DIGITIZING METHOD

Abstract: This invention relates to a digitizing method which digitizes model surface data by profiling a model (MDL) by a stylus (STL). When digitization is to be made, a time (T) required till predetermined conditions are established and a stylus moving distance (▵L) during this time are monitored so as to determine a profiling speed (F) from the time and the moving distance. The profiling speed is outputted along with the model surface shape data.

Description: Technical Field This invention relates to a digitizing method and, more particularly, to a digitizing method in which tracing velocity at the time of digitizing is outputted as velocity data along with model profile data. Background Art A method of creating NC data for performing machining in accordance with the profile of a model is available and includes tracing the surface of the model with a stylus by means of tracer control, digitizing the model surface profile by accepting stylus position data at a predetermined period T, and creating the NC data using the digitized data. Fig. 5 is an explanatory view in which profile data indicative of the surface of a model MDL is digitized by two-way surface tracing. A stylus STL is moved in the direction of the X axis at a predetermined tracing velocity and up and down along the model MDL in the direction of the Z axis, and stylus three-dimensional position data (coordinates) Xi, Yi, Zi and displacement data εx, εy, εz are accepted and stored at predetermined times or whenever predetermined conditions are satisfied. When the boundary of a tracing region TRR is reached, a predetermined amount of pick-feed is performed along the Y axis. Thereafter, the position and displacement of the stylus STL are monitored while surface tracing is performed in the same manner, the resulting position data and displacement data is accepted, the surface profile of the model MDL is digitized, and NC data is subsequently created using the digitized data. In general, when digitizing is carried out by such tracing, stylus center-position data and displacement data is read in but velocity information is not. When the NC data is created, feed rate is set by an F code using an MDI unit (manual data input unit) or the like. However, if the set F code (feed rate) is greater than the machining capability of the machine tool, tool breakage can result. Conversely, if the F code is less than the machining capability of the machine tool, too much machining time is required. Consequently, when performing machining by NC data created using digitized data, it is required conventionally that the operator manipulate an override switch or the like to vary the machining velocity, which is based on the F code, over a range of, say, 0 - 120%, or to revise the machining velocity to an appropriate value. As a preliminary step towards solving the above problems, European patent no. 0139011, belonging to the present patentees, is herein referred to. This document discloses a profiling control apparatus, designing to prevent any biting of a cutter at points at which the shape of a model to be copied suddenly changes. A sampling circuit samples a composite displacement signal at predetermined periods, whilst sampling circuits sample signals indicating displacements in the x-y and z axial directions respectively. An arithmetic circuit obtains the angle formed between the displacement vector of a stylus in the present sampling period and the displacement vector of the stylus in the last sampling period. A comparator compares the result of the calculation performed by the arithmetic circuit with a reference level to control the feed rate so that it is reduced or not reduced depending on the result of the comparison. Thus biting of the cutter is prevented but a number of problems including constant fluctuation of the machining velocity begin to appear. Accordingly, an object of the present invention is to provide a digitizing method in which tracing velocity at the time of digitizing is outputted as velocity information along with model profile data. Disclosure of the Invention In order to output tracing velocity at the time of digitizing as velocity information, travelling distance ΔL within a predetermined time period T is obtained, tracing velocity F (= ΔL/T) is calculated using this time period and travelling distance, and the tracing velocity F is outputted as velocity information along with model profile data. In accordance with a first aspect of the present invention there is thus provided a digitizing method for tracing a model surface with a stylus by tracer control and digitizing a profile of the model surface upon reading in stylus position data at predetermined periods T, comprising the steps of: for each period T calculating increments Δx, Δy, Δz, along respective axes of stylus movement, and calculating travelling distance using these increments; obtaining tracing velocity and travelling distance in each period T; and outputting said tracing velocity as velocity data F along with the calculated increments being data indicative of the model surface profile and characterised by: comparing said tracing velocity data F and the last previous outputted velocity data F', suppressing output of the velocity data if the difference ΔF between these two velocities is less than a set value and outputting said tracing velocity data F as velocity data along with the model surface profile data only if the difference ΔF exceeds the set value. In accordance with a second aspect of the present invention there is thus provided a digitizing method for tracing a model surface with a stylus (STL) by tracer control and digitizing a profile of the model surface upon reading in stylus position data whenever a predetermined condition is satisfied, comprising calculating increments Δx, Δy, Δz, along respective axes of stylus movement, during a time that said condition is satisfied and monitoring a time T required for the condition to be satisfied; calculating travelling distance using said increments and obtaining