WO2000014613A1

WO2000014613A1 - Power assist manual coordinate measuring machine and method for using same

Info

Publication number: WO2000014613A1
Application number: PCT/US1999/019025
Authority: WO
Inventors: Richard D. Sansom; Richard Mac Manus
Original assignee: Brown & Sharpe Manufacturing Company
Priority date: 1998-09-08
Filing date: 1999-08-20
Publication date: 2000-03-16

Abstract

A power assist system for use in a coordinate measuring machine (CMM) and method for using the same. Implementation of the power assist system into a manual CMM creates a new class of CMMs referred to herein as a power assist manual CMM, that incorporates the benefits of manual and servo-controlled CMMs while minimizing their respective drawbacks. The power assist system enables an operator to manually manipulate a relatively large CMM with minimal effort and with minimal distortion of the CMM structure and probe, thereby minimizing occupational injuries and measurement errors while increasing the speed and ease of performing dimensional metrology. The power assist system is an open loop control system that applies a control force to selected CMM axes that are parallel to the X-, Y- and Z-vector components of an operator-controlled control lever displacement. The magnitude of force applied to each selected CMM axis is dependent upon a gain factor for the controlled axis and the displacement experienced by the control lever along that axis. The power assist system may be mounted on and travel with the CMM probing member in response to the applied control forces, so as to return the control lever to its non-deflected equilibrium position. Thus, the power assist system incorporates the operator's visual monitoring of the probe position and subsequent manual feedback control to form an operator/power assist system closed loop control system. The power assist system may be implemented on any CMM now or later developed, such as a moving bridge or horizontal arm CMM, as well as machines other than CMMs which have moving arms or other structures which are to be manually controlled by an operator.

Description

POWER ASSIST MANUAL COORDINATE MEASURING MACHINE AND METHOD FOR USING SAME

Background Of The Invention

Field of the Invention

The present invention relates generally to metrology and, more particularly, to coordinate measuring machines.

Related Art

Coordinate measuring machines (CMMs) have traditionally been used to gather dimensional data for inspection and process control purposes. For example, CMMs operating in three axes of movement are commonly utilized to process measurement and dimensional data to analyze trends in manufacturing processes and to provide data that can correct such processes before a workpiece or a workpiece feature drifts out of tolerance.

Typically, a workpiece is secured to a fixed table, and a measuring probe is secured to an arm which is movable in the vertical and horizontal planes. To measure the position of a point on the workpiece, the probe is brought into contact with the point and the X, Y and Z measuring scales of the CMM are read. To measure a distance between two points, the points are contacted successively, the coordinates of both points are read and the distance is calculated from the coordinates. State of the art coordinate measuring machines have refinements such as high resolution measuring systems, electrical contact probes, motor drives, computer controlled drives and computer acquisition and data processing systems.

In a moving bridge CMM, a bridge mounted on rails over the table supports a carriage having a rail that moves toward and away from the workpiece. The bridge moves across the table on guideways in one linear axis (the X-axis) while the carriage moves perpendicular to the X-axis along the bridge (the Y-axis). The carriage has a vertical control column or ram that moves perpendicularly to the X- and Y- axes along the Z axis. A probe attached to the end of the ram can then be translated to any desired position within the measurement volume to measure points along a workpiece surface.

Similarly, in a horizontal arm CMM, an X carriage is supported on a base for movement along a horizontal axis (the X-axis). An XY carriage supporting a horizontally- suspended arm is movably supported on a rigid column attached to the carriage so as to be movable up and down along a vertical axis (the Z-axis). A probe is mounted on an end of the horizontal arm which moves along a second horizontal axis (the Y-axis) through bearings in the XY carriage. Thus, similar to the moving bridge CMM, a probe on a horizontal arm CMM may be positioned to any location within the measurement volume. In operation the moving components of the CMM are supported on respective bearing surfaces that substantially minimize friction. The CMM is typically interfaced with a computer or similar information storage or processing device. As an operator moves the probe in contact with the workpiece, the computer records the relative spatial position of the probe. This information is typically obtained by determining the position of the movable components of the CMM with respect to each of the machine's X, Y and Z bearing surfaces. The type or class of CMM determines the manner in which the probe is positioned within the measurement volume. Two common classes of CMMs are the unassisted manual CMM and servo controlled CMM. Manual CMMs provide control wheels mounted on each axis of the machine which are manually rotated by the operator to place the probe in a desired location in the measurement volume. Thus, there are typically three control wheels, one for controlling the motion of the probe in each of the three axes. The control wheels are connected to a movement transforming system, typically of the belt and pulley or rack and pinion type, integrated into the frame of the CMM. The probe assembly may include any type of probe assembly, such as an analog probe, passive probe or an electronic or manual trigger that generates a signal each time the probe touches a workpiece surface. Manual CMMs may be of the moving bridge or horizontal arm configurations, as is well known in the art.

A drawback to such manual CMMs is that it is extremely time-consuming to adjust the position of the probe to come into contact with a desired workpiece surface. This drawback is further exasperated by the requirement to accurately measure workpiece forms which, unlike prismatic shapes, require the compilation of a massive number of data points. Furthermore, constant manipulation of the control wheels causes operator fatigue to eventually develop, oftentimes resulting in occupational injuries.

Oftentimes, rather than using the control wheels in the former manual CMM, operators grasp the horizontal arm or vertical ram of the CMM, referred to as the probing member herein, and manually move the probe assembly to contact the workpiece surface. Other manual CMMs do not provide such control wheels, requiring the operator to physically move the probe assembly in three dimensions, typically as above; that is, by grasping the probing member and translating it in the desired direction. In this manner, a probe located at the end of the probing member can be positioned at different measurement points along the measurement volume of the CMM. However, this technique causes deflections of the CMM structure and probe tip, resulting in errors in the associated measurements. In contrast to manual CMMs, servo controlled CMMs, such as direct computer control

(DCC) CMMs, provide complete automatic control of the probe. Such systems, however, are also slow in that the CMM must rely on position feedback information to determine magnitude and direction of probe motion. Furthermore, servo controlled machines are considerably more expensive than manual CMMs, limiting their use to only certain markets and applications.

What is needed, therefore, is an accurate and cost effective CMM which can be utilized to provide quickly dimensional measurements without causing operator fatigue or occupational injuries.

