IMPACT PRINTER

Abstract: An impact printer having a plurality of printing wires (7); driving means (5) for driving said printing wires (7) to effect printing; control means (2,3) arranged to transmit selectively to the driving means (5) either a printing signal, as a result of which the driving means (5) are energized to effect printing, or a warming-up signal as a result of which the driving means (5) are energized without printing being effected, and selector means (1) for causing the control means (2,3) to produce either a printing signal or a warming-up signal, characterised in that the selector means comprises a temperature detecting means (1) such that a said warming-up signal is transmitted to the driving means (5) only when the temperature sensed thereby does not exceed a respective predetermined value.

Description: The present invention relates to an impact printer. Known impact printers have the problem that when their driving coils are selectively energized to cause respective printing wires to effect printing, the ink from the ink ribbon employed may enter the gap between the printing wires and the wire guides of the printer so as to interfere with the travel of the printing wires. This can result in dots being missed or in there being light and dark irregularities in the printing. Further, a lubricant that is employed in the impact head of the printer for the purpose of improving the durability of the head hinders the movement of the printing wires or of their driving levers and this can also result in dots being missed or in there being light and dark irregularities in the printing. To solve these problems, it is known to effect warming-up by means of a combination of a timer, which outputs a non-printing signal when it detects that no printing signal has been received for a predetermined period of time, and a pulse generator for driving the printing wires to such an extent that no printing is actually effected by the printing wires. Such a method of dealing with the problem is disclosed in JP-B-58-45351 (1983). This prior art method suffers, however, from the following problems. Warming-up is conducted simply by detecting that no printing has been carried out for a predetermined period of time since the completion of the last printing step. However, this does not take into consideration the temperature that has a great effect both on the ink from the ink ribbon and on the lubricant, both the ink and the lubricant being causes of interference with the movements of the printing wires and of the driving levers. Warming-up, moreover, is frequently carried out, in the prior art method, so that the time required to effect warming-up increases the total time taken to effect printing, and the throughput of the printer is therefore decreased. The prior art method further has the problem that, if warming-up driving conditions are such that the warming-up takes effect when the temperature is low, the force imparted by the printing wires is too strong when the temperature is average or is high, resulting in the printing paper being stained, whereas, if the warming up-driving conditions are such that the printing paper will not be stained with the ink, the effectiveness of the warming-up is halved when the temperature is low. According to the present invention, there is provided an impact printer having a plurality of printing wires; driving means for driving said printing wires to effect printing; control means arranged to transmit selectively to the driving means either a printing signal, as a result of which the driving means are energized to effect printing, or a warming-up signal as a result of which the driving means are energized without printing being effected; and selector means for causing the control means to produce either a printing signal or a warming-up signal, characterised in that the selector means comprises a temperature detecting means such that a said warming-up signal is transmitted to the driving means only when the temperature sensed thereby does not exceed a respective predetermined value. In a printer according to the present invention, warming-up can thus be effected in accordance with the temperature detected by the temperature detecting means and it is therefore possible to lower the viscosities of the ink and the lubricant or disperse a part of them. Thus, it is possible to ensure that dots are not missed and that there are no light and dark irregularities in printing. Hence precise printing can be obtained in accordance with given printing data. Preferably, adjustment means are provided to adjust the platen gap between a platen of the printer and a head which carries the printing wires, the adjustment means being controlled by the temperature detecting means so that the platen gap is increased when a said warming-up signal is transmitted by the control means. This enables the platen gap to be increased when warming-up is conducted so that it is possible to effect warming-up effectively and within a short period of time. Since a decision as to whether or not warming-up is to be effected is made on the basis of the ambient temperature, this ensures that no warming-up is carried out when the temperature is average or is high and therefore when no warming-up is needed. Accordingly, there need be no fear of the printing paper being stained due to the unnecessary warming-up which would otherwise be effected. It is therefore possible to provide an impact printer which has a high throughput without fear of the printing paper being stained. Preferably, the said head is carried by a carriage which is mounted