Patent Description:
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.

<CIT> discloses a prior art welding work piece processing device.

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.

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 <NUM> 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 <NUM> 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 <CIT> 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. <CIT> 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.

<CIT> for an "Ultrasonic Welding Device, Ultrasonic Welding Method, Wiring Device" discloses an ultrasonic welding which performs ultrasonic welding by pressing a tool horn <NUM> attached to an ultrasonic sliding unit <NUM> slidable relative to a body frame <NUM> against a workpiece that includes a first linear scale <NUM> for measuring a moving amount of the tool horn <NUM>, a compression spring pressing the ultrasonic sliding unit, a driving means <NUM> compressing the compression spring, a second linear scale <NUM> measuring a compressed amount of the compression spring, and a load cell <NUM> measuring a pressing force by the compression spring. When compressing the compression spring by driving the driving means <NUM>, the pressing force by the compression spring measured by the load cell <NUM>, the moving amount of the tool horn measured by the first linear scale <NUM>, and the compressed amount of the compression spring measured by the second linear scale <NUM> are fed back to the driving means <NUM> and controlled to perform ultrasonic welding while imparting an optional pressing force to the workpiece. However, when the compression spring can only be in compression, the weight of the tool horn and carriage bottom out and the system isn't able to distinguish forces exerted on the workpieces being welded at forces below the weight load of the tool horn and carriage.

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.

In an aspect, the compliance elastic member is either in compression or tension and the weight compensation elastic member is also in either compression or tension.

In an aspect, the work piece holder is disposed below the servo-actuator and the compliance elastic member and the weight compensation elastic member are disposed between the servo-actuator and the tool device and the weight compensation elastic member is disposed to support a weight of the tool device.

In an aspect, the work piece holder is disposed below the servo-actuator and the compliance elastic member and the weight compensation elastic member are disposed between the servo-actuator and a frame of the work piece processing device and the weight compensation elastic member is disposed to support a weight of the servo-actuator and the tool device.

In an aspect, the work piece holder is disposed above the servo-actuator and the weight compensation elastic member is disposed to support a weight of the work piece holder.

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 compliance elastic member in combination with the weight compensaton elastic member is deflected based on a spring deflection of these two elastic members.

In accordance with an aspect, first and second position sensors are disposed on opposite sides of the combination of the compliance elastic member and the weight compensation elastic member and coupled to the controller. The controller is configured to determine the spring deflection of the combination of these two elastic members based on positions sensed by the first and second position sensors as these two elastic members are deflected by movement of the servo-actuator.

In accordance with an aspect, a position sensor is disposed between opposed ends of the combination of the compliance elastic member and weight compensation elastic member that senses the spring deflection of the combination of these two elastic members as these two elastic members are 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 an aspect, 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.

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.

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 other member, component, element or layer, or intervening components, members, elements or layers may be present. In contrast, when a member, component, element or layer is referred to as being "directly on," "directly engaged to," "directly connected to," or "directly coupled to" another member, component, 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.).

<CIT> for "Work Piece Processing Device with Servo-Elastic Actuator System with Simultaneous Precision Force and Position Control" discloses various configurations of a work piece processing device that has a servo-elastic actuator system having simultaneous precision force and position control that moves a tool device or work piece holder to the other of the tool device and work piece holder. The servo-elastic actuator system applies force to a work piece during processing of 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: <MAT> where:.

If using a torsional spring constant, the torsional spring constant is chosen to achieve a certain torque precision by the following equation: <MAT> where:.

In an embodiment, the elastic member is in series with the servo-actuator relative to the frame, discussed in more detail below with reference to <FIG>, or in parallel with the servo-actuator on the frame itself, discussed in more detail below with reference to <FIG>. In each case, the elastic member is in series with the servo-actuator in a force transmission path and the overall spring constant is reduced relative to the surface being pushed against to raise the force sensitivity of the servo-actuator.

<FIG> show different example embodiments of such work piece processing devices having servo-elastic actuator systems. The work piece processing devices can be any device that applies force to the work piece during processing. The work piece processing devices can, for example, be 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. The work piece processing systems can also be devices where force is applied to the work piece to hold it in place during processing.