Summary of the Invention

The present invention is a power assist system for use in a coordinate measuring machine (CMM) and method for using the same. Implementation of the present invention into a manual CMM creates a new class of CMMs, referred to herein as a power assist manual CMM, that incorporates the benefits of manual and servo-controlled CMMs while minimizing their respective drawbacks. The power assist system of the present invention enables an operator to manually manipulate a relatively large CMM with minimal effort and with minimal distortion of the CMM structure and probe, thereby minimizing occupational injuries and measurement errors while increasing the speed and ease of performing dimensional metrology. Generally, the power assist system is an open loop control system that applies an amplified control force to selected CMM axes that are parallel to the X-, Y- and Z-vector components of an operator-controlled control lever displacement. The operator visually monitors the location of the probe assembly to determine whether positional changes are desired or necessary. Based on that determination, the operator provides the requisite feedback control to the power assist system by displacing the control lever from a non- deflected or equilibrium position to a plurality of deflected or activation positions, the direction of such displacement being in the direction in which the probe assembly is to travel. The magnitude of amplified force applied to each selected CMM axis is dependent upon a predetermined gain factor for the controlled axis and the displacement experienced by the control lever along that axis.

A force amplification servo is mounted on and travels with the CMM probing member in response to the applied control forces. The power assist system is constructed and arranged such that positional changes of the probe assembly are parallel to the motion of the control lever and have a magnitude proportional to the control lever displacement in that axis. This causes the force amplification servo to travel in the direction of the control lever displacement, returning the control lever to its equilibrium position. Continued application of a force by the operator would, then, result in the continuous motion of the probe assembly in the direction of the applied force. Once the control lever is returned to the equilibrium position, control pressures return to their associated equilibrium values and the acceleration of the selected CMM axes ceases. Thus, the power assist system is an open loop system that incorporates the operator's visual monitoring of the probe position and subsequent manual feedback control to form an operator/power assist system closed loop control system. The power assist system of the present invention may be implemented on any CMM now or later developed, such as a moving bridge or horizontal arm CMM. It should also be understood that the present invention may be implemented in machines other than CMMs which have moving arms or other structures which are to be manually controlled by an operator. Specifically and in one embodiment, the power assist system includes a machine- mounted pneumatic force amplification servo that receives a supply pressure and generates one or more control pressure signals each identifying the magnitude of control force which is to be applied to an associated CMM axis in a particular direction. The magnitude of each control pressure signal is a function of the magnitude and direction of the control lever displacement and a predetermined system gain factor for that assisted axis in that direction. Each dynamically controlled regulator generates a regulated pressure, the magnitude of which is a function of the magnitude of the control pressure generated by force amplification servo. The regulated pressure generated by one or two regulators is provided to an actuator to generate the control force that is applied to the associated CMM axis member through a any well-known force transfer mechanism.

Advantageously, the present invention provides a power assist manual CMM that is cost effective and responsive to an operator's control inputs while being considerably less expensive than servo controlled systems. Furthermore, the present invention provides the operator with immediate feedback, making the CMM intuitive and easy to use. Further, the operator need not apply significant pressure to the control lever to move the CMM components since the control force applied to each CMM axis member is subject to a predetermined system pressure gain. As a result, there is substantially less deflection of the CMM structure and probe assembly, significantly minimizing CMM and probe deflections that degrade measurement accuracy. This also reduces operator fatigue and occupational injuries traditionally associated with the use of manual CMMs.

Further features and advantages of the present invention as well as the structure and operation of various embodiments of the present invention are described in detail below with reference to the accompanying drawings.

Brief Description of the Drawings

The present invention is pointed out with particularly in the appended claims. The above and other advantages of this invention may be better understood by referring to the following description when taken in conjunction with the accompanying drawings in which similar reference numerals indicate like or functionally similar elements or method steps. Additionally, the left-most one or two digits of a reference numeral identify the figure in which the reference numeral first appear. Figure 1A is a schematic diagram of an exemplary horizontal arm type coordinate measuring machine (CMM) suitable for implementing of the present invention.

Figure IB is a perspective view of an exemplary moving bridge CMM suitable for implementing the present invention.

Figure 2 A is a system block diagram of one embodiment of the pneumatic power assist system of the present invention.

Figures 2B is a schematic diagram illustrating a portion of one embodiment of the power assist system of the present invention.

Figure 3 A is a cross-sectional view of a pneumatic force amplification servo configured in accordance with one preferred embodiment of the present invention. Figure 3B is an enlarged view the portion of the pneumatic force amplification servo called out in Figure 3 A, showing details of one embodiment of a variable control valve implemented in the embodiment of force amplification servo illustrated in Figure 3 A. Figure 3C is a sectional view of a portion of the pneumatic force amplification servo illustrated in Figure 3 A taken along the shown section line illustrating an exemplary multiple variable control valve arrangement.

Figure 4 is a cross-sectional view of one embodiment of a pneumatic regulator illustrated in Figure 2B.

Figure 5 is a cross-sectional view of one embodiment of a pneumatically controlled actuator illustrated in Figure 2B.

Detailed Description The present invention is a power assist system for use in a coordinate measuring machine (CMM) and method for using the same. Implementation of the present invention into a manual CMM creates a new class of CMMs, referred to herein as a power assist manual CMM, that incorporates the benefits of manual and servo-controlled CMMs while minimizing their respective drawbacks. The power assist system of the present invention enables an operator of a manual CMM to manually manipulate a relatively large CMM with minimal effort and with minimal distortion of the CMM structure and probe, thereby minimizing occupational injuries and measurement errors while increasing the speed and ease of performing dimensional metrology.

