Feed speed control system
BACKGROUND OF THE INVENTION 
     This invention relates to a system for controlling the feed speed of a movable member in numerical control equipment or the like. 
     In numerically controlled machining, the optimum feed speed of a movable member, for example, the workpiece table, is decided by taking into account such factors as the life of the cutter and the machining time. If the machining or feed speed is increased without considering the optimum feed speed in an effort to shorten the machining time, the cutter is subjected to an excessive load and is likely to sustain such damage as snapping or chipping. On the other hand, if the machining speed is decreased below the optimum speed in order to prolong the life of the cutter, the numerically controlled machining operation cannot be performed efficiently because of the excessive increase in machining time. In general, the optimum machining speed is determined by considering a variety of factors such as the hardness of the workpiece, the amount of the workpiece which is to be removed by cutting, the sharpness and flexibility of the cutter and the rigidity of the machine. However, once the optimum machining speed has been determined and punched in the command tape and the machine actually placed in operation, it is often found that the machine should be run at a speed slightly lower than the optimum speed to preclude cutter damage, or at a slightly higher speed to reduce machining time. Hence it is required that a manual adjustment be made to the feed speed of the movable member, which is actually being operated by the command type, to adjust the feed speed to the true optimum feed speed. 
     With the conventional feed speed control system of the type described, however, the manual adjustment of the speed is carried out by manipulating a number of speed command dials, the dials in turn operating in association with corresponding oscillators. The plurality of dials and oscillators which are necessary in the prior art represent a large number of component parts and, since the space required to mount them is limited, it is difficult to construct the apparatus inexpensively and compactly. Moreover, the existence of a plurality of dials makes manual adjustment a complicated matter so that the operator must exercise caution in manipulating the dials. 
     Accordingly, there is a demand for a feed speed control system which does not require a large number of dials and the associated peripheral equipment. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a feed speed control system having a small number of parts and requiring only a small amount of space for mounting. 
     Accordingly, it is an object of the present invention to provide a novel and simply constructed feed speed control system which has a small number of parts and which may be mounted in a small mounting space. 
     It is another object of the present invention to provide a feed speed control system in which manual adjustment of feed speed can be achieved by manipulating a small number of command buttons. 
     It is still another object of the present invention to provide a digitally operable feed speed control system. 
     It is a further object of the present invention to provide a feed speed control system which can be inexpensively constructed. 
     Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein like numerals refer to like parts throughout. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view showing the operation panel of a prior art feed speed control system; 
     FIG. 2 is a prior art block diagram of a feed speed control system; 
     FIG. 3 is a block diagram of an embodiment of a feed speed control system according to the present invention; and 
     FIG. 4 is a block diagram which is useful in describing another embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will first be had to FIGS. 1 and 2 which illustrate a conventional feed speed control system and which are useful for an understanding of the difference between the prior art and the present invention. The operation panel of the conventional system, as shown in FIG. 1, includes a plurality of dials 1, 2, 3 for setting feed speed. Prescribed ones of the dials corresponding to commands F1, F2, F3, which have been punched in a command tape for a machining operation, are designated by the commands, the designated dial being turned by the operator during the actual machining operation to set the optimum feed speed. In addition to the commands F1, F2, F3, a fast-feed command Fo has also been punched in the command tape. The operation panel of FIG. 1 further includes feed speed scales 4, 5, 6 for respective ones of the feed speed setting dials 1, 2, 3, as well as lamps 7, 8, 9 and 10 above which the panel is marked F0, F1, F2 and F3. Whenever the command tape supplies one of the commands F0, F1, F2 or F3, the lamp identified by the corresponding command will light up. 
     The above-described feed speed control system, which is illustrated by the block diagram of FIG. 2, further includes a plurality of pulse oscillators 11, 12, 13 for generating pulses at frequencies which correspond to values designated by the dials 1, 2, 3, respectively; a fast-feed oscillator 14; a tape 15 for designating which of the output pulse trains from the oscillators 11, 12, 13, 14 is to be selected; a tape reader 16; a register 17 for storing the commands F0, F1, F2, F3 punched in the tape 15; and a gate group 18 for selecting an output pulse train from a prescribed pulse oscillator on the basis of the speed command stored in the register 17. The lamps 8, 9, 10 are those described in connection with FIG. 1. 
     In accordance with the above arrangement, the dial designated by the feed speed command from the tape is turned by the operator to enable the setting of the optimum feed speed conforming to the machining conditions. The conventional system is therefore effective in establishing the optimum feed speed. However, a disadvantage is encountered due to the need for the plurality of dials 1, 2, 3, provided for the commands F1, F2, F3, respectively, and the need for the oscillators 11, 12, 13, 14. These components raise the cost of the apparatus considerably, and require a fairly large mounting area, so that the apparatus cannot be made compact. The increase in the number of component parts and in the size of the mounting area is especially great in numerical control systems that adopt the foregoing feed speed command arrangement, because as many as 9 dials are commonly provided in view of the fact that a greater number of dials facilitates more flexible programming. 
