Measurement control device and measurement control method

An approach controller (234) of a coordinate measuring instrument enables a position control loop (RP) and drives an actuator (133) so that a force sensor (1) is brought to a close position under a position control. When recognizing that the force sensor (1) reaches the close position, a contact controller (235) controls a switch (227) to enable a force control loop (RF) and drives the actuator (133) to bring the force sensor (1) into contact with a workpiece under a force control.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a measurement control device, a contour measuring instrument and a measurement control method. For example, the present invention relates to a measurement control device, a contour measuring instrument and a measurement control method used when a contour such as a profile and roughness of a surface of a workpiece is measured using a vibrating sensor.

2. Description of Related Art

There have been known contour measuring instruments that measure a contour such as a profile and roughness of a surface of a workpiece by scanning the surface of the workpiece, the contour measuring instruments including a roughness measuring instrument, a profile measuring instrument, a roundness measuring instrument and a coordinate measuring instrument.

In such measuring instruments, a vibrating force sensor (hereinafter, abbreviated as a force sensor)1as shown inFIG. 7has been used, the sensor detecting a surface of a workpiece based on a minute displacement of a contact section contacting with the surface of the workpiece.

The force sensor1shown inFIG. 7includes a metal base2, a stylus3integrally formed on the base2, a vibrating element4that vibrates (in an axial direction) the stylus3and a detecting element5that detects a vibration state of the stylus3and outputs the vibration state as a detection signal. A contact point (contact section)6formed of a diamond chip or ruby is fixedly bonded to a tip end of the stylus3. The vibrating element4and the detecting element5are formed by one piezoelectric element, the piezoelectric element fixedly bonded on each of front and back surfaces of the base2.

As shown inFIG. 8, when a vibration signal Pi (voltage signal) having predetermined frequency and amplitude is applied to the vibrating element4of the force sensor1, the detecting element5obtains a detection signal Qo (voltage signal) having predetermined frequency and amplitude.

FIG. 9shows variation in the amplitude of the detection signal Qo caused by contact with a workpiece W. In a state where the stylus3is not in contact with the workpiece W, when the vibration signal Pi having a certain amplitude at a resonance frequency of the stylus3is applied to the vibrating element4, the stylus3resonates, which provides the detection signal Qo having an amplitude Ao to the detecting element5. When the stylus3comes into contact with the workpiece W, the amplitude of the detection signal Qo attenuates from Ao to Ax.

A relationship between an attenuation rate k (Ax/Ao) and a measuring force is shown inFIG. 10.

Here, description will be given by taking an example of a case where the detection signal Qo in a contact state of the stylus3(force sensor1) and the workpiece W is attenuated to 90% of the non-contact state (i.e., attenuation rate k=0.9). As seen from the relationship inFIG. 10, the measuring force in the contact state is 135 [μN].

Accordingly, by controlling with an actuator or the like a distance between the force sensor1and the workpiece W such that the attenuation rate k is always constant when the force sensor1contacts with the workpiece W, a profile and roughness of the workpiece W can be measured with a constant measuring force.

In the contour measuring instrument having the force sensor1as described above, there has been a demand for an arrangement capable of minimizing overshoot in the contact state of the force sensor and the workpiece.

Meanwhile, there have also been known contour measuring instruments having a force sensor that can perform measurement using a principle similar to that of the force sensor1or a principle different therefrom (see, for instance, Document 1: JP-A-2000-180156, Document 2: JP-A-2005-43177 and Document 3: JP-A-2004-77307).

There have also been known arrangements for controlling a position of a certain component (see, for instance, Document 4: JP-A-2001-166831, Document 5: JP-A-2000-89829 and Document 6: JP-A-2000-11563).

In the arrangement disclosed in Document 1, the stylus is brought into contact with a surface of the workpiece. Then, a detecting electrode detects a measuring force of the stylus and transmits a detection signal to a measuring force control circuit via a detection circuit. In the measuring force control circuit, a difference between a signal value corresponding to a preset measuring force and the signal from the detection circuit is calculated and a measuring force adjusting mechanism is controlled, thereby maintaining the measuring force between the stylus and the workpiece to a predetermined value.