Generally, the power assist system is an open loop control system that applies a control force to selected CMM axes that are parallel to the X-, Y- and Z-vector components of a force applied to a control lever, displacing it from an equilibrium position to an actuation position. The magnitude of force applied to each selected CMM axis is dependent upon a predetermined gain factor for the controlled axis and the displacement of the control lever in that axis. The power assist system is mounted on and travels with the CMM probing member returning the control lever to its equilibrium position. Thus, the power assist system incorporates the operator's visual monitoring of the probe position and subsequent manual feedback control to form an operator/power assist system closed loop control system. Figure 1A is a schematic diagram of a horizontal arm type CMM suitable for implementing the present invention. Horizontal CMM 100 is a well-known CMM that includes various components closed by a cover system as is well known in the art such as bellows 108. A horizontal arm assembly 106 is enclosed with bellows 108 at the front and a hard cover 110 at the rear. Horizontal CMM 100 includes a base 112 on which is supported a vertical column assembly 114 attached to an X axis carriage 115 movable along a first horizontal coordinate axis (the X-axis). Vertical column assembly 114 movably supports horizontal arm assembly 106, having mounted thereon a probe assembly 116. Horizontal arm assembly 106 is carried on a YZ carriage 118 movable vertically on vertical column assembly 114 along a second coordinate axis (the Z-axis). Horizontal arm assembly 106 is movable horizontally on a YZ carriage 118 along a third or Y-axis parallel to the longitudinal axis of horizontal arm 106. Each of the X-, Y- and Z-axes are orthogonal to each other in a manner well known in the art. Base 112 supports a workpiece to be measured (not shown) which may be disposed within a measurement volume so as to be accessible for inspection by movement of probe assembly 116 to points of interest on the workpiece. Detachably mounted on base 112 and vertical column assembly 114 are pairs of spaced apart guideway members (not shown) each elongated and extending parallel to each other along the X-, Y- and Z-axes. Further features of horizontal CMM 100 are disclosed provided in U.S. Patent No. 4,887,360 to Hemmelgarn et al, the specification of which is hereby incorporated by reference in its entirety. An example of a horizontal arm coordinate measuring machine suitable for implementing the present invention is the model Layout Gauge 200H manufactured by Brown & Sharpe Manufacturing Company, North Kingston, Rhode Island, USA. Since horizontal CMMs are generally well-known in the art, the details of such machines are not described further herein. Another type of CMM suitable for implementing the present invention is a movable bridge CMM as shown in Figure IB. CMM 150 is intended for measurement of a workpiece 101 which is mounted on a fixed machine table 152. The X-, Y- and Z- axes of CMM 150 are illustrated. A bridge 154 moves along the Y-axis on guideway 156 mounted on table 152. A carriage 158 moves along the X-axis on guideways mounted on bridge 154. A ram 160 with a probe assembly 162 mounted to its lower end moves vertically through bearings on carriage 158. A scale 164 between bridge 154 and table 152, a scale 166 between carriage 158 and bridge 154, and a scale 168 between ram 160 and carriage 158 indicate the positions of the movable elements in the three axial directions. To measure the coordinates of a point on workpiece 101, probe 162 is brought into contact with the point of interest. Probe 162 senses contact and causes a system computer to read and store the readings on the three scale systems. An example of a moving bridge coordinate measuring machine suitable for implementing the present invention is the model MicroXcel 765 manufactured by Brown & Sharpe Manufacturing Company, North Kingston, Rhode Island, USA. As with horizontal CMMs, moving bridge CMMs are considered to be well-known in the art and, as such, are not described further herein.

The pneumatic assist system of the present invention will be described with reference to the exemplary horizontal arm CMM 100 illustrated in Figure 1 A. As will become apparent from the following description, the present invention may be implemented on any CMM now or later developed, such as moving bridge CMM 150 illustrated in Figure IB. It should also be understood that the present invention may be implemented in machines other than CMMs which have moving arms or other structures which are to be manually controlled by an operator, such as vision systems and pick and place systems.

Figure 2 A is a system block diagram of one embodiment of the power assist system of the present invention implemented to assist at least one selected axis in a CMM. The exemplary power assist system 200 includes a machine-mounted force amplification servo 202 that controls one or more dynamically controlled regulators 204 based on a manual force (F_m) 206 applied by an operator 208 to a control lever (not shown) of servo 202. Power assist system 200 is a closed system utilizing a transfer medium to transfer pressure signals between system components. In the embodiment illustrated in Figure 2A, the force transfer medium which is utilized in power assist system 200 is air. However, as will become apparent from the following description, other fluids may be used. Thus, in this exemplary embodiment, force amplification servo 202 is also referred to as a pneumatic force amplification servo due to the implementation of air as the transfer medium. Pneumatic force amplification servo 202 is a machine mounted, manually operated pneumatic control valve that receives a supply pressure (P_s) 212 and generates one or more control pressure signals (P_c) 210 each identifying the magnitude of control force 218 which is to be applied to an associated CMM axis. The magnitude of each control pressure signal 210 is a function of the magnitude and direction of applied force (F_m) 206 and a predetermined system gain factor for that axis.

Each dynamically controlled regulator 204 supplies a regulated pressure (P_r) 214 for use by an associated pneumatically-controlled actuator 216. Regulators 204 alter supply pressure 212 to generate regulated pressure 214, the magnitude of which is a function of the magnitude of control pressure (P_c) 210 generated by force amplification servo 202. The supply pressure which is regulated by regulators 204 may be the same or different than supply pressure 212. Regulated pressure 214 generated by each regulator 204 is used by an actuator 216 connected to an associated CMM axis member 262 of CMM 220 through a force transfer mechanism. The actuator 216 generates a control force (F_c) 218 that is applied to the associated CMM axis member 262.

Thus, power assist system 200 is an open loop control system that assists operator 208 in the control of coordinate measuring machine 220, providing a control force 218 to one or more of the movable axes of coordinate measuring machine 220 based on a magnitude and direction of a manual force 206 supplied by the operator. As shown by dashed line 222 in Figure 2A, power assist system 200 utilizes operator 208 as a feedback control mechanism to form an operator/power assist system closed loop control system. That is, operator 208 visually monitors the position of the probe assembly to determine whether positional changes are desired or necessary. Based on that determination, operator 208 provides the requisite command control to power assist system 200 by controlling the direction and magnitude of control lever displacement, manual force (F_m) 206. Manual force 206 causes the control lever to be displaced from a null or equilibrium position to an activation position as described below. Force amplification servo 202 is mounted on the CMM axis member supporting the probe assembly such as horizontal probe arm assembly 106 and ram 160 (the probing member). The power assist system 200 is constructed and arranged such that positional change of the probe assembly is parallel to the motion of the control lever and has a magnitude proportional to the control lever displacement. This causes force amplification servo 202 to travel in the direction of the force applied to the control lever, returning the control lever to its null or equilibrium position. Continued application of a force 206 would, then, result in the continuous motion of the probe assembly in the direction of the applied force. Once the control lever is returned to the equilibrium position, control pressures 210 return to their equilibrium values and the acceleration of the selected CMM axes ceases. Thus, the present invention provides a power assist manual CMM that is cost effective and responsive to an operator's control inputs. Incorporation of the present invention into a manual CMM results in a power assist CMM that is considerably less expensive than servo controlled systems. Furthermore, the present invention provides immediate feedback to operator 208 as the operator manually adjusts the location of the probe in the measurement volume. Also, as will be described in detail below, the operator need not apply significant pressure to the control lever to move the CMM components since control force 218 applied to each CMM axis member may be subject to a different pressure gain and, therefore have a different relationship with the applied force. As a result, there is substantially less deflection of the CMM structure and minimal pressure applied to the probe assembly, due to operator- applied forces, significantly minimizing probe deflections that degrade measurement accuracy. This also reduces operator fatigue and occupational injuries traditionally associated with the use of manual CMMs.