tracing velocity from the time T and the travelling distance; and outputting said tracing velocity as velocity data F along with the calculated increments being data indicative of the model surface profile, and characterised in that said condition is satisfied when a distance from a present position (Q3) of the stylus to a straight line connecting the two latest digitized points (Q,Q₂) is greater than a preset value (d) and wherein said tracing velocity data F and the last previous outputted velocity data F' are compared, output of velocity data is suppressed if the difference ΔF between these two velocities is less than a set value, and said velocity data F is output as velocity data along with the model surface profile data only if the difference ΔF exceeds the set value. Reference will now be made, by way of example to the accompanying drawings. Brief Description of the Drawings Fig. 1 is a schematic explanatory view of the method of the present invention; Fig. 2 is a block diagram of a system for practicing the method of the present invention; Fig. 3 is a flowchart of processing according to the method of the present invention; Fig. 4 is view for describing other conditions when processing according to the invention is performed; and Fig. 5 is an explanatory view in which data indicative of the surface of a model MDL is digitized by two-way surface tracing. Fig. 1 is a schematic explanatory view of the method of the present invention. STL represents a stylus, TH a tracer head, MDL a model, and T the time (e.g., period) required for predetermined conditions to be satisfied. Further, Δx, Δy, Δz denote increments along the respective axes, ΔL the resultant value (traveling distance) of the increments, F the tracing velocity, and F' the latest outputted velocity information. When model surface data for course machining is digitized by pencil tracing, manual tracing or the like, the operator takes the machining capability of the machine tool into consideration and digitizes the surface data while tracing is carried out at an appropriate velocity. Therefore, when NC data is created using digitized data resulting from pencil tracing or manual tracing, it is convenient if the tracing velocity prevailing at the time of digitizing is outputted as machining velocity. In the present invention, when digitizing is carried out, the increments Δx, Δy, Δz along the respective axes within the predetermined time period T are calculated, the traveling distance ΔL is calculated in accordance with the equation ΔL = √ Δx² + Δy² + Δz² the tracing velocity F is calculated from F = ▵L/T , and the tracing velocity F is outputted as velocity information along with the stylus position data and displacement data. Further, velocity information is not outputted when a difference ΔF between the calculated tracing velocity F and the latest outputted velocity information F' is less than a predetermined value. The velocity information F is outputted, and the velocity information F' is replaced by the velocity information F (F → F'), only when ΔF is greater than the predetermined value. Fig. 2 is a block diagram of a system for practicing the method of the present invention. Numeral 1 denotes a digitizer having a digitizing function for accepting the present position Xi, Yi, Zi of a stylus while tracer control is being performed. The digitizer 1 has a processor 1a, a ROM 1b storing a control program, a RAM 1c for storing digitized position data, and a working memory 1d. The digitizer 1 calculates the increments Δx, Δy, Δz along the respective axes, and calculates the resultant value (traveling distance) ΔL of the increments in accordance with the equation ΔL = √ Δx² + Δy² + Δz² (1) The traveling distance ΔL is calculated whenever predetermined conditions are satisfied, e.g., at a sampling period T. The digitizer then computes the tracing velocity F from the equation F = ΔL/T (2) and stores the tracing velocity F as velocity information, along with the stylus present-position data Xi, Yi, Zi and displacement data εx, εy, εz, in the RAM 1c. In actuality, the tracing velocity (velocity information) F and latest stored velocity information F' are compared and the velocity information is not stored in the RAM 1c when the difference ΔF is less than a predetermined value. The velocity information F is stored in the RAM 1c, and the velocity information F' is replaced by the velocity information F (F → F'), only when ΔF is greater than the predetermined value. Numeral 2 denotes an operator's panel having functions for inputting various operation signals and setting tracing conditions, tracing region TRR (see Fig. 5), tracing method and the like. Numerals 10X, 10Y, 10Z denote DA converters for converting velocity data (digital values) along respective axes commanded by the digitizer 1 into respective analog velocity signals Vx, Vy, Vz. Numerals 11X, 11Y, 11Z denote X-, Y- and Z-axis servo circuits, respectively; 12X, 12Y, 12Z denote X-, Y- and Z-axis servomotors, respectively; 13X, 13Y, 13Z represent pulse generators for generating single pulses Xf, Yf, Zf, respectively, each time the corresponding motors rotate through a predetermined angle; and 14 denotes a present-position register for reversibly counting the pulses Xf, Yf, Zf, in accordance with the direction of travel, to store the present positions Xi, Yi, Zi along the respective axes. TH represents a tracer head, SR a stylus, and MDL a model. The processing according to the method of the invention will now be described in accordance with the flowchart of Fig. 3. It is assumed here that two-way surface tracing is carried out manually with the X, Z and Y axes serving as the feed axis, tracing axis and pick-feed axis, respectively, that surface data is created upon reading in, at predetermined times, the coordinates of the stylus position (the black dots in Fig. 1), amount of stylus displacement and tracing velocity by means of digitizing processing performed in concurrence with the aforementioned tracing, and that the surface data is stored in the RAM 1c. When