Apparatus for measuring an object

The present invention relates to the use of measuring devices to determine if the dimensions of an object meet tolerances. In particular, the present invention relates to a method for determining whether the dimensions of an object meet tolerances using a measuring probe placed on a coordinate positioning device.

The conventional method for checking that an object meets tolerances involves the use of "go, no go" gauge blocks, as shown in Figure 1. Such "go, no go" gauge blocks are typically accommodated in plug, ring, taper, snap and threaded types and are reliable for tolerances up to about 0.05 mm. The "go" gauge 26 must be able to move smoothly inside the machined hole 30 or, conversely, on the machined protrusion, as in Figure 1. If it does not move smoothly, the object is above its maximum material state. The "no go" gauge 24 must not be able to move smoothly inside the machined hole or on the protrusions, as in Figure 1, and if that is possible, the object shall be its minimum. It is below the material state of.

<p><patcit num="1"><text>UK Pat. No. 1445977</text></patcit><patcit num="2"><text>UK Pat. No. 1551218</text></patcit></p>

<p> The disadvantage of this method stems from the fact that the gauges themselves must have assigned tolerances as they are also manufactured. All gauge tolerances must be within the working tolerance range to ensure that (bad) objects outside the tolerance range are not tolerated at all, however, this means that some good products are rejected. Means that. Another disadvantage of this method is the time it takes to check an object as each gauge must be manually moved into place. A "go" gauge should be used to check only one part of the size or shape of a part, and a "no go" gauge is one of any part, so that defective products do not accidentally pass through. It should be used to check only aspects (ie, the length and width of the rectangle should be checked separately).</p><p> The "go, no-go" gauge block gives a good or bad result. If the object is bad, the gauge block does not give any information as to why it is bad. For example, if a tool becomes dull during cutting and a cutting error occurs, it is useful to know the exact location where this happened, but this information cannot be obtained from the gauge block.</p><p> Another known method for checking that an object meets tolerances involves inspection of the object using a coordinate positioning device such as a machine tool. Objects inspected by machine tools are often workpieces machined by machine tools. A machine tool has a spindle on which a probe (contact or non-contact) is mounted, which can be moved in three orthogonal directions X, Y, Z within the range of motion of the machine.</p><p> Contact probes, including touch-trigger probes and analog probes, typically include a housing with a workpiece contact stylus that is flexible to the housing. In a touch-trigger probe, the stylus flexes from its placement position, producing a signal that the stylus has touched the surface of the workpiece (see, eg, UK Pat. No. 1,445977). For analog probes, probe runout is measured continuously while the stylus is moved along the surface of the workpiece (see, eg, UK Pat. No. 15,512,18). Of course, the analog probe can be connected to a digital processor to provide a digital output.</p><p> The non-contact probe is placed close to the surface of the workpiece without touching it. The probe uses, for example, capacitance, inductance or optical means to detect surface proximity.</p><p> For each feature, the contact probe and non-contact probe relay a significant amount of dimensional measurement data to the controller, which may include a computer program. For example, analog probes relay measurements of thousands of dimensions. The probe measurement data along with the position information of the machine allows the controller to construct a precise image of the dimensions of the workpiece. In order to assess whether the workpiece is within tolerances, the dimensional measurements obtained by the probe must be compared to the desired measurements of the workpiece.</p><p> The appearance must be measured at a sufficiently slow rate for the data collected from each point where the probe sways on the appearance. In some types of coordinate positioning devices such as machine tools, the probe is battery operated and measurement data is sent from the probe to the control device via a wireless link, such as an optical or wireless link. These communication signals run out of battery energy. With a significant number of measured points and the data relayed by them, the entire process consumes a lot of battery energy and time.</p>