Figure 2B is a high level diagram illustrating one implementation of power assist system 200 of the present invention. As noted, power assist system 200 translates a manual force 206 applied to force amplification servo 202 to one or more control forces 218 applied by one or more actuators 216 to selected associated CMM control axis member(s) 262. In this exemplary embodiment, pneumatic force amplification servo 202 is implemented with a control lever or joystick 254 which is controlled by operator 208. As shown in Figure 2B, manual force 206 which is applied to joystick 254 can be in any direction and of any magnitude suitable for causing a desired displacement of control lever 254. In the illustrative embodiment shown in Figure 2B, a portion of power assist system 200 associated with the control of a single CMM axis member 262 is illustrated. As shown, the force amplification servo 202 receives supply pressure 212 and generates control pressure signals 210A and 210B which are used by regulators 204 A and 204B, respectively, to generate regulated pressure signals 214A and 214B, respectively. The two regulators 204A and 204B control opposing sides of a pneumatic cylinder 216 that is connected to a controlled CMM axis member 262 via a force transfer mechanism 260. One or more dynamically controlled regulators 204 are each associated with the control of a pneumatically controlled actuator 216. The relationship between regulators 204 and actuators 216 is dependent upon the type of actuator which is being implemented. In the exemplary embodiment illustrated in Figure 2B, for example, pneumatically controlled actuator 216 is a dual port pneumatic cylinder 216. As shown, such a device receives two regulated pressure (Pr) signals 214A, 214B, each generated by a single regulator 204. In such an embodiment, then, two dynamically controlled regulators 204 are associated with this type of pneumatically controlled actuator 216. As will be described below, in other embodiments a single regulator 204 may supply a regulated pressure 214 to actuator 216. In the exemplary embodiment illustrated in Figure 2B, regulators 204 are implemented as pneumatic regulators 258 since in this exemplary embodiment air is utilized as the transfer medium. As introduced above with reference to Figure 2 A, supply pressure 212 is provided to force amplification servo 202 and pneumatic regulators 204. Force amplification servo 202 generates control pressure 210 in response to an application of manual force 206 to control lever or joystick 254 by operator 208. Control pressure 210 is then supplied to each pneumatic regulator 204 as shown in Figure 2B. Pneumatic regulators 204 modify supply pressure 212 in accordance with the magnitude of control pressure 210 to generate a regulated pressure 214. Regulated pressure 214 is then supplied to one or more pneumatically controlled actuators 216 which, in this embodiment, are pneumatic cylinders. In the embodiment illustrated in Figure 2B, force transfer mechanism 260 utilized by power assist system 200 to control CMM axis member 262 is a belt and pulley system. In such an arrangement a cable or belt is attached to an internal piston 266 in pneumatic cylinder 216 and to a controlled CMM axis member 262. As regulated pressures 214 cause cylinder 262 to alter its position within pneumatic cylinder 216 (described below), belt and pulley system 260 transfer the resulting control force 218 to CMM axis member 262, causing CMM axis member 262 to translate along its axis. Pneumatic force amplification servo 202 will now be described with reference to an exemplary embodiment illustrated in Figures 3A-3C. Figure 3A is a cross-sectional view of a pneumatic force amplification servo 300 configured in accordance with one preferred embodiment of the present invention. Figure 3B is an enlarged view the portion of the pneumatic force amplification servo called out in Figure 3 A, showing details of one variable control valve implemented in this embodiment of force amplification servo 300. Figure 3C is a sectional view of pneumatic force amplification servo 300 taken along the section lines illustrated in Figure 3A showing an exemplary multiple variable control valve arrangement.

In the exemplary embodiment shown in Figures 3A-3C, force amplification servo 202 is a machine-mounted pneumatic servo control valve. Force amplification servo 202 may be mounted on to horizontal arm 106 of a horizontal CMM 100 (Figure 1 A) or ram 160 of moving bridge CMM 150 (Figure IB). For purposes of the following discussion, machine- mounted pneumatic force amplification servo 202 is described as being mounted on rear cover 110 of horizontal arm assembly 106 of CMM 100. Force amplification system 202 is mounted on horizontal arm 106 such that control arm 310 extends from and is substantially parallel with the axis of horizontal arm 106. In this exemplary implementation the present invention is configured to provide assistance in the translation of probe assembly 116 vertically along the Z-axis on vertical column 114 and horizontally along the X-axis through movement of vertical column 114 along the X axis guideway s 122. Note that in this particular embodiment, power assist system 300 does not assist movement of probe assembly 116 horizontally along the Y-axis through YZ carriage 118. This is described in further detail below. Force amplification system 202 will now be described with respect to this exemplary implementation.

In the illustrative embodiment illustrated in Figures 3A-3C, force amplification servo 202 includes a valve spool 342 mounted as a cantilevered spring on a valve housing base 308 within a valve housing 302. Valve spool 342 is connected to and controlled by control lever or joystick 310. Valve spool 342 includes a valve spool shaft 340 connected to base 308, and a valve spool control head 326 integral with shaft 340 and control lever 310. As shown, control lever 310 extends through a top enclosure 306 terminating in a knob 311 to be grasped by operator 208. It should be understood that valve spool 342, control head 326 and shaft 240 may be separately manufactured components appropriately attached to each other or may be portions of a single, unitary member, as is known in the art. Generally, a force applied to control lever knob 311 in the Z- and X-axes causes the cantilevered valve spool stem 340 to flex in the direction of the applied force vector, causing one side of control head 326 to travel toward an adjacent wall 302 and the other side of control head 326 to travel away from its adjacent wall 302. Upon release of control lever 310, spool stem 340 returns to its equilibrium or null position, approximately centrally located within housing 302. Thus, as used herein, valve spool 342 may be positioned at a non- deflected equilibrium position or any one or a plurality of deflected activation positions. As noted, force amplification servo 202 is a machine-mounted pneumatic servo control valve that dynamically generates one or more control pressure signals 210 in response to application of a force 206 to control lever 310. Specifically, force amplification servo 202 includes one or more variable control valves 380 each of which alters supply pressure 212 to generate an associated control pressure signal 210. Fixed inlet supply pressure 212 is received at a supply pressure fitting 312 which sets up a flow that is channeled through movable valve spool 342 and eventually released to atmosphere at an exhaust pressure.

