure 5(b). This induces an unwanted oscillation in the whole structure of the machine, every time when the motion is initiated. Hence, when the machine is running in production, this will happen at every cycle which can affect the reliability of a machine in a short or long duration depending on the intensity of the pressure peaks.
As a result there is also an occurrence of cavitation in conventional Toggle clamping unit which can be seen in Figure 5(b). On the other hand in the present invention, with adequate acceleration to the Pressure or force and oil flow, present invention ensures a smooth start for the said Toggle Clamping unit keeping the pressure peak at cylinder relatively quite low(Figure 5(a)) with no signs of cavitation(Figure 5(b)).
Similarly at a higher speed point, as highlighted in Figure 6(a), while accelerating the movement, the conventional toggle clamp suffers with a pressure oscillation at the cylinder which is driving it. Whereas, in the present invention Toggle Clamping unit (1), the pressure at hydraulic cylinder rises smoothly without any pressure oscillation.
The conventional toggle also sees a pressure peak followed by cavitation at the tank line while accelerating the movement as shown in Figure 6(b). Contrast to this, the present improved toggled clamping unit (101) ensures a smooth pressure profile without any cavitation.
2. As shown in Figure 7 which represents a curve of pressure drop across the hydraulic cylinder for the conventional Toggle clamping unit and the present toggle clamping unit (1) during the three phases of the speed of clamp closing movement. During Acceleration phase, the pressure drop across hydraulic cylinder is low in case of the present toggle clamping unit (1) compared to the Conventional Toggle clamping unit. This provides less restrictions to speed gain and helps to accelerate the toggle clamping unit (1) to a higher speed value.
During constant speed phase, the pressure drop remains similar in both the cases. However during deceleration phase, when the speed requires to be brought down from a high point, the pressure drop across hydraulic cylinder in the present invention is quite high in negative quadrant to have adequate amount of restriction to the opposite side of the cylinder, which helps to swiftly but smoothly bring down the speed from a high point to a low point for mold safety.
In support to this the representation of the Pump flow utilization over the clamp closing movement in the conventional Toggle clamp along with the impact on the clamp speed are elaborated in Figure8(a)(b).
Figure 8(a) describes how the present invention ensures that while accelerating the closing movement of the said Toggle Clamping unit (1), the utilization of oil flow from hydraulic pump (22) goes beyond the oil flow utilization in the conventional toggle clamp. This helps to accelerate the speed faster as shown in Figure 8(b).
3. Figure 9(a) and (b) are the speed curves at an end position of clamp opening for the conventional Toggle and the present Toggle Clamping unit. More particularly, Figure 9(a) demonstrates the scenario for the slow speed of clamp opening movement and Figure 9(b) demonstrates the scenario for the high speed of clamp opening movement.
While looking into the highlighted area in Figure 9(a), it is clearly observed that in a conventional toggle how the pre-fixed amount of braking, that is same for all speed values. This creates an unwanted peak in speed at the stop of the toggle clamp cycle. This causes unwanted oscillation in the machine structure. Whereas in the present invention the toggle clamping unit (1), no such peak is produced during application of the brakes which results in a smoother stopping of the clamping cycle. Therefore the unwanted oscillation are reduced to negligible in the present invention.
In conventional toggle clamps at higher speed, with same pre-fixed amount of braking, the speed curve of the conventional Toggle Clamping unit remains slow and sluggish as shown in highlighted area of Figure 9(b). This adds an unwanted additional time in machine clamping cycle reducing the machine productivity. Whereas, in the present invention, the improved toggle clamp ensures a steep but smooth braking providing shorter time.
4. Referring to Figure 10, the Conventional Toggle clamp has pressure deceleration profile either a steep straight and without any ramp as shown as Pattern-1 in the Figure 10 or it has an absolute linear ramp shown as Pattern-2. Hence while decelerating or releasing the load, the pressure command to the pump perceives fixed trajectories irrespective or independent of the trajectory of the command to the said Flow Valve(17) or the trajectory of flow command to the hydraulic pump in the hydraulic drive. This results in an inadequate braking with respect to various speed points of clamp opening at which the Toggle Clamp is moving. Hence the consequences are, either over stroking or under stroking or sluggish braking resulting in either more unwanted oscillation in the machine structure and thereby reduces the machine productivity.
However, the present invention resolves the above problem. The present invention makes the trajectory of the Pump pressure command identical to the same of the Pump flow command and command to the said Flow valve while decelerating or in unloading phase. As shown in Figure 10, unlike the pattern-1 and pattern-2 of conventional toggle machines, present invention has the pressure deceleration profile following in synchronization with the profile of flow supplied to the hydraulic cylinder of the said Toggle Clamping unit.
5. As a result of the modulated characteristics of the Flow Valve, the spool position control is well distinguished to remain much smoother in the said Toggle Clamping unit in comparison to the conventional toggle clamp as shown in Figure 11(a).
Due to uneven spool profile in conventional toggle clamp, the braking of the speed remains sluggish or in other words braking is required to be set sluggish to avoid the overstriking or bangs in the machine. This can be seen in Figure 11(b) where the speed of the conventional toggle clamp is forcefully reduced well before in comparison to that of the present invention.
Advantages of the invention:
The present invention provides an improved toggle clamp for injection molding machine.
It provides an improved toggle clamp for injection molding machine that has accurate speed control of the toggle clamp during clamp opening and clamp closing movement; thereby making the toggle clamp stable and; thereby improves the efficiency of the toggle clamp.
The present invention controls the acceleration according to the speed of the toggle clamp; thereby providing smoother clamp closing movements which improves the stability and productivity of the injection molding machine.
