INPUT STATE DETECTION CIRCUIT

Abstract: In an input circuit which converts a contact signal into a voltage signal, the polarities of voltage signal outputs that correspond to on and off of the contact point change dif­ ferently depending upon the connection method of the con­ tact point and the current limiting resistor between the power source and the ground. Therefore, non-coincidence is detectet between the output voltage signal level and the voltage level at the other end of the current limiting resistor connected to the voltage signal output terminal, in order to obtain voltage signal outputs of which the polarities change in the same manner in response to the on and off of the contact point, irrespective of the abovementioned connec­ tion method. When the circuit thus constructed is to be used large in number, a non-coincidence detecting circuit is provided for each group of divided input circuits, and the voltage signal output of each group of the input circuits is switched and is applied to the non-coincidence detecting circuit. This enables the scale of circuit to be reduced and the number of parts of the circuit to be reduced.

Description: The present invention relates to an input state detection circuit, and in particular to a circuit for converting an interface signal from a controlled system into a voltage signal, and more particularly to an input state detection circuit by which an interface signal provided in the form of a contact signal or a signal equivalent thereto is converted into a voltage signal. Various types of input circuits are employed for converting an interface signal from a controlled system into a voltage signal, and the simplest and cheapest one of them is such a voltage input circuit as shown in Fig. 1. In the voltage input circuit depicted in Fig. 1, an input signal is applied to a filter circuit 1 to remove a noise component, and is then compared with a reference voltage Vref in a comparator 2, which yields a voltage signal output when the input signal is higher than a fixed level. On the other hand, an interface signal between a machine tool and a numerical controller or programmable controller is, in general, not a voltage signal but a contact signal or noncontact signal equivalent thereto which is produced by a semiconductor element, that is, a signal resulting from its ON/OFF operation. Accordingly, in order to read out such a contact signal and derive therefrom a voltage signal output, an input circuit is needed which is provided with a circuit for converting the contact signal into a voltage signal. With such an input circuit, when the interface signal is the above-mentioned contact signal, it is necessary to produce a voltage signal whose polarity always changes in the same manner in response to the turning ON and OFF of the contact, irrespective of the arrangement of the contact signal generating circuit; further, it is demanded that the input circuit be as simple in structure as possible even if many contact signal generating circuits are employed. Heretofore, such an input circuit as depicted in Fig. 2 has been proposed for converting the above-said contact signal into a voltage signal output. In Fig. 2, reference numeral 3 indicates generally a converting circuit, 4 a resistor, 5 a contact,1 ○ a power source terminal,3 ○ a signal terminal,2 ○ a terminal connected to one end of the resistor 4 connected at the other end to the signal terminal3 ○ , and4 ○ a grounding terminal. The signal terminal3 ○ is connected to the input side of the input circuit shown in Fig. 1. There are two kinds of methods for connecting the contact to the converting circuit shown in Fig. 2; one is to ground the contact at one end thereof and the other is to connect the contact at one end to the power source. Fig. 2A shows the connection of one end of the contact to the grounding terminal4 ○ , in which case the terminals1 ○ and2 ○ are short-circuited and the contact 5 is connected between the terminal3 ○ and4 ○ . Fig. 2B shows the connection of the contact to the power source terminal 1, in which case the contact 5 is connected between the terminals 1 and 3 and the terminals 2 and 4 are short-circuited. Usually, these two kinds of connections are selectively employed in accordance with the safety standards adopted and the contact connecting position on the side of the machine tool. With the input circuit shown in Fig. 2, the polarity of the voltage signal output resulting from the turning ON or OFF of the contact 5 differs with the methods of connection depicted in Figs. 2A and 2B. Accordingly, the proposed input circuit presents the problem that the sign of the input signal, which is applied to an internal control logic of the numerical controller or programmable controller in response to the ON/OFF operation of the contact, differs depending upon which of the above-mentioned methods of connection is employed. To solve the above problem, the input state detection circuit of the present invention basically has such an arrangement as shown in Fig. 3. Reference numeral 101 indicates the same input circuit as depicted in Fig. 2 (wherein circuit 1 and comparator 2 can be replaced by other voltage level detecting means if desired) which circuit responds to the turning ON and OFF