As shown, a supply pressure channel 314 axially extends through valve spool stem 340 and is pneumatically connected to inlet fitting 312 in base 308. Supply pressure 312 passes through supply channel 314 to one or more variable control valves 380, only one of which is illustrated in Figure 3A for clarity. In the exemplary implementation shown in Figures 3A-3C, variable control valve 380 is embodied as a pressure divider including a series arrangement of pneumatic restrictors 318, 320 separated by a control pressure channel 322.

Control pressure 210 is channeled through a flexible control pressure conduit 316 to a control pressure outlet fitting 324. Inlet and outlet fittings 312, 324 are mounted in corresponding channels in base 308. Supply pressure 212 sets up an airflow which passes through the two restrictors 318, 320 before escaping to the atmosphere. One such restrictor, inlet restrictor 318 is a fixed restrictor while the second restrictor, exit restrictor 320, is a variable restrictor alterable in response to an application of a control force 206 to control lever 310. A space 344 between control lever 310 and valve housing top enclosure 306 provides for a range of movement of control lever 310 and opens the housing to atmosphere.

Supply channel 314 is connected to inlet restrictor 318 in control head 326, which causes a predetermined decrease in pressure. Inlet restrictor 318 is connected to control pressure channel 322 from which control pressure 212 is derived. As noted, inlet restrictor 318 is a fixed orifice. However, it should be understood that any restrictor which provides a predetermined change in pressure of the selected transfer medium through control pressure channel 322 may be used. The air flow continues through control pressure channel 322 to variable restrictor 320 before escaping to atmosphere.

Referring to Figure 3B, variable restrictor 320 is a pneumatic passageway that changes the flow of supply pressure 212 passing therethrough in response to a force applied to control lever 310. In the illustrative embodiment, variable restrictor 320 includes an orifice 330 at which control pressure channel 322 terminates. Orifice 330 leads into an air gap or annulus 328 between valve spool control head 326 and an adjacent and opposing sidewall surface 336. Manual forces 206 applied to control lever 310 cause valve spool 342 to travel from an equilibrium position to an activation position, changing the position of valve spool control head 326 with respect to housing 302. This, in turn, causes a change in one or more variable restrictors 320, resulting in a predetermined alteration of one or more control pressures 210 in control pressure channel 322. Control pressure 210 has a predetermined relationship with the extent to which variable exit restrictor 320 restricts air flow, and therefore the position of valve spool 342 relative to valve housing side wall 304. It follows, then, that control pressure 210 generated by force amplification servo 202 has a predetermined relationship with the magnitude and direction of applied force 206. As such, the value of control pressure 210 is determined by a current value of supply pressure 212 and a current configuration of the associated variable restrictor 320. It should be understood that variable control valve 380 may include other valves now or later developed which are responsive to the application of a force 206 to control lever 310. Such valves include, for example, sliding spool valves, needle valves and the like. The association between variable control valves 380 and regulators 204 will now be described with reference to Figures 2 A, 2B and 3C. Figure 3C is a cross-sectional view of pneumatic force amplification servo 300 taken along a section line as shown in Figure 3A. As noted, single variable control valve 380 is illustrated in Figure 3 A for clarity. The illustrative variable control valve 380 generates a single control pressure signal 210 which is used to control an associated regulator 204. In anticipated embodiments of the present invention, additional variable control valves 380 are included in the force amplification servo 300. Four such variable control valves are illustrated in the cross-sectional view of Figure 3C.

As shown, valve spool control head 326 has four control pressure channels 322A- 322D with their associated fixed and variable restrictors 318A-318D, 320A-320D and annula 328A-328D. Supply pressure 212 is provided to the four variable control valves 380 through common supply pressure channel 314. Manual force (206) which is applied to control lever 310 has vector components in at least one of the X-, Y- and Z-axes. Each force vector component will cause valve spool control head 326 to deflect a corresponding distance in the same direction as the force vector component. The gain of each variable control valve 380 is expressed in terms of output pressure

(control pressure 210 pounds) per force applied to control lever 310 (psi); that is, lbs/psi. The gain is a function of supply pressure 212, cantilevered spring stiffness of spool stem 340 (that is, the diameter and length of spool stem 340), and characteristics which determine the resistance applied by inlet and exit restrictions 318, 320. Thus, the gain of each variable control valve 380 can be individually or collectively changed by changing any one or more of the above features.