With reference to <FIG>, a work piece processing device <NUM> includes a servo-elastic actuator system <NUM>. Servo-elastic actuator system <NUM> includes a servo-actuator <NUM> and elastic member <NUM>. Servo-actuator <NUM> includes a servo-motor <NUM> and an actuator member <NUM> coupled to servo-motor <NUM> that is moved up and down (as oriented in the drawings) by servo-motor <NUM>. Servo-motor <NUM> is coupled to a controller <NUM> that controls servo-motor <NUM>. Servo-motor <NUM> is affixed to a frame <NUM> of device <NUM>. An end <NUM> of elastic member <NUM> is affixed to an end <NUM> of actuator member <NUM> and an opposite end <NUM> of elastic member <NUM> is affixed to a tool device <NUM>. Device <NUM> also includes a work piece holder <NUM>, which for example could be an anvil of an ultrasonic welder or ultrasonic tube sealer. Work piece holder <NUM> is affixed to frame <NUM> of device <NUM>. A work piece <NUM>, which has a relatively non-compliant or stiff surface <NUM>, is situated on work piece holder <NUM>. Work piece <NUM> is a work piece that is to be processed by device <NUM>. Work piece <NUM> can for example be two plastic or metal pieces that are to be ultrasonically welded together when device <NUM> is an ultrasonic welder. Work piece <NUM> can for example be a tube that is to have an end ultrasonically sealed when device <NUM> is an ultrasonic tube sealer. Tool device <NUM> is that part of work piece processing device that is pressed against work piece <NUM> by the movement of servo-actuator <NUM> to process work piece <NUM>. Tool device <NUM> may for example be an ultrasonic stack of an ultrasonic welder or an ultrasonic sealer and a tip of an ultrasonic horn of the ultrasonic stack is what physically contacts work piece <NUM>. In such cases, tool device <NUM> is energized ultrasonically to work on work piece <NUM> to process it, such by ultrasonic welding or ultrasonic sealing, as applicable.

In <FIG>, work piece processing device <NUM>' has elastic member <NUM> disposed between actuator member <NUM> and servo motor <NUM>. Otherwise, work piece processing device <NUM>' is the same as device <NUM> in <FIG>.

In <FIG>, work piece processing device <NUM> has elastic member <NUM> disposed between servo-motor <NUM> of servo-actuator <NUM> and frame <NUM> and tool device <NUM> is affixed to end <NUM> of actuator member <NUM>. Otherwise, work piece processing device <NUM> is the same as work piece processing device <NUM>.

In <FIG>, work piece processing device <NUM> has elastic member <NUM> disposed between work piece holder <NUM> and frame <NUM> of work piece processing device <NUM>. Otherwise, work piece processing device <NUM> is the same as work piece processing device <NUM>.

In <FIG>, work piece processing device <NUM> has a frame <NUM> having an upper frame portion <NUM> (as oriented in <FIG>) and a lower frame portion <NUM> with elastic member <NUM> disposed between upper frame portion <NUM> and lower frame portion <NUM>. Work piece holder <NUM> is affixed to lower frame portion <NUM>. Servo-motor <NUM> of servo-motor <NUM> is affixed to upper frame portion <NUM>. Otherwise, work piece processing device <NUM> is the same as work piece processing device <NUM>.

In operation, servo-actuator <NUM> moves tool device <NUM> into contact with work piece <NUM> and servo-actuator <NUM> will thus be pushing against the relatively non-compliant surface of work piece <NUM>. 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 <NUM> in series with servo-actuator <NUM> in the force transmission path through which force is applied against the work piece <NUM> when the tool device <NUM> is brought into contact with work piece <NUM> adds an additional compliance to the system, which reduces the overall spring constant. This increases the force sensitivity of the servo-actuator <NUM> relative to its position. This allows the force to be controlled accurately with the servo-actuator <NUM> while maintaining accurate position control. The spring constant of the elastic member <NUM> is selected to provide a desired force to position fidelity.

In servo-elastic actuator system <NUM> when the work piece <NUM> is melted during operation such as in the case of ultrasonic welding or ultrasonic sealing, elastic member <NUM> will expand after servo-actuator <NUM> stops moving tool device <NUM>, thus changing the position of elastic member <NUM> after movement of tool device <NUM> stops. That is, although the servo movement has stopped, tool device <NUM> continues to move due to the compression of elastic member <NUM>. When the work piece <NUM> melts such as two parts being welded melt, the melt itself is being compressed or held until solidification. Reactive controls, discussed in more detail below, are used to compensate for this by countering this movement of elastic member <NUM>. With this compensation, the accuracy of position is enhanced.

