Patent Publication Number: US-4224670-A

Title: Tracer control system

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a tracer control system which enables arbitrary setting of the tracing path of a tracer head. 
     2. Description of the Prior Art 
     In conventional tracer control systems, limit switches are provided for defining the tracing path of a tracer head, for example, the range of tracing in the x-y plane. The limit switches are actuated by the movement of a tracing machine, by which a predetermined pick feed is carried out and then the direction of tracing is reversed, thus performing the tracing operation. By repeating such operations to trace a model with a stylus of a tracer head, a workpiece is machined. Accordingly, the positions of the limit switches must be adjusted in accordance with the size of the model, and the limit switches are mechanically actuated, so that the reliability of the tracing operation is relatively low. 
     SUMMARY OF THE INVENTION 
     This invention is to provide a tracer control system which is free from the abovementioned defects of the prior art and in which data for a tracing operation is previously inputted and stored in a memory to control the tracing path and in which the tracing path can be set, as desired, in accordance with a change in input data. 
     Briefly stated, in the tracer control system of this invention, data defining the tracing operation is inputted from an input device and stored in a memory, and the stored data is read out by a processor which controls the tracing path of a tracer head tracing a model. The tracing operation can be changed by modifying the stored data in the memory. Data defining the tracing operation, which is obtained by a manual feed, can also be stored in the memory. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram illustrating an embodiment of this invention; 
     FIG. 2 is a schematic diagram explanatory of an example of a tracing path; 
     FIG. 3 is a flowchart explanatory of the operation of the embodiment of this invention; and 
     FIG. 4 is a schematic diagram explanatory of the tracing path in another embodiment of this invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates in block form an embodiment of this invention. Reference characters DG and IND respectively indicate a displacement calculation circuit and an indexing circuit which are both supplied with displacement signals ε x , ε y  and ε z  derived from a tracer head TR; ARN and ART designate speed control circuits; ADD identifies an adder; DC denotes a distribution circuit; COMP represents a comparator; GC shows an analog gate circuit; DRVX, DRVY and DRVZ refer to amplifiers; MX, MY and MZ indicate servomotors; PCX, PCY and PCZ designate position detectors; MDL identifies a model for machining; ST denotes a stylus; CT represents a cutter; W shows a workpiece; MAC refers to a tracing machine; CONTX, CONTY and CONTZ indicate reversible counters each of which counts pulses from each of the position detectors PCX, PCY and PCZ to indicate the current tracer head position; MAN designates a manual operation control circuit; OPP identifies an operator panel; RS denotes a setting dial for the tracing speed, etc.; BT1 and BT2 represent push buttons; KB shows a keyboard; DSP refers to a display unit; DI indicates a data input unit; MEM designates a memory composed of a data memory M1 and a control program memory M2; DO identifies a data output unit; CPU denotes a processor; and DA1 and DA2 represent D-A converters. 
     In accordance with displacement of the stylus ST held in contact with the model MDL, the displacement signals ε x , ε y  and ε z  from the tracer head TR are applied to the displacement calculation circuit DG and the indexing circuit IND to derive therefrom a composite displacement signal ε=√ε x  2+ε y  2+ε z  2 and displacement direction signals sin θ and cos θ, respectively. The composite displacement signal ε is provided to the adder ADD to obtain a difference Δε between the signal ε and a reference displacement signal ε 0 . The output from the adder ADD is supplied to the velocity control circuits ARN and ART to produce a reference direction speed signal V N  and a tangential direction speed signal V T , respectively. The output signals V N  and V T  from the speed control circuits ARN and ART are both applied to the distribution circuit DC to derive therefrom command speed signals based on the displacement direction signals sin θ and cos θ  supplied from the indexing circuit IND. The command speed signal is applied to the analog gate circuit GC and then provided to that one of the amplifiers DRVX, DRVY and DRVZ which is selected by the analog gate circuit GC. The servo motors MX, MY and MZ are selectively driven in response to the command speed signal to operate the cutter CT and the tracer head TR together. Since the abovementioned operation is well-known in the art, no detailed description will be given. 
     In this invention, data for the tracing operation is inputted from the keyboard KB and stored in the memory MEM, from which the stored data is read out as the tracing operation proceeds, thereby controlling the tracing path. Thus, this invention dispenses with limit switches, which are required in the prior art, and permits easy setting and modification of the tracing path. By way of example, the input data may be such as shown in the following table. 
     