on an eccentrically mounted guide shaft which extends parallel to the platen, the adjustment means being arranged to effect rotation of the guide shaft so as to move the head towards and away from the platen. Gap detecting means may be provided for detecting whether the platen gap is at a predetermined value. Preferably, the energy transmitted to the driving means during warming-up is not substantially more than 60% of that transmitted to the driving means during printing. Preferably, moreover,the energy transmitted to the driving means during warming-up is in the form of a plurality of pulses. Thus there may be substantially 10 pulses having a duration of substantially 150 microseconds at substantially 100 Hz. A said respective predetermined value of the temperature may be substantially 10°C. There may be a plurality of predetermined temperatures each of which is associated with a respective warming-up signal. The invention is illustrated, merely by way of example, in the accompanying drawings, in which like reference numerals denote like elements, and in which:- Figure 1 is a schematic block diagram of a first embodiment of an impact printer according to the present invention; Figure 2 is a sectional side view of an impact head forming part of the said first embodiment of the present invention; Figure 3 is a schematic block diagram of a second embodiment of an impact printer according to the present invention; and Figure 4 is a plan view of the impact printer forming the second embodiment of the present invention. Terms such as "left" and "right", as used in the description below, are to be understood to refer to directions as seen in the accompanying drawings. Referring first to Figures 1 and 2, an impact printer is provided with a temperature detecting means 1 which receives a pre-printing signal from data transmission means (not shown), the latter transmitting the pre-printing signal in advance of transmitting printing data. A character generator 2 is arranged to receive printing data from the data transmission means and also to receive a signal from the temperature detecting means 1. The character generator 2 is arranged to generate either a warming-up signal or a printing signal corresponding to the printing data on the basis of the temperature detected by the temperature detecting means 1. A driving coil control means 3 is arranged to receive input signals from both the character generator 2 and from the temperature detecting means 1, and is arranged to transmit an output signal to an impact head 4. When the temperature sensed by the temperature detecting means 1 does not exceed a predetermined value (e.g. 10°C), the said output signal is a warming-up signal such that impact head 4 is warmed up but printing cannot be effected, whereas if the temperature is above the predetermined value, the said output signal is a printing signal. The impact head 4 is provided with a plurality of printing wires 7 (only one shown) which are respectively driven by driving coils 5. The driving coils 5 are selectively energized in a predetermined way by the character generator 2 and the driving coil control means 3 so as to effect magnetic attraction of the corresponding driving levers 6 each of which is provided with a printing wire 7. Each driving lever 6 is arranged to pivot about a pivot point so as to cause the respective printing wire 7 which is rigidly secured to the distal end thereof to strike against a printing paper 14 disposed between an ink ribbon 11 and a platen 15. Moreover, each driving lever 6 is urged against a respective damper 13 by means of a respective return spring 12 so that the driving lever 6 is held in a stand-by position when the respective driving coil 5 is not energized. Each printing wire 7 is held by several wire guides 10. A thermistor 8 is disposed on the impact head 4 and is connected to the temperature detecting means 1 through a head board 9. The sticking between the printing wires 7 and the wire guides 10 due to the presence of ink from the ink ribbon 11, and the sticking between the driving levers 6 and the dampers 13 due to the presence of the lubricant that is used for the purpose of improving the life of the equipment increases substantially at 10°C and below. Consequently, the driving coil control means 3, when the temperature is 10°C or below, has an output signal which puts the impact head 4 into a warming-up mode, whereas when the temperature is above 10°C, the output signal puts the impact head 4 into a printing mode. The energy transmitted to the driving coils 5 in the warming-up mode is set at about 60% of that transmitted in the printing mode. The warming-up is repeated 10 times at 100 Hz. The following is a description of the operation of the apparatus arranged as described above. When printing data are transmitted to the impact printer, the temperature detecting means 1 receives a pre-printing signal in advance of the printing data and detects the temperature from the resistance value of the thermistor 8 disposed on the impact head 4. If the detected value is not higher than 10°C, the temperature detecting means 1 judges that warming-up is necessary and instructs the character generator 2 to generate data for warming-up and further instructs the driving coil control means 3 to output data for warming-up, for example, 10 pulses having a duration of 150 microseconds at 100 Hz. When the temperature is not higher than 10°C, in the impact head 4 the ink and lubricant which are between the printing wires 7 and the wire guides 10, and the lubricant which is between the driving levers 6 and the dampers 