In the arrangement disclosed in Document 2, a control device receives a command value from the coordinate measuring instrument, position information in X, Y and Z directions from a scale provided on a three-axis slider and an actual measuring force detected by a strain gauge. Then, an actuator is controlled by a feed-back control such that a difference between the actual measuring force detected by the strain gauge and a measuring value commanded from the coordinate measuring instrument becomes small.

In the arrangement disclosed in Document 3, after a position control is started, a Z-axis slider is brought closer to a workpiece until a predetermined time period elapses under a condition in which a pressure is maintained to a contact-judging pressure. When the predetermined time period elapses, the Z-slider is stopped. Then, an average value of the pressure during the predetermined time period is obtained, where the control of the Z-slider is switched from the position control to a pressure control when the average value reaches a target pressure.

In the arrangement disclosed in Document 4, a position command issuing section outputs, as a position command, target position data of a position to which a movable body is desired to move. A speed feed-forward pulse setting section arbitrarily sets amplitude, range and cycle of a pulse. After the position command issuing section outputs the position command, the speed feed-forward pulse setting section outputs the pulse set by the speed feed-forward pulse setting section as a speed feed-forward signal. Then, the movable body is controlled by an attenuator or the like so as to be positioned at the target position based on the speed feed-forward signal.

In the arrangement disclosed in Document 5, the overshoot is controlled to be small by a distribution mechanism that feeds back a motor-rotation-angle position signal of a motor when an absolute value of a positional deviation between a position command and a fed-back signal is large while feeds back a position signal of a machine movable section when the absolute value of the positional deviation is small.

The arrangement disclosed in Document 6 includes a coarse actuator that positions a head at a predetermined position on a disc and a fine actuator that finely adjust the position of the head that has been positioned by the coarse actuator. Then, by controlling the coarse and fine actuators, the overshoot of the position of the head is suppressed.

However, in the arrangements of Documents 1 and 2, since measuring force of the force sensor is detected and a position of the force sensor is controlled based on the detected measuring force, the overshoot in the contact state of the force sensor and the workpiece might be large, resulting in breakage of the force sensor and the workpiece.

In the arrangement of Document 3, since the entire Z-slider is controlled, the overshoot might become large due to the inertia of the Z-slider, resulting in the breakage of the force sensor and the workpiece.

In the arrangement of Document 4, since the position of the movable body is controlled based on the position command of the preset target position, it might be difficult to apply the arrangement to the contour measuring instrument in which a distance between a current position of the force sensor and the workpiece varies in accordance with a contour of the workpiece.

In the arrangement of Document 5, since a ratio of the magnitude of the fed-back signal is determined by the positional deviation between the position command and the fed-back signal, the application of the arrangement to the contour measuring instrument lowers the speed of bringing the force sensor closer to the workpiece, which might result in degradation of measuring efficiency in a measurement with a lot of measuring points.

In the arrangement of Document 6, since the position is controlled by moving the coarse and fine actuators, the control of the two actuators might be complicated when the arrangement is applied to the contour measuring instrument.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a measurement control device, a contour measuring instrument and a measurement control method that can suppress overshoot in a contact state of a force sensor and a workpiece with a simple arrangement and without degrading measuring efficiency.

A measurement control device according to an aspect of the present invention includes: a probe including a force sensor that detects a measuring force generated when the probe contacts with a workpiece and outputs the measuring force as a force detection signal, a position detector that detects a measuring position of the workpiece detected by the force sensor and outputs the measuring position as measuring position information, and a force sensor moving unit that moves the force sensor relative to the workpiece; a force control loop that compares the force detection signal from the force sensor as a force fed-back signal with a set force value and drives the force sensor moving unit such that the force fed-back signal becomes equal to the set force value; a position control loop that compares the measuring position information from the position detector as a position fed-back signal with a set position value and drives the force sensor moving unit such that the position fed-back signal becomes equal to the set position value; a control loop switcher that enables one of the force control loop and the position control loop; an approach controller that controls the control loop switcher to enable the position control loop and drives the force sensor moving unit to position the force sensor in a close position that is close to the workpiece in such a manner that the position fed-back signal becomes equal to the set position value; and a contact controller that, when recognizing that the force sensor is brought to the close position to the workpiece under the control of the approach controller, controls the control loop switcher to enable the force control loop and drives the force sensor moving unit to bring the force sensor into contact with the workpiece in such a manner that the force fed-back signal becomes equal to the set force value.