Also, as will be discussed below, two variable control valves 380 may be positioned opposing each other along the same axis, providing a substantially symmetrical opposite change in control pressures 210. For example, an applied force 206 parallel with the X-axis will cause valve spool control head 326 to deflect along the X-axis as well. The deflection will cause annular clearance 328A to further restrict the airflow through control pressure channel 322A, while causing annular clearance 328C to expand, decreasing the airflow restriction through control pressure channel 322B. The utilization of two such opposing variable control valves 380 to control opposing sides of a dual port pneumatic cylinder 216 essentially doubles the gain of force amplification servo 300 in that axis. As will be explained in detail below with reference to the pneumatically controlled actuators 216 and dynamically controlled regulators 204, force amplification servo 300 is orientated with respect to CMM 220 such that the X-, Y- and Z-axes of force amplification servo 300 are parallel with the three corresponding axes of CMM 220. In addition, control pressures 210 generated by variable restrictors 320 are utilized to control the corresponding CMM axis. For example, as noted, in the illustrative embodiment described herein wherein force amplification servo 300 is fixably mounted to horizontal arm 106 of CMM 100, the X-axis (variable control valves 380A, 380D) of force amplification servo 300 is aligned with the X-axis of horizontal arm CMM 100, and pneumatic cylinder 216 applies a control force 218 along the X-axis to vertical column assembly 114. As a result, manual forces having a force vector component parallel to the X-axis will cause power assist system 200 to assist movement of vertical column assembly 114 in the X-axis. Importantly, such response by the CMM controlled axes completes the feedback control by returning control lever 310 to its equilibrium position. Specifically, base 308 and housing 302 "follow" the knob 311 of control lever 310 since they are mounted to the CMM probing member (the structure supporting the probe assembly and which moves in response to applied force 208). Thus, as the CMM axes travel in the desired directions, the control pressure signals decrease or increase toward the values associated with the equilibrium position. Once the valve stem 340 returns to its equilibrium position, control pressures 210 return to their associated values, and movement of the CMM ceases. It should be understood that such control pressure values which maintain the controlled CMM axis in a non-accelerated state (that is, stationary) may be any value or combination of values. As noted, valve spool 342 has an equilibrium or non-deflected position and any one of a plurality of activation or deflected positions. The intermediate pressure generated in the control pressure channel 322 is, as noted, provided as control pressure 210. This intermediate pressure varies as spool 340 is deflected to change the downstream, or exit, restrictor 320. It has been determined that there is a symmetrical relationship between the intermediate pressure and supply pressure 212, centered about the point where the intermediate pressure is approximately 50% of supply pressure 212. Accordingly, it is preferable that the spool equilibrium position coincide with the symmetrical output pressure characteristic. As a result, the pressure gain (the rate at which control pressure 210 changes with spool deflections) is substantially equal in both directions along the controlled axis. This, in turn, requires symmetric forces 206, making the power assist system 200 intuitively easy to use. Thus, annular clearances 328 are preferably adjusted using clearance adjustment screw 338 so that control pressure 210 is approximately 50% of supply pressure 212.

Returning again to Figure 2B, regulators 204 are, as noted, dynamically-controlled pneumatic regulators interposed between a source of supply pressure 212 and pneumatic actuators 216. Dynamically-controlled regulators 204 regulate supply pressure 212, generating a regulated pressure 214 which is provided to actuators 216. Regulation of supply pressure 212 is determined by a current value of control pressure 210 generated by force amplification servo 202. Two such regulators 204 were introduced above with respect to Figure 2B. There, regulators 204A, 204B provided regulated pressures to opposing sides of a dual port pneumatic cylinder 216. Regulators 204 will now be described below with reference to Figure 4, which shows a cross-sectional view of one embodiment of regulator 204, referred to herein as pneumatic regulator 400.

In the illustrative embodiment, pressure regulator valve 400 is configured to accept and operate in response to a remote variable pressure signal. Pneumatic regulator 400 channels supply pressure 212 through a needle valve 408, the position of which determines the value of regulated control pressure 214. Supply pressure 212 is received at pneumatic fitting 418 and passed through needle valve 408 to a regulated pressure pneumatic fitting 420. A sealed cavity 406, preferably having a minimal volume, houses spring 404 and receives as an input control pressure 210. Control pressure 210 is received at pneumatic fitting 416 through which it enters sealed cavity 406. Spring 404 and control pressure 210 each apply a force to diaphragm 412 which, in turn, controls the location of needle valve 408. This, in turn, alters regulated pressure 214 generated by regulator 400. Thus, the sum of the control pressure from spring 404 (spring force/diaphragm area) and control pressure 210 determines the value of regulated control pressure 214.

Rotation of an adjusting screw 402 adjusts the compression placed on spring 404 by compression plate 414, correspondingly adjusting the force applied by spring 404 on diaphragm 412. Adjustable spring 404 enables the operator to balance the applied regulated pressures such that piston 266 remains stationary in cylinder 216 while supporting the controlled CMM axis member 262. When providing regulated pressure 214 to an actuator 216 driving a vertical axis member of the CMM, the regulated pressure must counterbalance the weight of the CMM member as well as accelerate the member along the Z-axis. The spring force, as determined by the adjustment screw 402, provides the null pressure to counter the weight while control pressure 210 is utilized to accelerate the member along the Z-axis. When 2 regulators 204 drive a dual port pneumatic cylinder 216, the respective control pressure values are such that the controlled CMM axis member 262 is stationary. That is, it is not subject to acceleration forces. As one skilled in the relevant art would find apparent, other configurations of regulator 204 as well as other types of regulators appropriate for the selected force transfer medium may be used. For example, in one alternative embodiment, regulator 204 does not include a variably controlled spring. In such an embodiment, regulator 204 regulates supply pressure 212 based solely on the value of control pressure signal 212.

Figure 5 is a cross-sectional view of a pneumatic cylinder 500, which is one implementation of pneumatically controlled actuator 216. As noted, pneumatically-controlled actuator 216 may be any such pneumatically-controlled actuator that is responsive in a known manner to a variable pressure signal using the selected force transfer medium. Each actuator 216 generates control force 218 for use by the CMM controlled axis structure 262. In the illustrative embodiment shown in Figure 2B, control force 218 is applied through a belt and pulley system 260, although any force transfer system may be used. In the illustrative embodiment, control force 218 is applied through belts, cables, straps or the like connected to the controlled structure 262. Alternatively, pneumatic cylinder 216 may be a single port system as, for example, when CMM controlled axis member 262 is a vertical member such as ram 160, suspended by gravity. Is such circumstances, a single belt 508 would be connected to the controlled axis structure to support the load of the device.

Cylinder wall 502 defines a sealed cylinder 504 which houses a piston 506. Piston 506 is controlled by regulated control pressures 154 provided to the two input fittings 510A and 510B. As noted, each regulated control pressure is generated by an associated regulator 104. Attached to piston 506 are cables 508A and 508B which exit cylinder 504 through sealed output channels 512A, 512B. Cables 508 are connected to opposing sides of controlled CMM axis structure 262 such that the CMM structure translates along its guideways in response to the movement of piston 506. It should be understood that two variable control valves 380, two associated regulators 204 and a dual port pneumatic cylinder 216 are not necessary to control a CMM axis structure in two directions along one axis. A single port cylinder driven by one regulator and one variable control valve in force amplification servo 202 may be used instead. It is desirable, however, to establish a differential pressure across the cylinder to more responsively and easily move controlled CMM axis structure 262. Providing such additional assistance under certain circumstances enables operator 208 the control even extremely large gantry CMM structures without the assistance of an externally generated force beyond manual force 206.