In embodiment, a simple algorithm using the spring constant of the elastic member <NUM> and the spring deflection is used to calculate the force being applied to work piece <NUM> when tool device <NUM> is brought into contact with work piece <NUM> by servo-actuator <NUM>. The spring deflection is the amount in distance that elastic member <NUM> is deflected. A closed loop of this calculated force of the elastic member <NUM> controls the position of servo-actuator <NUM>. By this means, precise control of the force being applied to work piece <NUM> can be achieved while simultaneously precisely monitoring position of the tool device <NUM>.

While springs and elastomers were discussed above as examples for elastic member <NUM>, 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 <NUM> positioned in different positions in the work piece processing device. <FIG> shows an example of a work piece processing device <NUM> having a plurality of elastic members <NUM> positioned in different positions in work piece processing device <NUM>. In this example, the different positions are the positions described above with reference to <FIG>, <FIG>. It should be understood that the plurality of elastic members could be positioned in other than all these positions. For example, the plurality of elastic members could be positioned in some but not all of these positions.

It should be understood that the work piece processing device could be configured so that the work piece holder is moved by servo-actuator <NUM> against tool device <NUM>.

<FIG> shows a control diagram of exemplar control logic <NUM> for control of servo-motor <NUM> of servo-elastic actuator system <NUM>. Control logic <NUM> is illustratively implemented in controller <NUM>. The control logic <NUM> uses two position sensors <NUM>, <NUM> (position encoders for example), to determine the spring deflection of elastic member <NUM>. Position sensors <NUM>, <NUM> are located in the work piece processing device so that they are on opposite sides of elastic member <NUM>. By way of example and not of limitation and with reference to device <NUM> shown in <FIG>, position sensor <NUM> senses the position of end <NUM> of elastic member <NUM> and position sensor <NUM> senses the position of end <NUM> of elastic member <NUM> as servo-actuator <NUM> moves tool device <NUM> into contact with work piece <NUM>. The difference in the positions sensed by position sensors <NUM>, <NUM> is determined by summer <NUM> which subtracts the position sensed by position sensor <NUM> from the position sensed by position sensor <NUM> with this difference being the spring deflection of elastic member <NUM>. The force being applied to work piece <NUM> is calculated at <NUM> using equation <NUM> above and the force calculated at <NUM> input to a PID (proportional-integral-differential) controller <NUM>. It should be understood that alternatively a PI (proportional-integral), P (proportional) or I (integral) controller could be used. A force set-point <NUM> is also input to PID controller <NUM>. PID controller <NUM> controls servo-motor <NUM> and thus controls the position of servo-actuator <NUM> based on the calculated force (calculated at <NUM>) of elastic member <NUM>. It should also be understood that alternatively, any appropriate closed loop control methodology using the calculated or measured force could be used.

The position sensed by position sensor <NUM> is also used to limit the maximum travel of servo-actuator <NUM>. A position set-point <NUM> is input to a summer <NUM> as is an overshoot distance compensation <NUM> and the position sensed by position sensor <NUM>. Summer <NUM> subtracts the sum of the overshoot distance compensation <NUM> and the position sensed by position sensor <NUM> from position set-point <NUM> and stops servo-motor <NUM> when the sum of the position sensed by position sensor <NUM> and the overshoot distance compensation <NUM> exceed the position set-point <NUM>. It should be understood that in additional to determining when to stop servo-motor <NUM>, this determination can also be used to initiate or terminate processing, change target force or intensity, initiate retraction of servo-actuation <NUM>, and the like. It should also be understood that these decisions can also be made based upon the calculated force (calculated at <NUM>). In an aspect, overshoot distance compensation <NUM> 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 <FIG>, or determined using an iterative method of past samples to estimate the overshoot distance compensation.

<FIG> shows a control diagram of control logic <NUM> for control of servo-motor <NUM> of servo-elastic actuator system <NUM> that is a variation of control logic <NUM> and only the differences will be discussed. A position sensor <NUM> disposed between opposed ends of elastic member <NUM>, such between ends <NUM>, <NUM> (<FIG>) of elastic member <NUM>, senses the spring deflection of elastic member <NUM> and is used to obtain the spring deflection of elastic member <NUM> instead of position sensors <NUM>, <NUM>. Position sensor <NUM> is still used in the control limiting the maximum travel of servo-actuator <NUM>.