13, have relatively high viscosities and hinder the driving levers 6 and the printing wires 7 from moving in the direction of the illustrated arrow in accordance with the printing signal. However, by carrying out the warming-up referred to above, the driving levers 6 and the printing wires 7 are actuated to operate within the range where no printing is actually effected, so that the ink and lubricant between the printing wires 7 and the wire guides 10 and the lubricant between the driving levers 6 and the dampers 13 have their viscosity lowered, or the ink and the lubricant are partially dispersed, thus enabling printing to be accurately effected in accordance with the given printing data, without dots being missed and without there being light and dark irregularities. Although in the foregoing embodiment the predetermined temperature of the temperature detecting means 1 is 10°C or lower and the warming-up is effected by transmitting 10 pulses having a duration of 150 microseconds at 100 Hz, it should be noted that these values are not necessarily exclusive and that the predetermined temperature and the warming-up conditions may, of course, be changed so as to be optimal by further taking into consideration the kind and amount of ink from the ink ribbon 11 and the lubricant used in the impact head 4. Moreover, the impact head 4 need not be a clapper type head since similar advantages are obtained in the case of a spring charge type head also. Figure 3 shows a second embodiment of the present invention which is additionally provided with a platen gap detecting means 18 and a platen gap adjusting means 19 to increase the gap between the impact head 4 and the printing wires 7 on the one hand and the platen 15 on the other hand when the temperature sensing means 1 transmits a warming-up signal to the driving coil control means 3. This ensures that the printing paper 14 will not be stained during warming-up. The platen gap detecting means 18 and the platen gap adjusting means 19 are arranged as shown in Figure 4. More specifically, a carriage 27 having the impact head 4 mounted thereon is slidably mounted on an eccentric carriage guide shaft 26 so as to be longitudinally movable, i.e. in a direction parallel to the axis of the platen 15. The eccentric carriage guide shaft 26 is supported in through-holes which are provided in a left side frame 28 and in a right side frame 29, respectively, in such a way that the shaft 26 is only allowed to rotate. A platen gap adjusting gear 23 is rigidly secured to the left-hand end of the eccentric carriage guide shaft 26. The gear 23 is arranged to be rotated by a motor 25 through a driving gear 24 and a transmission gear 30. Thus, as the motor 25 rotates forward or backward, the eccentric carriage guide shaft 26 rotates forwards or backwards with respect to the platen 15 through the gear train comprising the driving gear 24, the transmission gear 30 and the platen gap adjusting gear 23. As a result, the carriage 27 moves forwards and backwards with respect to the platen 15 by virtue of the eccentric action of the eccentric carriage guide shaft 26. A reference position detecting member 21 is rigidly secured to one side of the platen gap adjusting gear 23. In addition, a photo-sensor 22 which has a light-emitting element and a light-receiving element is installed on the outer side of the left hand side frame 28 to detect the home position of the platen gap. When receiving a pre-printing signal in advance of the printing data, the temperature detecting means 1 effects temperature detection. If the detected temperature is not higher than the predetermined temperature, data for effecting warming-up are produced in the character generator 2 and in the driving coil control means 3. At the same time, the motor 25 is driven to rotate the platen gap adjusting gear 23, thereby disposing the eccentric carriage guide shaft 26 at the home position. At this time, the platen gap reaches a maximum and, in this state, warming up is carried out. After the completion of the warming-up, data relating to the distance through which the carriage 27 should move toward the platen 15 are outputted in the form of a signal representative of the required angle of rotation of the motor 25. Then, the motor 25 is driven to rotate the eccentric carriage guide shaft 26 so as to set a predetermined platen gap before printing is effected in accordance with the printing data. Thus, the platen gap is increased to its maximum when warming-up is conducted. Therefore, even if the energy for driving the printing wires 7 and the driving levers 6 to effect warming-up is increased with respect to that used in the prior art, the printing paper 14 will not be stained and it is possible to lower the viscosities of the ink and of the lubricant or to disperse them effectively and within a short period of time and hence to obtain printing free from missed dots and from light and dark irregularities. It should be noted that, although in the foregoing embodiments only one predetermined temperature, i.e. 10°C, is referred to, it is also possible to use a plurality of predetermined temperatures and to set optimal warming-up conditions for each of the predetermined temperatures. The detection of temperature may also be effected by using a device other than a thermistor. Although in the foregoing embodiments the detection of temperature is effected by means of the thermistor 8 provided in the impact head 4, the thermistor 8 may be installed at any position other than the impact head 4, provided that the temperature in the impact printer can be detected thereby.