The present invention adjusts the ratio between the utilization of the flow valve and the flow from pump while clamp closing thereby providing higher gain in the speed of the toggle clamp while accelerating and quick braking while decelerating the speed for mold safety phase which improves the productivity and stability of the toggle clamp in injection molding machine.
The improved toggle clamp for injection molding machine that has smooth switching of speed from high speed to low speed during the toggle clamp opening and closing movement; eliminating jerks in the toggle; thereby providing a mechanically stable toggle clamp.
The improved toggle clamp for injection molding machine that has speed controlled braking; providing smooth slowing down of the toggle clamp during clamp opening movement; thereby reducing the unwanted oscillations in the toggle clamp thereby providing more stability to the toggle clamp.
The present invention provides smoother control of the spool position of the flow valve thereby providing smooth braking for the clamp opening movement which improves the stability of toggle clamp in injection molding machine.
Hence the present invention provides improved control of speed and position of the toggle clamp; thereby providing improved efficiency and increased productivity of the injection molding machine.
,CLAIMS:We Claim:
1. A stabilized toggle clamp (1) increasing productivity of an injection molding machine by 20%, reducing unwanted oscillations by 25% providing speed and position control, wherein the present improved toggle clamp for injection molding machine utilizes existing injection molding machine (100) comprising of :
• A toggle clamping unit (1),
• An Injection unit (2)
wherein, said existing injection molding (100) machine comprises of:
• A Machine base (3);
• A Moving platen (4);
• A Die height platen (5);
• A Stationary platen (6);
• A Toggle linkage (7);
• A Tie bar (8);
• A Hydraulic cylinder (9);
• A Crosshead (10);
• An Ejector Axis (11);
• A Barrel (12);
• A Hopper (13);
• A Feed screw (14);
said toggle clamping unit (1) and the injection unit (2) are connected to each other upon the machine base (3); said Moving Platen (4) and said Die Height Platen (5) connected through the Toggle Linkages (7) and is also connected to the stationary Platen (6) through Tie bar (8); wherein the moving platen (4) guides over the tie bar (8);
said hydraulic Cylinder (9) is directly connected with the Crosshead (10) is further connected with the Toggle link (7);
said Material Hopper (13) is connected to feedscrew(14); wherein the plastic raw material is fed in through the machine hopper; said barrel (12) is mounted with heaters to melt the plastic material;
characterized in that;
present invention (1) comprises of:
• A Controller (15);
• A Motor(21);
• A Hydraulic Pump(22);
• A Flow Valve (17);
• A Driver (18);
• A Pressure Transducer (19); and
• A Position transducer (20);
wherein,
said Pressure Transducer (19) and the Position transducer (20) are connected to the said controller(15) and controls the operation of the injection molding machine including the toggle clamping unit (1);
said controller (15) is connected to interfacing unit (16); wherein the interfacing unit (16) facilitates the input of the set points of pressure, speed and position in the Controller(15); wherein the pressure set value is in the range of 0 to 250bar, speed set value is in the range of 0 to 2000mm/sec and position that is set is in the range of 0 to 2000mm;
the pressure transducer (19) connected in line connecting pump (22) to the flow valve (17) and is configured to sense the pressure of the hydraulic Pump (22); said position transducer (20) connected to the hydraulic cylinder (9) is configured to sense the position of the toggle clamping unit (1); the pressure transducer (19) and position transducer (20) is in turn configured to provide feedback to the controller (15) through signals;
said controller (15) connected to the motor(21), hydraulic pump(22) and to the Driver (18) of the flow valve(17) is configured to receive the sensed pressure and position from pressure transducer (19) and position transducer (20) and in turn controls the speed of the motor (21) and the oil flow from the hydraulic pump(22) ; Said motor(21) and hydraulic pump(22) is connected to the hydraulic cylinder (9) through a flow valve(17);
said Flow Valve (17) is connected to said driver (18) which in turn is connected to the controller (15) and is configured to receive signals that actuates the flow valve (17); said flow valve (17) directs the oil flow from the hydraulic pump (22) to the hydraulic cylinder (9), providing controlled acceleration to the toggle clamping unit (1) at the clamp closing movement and controlled deceleration to the toggle clamping unit (1) at the clamp opening movement, receiving the sensed pressure and position.
2. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1, wherein the speed sensed is in the range of 0 to 2000mm/sec and position sensed is in the range of 0 to 2000mm.
3. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1 and 2, wherein the pressure of the hydraulic pump (22) is in the range of 0 to 250 bar, the oil flow from the hydraulic pump (22) is in the range of 0 to 1000 lpm and the speed of motor is in the range of 0 to 3500rpm to provide speed and position control of the toggle clamping unit (1).
4. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1 to 3, improves the productivity of the toggle clamping unit(1) by 15-20%
5. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1 to 4, reduces the oscillation in hydraulic pressures across the Flow valve (17) by 20-25%.
6. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1, wherein in the clamp closing movement, the acceleration of the toggle clamping unit (1) is directly proportional to the speed of the toggle clamping unit (1) and is in the range of 1 to 10 meter /second2.
7. The improved toggle clamp for an injection molding machine (1) as claimed in claim 1, wherein in the clamp opening movement, the deceleration of the toggle clamping unit (1) is directly proportional to the speed of the toggle clamping unit (1) and is in the range of 1 to 10meter /second2.
Dated this 18th day of January 2019

___________________
GOPI J. TRIVEDI
IN/PA/993
Authorized agent of the applicant
To,
The Controller of Patent
The Patent Office,
At Mumbai.