     The feed speed control system of the present invention is free of the above-mentioned problems and will now be described with reference to the block diagram of FIG. 3. Numeral 101 denotes a paper tape, into which a machining program has been punched, and which serves as a medium for storing feed speed commands, the feed speed being designated by the feed speed commands F0, F1, . . . F9 which have been punched in the tape. A tape reader 102 reads the tape 101 and delivers the data to an input circuit 103 which includes a buffer memory or the like to store the data such as the feed speed command read in from the paper tape. The paper tape 101, tape reader 102 and input circuit 103 constitute speed command means. A memory 104 stores numerical values corresponding to, for example, the feed speed commands F1, F2, . . . F9. Coupled to the memory 104 are a write control circuit 105, a read control circuit 106 and an address register 107. Set in the address register 107 are addresses in accordance with the feed speed commands F1, F2, . . . , F9 from the paper tape 101. Numerical values Nf 1 , Nf 2 , . . . , Nf 9  corresponding to the commands F1, F2 . . . , F9 are read, through the intermediary of the read control circuit 106, from the locations of the memory 104 that are designated by the addresses. In addition, through the intermediary of the write control circuit 105, the results of arithmetical operations, based on an addition and substraction process to be described later, are written in the locations of the memory 104 that are designated by the address register. The memory 104, write control circuit 105, read control circuit 106, and address register 107 constitute memory means. An output register 108 stores the numerical values which are read from the memory 104. 
     An arithmetic circuit 109 is adapted to increment or decrement the content of the output register 108 by a unit quantity, such as the numerical value &#34;2&#34;, whenever an up-pulse UPP or down-pulse DWP is generated by depressing an UP-button or DOWN-button located on an operation panel (not shown). The arithmetic circuit 109 per se may be of any construction which is known in the art. The result of the arithmetical operation is applied to the output register 108 and to a digital pulse generator 110 which will be described immediately hereinbelow. The output register 108 and arithmetic circuit 109 constitute arithmetic means. 
     The digital pulse generator 110 includes a register 110a, an accumulator 110b, and an adder 110c which is clocked by clock pulses CP at a frequency F to add the contents of the register 110a and accumulator 110b and to place the result back in the accumulator 110b. Let A represent the numerical value set in the register 110a, and let 2 n  -1 represent the capacity of the accumulator 110b, the accumulator being an n-bit register. As the adder 110c performs the addition operation described above each time a clock pulse CP arrives, the accumulator 110b delivers an overflow pulse signal OVFP whose frequency Fo will be expressed by Fo=A·F/(2 n  -1). In other words, the accumulator 110b generates an overflow pulse signal OVFP of a frequency which is proportional to the numerical value which has been set in the register 110a. The signal OVFP is applied to drive the movable member, such as the workpiece table, of the machine tool. 
     In operation, let it first be assumed that the tape reader 102 has read in the feed speed command F3 from the paper tape 101. The input circuit 103 converts the feed speed command F3 into the address in the memory 4 that stores the numerical value Nf 3  corresponding to the command F3, and then sets this address in the address register 107. The read control circuit 106 reads the numerical value Nf 3  from the location of the memory 104 which has been designated by the address set in the address register 107, and sets this numerical value in the output register 108. The numerical value Nf 3  is then set in the register 110a of the pulse generator 110 through the arithmetic circuit 109. As a result, the pulse generator 110 delivers the overflow pulse signal OVFP, having a frequency proportional to Nf 3 , in the manner described above. This signal is applied to a well-known pulse distributor (not shown) that responds by generating and distributing pulses, which are proportional in number to the frequency of the signal OVFP, for driving such movable members as tools and the workpiece table on the basis of these distributed pulses. 
     If it is desired that the feed speed of a movable member be changed during an actual machining operation, then an UP- or DOWN-button on the operation panel (not shown) is depressed. More specifically, the UP-button is depressed when it is desired to raise the feed speed, and the DOWN-button is depressed when it is desired to lower the feed speed. If the UP-button is depressed, up-pulses UPP of a prescribed frequency will be generated for as long as the UP-button is held depressed, and the pulses will be applied to the arithmetic circuit 109. Each time a pulse UPP arrives, the arithmetic circuit 109 adds a fixed quantity, such as the numerical value &#34;2&#34;, to the numerical value Nf 3  stored in the output register 108, places the sum in the output register 108, and sets the sum in the register 110a. Therefore the content of the register 110a gradually increases, as does the frequency of the overflow pulses OVFP delivered by the pulse generator 110. The arithmetic circuit 109 stops performing the arithmetical operation when the operator removes his finger from the UP-button, so that the output pulse frequency of the pulse generator 110 is fixed at the higher frequency. Hence the feed speed of the movable member is also fixed at the new constant speed. The numerical value stored in the output register 108 is placed in that location of the memory 104 corresponding to the feed speed command F3 through the write control circuit 105, this occurring when the UP-button is released, or in response to a signal indicating the termination of the pulse distribution operation or the like. 