According to the aspect of the present invention, the approach controller enables the position control loop and drives the force sensor moving unit such that the position fed-back signal becomes equal to the set position value, thereby positioning the force sensor at the close position to the workpiece. When recognizing that the force sensor is positioned at the close position to the workpiece, the contact controller controls the control loop switcher to enable the force control loop and drives the force sensor moving unit such that the force fed-back signal becomes equal to the set force value, thereby bringing the force sensor into contact with the workpiece.

With the arrangement, by switching the control from the position control to the force control before the force sensor contacts with the workpiece and by bringing the force sensor into contact with the workpiece under the force control, the overshoot at the time of contact can be suppressed as compared to a related art arrangement in which the force control is performed after the force sensor contacts with the workpiece.

In addition, since only the force sensor is moved instead of the entire probe, the inertia in moving the fore sensor can be reduced, so that an increase of overshoot due to the inertia can be suppressed.

Since a moving amount required in bringing the force sensor into contact with the workpiece does not have to be preset, the present invention can be applied to a contour measuring instrument in which a distance between a current position of the force sensor and the workpiece varies in accordance with the contour of the workpiece.

Further, since the force sensor is brought close to the workpiece under the position control and then the control is switched to the force control, measuring efficiency can be prevented from degrading even in a measurement with a lot of measuring points.

Still further, the force sensor can be moved relative to the workpiece by the single force sensor moving unit, so that an arrangement for controlling the movement will not be complicated.

Accordingly, the overshoot in contacting the force sensor with the workpiece can be suppressed with such a simple arrangement and without degrading the measuring efficiency.

In the measurement control device according to the aspect of the present invention, it is preferable that the force sensor includes a stylus having a contact section on a tip end thereof, a vibrating element that vibrates the stylus and a detecting element that detects a vibration state of the stylus and outputs the vibration state as a detection signal.

According to the aspect of the present invention, the force sensor includes the stylus, the vibrating element and the detecting element.

The arrangement can suppress the overshoot in contacting a so-called vibrating force sensor, which can perform highly accurate measurement with a small measuring force, with the workpiece, thereby providing a measuring control device realizing measurement with even higher accuracy.

A contour measuring instrument according to another aspect of the present invention includes: the above-described measurement control device of the present invention; a probe holder that holds the probe of the measurement control device; a probe-relative-movement unit that relatively moves the probe holder and the workpiece; a probe position controller that controls the probe-relative-movement unit to position the force sensor of the probe and the workpiece such that the force sensor and the workpiece are positioned remoter as compared to the close position in the control of the approach controller of the measurement control device, in which when recognizing that the force sensor and the workpiece are positioned remoter as compared to the close position in the control of the probe position controller, the approach controller positions the force sensor and the workpiece close to each other.

According to still another aspect of the present invention, a measurement control method using a measurement control device including: a probe that includes a force sensor that detects a measuring force generated when the probe contacts with a workpiece and outputs the measuring force as a force detection signal, a position detector that detects a measuring position of the workpiece detected by the force sensor and outputs the measuring position as measuring position information, and a force sensor moving unit that moves the force sensor relative to the workpiece; a force control loop that compares the force detection signal from the force sensor as a force fed-back signal with a set force value and drives the force sensor moving unit such that the force fed-back signal becomes equal to the set force value; a position control loop that compares the measuring position information from the position detector as a position fed-back signal with a set position value and drives the force sensor moving unit such that the position fed-back signal becomes equal to the set position value; and a control loop switcher that enables one of the force control loop and the position control loop includes: controlling the control loop switcher to enable the position control loop and driving the force sensor moving unit to move the force sensor to a close position to the workpiece in such a manner that the position fed-back signal becomes equal to the set position value; controlling, when recognizing that the force sensor is brought to the close position to the workpiece, the control loop switcher to enable the force control loop and driving the force sensor moving unit to bring the force sensor into contact with the workpiece in such a manner that the force fed-back signal becomes equal to the set force value.

According to these aspects of the present invention, the contour measuring instrument and the measurement control method which have advantages similar to those of the above-described measurement control device can be provided.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT(S)

An embodiment of the present invention will be described with reference to the attached drawings.