<FIG> shows a control diagram of control logic <NUM> for control of servo-motor <NUM> of servo-elastic actuator system <NUM> that is a variation of control logic <NUM> and only the differences will be discussed. Control logic <NUM> uses a force sensor <NUM> to obtain the force being applied to work piece <NUM> instead of calculating this force based on the spring constant of elastic member <NUM> and the spring deflection of elastic member <NUM>. The force sensed by force sensor <NUM> is input to PID controller <NUM> in lieu of the force calculated at <NUM> in control logic <NUM> and control logic <NUM> thus also does not use position sensor <NUM>. Position sensor <NUM> is still used in the control limiting the maximum travel of servo-actuator <NUM>. Force sensor <NUM> is illustratively a torque sensor that senses torque applied between servo-motor <NUM> and actuator member <NUM>.

<FIG> shows a flow chart of control logic <NUM> for determining overshoot distance compensation <NUM> by using a test sample to measure an overshoot distance to use as the overshoot distance compensation <NUM>. The following discussion is in the context of a work piece processing device that is a welder, such as an ultrasonic welder, but it should be understood that it is applicable to the other types of work piece processing devices. The control logic <NUM> starts at <NUM>. At <NUM>, the control logic <NUM> determines whether the work piece processing device is being used in the measurement of an overshoot distance using a sample weld or being used for a regular weld. In this context, a regular weld is the welding of the work pieces together for their intended use. If a regular weld, the control logic <NUM> branches to <NUM> where the work piece processing device is used for a regular weld where it performs the weld with the overshoot distance compensation <NUM> (as discussed above) and then branches to <NUM> where it determines whether the work piece processing device will be used to perform another weld. If so, the control logic <NUM> branches back to <NUM>. If not, the control logic branches to <NUM> where it "stops" the work piece processing device - for example, idles the work piece processing device until it is used again. If at <NUM> the control logic determines that an overshoot distance to use as the overshoot distance compensation is to be measured using a sample weld, it branches to <NUM> where it performs a sample weld with the overshoot distance <NUM> compensation set to zero. At <NUM>, an overshoot distance is measured after the collapse of the sample weld and set as the overshoot distance compensation <NUM>. The control logic <NUM> then branches to <NUM> where the total collapse is compared to the desired collapse to see if it is in tolerance. If it is not, the control logic <NUM> branches to <NUM> where is performs a sample weld using the overshoot distance compensation <NUM>. From <NUM>, the control logic continues to <NUM>, then to <NUM> again. If the total collapse is in tolerance of the desired collapse at <NUM>, the control logic <NUM> branches to <NUM>. In this way, control logic <NUM> hones into the desired overshoot distance <NUM> by successive iterations of sample welds.

Controller <NUM> 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 <NUM> performs a function or is configured to perform a function, it should be understood that controller <NUM> is configured to do so with appropriate logic (such as in software, logic devices, or a combination thereof), such as control logic <NUM>, <NUM> or <NUM>, and also control logic <NUM> as applicable. When it is stated that controller <NUM> has logic for a function, it should be understood that such logic can include hardware, software, or a combination thereof.

The above discussed elastic member <NUM>, which will be referred to hereinafter as a compliance elastic member, can be affixed in such a way to run in the range of tension to compression. If the compliance elastic member is affixed in this way, the system can account for tooling and carriage load due to the weight of tooling (such as tool device <NUM> in <FIG> & <NUM>) and associated carriage components to which the tooling is affixed that carry the tooling as it is moved to and from the workpieces. For example as shown in the embodiment of <FIG>, tool device <NUM> is affixed to end <NUM> of compliance elastic member <NUM>. The weight of tool device <NUM> exerts a downward force on compliance elastic member <NUM> and in <FIG>, tool device <NUM> is a supported component.

A problem with the above discussed servo-elastic actuator system <NUM> in that it is often impractical to have compliance elastic member <NUM> affixed for both tension and compression. If the compliance elastic member <NUM> is just in compression as in <FIG> or just in tension as in <FIG>, the servo-elastic actuator system <NUM> cannot account for the weight of the tool device <NUM> and carriage load. Therefore, the minimum force that could be exerted by the servo-elastic actuator system <NUM> is equal to the tool device <NUM> and carriage load weight using just the compliance elastic member <NUM> in just a compression configuration or a tension configuration.

