EP1762138B1

EP1762138B1 - Electronic porportioner using continuous metering and correction

Info

Publication number: EP1762138B1
Application number: EP06076914A
Authority: EP
Inventors: David Pittman; Vu Nguyen
Original assignee: Graco Minnesota Inc
Current assignee: Graco Minnesota Inc
Priority date: 2001-11-27
Filing date: 2002-11-27
Publication date: 2010-02-17
Anticipated expiration: 2022-11-27
Also published as: EP1762138A1

Description

TECHNICAL FIELD

Related applications include US Application serial number 60/186405, filed March 2, 2000 , PCT application serial number PCT/ US01/069 , filed March 2, 2001 and US Application serial number 60/333,697, filed November 27, 2001 .

BACKGROUND ART

Proportioners such as those shown and described in the above applications are sold in the market by the assignee of the instant invention under the trademark VALUEMIX®.
European patent application, published as EP 0630810 , describes a method and a device for metering out a quantity of paste-like material. The device comprises a piston housed inside a cylinder. The piston is hydraulically driven so as, in one direction of movement of the piston, to draw paste from a hopper into the cylinder in a withdrawal stroke and, in the other direction of movement of the piston, to force the paste out of the cylinder through an outlet valve during a compression stroke. The hopper comprises an outlet, which communicates with the space inside the cylinder and this outlet is blocked by the passage of the piston inside the cylinder, this constituting a type of check-valve action during at least the compression stroke. Just prior to the compression stroke, and following changeover of the piston movement, a pre-compression stroke is carried out, in which the paste is compressed while the outlet valve is still closed. This helps to force air out of the cylinder and out of the paste, which is inside the cylinder. The outlet valve is closed as the piston starts its withdrawal stroke and is opened again just prior to the compression stroke.
US 4,191,309 discloses a product proportioner for food products. The proportioner comprises a pump consisting of a pair of sleeve-and-piston arrangements, which dispense product through respective outlets in alternating fashion. It is described how the piston-and-sleeve arrangement may enter a stalled state, since the piston is not driven hard enough against the product in the sleeve so as propel the product through the outlet. However, the piston is forced with lower pressure against the product, and this produces a precompressing effect in order to remove air pockets. It is only when one of the pistons is in its fully dispensed position and is about to retract that the other piston is driven hard enough to dispense the product in its associated sleeve out through the outlet. The document describes the use of a "check valve" which is located at the confluence of the outlet passages. The valve is a dual-position valve, which allows product from one of two passages to pass into the discharge passage. In addition a valve in the discharge line acts to cut off product discharge through the outlet when a desired amount of product has been dispensed, taking into account the removal of the air pockets in the product.

DISCLOSURE OF THE INVENTION

In the instant invention, each of a pair (or more) of air-operated reciprocating piston pumps (such as those sold by the assignee of the instant invention under the trademark KING^™) is provided with a linear displacement transducer (LDT) which is capable of communicating a precise indication of the linear position of the air motor and pump rod. Also provided is a controllable valve connected to the output of each of the pumps.
Unlike the aforementioned VALUEMIX (which sequentially dispenses first one component and then the other of a plural component material), the controller of the instant invention dispenses both components (or all three if a three component material) simultaneously and maintains ratio at the end of each predetermined volume of material.
For example, if a material calls for a 2:1 (for components A and B) ratio, both valves will be open initially. The controller then looks at whichever side has hit its mark first (2 for the A side and one for the B side) and closes the valve on that side until the other side "catches up" and hits its mark.
Cavitation, air entertainment, compressibility, or poor inlet check performance all can result in a loss of correlation between pump travel and fluid dispensing. The following process is meant to correct for these issues. First, the controller determines when the pump has changed over. (This is predictable from previous cycles, or observable from the LDT reading) The controller will then close the fluid valve. This allows the pump to compress any gases and positively close the check valve. When the pump stalls, the fluid valve is reopened. The position of the pump at that point is starting value for fluid dispensed on that stroke.
These and other objects and advantages of the invention will appear more fully from the following description made in conjunction with the accompanying drawings wherein like reference characters refer to the same or similar parts throughout the several views.

