Patent Application
20170129062
The present disclosure relates to a work piece processing device with a servo-elastic actuator system having simultaneous precision force and position control.
This section provides background information related to the present disclosure which is not necessarily prior art.
Work piece processing devices as used herein are devices that apply force to a work piece (or work pieces) during processing of the work piece. In some devices, the force is part of and contributes to the performance of the work on a work piece (or work pieces), such as in welding, and in other cases, the force is not part of the performance of the work on the work piece but rather is applied to clamp the work piece in place as the work is performed on the work piece. Such work processing devices have actuators that apply the force to the work pieces such as by moving a tool against the work piece or applying a clamp to the work piece to hold it in place during processing. Such work piece processing devices can include devices for ultrasonic, vibration, laser, thermal, spin or infrared processing of plastics or metal where force is applied to the work piece, such as welding, staking, swaging, and cutting. Work piece processing devices that apply force to the work piece during processing need actuators that can control both force and position.
Pneumatic actuators are good at providing a constant force regardless of the actuator's position when in contact with a relatively stiff surface, but are not very precise at controlling position. Servo-actuators on the other hand are precise at controlling position but not that good at controlling force when in contact with a relatively non-compliant or stiff surface. A servo-actuator is a mechanism that provides position controlled motion in a mechanical system in response to an electrical input signal using feedback of an output of the servo actuator for position control.
Previous use of servo-actuators for ultrasonic welding, vibration welding, laser welding, thermal welding, spin welding, infrared welding and ultrasonic cutting could control position very accurately, on the order of a thousandth of an inch, but could not control force to under plus or minus 40 pounds. The problem arises from the relative non-compliance of the material of the work piece being pressed against during welding. Even though the servo-actuators can resolve the position to within a thousandth of an inch, this small relative motion, given the stiffness of the material being pressed against, results in a large change in force—on the order of about 40 pounds for a typical piece of plastic, and even higher for a piece of metal. This problem of force to position sensitivity is inherent with servo-actuators when pushing against a relatively non-compliant surface, regardless of how good the control system is for the servo-actuator.
Servo actuators often have a torque control mode that gives a degree of control of the force, such as that described in U.S. Pat. No. 8,720,516 for “Ultrasonic Press Using Servo Motor with Delayed Motion.” But again, because of the noncompliance of the surface being pushed against, the force varies by a high percentage of the total load.
One well understood method in the prior art to control force precisely with a servo-actuator is to have the servo-actuator press against a long travel spring. This gives very good force control, but does not have any position control. U.S. Pat. No. 4,817,848 for “Compliant Motion Servo” discloses the use of a long travel spring with a servo-actuator to control force, but switches over to a closed loop position control at the end of motion, and therefore loses control of force at the end of the process.
In many processes, there is a need for precise force control of actuation, while maintaining precise position control. Specifically, in ultrasonic, vibration, laser, thermal, spin or infrared processing of plastics or metal where force is applied to the work piece, such as welding, staking, swaging, and cutting, there is a need for simultaneous precise force control and position control of actuation.
This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features.
In accordance with an aspect of the present disclosure, a work piece processing device includes a tool piece, a work piece holder, and a servo-elastic actuator system having simultaneous precision force and position control that moves one of the tool piece and the work piece holder to the other of the tool piece and work piece holder. In accordance with an aspect, the servo-elastic actuator system includes a servo-actuator and one or more elastic members mechanically coupled with each other (directly or indirectly through another component or components) in a force transmission path. In an aspect, the force transmission path is a linear force transmission path and in an aspect is a rotational force transmission path (i.e., a torque transmission path).
In accordance with an aspect, the servo-actuator includes a servo-motor and an actuator member coupled to the servo-motor. The servo-motor and the work piece holder are affixed to a frame of the work piece processing device, an end of the elastic member is affixed to an end of the actuator member and an opposite end of the elastic member affixed to the tool device.
In accordance with an aspect, the servo-actuator includes a servo-motor and an actuator member coupled to the servo-motor. The elastic member is disposed between the servo-motor and a frame of the work piece processing device with the tool device affixed to an end of the actuator member, the work piece holder affixed to the frame.