<p> According to the present invention, a method of using a measuring probe on a measuring device to determine whether the dimensions of an object (such as a workpiece) meet tolerances. Steps to move the measurement probe around the path to the object, based on the tolerance of the object, A step of monitoring any probe measurement data acquired by the measurement probe as it is moved around the path, and It includes a step indicating that the dimensions of the object do not match the tolerance only if the state of the probe measurement data acquired as the measurement probe is moved around the path changes.</p><p> This method can be performed using a contact probe. In a contact probe, such as a touch trigger probe, the change in state of the probe measurement data acquired by the measurement probe can be a change between a biased probe state and an unbiased probe state.</p><p> The contact probe may also include an analog probe. In the case of analog probes, changes in the state of the probe measurement data occur, for example, when the probe measurement data changes from a predetermined measurement range to outside that range, or when the probe measurement data exceeds a predetermined measurement threshold. obtain.</p><p> In analog probes, the change in state between the biased and non-biased states occurs when the probe runout measurement exceeds a predetermined runout measurement threshold. For example, a deflected state occurs when the probe runout is greater than a predetermined runout measurement threshold, and an unbiased state occurs when the probe runout is less than a predetermined runout measurement threshold.</p><p> This method can also be performed using a non-contact probe. In a non-contact probe, a change in the state of the probe measurement data occurs, for example, when the probe measurement data changes from within a predetermined measurement range to outside the predetermined measurement range, or when the probe measurement data exceeds a predetermined measurement value threshold. Occurs.</p><p> Advantageously, the predetermined measurement range depends on the tolerance of at least one object. Preferably, the given measurement threshold depends on the tolerance of at least one object.</p><p> Object tolerances define the maximum and minimum size of an acceptable object. For example, in the case of cylinders, the minimum tolerance is a smaller diameter concentric cylinder and the maximum tolerance is a larger diameter concentric cylinder. The path by which the measuring probe is moved is based on the tolerance of the object, i.e. the probe is moved through the coordinates that define the tolerance of the object, or the probe deviates from the coordinates that define the tolerance of the object. It is moved through the coordinates.</p><p> The method of the present invention is faster and more versatile than the prior art "go, no-go" gauges described above. The "no-go" block can only check one aspect of a part at a time to prevent defective products from accidentally passing the inspection, but the probe is in "go" or "no-go" mode. Any number of parts can be measured at one time. The present invention also overcomes the problem of rejecting non-defective products due to the tolerances of the gauge block itself. Using the present invention, it is possible to measure the exact point at which an object fails the tolerance test, which is not possible with the use of simple gauge blocks.</p><p> Advantageously, the step of monitoring any probe measurement data acquired by the probe as it is moved around the path is performed within the probe itself. In other words, the measurement probe can include a check unit for performing a step of monitoring probe measurement data acquired by the measurement probe as it is moved around the path.</p><p> This has the advantage that when utilizing a wireless analog or non-contact probe, it uses significantly less battery energy than the method of inspecting with a conventional probe and is much faster, which is when the test fails. The reason is that only the signal needs to be sent. As a result, when testing object tolerances, only a few signals, if any, are sent. This significantly reduces the amount of data transmitted compared to the thousands of signals required to generate precise 3D images, thereby reducing battery energy.</p><p> Alternatively, the measurement probe outputs all or most of the probe measurement data to the associated check unit, which performs the step of monitoring any probe measurement data. The interface or controller may include an associated check unit. This method has the advantage of being faster than the prior art methods described above, because it is not necessary to calculate the 3D representation of the object by combining machine position and probe measurement data. is there.</p><p> Advantageously, if the measuring device is equipped with a machine tool having a main processor for controlling machine tool operation, the step of indicating that the dimensions of the object do not meet the tolerances is described above as the main processor. Includes steps to provide to. This allows the main processor to determine the next action to take. If the size of the object is too large, for example, the main processor of the machine tool can operate the machine to machine the object again.</p><p> Advantageously, a sensor output is provided somewhere on the probe or associated check unit to indicate to the operator that the dimensions of the object do not meet tolerances. The sensor output unit may be, for example, an LED or a buzzer.</p><p> The measurement probe may be, for example, a contact probe such as a touch trigger probe or an analog probe, or a non-contact probe such as a capacitance, inductance or optical probe.</p><p> The measuring device used in the method of the present invention may include, for example, a coordinate positioning device such as a dedicated coordinate measuring machine (CMM) or a machine tool such as a lathe or a machining center.</p><p> Preferably, the step of moving the measurement probe around the path to the object is performed by a "rapid" mode, i.e., a probe at such a speed that the probe can proceed without providing erroneous measurement data.</p><p> Advantageously, the path to the object may include only the first path. In such an example, when the measurement probe is moved around the first path, the probe measurement data needs to remain in one state with respect to the object that should be within the tolerance. In order for the probe measurement data to remain in one state, it must remain within a predetermined measurement data range that depends on the tolerance of at least one object. When the probe measurement data moves out of a certain range and changes the state of the probe measurement data, a signal is sent indicating that the object does not meet the tolerance. Advantageously, such methods are used with contact probes such as analog probes and non-contact probes such as capacitance, inductance or optical probes.</p><p> Conveniently, the path to the object may include a first path and a second path. The first and second paths may be based on the dimensions of the object allowed by the maximum and minimum tolerances. The dimension allowed by the maximum tolerance is, for example, in the case of a cylinder, the maximum allowable size of the cylinder. The dimension allowed by the minimum tolerance is, for example, in the case of a cylinder, the minimum allowable size of the cylinder. When the measurement probe is moved around the first path, the probe measurement data must remain in the first specific state, and when the probe is moved around the second path, the probe measurement data is within tolerance. It is necessary to stay in the second specific state for the object that should be in. This method can be used with contact probes such as touch trigger probes or analog probes, and non-contact probes such as capacitance, inductance or optical probes and is most suitable for touch trigger probes.</p><p> This method may include a further step of rescanning within said area of the object to find the exact location of the failure if the first scan informs of an obstacle within that area. The rescan step is preferably performed at a slower rate than the first scan in order to more accurately find the point where the object failed.</p><p> Preferred embodiments of the present invention are described with reference to the accompanying drawings for illustrative purposes only.</p>