BRIEF DESCRIPTION OF DRAWINGS

Figure 1 is a front perspective view of the instant invention.
Figure 2 is a rear perspective view of the instant invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In the instant invention 10, each of a pair (or more) of air-operated reciprocating piston pumps 12 (such as those sold by the assignee of the instant invention under the trademark KING^™) is provided with a linear displacement transducer (LDT) 14 which is capable of communicating (as discussed in the aforementioned applications) a precise indication of the linear position of the air motor 12a and pump rod 12b. Of course any reciprocating power source may be used to power the pump rod 12b. The LDT 14 provides an output in units of travel or resolution which may vary with the model used. In the preferred embodiment, the resolution may be in the range of ¼ to ½ inch. Also provided is a controllable valve 16 connected to the output of each of the pumps 12.
Unlike the aforementioned prior art VALUEMIX (which sequentially dispenses first one component and then the other of a plural component material), the controller of the instant invention dispenses both components (or all three if a three component material) simultaneously (at least initially) and maintains ratio at the end of each predetermined volume of material.
For example, if a material calls for a 2:1 (for components A and B) ratio, both valves will be open initially. The controller 18 then looks at whichever side has hit its mark first (2 units of travel for the A side and one for the B side) and closes the valve on that side until the other side "catches up" and hits its mark. Thus, the system truly controls both sides rather than letting one run and trying to match the other as commonly occurs.
Cavitation, air entertainment, compressibility, or poor inlet check performance all can result in a loss of correlation between pump travel and fluid dispensing. The following process is meant to correct for these issues. First, the controller determines when the pump has changed over. (This is predictable from previous cycles, or observable from the LDT reading) The controller will then close the fluid valve. This allows the pump to compress any gases and positively close the check valve. When the pump stalls, the fluid valve is reopened. The position of the pump at that point is starting value for fluid dispensed on that stroke.
The air pressure can be varied so as to effectively run both pumps simultaneously and continuously. Also, the control may be set to control flow rather than pressure. If desired and sufficient length is available, the hose may be used as an integrator to aid in mixing. In another alternative embodiment, the lower volume side or material may be run at a higher pressure and with a single dosing valve.
The interface is divided into three sections. The basic section are a run and a stop button. Under a cover are a display that shows ratio, and a cycle counter and a 4-position rotary switch for

Run
Test
Independent Run A Pump
Independent Run B Pump
5-digit 7-segment with decimal point to display ratio
Lighted "Start" button (light while running) - momentary, non-latching
Stop button - momentary, non-latching
Ratio setting increments are 0.1, range is 0 to 10.
Error code displayed in digital display (e.g. E:27).

Following are operational modes:

Run (proportion): Open both fluid valves. Monitor travel of each pump. If one pump has traveled disproportionately ahead of the other pump, close its fluid valve. Monitor travel of the remaining pump. Once the trailing pump has caught up, open the other fluid valve. Repeat.
Within the run mode, and pump test mode the controller will compensate for physical problems associated with top change-over. Cavitation, air entertainment, compressibility, or poor inlet check performance all result in a loss of correlation between pump travel and fluid dispensing. The following algorithm is meant to correct for these issues.
Determine when the pump has changed over. (This is predictable from previous cycles, or observable from the LDT reading) Close the fluid valve. This allows the pump to compress any gases and positively close the check valve. When the pump stalls reopen the fluid valve. The position of the pump at that point is starting value for fluid dispensed on that stroke.
Independent run: Run any one (and only one) pump just like a normal pump. Fluid valve is constantly open throughout cycle. Do not repeat change-over in less than 500ms (Runaway control). Stop after 5 cycles.
Pump test: Run each pump through 3 full cycles plus extra distance necessary to compensate for top change-over error. (See Run Mode for description of change-over error compensation algorithm). Close the fluid valve once during the middle of each stroke and measure time delay until the pump stalls. This checks for a failed fluid valve, piston packings or check valve, or inlet valve failure.
Stop: Fluid valves and air valves closed.
Error: Special case of the stop mode. Fluid valves and recirculation valves closed. Error must be " acknowledged".
Calibration: Each LDT has a different offset and gain. The controller needs this data to work properly.

Claims

A method for compensating for changeover in a reciprocating pump (12) having a check valve, where said pump has a displacement transducer (14) and a fluid valve (16) at the outlet of said pump, the method comprising the steps of:
closing said fluid valve (16) as the pump reaches changeover to allow said pump to compress any gases and positively close the check valve, the pump being allowed to stall, upon which the fluid valve (16) is opened; and

disregarding any travel and imputed flow during the portion of the cycle when said fluid valve is closed.