In accordance with an aspect, the servo-actuator includes a servo-motor and an actuator member coupled to the servo-motor. The elastic member is disposed between the work piece holder and a frame of the work piece processing device and the tool device is affixed to an end of the actuator member.
In accordance with an aspect, the servo-actuator includes a servo-motor and an actuator member coupled to the servo-motor. The elastic member is disposed between lower and upper portions of a frame of the work piece processing device. The work piece holder is affixed to the lower portion of the frame and the servo-motor is affixed to the upper portion of the frame and the tool piece affixed to an end of the actuator member.
In accordance with an aspect, the servo-actuator includes a servo motor and an actuator member coupled to each other through an elastic member. The work piece holder is affixed to the lower portion of the frame and the servo-motor is affixed to the upper portion of the frame and the tool piece affixed to an end of the actuator member.
In accordance with an aspect, the elastic member is in one of torsion, compression or tension as the servo actuator moves.
In accordance with an aspect, the work piece processing device includes a plurality of elastic members where each elastic member is in one of torsion, compression or tension as the servo actuator moves. In accordance with an aspect, elastic members are disposed in different ones of two or more of the above locations.
In accordance with an aspect, a controller is coupled to the servo-actuator wherein the controller is configured to control movement of the servo-actuator to an end position based on force being applied to a work piece held by the work piece holder and a force set-point, moving the servo-actuator to maintain the force being applied to the work piece at the force set-point once the force being applied to the work piece reaches the force set-point, and stopping movement of the servo-actuator when the servo-actuator reaches a maximum travel.
In accordance with an aspect, the controller is configured to determine the force being applied to the work piece as the elastic member is deflected based on a spring deflection of the elastic member.
In accordance with an aspect, first and second position sensors are disposed on opposite sides of the elastic member and coupled to the controller. The controller is configured to determine the spring deflection of the elastic member based on positions sensed by the first and second position sensors as the elastic member is deflected by movement of the servo-actuator.
In accordance with an aspect, a position sensor is disposed between opposed ends of the elastic member that senses the spring deflection of the elastic member as the elastic member is deflected. The position sensor is coupled to the controller.
In accordance with an aspect, a force sensor is coupled to the controller that senses the force being applied to the work piece. In accordance with an aspect, the force sensor is a torque sensor that senses torque applied between the servo-motor and the actuator member.
In accordance with an aspect, the controller is configured to limit maximum travel of the servo-actuator based on a position sensed by a position sensor and a position set-point.
In an aspect, the controller is configured to limit maximum travel of the servo-actuator based on an overshoot distance compensation as well as the position sensed by the position sensor and the position set-point.
In accordance with an aspect of the present disclosure, the work piece processing device is any of an ultrasonic welder, a vibration welder, a laser welder, a thermal welder, a spin welder, an infrared welder, or an ultrasonic cutter
Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. The orientation of the drawings are not intended to limit the actual orientation of the servo-elastic actuator system relative to the work piece being processed. Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,” “lower,” “above,” “upper,” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially relative terms may be intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the example term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
Example embodiments will now be described more fully with reference to the accompanying drawings.
In accordance with an aspect of the present disclosure, a work piece processing device in which force is applied against the work piece during processing has a servo-elastic actuator system that applies the force to the work piece. The servo-elastic actuator system includes an elastic member, such as a spring or elastomer, mechanically disposed with a servo-actuator in a force transmission path to create additional compliance in the system in order to adjust force versus position sensitivity ratio. This allows the force to be controlled accurately with the servo-actuator, while retaining accurate position control. In should be understood that the force transmission path can be a linear force path or a rotational force transmission path (that is, a torque transmission path).