As noted, power assist system 200 is constructed and arranged so as to provide a control force 218 in those axes of the horizontal CMM which are parallel with vector components of force 206 applied to control lever 252. In the embodiment illustrated in Figure 2 A implemented on horizontal arm CMM 150 shown in Figure IB, one pneumatically- controlled actuator 216 is a dual -port cylinder driven by two regulators, and a second cylinder is a single port cylinder driven by a single regulator. Thus, a total of three regulators driving two cylinders are used in this embodiment of the present invention. The dual port cylinder is connected to vertical column assembly 114 so as to control the movement of the probe assembly on the X-axis. The single port cylinder is connected to YZ carriage 118 so as to control the movement of the probe assembly along the Z-axis (gravity supplies the counter balancing force). As noted, belt and pulley system 260 may be used to integrate power assist system 200 into CMM 150, although other force transfer mechanisms may be used. Note that this embodiment of power assist system 200 does not provide assistance for moving the horizontal arm along the X-axis, although another series of regulators and cylinder may have been incorporated into this embodiment of the present invention so as to provide such assistance.

As noted, each variable control valve 380 has a pressure gain associated with it that determines the magnitude of control pressure 210 generated by that valve in response to an applied manual force 206. Also, each pneumatic cylinder 216 has what is referred to herein as an "area gain". The area gain of each cylinder 216 is determined by its diameter (that is, the cross-sectional area). The overall system gain of force amplification system 200 in an assisted axis is determined by the product of the pressure gain (psi/lb) of the variable control valve 380 and the area gain (lb/psi) of the cylinder 216. For example, for a pressure gain of 8psi/lb from a variable control valve 380, and an area gain of 1.2 lb/psi of a cylinder 216, the total amplification for the controlled axis is 9.6 (8psi/lb X 1.2 lb/psi). That is, a one-lb force 206 applied by operator 208 would be amplified to 9.6 lbs on the controlled axis member 262 of the machine.

In one preferred embodiment, these relationships are utilized to achieve a sensation that all CMM axes feel equally light and require substantially the same force to be moved despite the large variations in mass. For example, horizontal arm 106 has relatively less mass than YZ frame 118 and column 114. As noted, movement in the Y-axis is not supplemented by one embodiment of the presented invention while movement in the X- and Z-axes is assisted. In this embodiment, the present invention provides assistance in the two heavier axes to an extent that causes them to respond in the same manner as the unassisted axis. This enables the operator to move either of the three axes in the same manner with the same degree of force despite their being of different mass.

This is easily achieved by changing either the pressure gain of force amplification servo 202 or the area gain of cylinders 216. To make all axes respond essentially the same, each assisted axis is initialized to have a gain which is proportional to the ratio of weight of the unassisted to the assisted axis. For example, if the assisted axes weight 250 lbs and 75 lbs while the unassisted axis weighs 25 lbs, then the system gains in each axis should be approximately 10 and 3, respectively. However, it should be apparent to those skilled in the art the power assist system 200 of the present invention can provide any degree of assistance to any axis independent of any other axis which is being assisted or not assisted by the present invention.

While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only, and not limitation. For example, force amplification servo 202 may be configured with an additional valve arrangement controlled by manual forces 206 having force vector components parallel to the Y-axis. Thus, the breadth and the scope of the present invention are not limited by any of the above exemplary embodiments, but are defined only in accordance with the following claims and their equivalents.

Claims

1. A coordinate measuring system comprising: a coordinate measuring machine (CMM) having at least one user-adjustable axis; a power assist system including, a pneumatic force amplification servo secured to one axis arm of said CMM, said force amplification servo generating a pneumatic control signal in response to a control force applied to a joy stick of said force amplification servo; a dynamically-controlled pneumatic regulator generating a regulated supply pressure is response to said pneumatic control signal; a pneumatically-controlled piston/cylinder apparatus, responsive to said regulated supply pressure, operatively coupled to an associated one of said at least one user-adjustable axis such that a movement of said piston within said cylinder causes an associated movement of said associated CMM axis.

2. A power assist system constructed and arranged as an open loop control system that assists an operator in the control of a coordinate measuring machine, said power assist system providing a control force to one or more movable axes of the coordinate measuring machine based on a magnitude and direction of a manual force applied by the operator to the power assist system, whereby said power assist system utilizes the operator as a feedback control mechanism to form a closed loop control system that includes the operator and said power assist system.

3. A power assist system for use in a manual coordinate measuring machine (CMM), said power assist system constructed and arranged to provide power assist forces to assist an operator to manually manipulate a probing member of the CMM in a measurement volume of the CMM.

4. The power assist system of claim 3, wherein said power assist system is constructed and arranged to apply, in response to an operator displacement of a control lever of the power assist system, an amplified control force to selected CMM axes that are parallel to X-, Y- and Z-vector components of said operator-controlled displacement of said control lever.

5. A power assist system for use in a coordinate measuring machine (CMM) constructed and arranged to generate power assist forces to assist an operator to manually manipulate a probing member of the CMM in a measurement volume based on an operator's manual feedback control input.

6. The power assist system of claim 5, wherein said power assist system includes a control lever and wherein said feedback control input is a displacement of said control lever from a non-deflected position to a deflected position, wherein said power assist forces cause said probing member to travel in a direction substantially the same as the direction of said displacement of said control lever.

7. The power assist system of claim 5, wherein said power assist forces comprise a plurality of power assist forces and wherein said power assist system is constructed and arranged to apply each of said power assist forces to a CMM member to cause the CMM probing member to travel in a direction parallel to a CMM axis associated with said power assist force.

8. The power assist system of claim 7, wherein, for each said controlled axis, a magnitude of said power assist force is dependent on a gain factor for said controlled axis and said control lever displacement parallel to said controlled axis.

9. The power assist system of claim 7, wherein said power assist system comprises: a force amplification servo mounted on the CMM probing member, whereby said force amplification servo travels with the probing member in response to said power assist forces to cause said force amplification servo to travel in the direction of said control lever displacement, tending to return said control lever to its equilibrium position.

10. The power assist system of claim 5, wherein positional changes of the probing member is substantially parallel to said displacement of said control lever.

11. The power assist system of claim 5, wherein a magnitude of positional changes of the probing member parallel to each CMM axis is proportional to said control lever displacement parallel to that axis.