[Arrangement of Coordinate Measuring Instrument]

Now, a coordinate measuring instrument as a contour measuring instrument according to an embodiment of the present invention will be described.

FIG. 1is a perspective view of a coordinate measuring device of the coordinate measuring instrument according to the embodiment of the present invention.FIG. 2is a block diagram showing an outline of a primary part of the coordinate measuring instrument.FIG. 3is a schematic diagram showing outlines of a controller and a probe.

The coordinate measuring instrument10includes a coordinate measuring device100as shown inFIG. 1and a control device200as shown inFIG. 2.

As shown inFIG. 1, the coordinate measuring device100includes a mounting section110and a measuring unit120.

The mounting section110is formed in a flattened prism shape having an upper surface that is precisely flattened to mount a workpiece.

For convenience of explanation, two directions orthogonal to each other on the upper surface of the mounting section110are respectively defined as an X-direction and a Y-direction, while a direction vertical to the upper surface of the mounting section110is defined as a Z-direction.

The measuring unit120includes a probe130and a relative movement mechanism140that moves the probe130in the X-, Y- and Z-directions.

As shown inFIGS. 1 and 3, the probe130includes: a casing131having a substantially rectangular box-like shape provided on the relative movement mechanism140; a probe body132provided in the casing131with one end in a longitudinal direction exposed outside; a force sensor1provided on the one end side in the longitudinal direction of the probe body132; an actuator133(force sensor moving unit) that holds the probe body132and advances and retracts the force sensor1relative to the workpiece in the Z-direction; a scale134that is attached to the probe body132; and a scale detector135(position detector) that detects based on the scale134a displacement amount of the force sensor1displaced by the actuator133(i.e., measuring position information in measuring the workpiece the force sensor1).

The relative movement mechanism140includes a Y-direction slide mechanism150, an X-direction slide mechanism160and a Z-direction slide mechanism170.

As shown inFIGS. 1 and 2, the Y-direction slide mechanism150includes: a Y-guide rail151provided in the Y-direction on the mounting section110; a Y-slider152R (probe-relative-movement mechanism) provided so as to be movable along the Y-guide rail151; a Y-slider152L (probe-relative-movement mechanism) provided as a pair with the Y-slider152R so as to be movable in the Y-direction on the mounting section110; supporting columns153R,153L that are respectively provided on the Y-sliders152R,152L; an X-beam154having ends that are respectively supported by the two supporting columns153R,153L; and a Y-direction driver155that moves the Y-sliders152R,152L in the Y-direction.

The Y-direction driver155is connected to the control device200and moves the Y-sliders152R,152L in the Y-direction under the control of the control device200.

Air bearings (not shown) are each provided between the Y-guide rail151and the Y-slider152R and between the mounting section110and the Y-slider152L. A relative moving amount of the Y-guide rail151and the Y-slider152R is measured by a displacement detector (not shown).

As shown inFIGS. 1 and 2, the X-direction slide mechanism160includes: an X-slider161(prove relative movement mechanism) that is provided to be movable in a longitudinal direction of the X-beam154(i.e., in the X-direction); and an X-direction driver162that moves the X-slider161in the X-direction.

The X-direction driver162is connected to the control device200and moves the X-slider161in the X-direction under the control of the control device200.

A relative moving amount of the X-beam154and the X-slider161is measured by a displacement detector (not shown).

As shown inFIGS. 1 and 2, the Z-direction slide mechanism170includes: a Z-axis supporter171fixed on the X-slider161; a movable arm172(probe-relative-movement mechanism and probe holder) that is moved relative to the Z-axis supporter171in a manner sliding in the Z-direction; and a Z-direction driver173that moves the movable arm172in the Z-direction.

The casing131of the probe130is attached on a the tip end of the movable arm172.

The Z-direction driver173is connected to the control device200and moves, under the control of the control device200, the movable arm172independently of the probe body132in the Z-direction.

A relative moving amount of the Z-axis supporter171and the movable arm172is measured by a displacement detector (not shown).

As shown inFIG. 2, the control device200includes: an XYZ-drive controller210(probe position controller) that controls the Y-direction driver155, the X-direction driver162and the Z-direction driver173; and a controller220that controls the probe130.

