Patent Application
20160114348
The present invention relates to liquid dispensing apparatus and methods. More particularly, the present invention relates to liquid dispensing apparatus and methods for dispensing single-part and multi-part compounds at precise volumes.
Single-part or one-part compounds may cure, set, or harden via a chemical reaction with an external energy source, such as radiation, heat, moisture or the like. Multi-part compounds may cure, set, or harden by mixing one or more component parts which chemically react. This reaction causes polymers to cross-link into acrylics, urethanes, and epoxies.
Polyepoxides, commonly known as epoxy resins or epoxies, are a class of reactive pre-polymers and polymers. As described above, epoxy resins may react with themselves, (e.g., one-part compound), or may react with various co-reactants, commonly referred to as hardeners or curatives, such as phenols, alcohols, and thiols, (e.g., two-part compounds). Reactions of epoxy resins, both with themselves or with a co-reactant, form a thermosetting polymer. Thermosetting polymers are generally characterized as strong, hard materials that are resistant to chemicals and temperature changes. Thermosetting polymers have a wide range of industrial applications, including adhesives, insulators, sealants, coatings, potting/encapsulation, automotive primer, use in electronic and electrical components, or the like.
Single-part or one-part compounds may be dispensed directly from their packaging, (e.g., a tube, a cartridge, or the like), whereas two-part compounds must be pre-mixed. Pre-mixing component parts ensures uniformity in the mixed components prior to a dispensing process. The pre-mixing process may be conducted manually or by an automated device.
A manual pre-mixing process generally requires a user to manually mix both component parts, for example with a mixing spatula and tray. This process is time consuming, results in a high rate of compound consumption, and is attributable to a high incidence of user rotation due to the physical labor required to mix the component parts. In addition, if the user employs a dispensing device, the user generally must load the compound into the dispensing device, which may result in a loss of some compound during a transfer.
Alternatively, an automated device may mix the two component parts and release the resulting compound into a separate compartment, such as a dispensing device, a dispensing syringe, or the like. Two-part compounds, generally characterized by limited working times, (e.g., 20 minutes or less), may begin to cure in the dispensing device and/or related components. This attribute may lead to clogging or inoperability of the dispensing device. This may result in increased maintenance, increased part replacement events, increased cleaning costs, and a high rate of liquid compound waste. One-part compounds may have similar limited working times and deficiencies. This problem may be common to high pressure dispensing valve systems with multiple component parts, such as a spool valve. Such systems are generally self-contained and are difficult to disassemble or are incapable of being disassembled. In such a system, a spool valve may become engulfed by cured compound and prevented from operating properly (e.g., the precision of liquid compound dispensed may vary substantially). Thus, there is a need for a dispensing system and related components that are designed to accommodate the limited working time of one-part and multi-part compounds.
Dispensing systems known in the art employ manual or pneumatically operated dispensing devices. Both manual and pneumatic dispensing devices use a time/pressure system.
One of the deficiencies in such a time/pressure system is the inconsistent dispensing quantity caused by internal and external variations. For example, when pressure or force is applied to the liquid compound or a cartridge piston to dispense a quantity of liquid compound, there is a reactionary exertion of force on the piston in the opposite direction. This reaction force may increase when viscosity properties of the liquid compound increase. For example, pulsed pressure may heat the material, which may change the viscosity of the liquid compound and in turn may alter the volume of liquid compound that is dispensed. In addition, the reaction force may decrease as the amount of liquid compound in the dispensing device decreases. The dispensing pressure is generally maintained at a constant level and does not take into account the change in the reaction force, resulting in a high degree of variation in the quantity of liquid compound that is dispensed.
Moreover, additional dispensing parameters may vary as the syringe empties, resulting in variations in the amount of liquid compound dispensed. Vacuum-pull back systems may also be ineffective from preventing liquid compound from dripping and may pull the liquid compound away from the tip resulting in a variation in the volume of the next dispensed amount of liquid compound. Thus, there is a need for a dispensing device and related components that are designed to dispense precise amounts of liquid compound with a high degree of repeatability while taking into account the internal and external variations impacting such as system.
A liquid compound dispensing apparatus for dispensing a controlled amount of liquid compound onto a workpiece is described. The apparatus comprises a cartridge system. The cartridge system may accept a liquid compound cartridge containing liquid compound. The apparatus also comprises a plate, having a threaded bore, positioned above the cartridge system that is movable in a first and a second direction, at least one plunger attached to the plate at a first end and attached to a piston at a second end. The piston is dimensioned to move within the liquid compound cartridge to displace liquid compound when the plate is moved in the second direction. A driving mechanism moves the plate in the first and the second directions to dispense product and comprises a motor, a threaded rod disposed through the threaded bore of the plate that is driven by a driving belt attached to the motor.
Motorized liquid dispensing apparatus 205 may be mounted to the top and front portion of robotic arm 280 via mount 207. It should be noted that any mounting design may be used to mount the motorized liquid dispensing apparatus 205 onto any compatible desktop robot. In addition, the motorized liquid dispensing apparatus 205 may be mounted to a manually movable frame for positioning by a user.
Supported by mount 207 is motor unit 209 which may be attached to and may drive driving belt 211. The motor unit 209 may be a servo motor, a stepper motor, or the like. For example, a standard 2-phase stepper motor may be used, and may provide 200 full steps per full revolution, which is the equivalent of 1.8 degrees per step. Motor resolution may be increased by increasing the number of microsteps per full step. For example, each full step may include a total of 256 microsteps, which would result in 51,200 microsteps per one full revolution, which is the equivalent of 0.007 degrees per microstep. However, as shown in Table 1, below, increasing the number of microsteps per full step may result in a decrease in holding torque of the motor.