In embodiments of servo-actuator system <NUM> discussed above, a combination of two position sensors, or a position encoder, determines the compression or tension (spring deflection) of the compliance elastic member <NUM>. The compression or tension along with the spring constant of the compliance elastic member determines the force exerted on the work piece <NUM> by servo-actuator <NUM>. When the compliance elastic member <NUM> can only be in compression, the weight of the tool device <NUM> and carriage bottom out and therefore the servo-actuator system <NUM> cannot distinguish forces exerted on the workpiece <NUM> at forces below the weight load of tool device <NUM> and carriage. This situation is shown in <FIG>.

To address the foregoing, a servo-elastic actuator system <NUM>' in accordance with an aspect of the present disclosure has a weight compensation elastic member <NUM> in between the servo and the load to compensate for the weight of the load as shown in <FIG>. In this way, the servo-elastic actuator system <NUM>' can precisely control force down to zero while simultaneously precisely controlling position. Also, in an aspect, one or both ends of compliance elastic member <NUM> are not affixed to adjacent components of servo-elastic actuator system <NUM>' in the serial force transmission path but simply abuts the adjacent component or components. For example, in the embodiment shown in <FIG>, end <NUM> of compliance elastic member <NUM> abuts but is not affixed to mounting member <NUM> which is affixed to actuator <NUM>, end <NUM> of compliance member <NUM> abuts but is not affixed to mounting member <NUM>, or both. It should be understood that servo-elastic actuator system <NUM>' is otherwise the same as servo-actuator system <NUM> (including any of its variations discussed above) and the following discussion will thus focus on the differences. It should also be understood that with these differences, servo-actuator system <NUM>' can otherwise be any of the variations of servo-actuator system <NUM> described above.

The weight compensation elastic member <NUM> is disposed in servo-actuator system <NUM>' so that the spring forces exerted by the compliance elastic member <NUM> and the weight compensation elastic member <NUM> are opposed to each other, as shown <FIG>. In this regard, the weight compensation elastic member is disposed so that its spring force exerts an upward force on the tooling and carriage load.

With the addition of the weight compensation elastic member <NUM> opposed to the compliance elastic member <NUM> to compensate for the weight of the tooling and carriage load, the force to position sensitivity ratio is equal to the combination of the compliance elastic member <NUM> and the weight compensation elastic member <NUM>: <MAT> where:.

and the total travel of the weight compensation elastic member <NUM> has to account for the total tooling and carriage weight (total weight of the tooling and associated carriage components), and the total travel of the compliance elastic member <NUM> has to account for the total force that is exerted by the servo-actuator <NUM>. That is, the weight compensation elastic member <NUM> at full compression (or extension as applicable) has to account for the full effective weight of the tooling and carriage, and the compliance elastic member <NUM> at full compression (or extension as applicable) has to account for the total force exerted by the servo-actuator <NUM>. The distance traveled by each of the compliance elastic member <NUM> and the weight compensation elastic member <NUM> under full compression (or extension as applicable) is the same (Total Travel Distance) so: <MAT> and, <MAT> where:.

By this combination of weight compensation elastic member <NUM> and compliance elastic member <NUM>, the servo-elastic actuator system <NUM>' can precisely simultaneously control force and position, when the compliance elastic member <NUM> is only in compression or tension, while allowing the force to be determined to values down to zero. It should be understood that in an aspect, servo-elastic actuator system <NUM>' is controlled with any of the control logic described above with reference to <FIG> and in the case of the control logic described with reference to <FIG> and <FIG>, modified to utilize the spring constant for the combination of the compliance elastic member <NUM> and weight compensation elastic member <NUM> as the spring constant.

It should be understood that the weight compensation elastic member <NUM> and the compliance elastic member <NUM> can be any type of device having a spring force, such as a coil spring, a leaf spring, a conic spring, a pneumatic spring, or an elastomer. It should also be understood that the weight compensation elastic member <NUM> can be in a compression configuration, or in a tension configuration.