<figref num="1">FIG. 5 is a side view of a "go, no-go" gauge block in the prior art and an object having an appearance tested by the gauge.</figref><figref num="2">The probe installed in the machine tool on the workpiece is shown schematically.</figref><figref num="3">The plan view of the workpiece having a hole is shown.</figref><figref num="4a">The perspective view of the cylinder is shown.</figref><figref num="4b">The plan view of the cylinder is shown.</figref><figref num="5a">The plan view of the workpiece having a hole is shown.</figref><figref num="5b">The change in stylus runout over time when scanning the hole in Figure 5a is shown.</figref><figref num="6a">It is a flow chart which shows the data outside the tolerance output by a probe.</figref><figref num="6b">It is a flow chart which shows the data which is out of tolerance output by an interface, that is, a control device.</figref>

FIG. 2 in the attached drawing shows the workpiece installed on the machine tool. The measuring probe 6 is placed on the spindle 2 of the machine and held in place by the tool holder 4. This is the same position where the cutting tool would be held when machining the appearance 12 on the workpiece 14. The probe includes a probe body 5, a stylus 8, and a stylus tip 10. The workpiece 14 is installed on the machine tool base 16.

In this case, the spindle 2 and the measuring probe 6 can move in the X, Y and Z directions under the action of X, Y and Z drives controlled by a computer, interface or machine control device. Meanwhile, the platform remains stationary. The X, Y and Z scales (including the counter for the output of that scale) indicate the instantaneous three-dimensional coordinates of the position of the spindle 2 where the measuring probe 6 is installed. The measured readings sent from the measuring probe 6 are combined with the readings from the X, Y and Z scales to allow the calculation of the position of the stylus tip and thus the position on the surface of the workpiece.

A stationary platform is shown, but the machine tool can include a spindle and measuring probe that move only in the Z direction, whereas the platform moves in X and Y. Any combination of three degrees of freedom resulting in the movement of the probe relative to the workpiece is possible.

Machine tools have been described above, but other measuring devices such as dedicated CMMs, robots and non-Cartesian measuring machines can be used.

FIG. 3 shows a plan view of the workpiece 14 having the machined holes 20. The device described with reference to FIG. 2 can be used to check hole tolerances.

When checking the hole 20 in "go" mode, the probe stylus is initially unbiased and is moved by the controller along the "go" path 22 based on the minimum acceptable diameter d1 of the hole. If the probe stylus remains unbiased at all positions on this path, no signal is sent to the data collector (eg, machine control) and the workpiece passes the "go" inspection. If the stylus is deflected somewhere along the "go" path, the machine latches at that point, records the XYZ position of the probe runout, and the hole is smaller than the minimum acceptable diameter d1. Having a diameter, the workpiece fails the "go" tolerance test.

In this case, passing the "go" test means that the diameter of the hole is greater than the smallest diameter specified by the tolerance. If the workpiece fails the "go" inspection, it is further machined and checked again.

When checking the hole 20 in "no go" mode, the probe stylus is first deflected against the surface of the hole and by the controller a "no-go" path 18 based on the maximum acceptable diameter d2 of the hole 18 Moved around. The "no-go" path is chosen so that the stylus repositioning position is outside the tolerance. If the stylus remains deflected at all positions on the path, no signal is sent and the workpiece passes a "no-go" inspection. If the stylus is repositioned, i.e., the stylus is not deflected during the process, the machine latches at that position and records the XYZ position where the stylus is repositioned. The feature fails the "no-go" tolerance test.