the abovementioned digitizing is carried out, first the velocity data is set and digitizing is started by the operation 0 → F' (step 101). Thereafter, the digitizer 1 determines whether digitizing in a predetermined region, such as the tracing region TRR shown in Fig. 5, by way of example, has ended (step 102). If the answer is NO, the digitizer reads in the position data Xi, Yi, Zi in the present-position register 14 at the sampling period T (step 103) and calculates the increments Δx, Δy, Δz along the respective axes based on the position data Xi, Yi, Zi and position data Xi-1, Yi-1, Zi-1 read in one sampling instant earlier (step 104). Next, the traveling distance ΔL is calculated in accordance with Eq. (1) (step 105), and the tracing velocity F is calculated from Eq. (2) (step 106). Thereafter, the tracing velocity F and velocity information F' (the initial value of which is zero) one sampling instant earlier are compared (step 107). If the velocity difference between the two is greater than a predetermined value, the velocity data F' is updated by the operation F → F' (step 108) and the velocity data F' is stored in the RAM 1c along with the stylus center-position data (Xi, Yi, Zi) and displacement data (εx, εy, εz) prevailing at the sampling period T (step 109). When the processing of step 109 is terminated, operation returns to step 102 and processing from this step onward is repeated. When it is determined at step 102 that digitizing in the predetermined region has ended, processing according to the present invention is terminated. If the velocity difference ΔF is found to be less than the predetermined value at the decision of step 107, then processing jumps to step 109 without the velocity information F' being updated. In this case, only the stylus center-position data and displacement data is stored in the RAM 1c; velocity information is not stored. According to the foregoing embodiment, a case is described in which digitizing data is created at the predetermined sampling time T. However, as shown in Fig. 4, an arrangement can be adopted in which, when the two latest digitized points are designated by Q1, Q2 and the position sampled at the period T is designated by Q3, the distance d from the point Q3 to the straight line Q1Q2 is compared, in terms of magnitude, with a preset tolerance value a , and the point Q3 is not digitized if the distance d is less than the tolerance value a but is digitized if d is greater than a . In this case, if the digitized point Q3 is a point sampled a time n·T after the digitized point Q2, then the tracing velocity F is calculated in accordance with the equation F = ΔL/n·T (3) Thus, in accordance with the present invention, the arrangement is such that the increments Δx, Δy, Δz along the respective axes during the time that the predetermined conditions are satisfied are calculated, the time T required for the conditions to be satisfied is monitored, tracing velocity at digitizing is calculated using these increments and time data, and the tracing velocity is outputted as velocity information (an F code). This is advantageous in that machining can be performed at a velocity identical with that at the time of digitizing. Further, in accordance with the present invention, the arrangement is such that the calculated tracing velocity F and the latest outputted velocity information F' are compared, and the velocity information F is outputted only when the difference between these velocities has exceeded a predetermined value.. As a result, the machining velocity will not undergo small fluctuations.

Claims: A digitizing method for tracing a model surface with a stylus (STL) by tracer control and digitizing a profile of the model surface upon reading in stylus position data at predetermined periods T, comprising the steps of: for each period T calculating increments Δx, Δy, Δz, along respective axes of stylus movement, and calculating travelling distance using these increments; obtaining tracing velocity and travelling distance in each period T; and outputting said tracing velocity as velocity data F along with the calculated increments being data indicative of the model surface profile and characterised by: comparing said tracing velocity data F and the last previous outputted velocity data F', suppressing output of the velocity data if the difference ΔF between these two velocities is less than a set value and outputting said tracing velocity data F as velocity data along with the model surface profile data only if the difference ΔF exceeds the set value. A digitizing method for tracing a model surface with a stylus (STL) by tracer control and digitizing a profile of the model surface upon reading in stylus position data whenever a predetermined condition is satisfied, comprising calculating increments Δx, Δy, Δz, along respective axes of stylus movement, during a time that said condition is satisfied and monitoring a time T required for the condition to be satisfied; calculating travelling distance using said increments and obtaining tracing velocity from the time T and the travelling distance; and outputting said tracing velocity as velocity data F along with the calculated increments being data indicative of the model surface profile, and characterised in that said condition is satisfied when a distance from a present position (Q3) of the stylus to a straight line connecting the two latest digitized points (Q,Q₂) is greater than a preset value (d) and wherein said tracing velocity data F and the last previous outputted velocity data F' are compared, output of velocity data is suppressed if the difference ΔF between these two velocities is less than a set value, and said velocity data F is output as velocity data along with the model surface profile data only if the difference ΔF exceeds the set value.

Inventors: ARAMAKI HITOSHI, MATSUURA HITOSHI KEIOH-YAMADA, ARAMAKI, HITOSHI, MATSUURA, HITOSHI,KEIOH-YAMADA MANSHON 1-406
Applicants: FANUC LTD, FANUC LTD.
Application year: 1989
Main classification: B23Q35
IPC codes: G05B19, B23Q35