     If the DOWN-button is depressed, the down-pulses DWP are generated. Each time a pulse DWP arrives the arithmetic circuit 109 subtracts a fixed quantity stepwise from the numerical value Nf 3  stored in the output register 108, places the difference in the output register 108, and sets the difference in the register 110a. The content of the register 110a is gradually reduced thereby, as is the frequency of the pulses from the pulse generator 110. 
     Although the arithmetic circuit 109 described above increments or decrements the numerical value which corresponds to the particular feed speed command by fixed values whenever an up- or down-pulse arrives, it is also possible to increase or decrease the numerical value geometrically by means of a suitable arrangement. Moreover, though the foregoing description relates to an arrangement in which the up-pulses UPP and down-pulses DWP are generated by depressing UP- and DOWN-buttons located on the operation panel, these buttons can be eliminated and in their stead it is possible to make use of a manual feed jog button and a manual pulse generator or the like which are already provided on the operation panel of the numerical control apparatus. Such an expedient permits an even greater reduction in the number of component parts. 
     Another embodiment of the present invention is illustrated in the block diagram of FIG. 4, in which component parts identical to those of FIG. 3 bear the same reference numerals and which are not described in detail again in order to avoid prolixity. In FIG. 4, numeral 201 denotes a conversion memory for storing numerical values which correspond to a number of feed speeds. Numerical values are stored in respective locations of the memory 201 in such a manner that the numerical values become progressively larger as the addresses of these locations increase in value. The arrangement further includes an address register 202, a table 203 for storing the corresponding relationships between speed commands F1, F2, . . . , F9 on the one hand and addresses Af1, Af 2 , . . . , Af 9  on the other, and a register 204 for storing addresses read from the table 203. 
     In operation, let it be assumed that the feed speed command F5 has been read from the paper tape, so that the address Af 5  corresponding to the command F5 is read from the table 203 and transferred to the register 204 and the address register 202. When Af 5  is transferred to the address register 202, a numerical value such as &#34;1100&#34; corresponding to the feed speed is read from the address Af 5  of memory 201 and then set in the register 110a of the pulse generator 110. As a result, the pulse generator 110 generates pulses OVFP of a frequency which is proportional to the numerical value &#34;1100&#34;. Depressing the UP-button under these conditions generates the up-pulses UPP. When an up-pulse UPP, arrives, the arithmetic circuit 109 increments the content of the register 204 by +1, and applies the sum to the register 204 and to the address register 202. As a result, the content of the address register 202 is increased by +1, the numerical value &#34;1150&#34; is read from the location having the address Af 5+1 , and the numerical value is set in the register 110a. Since the numerical value &#34;1150&#34; is larger than the numerical value &#34;1100&#34; stored at the address Af 5 , there is a gradual increase in the frequency of the pulse signal from the pulse generator 110. Thus, if the UP-button continues to be depressed to permit continuous generation of the up-pulses UPP, there is a gradual increase in the numerical value set in the register 110a, and a corresponding gradual increase in the frequency of the output pulses OVFP, thereby raising the feed speed of a movable member. Then, in response to release of the UP-button or, for example in response to termination of the pulse distribution operation, the address which is stored in register 204 is placed in the table 203 as the new address Af 5 , thereby completing the feed speed adjustment operation. It should be noted that the operation proceeds in virtually the same manner if the DOWN-button is depressed. 
     In the above-mentioned embodiments each of the functions is realized through hardware but no analog elements are used. Hence the apparatus can be realized through the use of a processor such as a microprocessor. 
     In accordance with the present invention as described above only one set of elements such as push-buttons and only one pulse generator need be provided for common use with a number of feed commands, rather than having a set for each individual feed speed command. This reduces the number of parts and greatly simplifies the overall structure, reduces the space occupied by the parts, and lowers the cost. An even greater reduction in space and cost can be achieved if, instead of the push-buttons, use is made of job buttons and a manual pulse generator which are already mounted on the NC operation panel. Furthermore, additional structural components will not be necessary if a processor with a bult-in NC apparatus is made to execute the above described speed command processes. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.