Therefore, motor selection and configuration may depend on the resolution and torque/accuracy requirements of the user. An optimal setting may be two (2) or four (4) microsteps per full step. Such a configuration may provide a sufficient amount of holding torque (i.e., 70.71% and 38.27%) as well as a sufficient level of precision. However, it should be noted that a user may vary the application to achieve more or less precision.
Referring again to
Attached to front plate 215 are plungers 217a, 217b that terminate into pistons 219a, 219b which are driven in the “Z” direction via their attachment to front plate 215. Pistons 219a, 219b are driven into cartridge system 221 to displace the liquid compound housed in the cartridge system 221. In this way, the amount of volume of the liquid compound dispensed may be controlled by the displacement of compound in the cartridge system and the rate of speed at which it is displaced. In addition, dripping from the cartridge system may be controlled by releasing the pressure in the cartridge system by turning the motor unit in the opposite direction. Moreover, the cartridge system may be configured to automatically dispense preset volumes of liquid compound to prevent the liquid compound from curing.
Although shown as a two-part cartridge system, cartridge system 221 may be a multi-part cartridge system including more than two cartridges or may be a one-part cartridge system, having only a single cartridge. The cartridge system may also be easily detachable to accommodate different sized cartridge systems.
A mixer 223 is attached to cartridge system 221 and receives the liquid compound displaced from the cartridge system 221. In the two-part arrangement as shown, the mixer 223 serves to mix both component compounds together. The mixer may be removably attached to the cartridge system to allow for ease in cleaning the apparatus. A hose 225 is attached to mixer 223 and functions to carry the liquid compound to dispensing tip 227. Hose 225 may be removably attached to both the dispensing tip 227 and mixer 223. Hose 225 may be made from a flexible durable material such as polyurethane or the like. Hose 225 and dispensing tip 227 may be attached to Z-axis member 285 via Z-axis attachment plate 287.
Motor unit 209 may be controlled by motor driver unit 290 and control unit 293. Control unit 293 may include one or more processors, memory, and one or more programs. The one or more programs may be stored in the memory and configured to be executed by the one or more processors. The one or more programs may include instructions for operating the motorized liquid dispensing apparatus 205 and the X-Y-Z robotic table 250. The one or more programs may be presented to an operator by operator interface (OI) 295. OI 295 may include a display, a touch-sensitive surface, one or more processors, memory, and other components. The OI 295 may enable an operator to configure and control the motorized liquid dispensing apparatus 205 and X-Y-Z robotic table 250.
For example, the operator interface may allow an operator to select an operating configuration from a plurality of preset operating configurations. The associated memory may include a database of selectable operating configurations including a plurality of standard cartridge sizes, two-part compound application ratios, and the like that are selectable by the operator. Alternatively, an operator may input cartridge sizes and ratios, which may be added to the database stored in the memory.
The OI may also allow an operator to manually control movement of the front attachment plate 215 in the “Y” direction or return the front attachment plate 215 to a pre-configured home position. The OI may allow an operator to select from a plurality of dispensing speed presets. The plurality of dispensing speed presets may be preconfigured by the operator. For example, an operator may define a certain preset, (e.g., slow), by entering a specified dispensing rate, (e.g., in milliliters per minute).
The OI may also allow an operator to define auto purge parameters to dispense liquid compound during idle periods to prevent clogging. For example, an operator may set the idle time and volume of liquid compound to be purged. Additionally, the OI may also allow an operator to reset the system and return all parameters to a default setting.
The following formula may be used to determine the piston travel distance to dispense a desired volume of liquid compound in a single-part cartridge system:
where A is the cross section area of the single-part cartridge and V is the desired volume to be dispensed. To calculate piston travel distance to dispense a desired volume of liquid compound in a two-part cartridge system, the following formula may be used:
where AA is the area of a first cartridge of the two-part cartridge system, AB is the area of a second cartridge of the two-part cartridge system, and V is the desired volume to be dispensed.
For example, if the diameter of a standard 200 ml 1:1 two-part cartridge system is 37 mm per cartridge, given A=πr2, the total area of two 200 ml cartridges may be defined as A=π×18.5 mm2+π×18.5 mm2=2,150 mm2. If 100 ml (i.e., 100 mm3) of liquid compound is desired to be dispensed,
To determine the number of turns required by the threaded rod to drive the front plate the appropriate distance in the “Z” direction to achieve a dispensing of the desired volume, the following formula may be used:
In this example, since the piston travel distance=0.0465 mm, using a threaded rod with a travel distance per turn=2 mm, Equation 3 will yield a total of 0.0233 turns to dispense a desired volume of 100 ml. The number of turns may then be converted to determine an equivalent rotation angle using the following formula:
Rotation Angle=360°×number of turns, Equation 4
where one revolution is equal to 360°.
In the above example, Rotation Angle=360°×0.0233 turns=8.388°. If a 2 microstep driver is used (e.g., using 0.9000° rotations per step), the number of steps required to achieve a 8.388° rotation may be determined using the following formula:
In the above example, since the rotation angle=8.388°, and the rotations per microstep=0.9°, Equation 5 will yield 9.32 steps. In this case, if the motor is driven 10 steps, the total adhesive dispensed may be 107.5 ml, which yields an error margin of 7.5%. The error margin may be improved by using a finer threaded rod or a smaller sized cartridge.
Table 2, below, is a table comparing desired liquid dispensing volumes using a 2 microstep per full step motor configuration and 4 microstep per full step motor configuration. As shown in Table 2, the accuracy of the 4 microstep per full step motor configuration is generally more accurate than the 2 microstep motor. However, as noted above, the 4 microstep per full step motor configuration has less of holding torque when compared to the 2 microstep motor configuration.
Although features and elements are described above in particular combinations, one of ordinary skill in the art will appreciate that each feature or element can be used alone or in any combination with the other features and elements.