The XYZ-drive controller210is connected to the Y-direction driver155, the X-direction driver162and the Z-direction driver173. The XYZ-drive controller210controls the drivers155,162,173to respectively move the Y-sliders152R,152L, the X-slider161and the movable arm172in order to move the probe130to the probe-controllable position. The probe-controllable position is a position where the force sensor1can be brought into contact with the workpiece only by the drive of the actuator133.

As shown inFIG. 3, the controller220includes: an oscillator221that applies a vibration signal to the force sensor1to vibrate the force sensor1; an A/D conversion circuit222that converts an analogue detection signal from the force sensor1to a digital signal; a counter223that counts a signal from the scale detector135and outputs the measuring position information from the force sensor1as a position measuring value; a processing unit224that calculates a deviation between the output from the A/D conversion circuit222(force fed-back signal) and a target measuring force; a force control compensator225that receives an output from the processing unit224; a time differentiating circuit226that differentiates the position signal from the counter223to convert the position signal to a speed signal; a switch227(control loop switcher); a processing unit228that calculates a deviation between an output from the time differentiating circuit226and an output from the force control compensator225that is received via the switch227; a speed compensator229that receives an output from the processing unit228; a drive amplifier230that drives the actuator133based on an output from the speed compensator229; a processing unit231that calculates a deviation between a measured value (position information) of the counter223and the target position; a position control compensator232that applies an output from the processing unit231to the processing unit228via the switch227; and a controller controlling section233(measurement control device) connected to the processing units224,231and the counter223.

The force sensor1, the A/D conversion circuit222, the processing unit224, the force control compensator225, the processing unit228, the speed compensator229, the drive amplifier230and the actuator133form a force control loop RF that compares the force detection signal from the force sensor1as the force fed-back signal with the target measuring force (set force value) and drives the actuator133such that the force fed-back signal becomes equal to the target measuring force.

The scale detector135, the counter223, the processing unit231, the position control compensator232, the processing unit228, the speed compensator229, the drive amplifier230and the actuator133form a position control loop RP that compares the measuring position information from the scale detector135as the position fed-back signal with a set position value (target position) and drives the actuator133such that the position fed-back signal becomes equal to the target position.

The switch227is controlled by the controller controlling section233to enable one of the force control loop RF and the position control loop RP.

Hereinafter, the control of the actuator133by the force control loop RF will be referred to as a force control, while the control of the actuator133by the position control loop RP will be referred to as a position control.

The controller controlling section233includes an approach controller234that controls the force sensor1to approach the workpiece and a contact controller235that controls the force sensor1to come into contact with the workpiece.

When recognizing that the probe130reaches the probe-controllable position under the control of the XYZ-drive controller210, the approach controller234controls the switch227to enable the position control loop RP. Then, the actuator133is driven by the position control to bring the force sensor1to a close position where the force sensor1is positioned close to the workpiece.

When recognizing that the probe1reaches the close position under the control of the approach controller234, the contact controller235controls the switch227to enable the force control loop RF. Then, the actuator133is driven by the force control to bring the force sensor1into contact with the workpiece.

[Operation of Coordinate Measuring Instrument]

Now, an operation of the coordinate measuring instrument10will be described.

FIGS. 4A to 4Dare each a schematic diagram showing a positional relationship of the force sensor and the workpiece in the measurement. Specifically,FIG. 4Ashows an initial state;FIG. 4Bshows a state in which the force sensor is moved by the X-direction driver, the Y-direction driver and the Z-direction driver from the state shown inFIG. 4Ato the probe-controllable position;FIG. 4Cshows a state in which the force sensor is moved by the actuator from the state shown inFIG. 4Bto the close position under the position control; andFIG. 4Dshows a state in which the force sensor is moved by the actuator from the state shown inFIG. 4Cand brought into contact with the workpiece under the force control.FIG. 5is a flowchart showing the measurement using the coordinate measuring instrument.FIG. 6is a conceptual diagram showing how the workpiece is measured.

A measurer mounts a workpiece W on the mounting section110as shown inFIG. 4A.

The coordinate measuring instrument10operates the XYZ-drive controller210to drive the X-direction driver162, the Y-direction driver155and the Z-direction driver173as shown inFIG. 5(Step S1) and judges whether or not the force sensor1reaches the probe-controllable position as shown inFIG. 4B(Step S2). When it is judged that the force sensor1does not reach the probe-controllable position in Step S2, the process of Step S1is performed.