12. The power assist system of claim 5, wherein the CMM is a moving bridge CMM.

13. The power assist system of claim 5, wherein the CMM is a horizontal arm CMM.

14. A power assist system for assisting an operator manually adjust at least one structural member that travels along an axis of a machine, the power assist system comprising: a force amplification servo that receives a first supply pressure and generates at least one control pressure signal in response to an operator control input; at least one regulator that generates a regulated pressure in response to one of said at least one control pressure signal; and an actuator that applies a control force to a machine structural member in response to a regulated pressure.

15. The power assist system of claim 14, wherein each of said at least one control pressure identifies a magnitude of an associated control force that is to be applied to an associated machine structural member.

16. The power assist system of claim 14, further comprising: a force transfer mechanism connected to said at least one structural member that travels along an axis of a machine and said actuator to apply said control force generated by said actuator to said machine structural member.

17. The power assist system of claim 14, wherein said force amplification servo is machine-mounted and includes a control lever and wherein said operator control input is a manual force applied to said control lever.

18. The power assist system of claim 17, wherein a magnitude of each control pressure signal is a function of magnitude and direction of said control lever displacement and a system gain factor for that assisted axis in that direction.

19. The power assist system of claim 17, wherein a magnitude of said control force applied to an associated machine structural member is proportional to a magnitude of a vector component of a manual operator control input that is substantially parallel with said machine axis along which said associated structural member travels.

20. The power assist system of claim 17, wherein a magnitude of said regulated pressure generated by each of said at least one regulator is a function of said control pressure magnitude.

21. The power assist system of claim 17, wherein said power assist system utilizes a pressure transfer medium to transfer said first supply pressure, said control pressure and said regulated pressure signals.

22. The power assist system of claim 17, wherein said transfer medium is a fluid.

23. The power assist system of claim 22, wherein said transfer medium is air.

24. The power assist system of claim 20, wherein said at least one regulator alters a second supply pressure to generate said regulated pressure based on a magnitude of said control pressure.

25. The power assist system of claim 24, wherein said first and second supply pressures are the same.

26. The power assist system of claim 14, wherein said actuator is a pneumatic cylinder comprising: a cylinder that receives said control pressure; and a piston connected to said machine structural member via said force transfer mechanism such that movement of said piston in said cylinder in response to changes in said regulated pressure causes said force transfer mechanism to apply said control force to said machine structural member.

27. The power assist system of claim 14, wherein said at least one regulator comprises: a first regulator constructed and arranged to receive a first control pressure signal from said force amplification servo and to supply a first side of said pneumatic cylinder with a first regulated pressure; and a second regulator constructed and arranged to receive a second control pressure signal from said force amplification servo and to supply a second side of said pneumatic cylinder opposite said first side with a second regulated pressure, wherein said first regulated pressure behaves inversely to said second regulated pressure.

28. The power assist system of claim 26, wherein said force transfer mechanism is a belt and pulley system comprising: at least one cable having a first end attached to said piston in said pneumatic cylinder; and a series of pulleys connecting a second end of said cable to said controlled structural member, wherein changes in said regulated pressure causes said piston to alter its position within said pneumatic cylinder causing said force transfer system to transfer forces to said structural member causing said structural member to translate along its axis.

29. The power assist system of claim 26, wherein said force amplification servo is mounted on to a ram of a moving bridge CMM.

30. The power assist system of claim 26, wherein said force amplification servo is mounted on a horizontal arm of a horizontal arm CMM such that said control lever extends from and is substantially parallel with an axis of said horizontal arm.

31. A force amplification servo for generating one or more control pressure signals in response to application of a manual force, comprising: a control lever; a valve housing having a base, side walls and a top enclosure defining an interior region of said valve housing; a cantilevered elongate valve spool including a shaft with a first end mounted on said base within said valve housing, a control head connected to a second end of said shaft, and a supply pressure channel axially extending through said shaft from said first end into said control head through which supply pressure travels, wherein said control lever extends through an opening in said top enclosure to attach to said control head; one or more pneumatic servo control valves each located in said control head and connected to said supply pressure channel to generate a control pressure signal based on a size of an air gap between each said servo control valve and an adjacent side wall of said valve housing, whereby said valve spool deflects in response to the manual pressure applied to said control lever to alter a relative position of said control head and said valve housing side walls to cause a change in said control pressure signal generated by said servo control valves for which said deflection causes a change in said air gap distance.

32. The force amplification servo of claim 31 , wherein each said one or more pneumatic servo control valve releases said supply pressure into said air gap through a variable control valve positioned on a side of said air gap opposing said adjacent side wall.

33. The force amplification servo of claim 32, wherein said variable control valve is a pressure divider apparatus including a series arrangement of pneumatic restrictors with a control pressure channel interposed between two of said pneumatic restrictors.

34. The force amplification servo of claim 33, further comprising: a flexible control pressure conduit connected to said control pressure channel to provide one of said control pressure signals to a location external to said valve housing..

35. The force amplification servo of claim 33, wherein said series arrangement of pneumatic restrictors comprises: a fixed inlet restrictor that causes a decrease in said supply pressure; a control pressure channel fluidly connected to said fixed inlet restrictor; and a variable exit restrictor fluidly connected to said control pressure channel and opening into said air gap, said variable exit restrictor alterable in response to an application of the control force to said control lever that causes a change in said air gap.

36. The force amplification servo of claim 35, wherein said inlet restrictor is a fixed orifice.

37. The force amplification servo of claim 31 , wherein said one or more variable control valves comprises: two variable control valves positioned in said control head so as to oppose each other along a same axis to provide a substantially symmetrical opposite change in control pressures in response to a manual force having a force vector component parallel to said axis.

38. A dynamically-controlled pneumatic regulator for regulating a supply pressure in response to a control pressure, comprising: a sealed cavity that receives the control pressure; a needle valve the position of which determines the value of a regulated supply pressure, wherein said needle valve is responsive to a diaphragm forming a portion of said sealed cavity; and a manually adjustable spring located in said sealed cavity to apply a force against said diaphragm, wherein said spring and said control pressure each apply a force to said diaphragm which, in turn, controls said needle valve, thereby altering a regulated pressure generated by said regulator.

39. The regulator of claim 38 , further comprising : an adjusting screw the rotation of which adjusts the compression placed on said spring by a compression plate, correspondingly adjusting the force applied by said spring on diaphragm.