In this case, passing the "no-go" test means that the diameter of the hole is smaller than the maximum diameter specified by the tolerance. If the work fails the "no-go" inspection, the work should be eliminated.

The maximum and minimum dimensions of the workpiece can be calculated by adding and subtracting tolerances to the known desired surface shape of the workpiece.

In the examples of this method, it is most preferable to use the touch trigger probe described above. The analog probe must be in a deflected state due to this embodiment of the method, ie, the workpiece that should be within tolerances within one path (ie, the deflection of the probe is capped). Two paths (greater than), within the other path, where the probe must be unbiased (ie, probe runout must be less than the lower bound) due to the workpiece to be within tolerances. It can be used in the same way as a touch trigger probe when following the embodiment by moving the probe around.

This embodiment is also suitable for use with non-contact probes such as optical, capacitance, and inductance probes. In this case, the distance of the workpiece from the probe is measured at a point along the path. A geographic object passes the "go" test if it follows a "go" path and the distance reading is above a defined level (ie, the workpiece is further away from the probe than the tolerance limit). However, if the distance reading drops below the defined level, the part fails the "go" test. If the distance reading is below a defined level (ie, the feature is closer to the probe than the tolerance limit) following a "no-go" path, the feature is tested "no-go". However, if the distance reading rises above the defined level, the part fails the "no-go" test. In each case, the defined level is divided into two state states of the probe (eg, activated and inactive).

From the hole to the protrusion, the "go" and "no-go" paths are reversed. FIG. 4a shows a geographic feature 40, which is a cylinder with a reference diameter of 42. FIG. 4b is a plan view of the cylinder showing its diameter tolerance limits. In this case, the path 44 describing the minimum acceptable diameter d1 of the cylinder forms a "no-go" path and the path 46 describing the maximum acceptable diameter d2 of the cylinder forms a "go" path. To do.

With reference to FIG. 5, other methods of the present invention are shown. FIG. 5a shows the workpiece 50 with the holes 52, and FIG. 5b shows the change in stylus runout over time as the workpiece is scanned. In this example, the probe stylus is associated with a maximum runout 56 and a minimum runout 54 corresponding to the minimum tolerance diameter d3 and the maximum tolerance diameter d4 of the holes 52, respectively. If the probe stylus runout is within the range 54-56 when the probe is moved around the path, the workpiece is within tolerance and passes inspection. If the probe stylus is deflected beyond the upper limit 56 (at 36), the machine latches and signals the machine controller that the workpiece needs further machining. If the probe stylus is deflected below the lower limit 54, the machine latches and signals that the workpiece should be eliminated.

For cylinders, the minimum acceptable cylinder diameter can be associated with the minimum acceptable runout, and the maximum acceptable cylinder diameter can, as a result, be associated with the maximum allowable runout. Again, if the probe stylus swings beyond the upper limit 56, the machine latches and signals the machine controller that the workpiece needs further machining. If the probe stylus swings below the lower limit 54, the machine latches and signals that the workpiece should be eliminated.

This method is made feasible using analog probes, as described above. This method is also suitable for non-contact probes such as, for example, optical, inductance, and capacitance probes. Such a probe measures the distance from the probe of the workpiece. The upper and lower distances are set corresponding to the tolerance limits to define the probe output in the range allowed by the tolerance. The machine will latch and signal only if the probe output is out of the allowed range.

The method of determining whether the dimensions of the workpiece meet the tolerances may include a further step of rescanning the area of the workpiece. If the first scan signals that a given area is faulty, the scan may be repeated at a slower rate in that area to more precisely determine where the feature failed. Becomes possible.

Other types of machined appearances that can be checked for tolerance support using the present invention include, for example, corners, chamfers and straight edges.

FIG. 6a is a flow chart showing the method according to the present invention, in which the probe 60 outputs only out-tolerance data to the interface, that is, the control device 62. FIG. 6b is a flow diagram showing that the probe 60 outputs all the measurement data to the interface or the control device 62.

The examples described above with respect to FIGS. 2-5 include signals sent from the probe to the controller / interface only when the workpiece is out of tolerance, as shown in the flow diagram of FIG. 6a. Alternatively, the probe can send a controller / interface signal at all points along its path, and the controller / interface will machine the signal if the dimensions of the workpiece do not meet tolerances. It can be sent to a controller or interface, which is shown in the flow diagram of Figure 6b. In this case, only the out-tolerance data is output to the interface, i.e. the controller 62.