On the other hand, when it is judged that the force sensor1reaches the probe-controllable position in Step S2, the approach controller234enables the position control loop RP to drive the actuator133under the position control (Step S3), and the coordinate measuring instrument10judges whether or not the force sensor1reaches the close position as shown inFIG. 4C(Step S4). When it is judged that the force sensor1does not reach the close position in Step S4, the process of Step S3is performed.

On the other hand, when it is judged that the force sensor1reaches the close position in Step S4, the contact controller235enables the force control loop RF to drive the actuator133under the force control (Step S5). Then, as shown inFIG. 4D, the force sensor1is brought into contact with the workpiece W while keeping the force control, and the measurement is performed under the force control (Step S6).

With the above-described control, the contour of the workpiece W can be measured under the force control as shown inFIG. 6.

Advantage of Embodiment

According to the embodiment above, the following advantages can be attained.

(1) The coordinate measuring instrument10operates the approach controller234to enable the position control loop RP and drives the actuator133under the position control, thereby bringing the force sensor1to the close position. Then, when recognizing that the force sensor1reaches the close position, the contact controller235controls the switch227to enable the force control loop RF and drives the actuator133under the force control so that the force sensor1is brought into contact with the workpiece W.

With the arrangement, by switching the control from the position control to the force control before the force sensor1contacts with the workpiece W and by bringing the force sensor1into contact with the workpiece W under the force control, the overshoot at the time of contact can be suppressed as compared to a related art arrangement in which the force control is performed after the force sensor1contacts with the workpiece W. Specifically, although in the related art arrangement described earlier, overshoot of several micrometers to several tens of micrometers might occur, the present embodiment can reduce the overshoot to that of about 10 nm.

In addition, since only the force sensor1is moved instead of the entire probe130, the inertia in moving the fore sensor1can be reduced, so that an increase of the overshoot due to the inertia can be suppressed.

Since a moving amount for bringing the force sensor1into contact with the workpiece W does not have to be preset, the present embodiment can be applied to the coordinate measuring instrument10in which a distance between a current position of the force sensor and the workpiece varies in accordance with the contour of the workpiece W.

Further, since the force sensor1is brought close to the workpiece W under the position control and then the control is switched to the force control, measurement efficiency can be prevented from degrading even in a measurement with a lot of measuring points.

Still further, the force sensor1can be moved by the single actuator133, so that an arrangement for controlling the movement will not be complicated.

Accordingly, the overshoot in contacting the force sensor1with the workpiece W can be suppressed with such a simple arrangement and without degrading the measuring efficiency.

(2) The vibrating force sensor1including the stylus3, the vibrating element4and the detecting element5is employed as the force sensor of the present invention.

The arrangement can suppress the overshoot in contacting the vibrating force sensor1, which can perform highly accurate measurement with a small measuring force, with the workpiece W, thereby providing the coordinate measuring instrument10realizing a measurement with even higher accuracy.

(3) The coordinate measuring instrument10includes: the probe130having the force sensor1, the scale detector135, the actuator133; the force control loop RF; the position control loop RP; the switch227; the above-described approach controller234and contact controller235; the Y-direction driver155, the X-direction driver162and the Z-direction driver173for moving the probe130; and the XYZ-drive controller210that controls the drivers155,162and173to move the probe130to the probe-controllable position.

Accordingly, the coordinate measuring instrument10capable of attaining the advantages (1) and (2) can be provided.

Modification of Embodiment

The present invention is not limited to the embodiment above but includes the following modifications as long as the object of the present invention can be achieved.

As an example, although the force sensor1is formed by the base2and the stylus3that are integrated in the embodiment above, the force sensor1may alternatively be formed by separate components. Specifically, the base2and the stylus3may be individually prepared, where the stylus3is fixedly bonded to the base3. As another example, although the stylus3is adapted to vibrate in the axial direction in the embodiment above, the stylus3may be vibrated in a direction orthogonal to the axis thereof.

As still another example, although the vibrating force sensor1is used in the embodiment above, the arrangement is not limited thereto. Another sensor may be employed as long as the sensor detects a measuring force generated when contacting with the workpiece and outputs the measuring force as a force detection signal.

The priority application Number JP2006-136628 upon which this patent application is based is hereby incorporated by reference.