Claims: An impact printer having a plurality of printing wires (7); driving means (5) for driving said printing wires (7) to effect printing; control means (2,3) arranged to transmit selectively to the driving means (5) either a printing signal, as a result of which the driving means (5) are energized to effect printing, or a warming-up signal as a result of which the driving means (5) are energized without printing being effected; and selector means (1) for causing the control means (2,3) to produce either a printing signal or a warming-up signal, characterised in that the selector means comprises a temperature detecting means (1) such that a said warming-up signal is transmitted to the driving means (5) only when the temperature sensed thereby does not exceed a respective predetermined value. An impact printer as claimed in claim 1 characterised in that adjustment means (19) are provided to adjust the platen gap between a platen (15) of the printer and a head (4) which carries the printing wires (7), the adjustment means (19) being controlled by the temperature detecting means (1) so that the platen gap is increased when a said warming-up signal is transmitted by the control means (2,3). An impact printer as claimed in claim 2 characterised in that the said head (4) is carried by a carriage (27) which is mounted on an eccentrically mounted guide shaft (26) which extends parallel to the platen (15), the adjustment means (19) being arranged to effect rotation of the guide shaft (26) so as to move the head (4) towards and away from the platen (15). An impact printer as claimed in claim 2 or 3 characterised in that gap detecting means (21,22) are provided for detecting whether the platen gap is at a predetermined value. An impact printer as claimed in any preceding claim characterised in that the energy transmitted to the driving means (5) during warming-up is not substantially more than 60% of that transmitted to the driving means (5) during printing. An impact printer as claimed in any preceding claim characterised in that the energy transmitted to the driving means (5) during warming-up is in the form of a plurality of pulses. An impact printer as claimed in claim 6 characterised in that there are substantially 10 pulses having a duration of substantially 150 microseconds at substantially 100 Hz. An impact printer as claimed in any preceding claim characterised in that a said respective predetermined value of the temperature is substantially 10°C. An impact printer as claimed in any preceding claim characterised in that there are a plurality of predetermined temperatures each of which is associated with a respective warming-up signal. An impact printer having a printing wire (7), a driving coil (5) for magnetically driving said printing wire (7), a control means (3) for controlling said driving coil (5), and a temperature detecting means (1) wherein the improvement comprises a means for energizing, before printing data is printed, said driving coil (5) to such an extent that no printing is actually effected in accordance with the value detected by said temperature detecting means. An impact printer according to claim 1, further comprising a means for enlarging the gap between the platen (15) and said printing wire (7) when said driving coil (5) is energized to such an extent that no printing is actually effected.

Inventors: KOIKE, KIYOFUMI
Applicants: SEIKO EPSON CORPORATION
Application year: 1989
Main classification: B41J2
IPC codes: B41J25, B41J2, B41J29