In an aspect, there are four different combinations of compliance elastic member <NUM> and weight compensation elastic member <NUM>. The compliance elastic member <NUM> is in compression only and the weight compensation elastic member <NUM> is also in compression only, as shown in <FIG>, which is a preferred embodiment. The compliance elastic member <NUM> is in compression only, and the weight compensation elastic member <NUM> is in tension only as shown in <FIG>. The compliance elastic member <NUM> is in tension only, and the weight compensation elastic member is in tension only as shown in <FIG>. The compliance elastic member <NUM> is in tension only, and the weight compensation elastic member is in compression only as shown in <FIG>.

Illustratively, the compliance elastic member <NUM> and the weight compensation elastic member <NUM> are configured together in a combination, referred to herein as elastic member combination <NUM> (<FIG>). Elastic member combination <NUM> can be located at different locations in servo-elastic actuator system <NUM>'. Elastic member combination <NUM> can be located between the servo-actuator <NUM> and the tool device <NUM>, as shown in <FIG>, in which case, the weight compensation elastic member compensates for the weight of the tool device <NUM> and associated carriage components (not shown), which is a preferred embodiment as mentioned above. Elastic member combination <NUM> can be located between the servo-actuator <NUM> and the frame <NUM> as shown in <FIG>, in which case, the weight compensation elastic member <NUM> compensates for the weight of the servo-actuator <NUM>, tool device <NUM> and associated carriage components.

In a reversed situation, where the servo-actuator <NUM> is directed upwards and the compliance elastic member is located above the work piece holder <NUM> as shown in <FIG>, illustratively between work piece holder <NUM> and frame <NUM>. In this variation, the weight compensation elastic member <NUM> compensates for the weight of the work piece holder <NUM>.

It should be understood that servo-elastic actuator system <NUM>' is useful where a servo-actuator pushes against a relatively non-compliant surface where both accurate force and position control are desirable. By way of example and not of limitation, servo-elastic actuator system <NUM>' can be used for compliant for any ultrasonic process, such as welding, cutting, staking, and swaging. Servo-elastic actuator system <NUM>' can also be used for laser welding, printing, cutting, staking or swaging, where the workpiece(s) being laser processed are clamped by the servo-actuator <NUM>. The servo-elastic actuator system <NUM>' can also be used for spin welding, vibration welding, and hot plate welding.

An advantage of adding weight compensation elastic member to a servo-elastic actuator system having a compliance elastic member is that force can be precisely controlled to a level below the weight of a supported component (s) while simultaneously precisely controlling position.

While the foregoing example embodiments of servo-elastic actuator system <NUM>' shown in <FIG> are shown as vertically oriented servo-elastic actuator systems with servo-actuator <NUM> orieinted vertically so that actuator member <NUM> travels vertically up and down, it should be understood that servo-actuator system <NUM>' can be other than vertically oriented. If servo-elastic actuator system <NUM>' is other than vertically oriented, it would illustratively include a linear guide to counteract any non-axial components of a gravity vector. That is, any components of the gravity vector that are not axial with actuator member <NUM> of the servo-actuator <NUM>. It should be understood that servo-elastic actuator system <NUM>' that is vertically oriented may also include the linear guide.

Claim 1:
A work piece processing device (<NUM>), comprising:
a tool device (<NUM>) and a work piece holder (<NUM>);
a servo-elastic actuator system (<NUM>) having simultaneous precision force and position control that moves the tool device (<NUM>) to the work piece holder (<NUM>) or the work piece holder (<NUM>) to the tool device (<NUM>);
the servo-elastic actuator system (<NUM>) including a servo-actuator (<NUM>), a compliance elastic member (<NUM>) and a weight compensation elastic member (<NUM>) disposed in a force transmission path, wherein the compliance elastic member (<NUM>) and the weight compensation elastic member (<NUM>) are disposed with respect to each other so that a spring force exerted by the weight compensation elastic member (<NUM>) is opposed to a spring force exerted by the compliance elastic member (<NUM>); and
a controller configured to determine a force being applied by the servo-actuator (<NUM>) to a work piece (<NUM>) held by the work piece holder (<NUM>) as the compliance elastic member (<NUM>) in combination with the weight compensation elastic member (<NUM>) is deflected based on a spring deflection of these two elastic members (<NUM>, <NUM>) and simultaneously control force and position of the servo-actuator (<NUM>) based on a spring constant for the combination of the compliance elastic member (<NUM>) and weight compensation elastic member (<NUM>).