The servo-actuator controls position to a given precision. The spring constant of the elastic member if using a linear spring constant is chosen to achieve a certain force precision by the following equation:
K=ΔF/Δx (1)
where:
If using a torsional spring constant, the torsional spring constant is chosen to achieve a certain torque precision by the following equation:
K
⊖
=ΔT/Δ⊖ (2)
where:
In an aspect, the elastic member is in series with the servo-actuator relative to the frame, discussed in more detail below with reference to
With reference to
In
In
In
In
In operation, servo-actuator 104 moves tool device 120 into contact with work piece 124 and servo-actuator 104 will thus be pushing against the relatively non-compliant surface of work piece 124. When pushing against a relatively non-compliant surface, the ratio of force to position sensitivity of the servo-actuator is determined by the spring constant of the material being pushed upon. Having elastic member 106 in series with servo-actuator 104 in the force transmission path through which force is applied against the work piece 124 when the tool device 120 is brought into contact with work piece 124 adds an additional compliance to the system, which reduces the overall spring constant. This increases the force sensitivity of the servo-actuator 104 relative to its position. This allows the force to be controlled accurately with the servo-actuator 104 while maintaining accurate position control. The spring constant of the elastic member 106 is selected to provide a desired force to position fidelity.
In servo-elastic actuator system 102, elastic member 106 will expand after servo-actuator 104 stops moving tool device 120, thus changing the position of elastic member 106 after movement of tool device 120 stops. Reactive controls, discussed in more detail below, are used to compensate for this by countering this movement of elastic member 106. With this compensation, the accuracy of position is the original position resolution of servo-actuator 104.
In an aspect, a simple algorithm using the spring constant of the elastic member 106 and the spring deflection is used to calculate the force being applied to work piece 122 when tool device 120 is brought into contact with work piece 122 by servo-actuator 104. The spring deflection is the amount in distance that elastic member 106 is deflected. A closed loop of this calculated force of the elastic member 106 controls the position of servo-actuator 104. By this means, precise control of the force being applied to work piece 124 can be achieved while simultaneously precisely controlling position of the tool device 120.
While springs and elastomers were discussed above as examples for elastic member 106, it should be understood that elastic member can be any type of member that has the requisite spring constant (linear or torsional as applicable), and can include combinations of elements such as a plurality of elastic members 106 positioned in different positions in the work piece processing device.
It should be understood that the work piece processing device could be configured so that the work piece holder is moved by servo-actuator 104 against tool device 120.
The position sensed by position sensor 504 is also used to limit the maximum travel of servo-actuator 104. A position set-point 514 is input to a summer 516 as is an overshoot distance compensation 518 and the position sensed by position sensor 504. Summer 516 subtracts the sum of the overshoot distance compensation 518 and the position sensed by position sensor 504 from position set-point 514 and stops servo-motor 108 when the sum of the position sensed by position sensor 504 and the overshoot distance compensation 518 exceed the position set-point 514. In an aspect, overshoot distance compensation 518 is be determined using a test sample to measure an overshoot distance to use as the overshoot distance compensation, discussed in more detail below with reference to
Controller 112 can be or includes any of a digital processor (DSP), microprocessor, microcontroller, or other programmable device which are programmed with software implementing the above described logic. It should be understood that alternatively it is or includes other logic devices, such as a Field Programmable Gate Array (FPGA), a complex programmable logic device (CPLD), or application specific integrated circuit (ASIC). When it is stated that controller 112 performs a function or is configured to perform a function, it should be understood that controller 112 is configured to do so with appropriate logic (such as in software, logic devices, or a combination thereof), such as control logic 500, 600 or 700, and also control logic 800 as applicable. When it is stated that controller 112 has logic for a function, it should be understood that such logic can include hardware, software, or a combination thereof.
When a member, component, element or layer is referred to as being “on,” “engaged to,” “connected to,” or “coupled to” another member, component, element or layer, it may be directly on, engaged, connected or coupled to the othermember, component, element or layer, or intervening components, members, elements or layers may be present. In contrast, when a member, compoinent, element or layer is referred to as being “directly on,” “directly engaged to,” “directly connected to,” or “directly coupled to” another member, compoinent, element or layer, there may be no intervening members, components, elements or layers present. Other words used to describe the relationship between members, components, elements or layers should be interpreted in a like fashion (e.g., “between” versus “directly between,” “adjacent” versus “directly adjacent,” etc.).
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
This application claims the benefit of U.S. Provisional Application No. 62/253,742 filed on Nov. 11, 2015. The entire disclosure of the above application is incorporated herein by reference.
| Number | Date | Country | |
|---|---|---|---|
| 62253742 | Nov 2015 | US |