of the contact 5, or a signal equivalent thereto, to yield voltage signal outputs whose polarities differ with the methods of connection of Figs. 2A and 2B indicated by the solid and broken lines. Reference numeral 102 designates voltage level detecting means, which detects the voltage level at the terminal2 ○ in the input circuit 101 and produces an output signal. Reference numeral 103 identifies noncoincidence detecting means, which detects noncoincidence between the output signal of the input circuit 101 and the output signal of the voltage level detecting means 102 and yields a voltage signal output. According to the interface circuit of the present invention, even if the polarities of the voltage signal outputs from the input circuit 101 responsive to the turning ON and OFF of the contact or equivalent are reversed dependent upon the method of connection of the contact in the converting circuit, the output signals of the input circuit 101 are each inverted by the noncoincidence detecting means 103 or held noninverted in accordance with the output signal corresponding to the voltage level at the other end of the resistor detected by the voltage level detecting means 102. Therefore, the voltage signal output which undergoes the same polarity change can be obtained in response to the ON/OFF operation of the contact, irrespective of the method of connection in the converting circuit. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagram illustrating a voltage input circuit; Fig. 2 shows conventional input circuits; Fig. 3 is a diagram illustrating the basic constitution of the present invention; Fig. 4 is a diagram illustrating the arrangement of an embodiment of the present invention; and Fig. 5 is a diagram showing the arrangement of another embodiment of the present invention. Fig. 4 illustrates the arrangement of an embodiment of the input circuit of the present invention, Fig. 4A showing the case where the contact is connected to grounding side of the converting circuit, and Fig. 4B the case where the contact is connected to the power source side of the converting circuit. In Figs. 4A and 4B the part corresponding to those in Figs, 2A and 2B are identified by the same reference numerals. Reference numeral 6 designates a voltage level detecting circuit and 7 an exclusive OR circuit. In Fig. 4A, a low-level or high-level output is provided at the terminal3 ○ depending upon whether the contact 5 has been turned ON or OFF, and the output level of the comparator 2 goes high or low correspondingly. On the other hand, the output of the voltage level detecting circuit 6 remains high-level at all times. The exclusive OR circuit 7 detects noncoincidence between the output of the comparator 2 and the output of the voltage level detecting circuit 6, and generates a low-level or high-level output depending upon whether the contact 5 is in the ON or OFF state. That is, the output level of the exclusive OR circuit is an inverted version of the voltage output level of the input circuit 101. In Fig. 4B, a high-level or low-level output is provided at the terminal3 ○ depending upon whether the contact 5 has been turned ON or OFF, and the output level of the comparator 2 goes low or high accordingly. The output of the voltage level detecting circuit is always low-level. The exclusive OR circuit 7 detects noncoincidence between the output of the comparator 2 and the output of the voltage level detecting circuit 6, and yields a low-level or high-level output depending upon whether the contact 5 is in the ON or OFF state. Namely, the output level of the exclusive OR circuit is a noninverted version of the voltage output level of the input circuit 101. The input circuit depicted in Fig. 4 necessitates the voltage level detecting circuit and the exclusive OR circuit for each interface signal. Accordingly, when the number of interface signals used is large, the input circuit inevitably becomes enlarged in scale, which goes against a demand for smaller and more economical circuit structures. Fig. 5 illustrates the arrangement of another embodiment of the present invention which is designed to overcome such a defect. Reference numerals 10₋₁ to 10₋₄ and 10₋₅ to 10₋₈ indicate input circuits which are identical in construction with the input circuit 101 shown in Fig. 4, and quartets of such input circuits constitute input circuit groups, respectively In the circuits 10₋₁ to 10₋₄, the grounding terminal4 ○ is common to them, the contact 5 is connected between the terminals 3 ○ and4 ○ , and the terminals1 ○ and2 ○ are short-circuited. In the input circuits 10₋₄ to 10₋₈, the power source terminal 1 is common to them, the contact 5 is connected between the terminals1 ○ and3 ○ , and the terminals2 ○ and4 ○ are short-circuited. The outputs of the input circuits 10₋₁ to 10₋₄ and 10₋₅ to 10₋₈ are respectively connected to gate circuits 11₋₁ to 11₋₄ and 11₋₅ to 11₋₈. The terminals2 ○ of the input circuits 10₋₁ to 10₋₄ and 10₋₅ to 10₋₈ are connected together to voltage level detecting circuits 12₋₁ and 12₋₂, respectively, which are, in turn, connected to a multiplexer 13 for selectively outputting signals from the voltage level detecting circuits 12₋₁ and 12₋₂. The corresponding outputs of the input circuits 10₋₁ to 10₋₄ and 10₋₅ to 10₋₈ are respectively connected in parallel and are connected to exclusive OR circuits 15₋₁ to 15₋₄ at one input thereof. The output selected by the multiplexer 13 is applied to the other inputs of the exclusive OR circuits in common to them. Now, in the case of obtaining from one of the input circuit groups, for example, the input circuits 10₋₁ to 10₋₄, voltage signal outputs converted from contact signals, the output of the voltage level detecting circuit 12₋₁ is selected by the multiplexer 13 in accordance with an address signal, and the gate circuits 11₋₁ to 11₋₄ are enabled by the same address signal via a decoder 14. As a result of this, the exclusive OR circuits 15₋₁ to 15₋₄ are supplied with the voltage outputs of the input circuits 10₋₁ to 10₋₄ and the output of the voltage level detecting circuit 12₋₁. In this instance, since the input circuits 10₋₁ to 10₋₄ each creates a high-level or low-level output depending upon whether the contact 5 is in the ON or OFF state and the voltage level detecting circuit 12₋₁ always yields a high-level output, as referred to previously in respect of Fig. 4A, the exclusive OR circuits 15₋₁ to 15₋₄ each detects noncoincidence between the both inputs and generate a low-level or high-level voltage signal output in dependence upon whether the contact 5 is in the ON or OFF state. In the case of obtaining from the other input circuit group (10₋₅ to 10₋₈) voltage signal outputs converted from contact signals, the output of the voltage level detecting circuit 12₋₂ is selected by the address signal in the multiplexer 13 and the gate circuits 11₋₅ to 11₋₈ are turned ON via the decoder 14 in the same manner as described above. In consequence, the exclusive OR circuits 15₋₁ to 15₋₄ are supplied with the voltage outputs of the input circuits 10₋₅ to 10₋₈ and the output of the voltage level detecting circuit 12₋₂. In this instance, since the input circuits 1₋₅ to 10₋₈ each yield a low-level or high-level output depending upon whether the contact 5 is in the ON or OFF state and the voltage level detecting circuit 12₋₂ always creates a low-level output, as described previously with regard to Fig. 4B, the exclusive OR circuits 15₋₅ to 15₋₄ each generate a low-level or high-level voltage signal output in dependence upon whether the contact 5 is in the ON and OFF state. As described above, according to the input circuit system of this embodiment, the output from the input circuit, which differs in polarity with the methods of connection of the contact to the converting circuit is inverted by a noncoincidence circuit or held noninverted, by which it is possible to obtain a voltage signal output which undergoes the same polarity change in response to the ON/OFF operation of the contact. While this embodiment has been described in connection with the case of employing two input circuit groups each composed of four input circuits, the input circuit system of the present invention is more effective when employed for more input signals. For instance, when the number of input signals is 64, the voltage level detecting circuits (12₋₁∼) can be reduced to 1/8 by using eight input circuit groups each composed of eight input circuits.

Claims: An input state detection circuit which is provided with a resistor connected at one end to a power source or ground, a contact or an equivalent connected between the other end of the resistor and the ground or power source respectively, and first voltage level detecting means for detecting the voltage level at the connection point between the contact or equivalent and the resistor, characterized by the provision of: second voltage level detecting means for detecting the voltage level at said one end of the resistor; and means for detecting noncoincidence between the output signal of the second voltage level detecting means and the output signal of the first voltage level detecting means and generating a voltage signal output. An input circuit system which is provided with a plurality of input state detection circuits according to Claim 1, each having first and second terminals interconnected via a resistor and a voltage level detecting circuit for detecting the voltage level at the second terminal, a third terminal connected to a power source, and a grounded fourth terminal, the input circuits being divided into a plurality of groups, in each of which the first terminals of the input circuits are connected together, characterized by the provision of: a plurality of gate circuits for turning ON and OFF the outputs of the voltage level detecting circuits; voltage level detecting means for detecting the voltage levels at each of the first terminals connected together for each group; a multiplexer for selecting the output of the respective voltage level detecting means; and a plurality of noncoincidence detecting means, each connected at one input to a parallel connection of the outputs of the corresponding gate circuits of the respective groups and at the other input to the output of the multiplexer, for detecting noncoincidence between the both inputs and generating an output corresponding thereto.

Inventors: INOUE, MICHIYA, SATOH, JUNICHI
Applicants: FANUC LTD.
Application year: 1986
Main classification: H03K17
IPC codes: H03K17