                       TABLE 1                                                     
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Item              Symbol       Code                                       
______________________________________                                    
Mode              (Refer to    A01                                        
                  table 2)                                                
Reference displace-                                                       
                  ε.sub.o                                         
                               A02                                        
ment value                                                                
Approach axis     X, Y, Z      A03                                        
Approach direction                                                        
                  +, -         A04                                        
Approach speed    V.sub.AP     F1                                         
Tracing direction +, -         A05                                        
Tracing speed     V.sub.TF     F2                                         
Pick feed direction                                                       
                  +, -                                                    
Pick feed speed   V.sub.PF     F3                                         
Pick feed value   P            A06                                        
Tracing stroke limit                                                      
                  L.sub.P      X1                                         
Tracing stroke limit                                                      
                  L.sub.N      X2                                         
Tracing control end                                                       
                  L.sub.TE     Y1                                         
Automatic return  ON, OF       A07                                        
Automatic return speed                                                    
                  V.sub.AR     F4                                         
Automatic return  L.sub.RP     Z1                                         
position                                                                  
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                       TABLE 2.                                                    
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Mode                 Submode                                              
______________________________________                                    
1      Manual tracing                                                     
2      Forward/reverse scan                                               
       tracing           45 degree tracing                                
3      Partial contour                                                    
       tracing                                                            
4      360 degree contour                                                 
                         Axial pick feed                                  
       tracing           Z-axis pick feed                                 
5      Partial contour                                                    
       tracing                                                            
6      3-dimensional                                                      
       tracing                                                            
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     In the case of achieving such a tracing operation as shown in FIG. 2 in which the tracing operation starts from the point A towards the point a and proceeds via the route [a-b-c- . . . u-v], with the tracing stroke limit L P  =X1,L N  =X2, the pick feed value=P, the tracing control end L TE  =Y1 and the automatic return position L RP  =Z1, and then the tracing operation is automatically returned from the tracing control end Y1 to the position Z1, control is performed in accordance with the flow-chart shown in FIG. 3. 
     Upon depression of an approach button (not shown), the processor CPU reads out data of the approach axis, the approach direction and the approach speed from the memory MEM to apply a signal via the data output unit DO to the analog gate circuit GC to actuate the amplifier DRVZ, causing the servo motor MZ to lower the tracer head TR and the cutter CT. The lowering speed of the tracer head TR and the cutter CT can be determined by data supplied via the data output unit DO to the D-A converter DA2. 
     Before the stylus ST is lowered into contact with the model MDL, the deflection signals ε x , ε y  and ε z  are zero, so that the difference signal Δε remains equal to the nominal deflection signal ε 0 . When the stylus has been brought into contact with the model and the signal ε has become equal to the reference displacement signal ε 0 , the comparator COMP detects that Δε=0, and provides an approach end signal AE to the data input unit DI. When the processor CPU has read the approach end signal AE to detect completion of the approach, the tracing operation is initiated. 
     Upon starting of the tracing operation, the processor CPU reads data of the tracing mode, the reference displacement value, the tracing direction and the tracing speed to start tracing control. The reference displacement data is converted by the D-A converter DA1 into the reference displacement signal of an analog form for input to the adder AND. The servo motor MX is driven in the direction dependent upon the tracing direction data. The processor CPU also reads out the tracing stroke limits L P  and L N  from the memory MEM to compare them with the content of the reversible counter CONTX indicating the current position of the stylus ST. 
     For instance, in a one-way tracing operation, when the content of the reversible counter CONT X is equal to the tracing stroke limit L N , the axis is switched, and the processor CPU reads data of the pick feed direction, the pick feed rate and the pick feed value P to control the pick feed. When the content of the reversible counter CONT Y has become equal to the pick feed value P after starting of the pick feed, the processor CPU achieves a tracing return operation, i.e. tracing in the + direction. Further, the processor CPU reads the tracing control end position L TE  to detect whether or not the tracing has reached there during the pick feed operation. 
     If it is detected that the tracing has reached the tracing control end position L TE  during the pick feed operation, the processor CPU reads out the data of the automatic return, the automatic return speed and the automatic return position L RP  from the memory MEM, and based on the data of the automatic return being ON, the servo motor MZ is driven, and when the content of the reversible counter CONTZ becomes equal to the value of the automatic return position L RP , the tracing control is completed. 
     The data of the tracing stroke limits L P  and L N , the tracing control end position L TE , the automatic return position L RP  and the pick feed value P, mentioned above, need not always be inputted from the keyboard KB but may also be set in the memory MEM. That is, the contents of the reversible counters actually obtained in the case of tracing in the manual feed mode are set in the memory MEM. 
     Also it is possible to rewrite the data of the memory MEM during the tracing operation. In other words, the tracing path can be modified at any time. The rewrite is achieved, for example, by modifying input data from the keyboard KB which is read and displayed on the display unit DSP. Thus, the pick feed start position, that is, the tracing stroke limit L P  or L N , can be easily changed. In the case of changing the tracing speed, the push button BT1 on the operator panel OPP is depressed to provide an override and when the tracing speed has been adjusted by the actuation of the setting dial RS to a value which is considered to be optimum for the cutter CT, the push button BT2 is depressed to write the speed data in the memory MEM. Thereafter, the tracing takes place at the newly set speed. 
     Also in the case of performing partial tracing, for example, from a start point S1 to an end point E1 and from a start point S2 to an end point E2, as shown in FIG. 2, tracing control can be achieved continuously by predetermining the pick feed value and the tracing stroke limits for each area of tracing. Moreover, modes of tracing operation can also be set so that scan tracing is followed by contour tracing. 
     As has been described in the foregoing, in the present invention, data defining tracing operations, such as shown in Tables 1 and 2, are inputted from the keyboard KB and stored in the memory MEM and then read out therefrom to perform arithmetic operations, decision operations, etc. under the control of the processor CPU, thereby controlling the tracing path. This invention does not require any mechanical limit switches, and hence provides for enhanced reliability in tracing and permits a desired setting of the tracing path. Furthermore, the tracing path can be changed by rewriting the content of the memory MEM during tracing, so that tracer machining can be achieved under optimum conditions. 
     It will be apparent that many modifications and variations may be effected without departing from the scope of the novel concepts of this invention.