GB2138190A - Hand-held labeller utilizing thermographic recording apparatus - Google Patents

Abstract

A hand-held labeller employing a thermographic recording apparatus utilizes compensating circuitry (40,70,42) for adjusting the energy applied to the print head (66) to assure uniform printing over various operating conditions. The compensating circuit includes circuitry that adjusts the length of time that each printing element of the print head (66) is energized as a function of battery voltage, ambient temperature, element resistance and the elapsed time since the element was previously energized. In addition, the monitoring of resistance and voltage permit detection of open or shorted printing elements and discharged or faulty battery cells. A D.C. motor (50) that is driven by a variable pulse width circuit (48) drives a web of labels past the print head. <IMAGE>

Description

SPECIFICATION Hand-held labeler utilizing thermographic recording apparatus This invention relates generally to printing devices, and more particularly to hand-held labelers utilizing thermographic printing devices.

Thermographic printing devices as well as hand-held labelers utilizing thermographic printing devices are known. Examples of hand held labelers utilizing thermographic printing devices are illustrated in United States Patent No. 4,264,396 to Stewart and in United States patent applications Serial No. 268,590 filed May 29,1981.

While the devices disclosed in the above-described references do provide a way to make imprints on a thermosensitive web, they do not contain many of the features provided by the device of the present invention. For example, when printing with a thermal printing device, particularly with a hand-held battery-powered printing device, the density of the printing varies as a function of battery voltage. In addition, because the battery voltage varies as a function of the number of print elements that are simultaneously energized, the print density varies as a function of the number of elements that must be simultaneously energized to form the various portions of a character.Also, the temperature to which each printing element is heated when it is energized is not only a function of the amount of energy applied to that print element, but is also a function of the previous history of that element, i.e. the amount of time that has passed since the element was previously energized. Also, in the prior art devices, faulty print elements and faulty cells within the battery powering the device can cause many defective labels to be printed before they are detected, and the repetitive printing of the same character can cause premature head failure when the same print elements of the print head are repetitively energized. Also, the stepping motors of the prior art devices used to advance the web of labels past the print head tend to have limited low speed torque.

Accordingly, it is an object of the present invention to overcome many of the disadvantages of the prior art systems.

It is another object of the present invention to provide a hand-held labeler utilizing a thermographic printing device that monitors the voltage applied to the print elements and adjusts the time that the print elements are energized as a function of voltage to thereby apply substantially constant energy to the print elements and maintain substantially constant print density.

It is another object of the present invention to provide a thermal printing device that measures the resistance of the individual print elements and adjusts the time that the individual elements are energized as a function of their resistance to apply substantially constant energy to the various print elements and maintain substantially uniform print density.

It is yet another object of the present invention to provide hand-held labeler utilizing a thermal printing device that adjusts the time that the thermal print elements are energized as a function of how recently the print elements were previously energized.

It is yet another object of the present invention to provide a thermographic printing device capable of detecting faulty print elements and faulty battery cells.

It is another object of the present invention to provide a hand-held labeler utilizing a thermographic printing device that automatically staggers the printing of repetitive characters to avoid premature wear of the print head when repetitive characters are printed.

It is yet another object of the present invention to provide a hand-held thermographic printer that is capable of printing both alphanumerics and bar codes such as the Universal Product Code (UPC) and the European Article Number (EAN).

It is yet another object ofthe present invention to provide a hand-held thermographic labeling machine wherein data can be input either via a keyboard or by interfacing an external computer.

It is yet another object of the present invention to provide a microprocessor controlled hand-held labeler that adjusts the length of time that the various print elements are energized as a function of battery voltage, ambient temperature, the elapsed time since various elements were energized, the resistance of the various elements or any combination of the above factors.

It is yet another object of the invention to provide a hand-held labeler that utilizes a microprocessor controlled D.C. motor to advance the web of labels.

Therefore, in accordance with a preferred embodiment of the invention, there is provided a hand-held labeler utilizing a microprocessor controlled printing apparatus wherein the microprocessor adjusts the printing function to compensate for various ambient conditions, print head and paper parameters and the characteristics of the particular information being printed. To achieve this function, the microprocessor monitors the voltage applied to the thermographic print head and the resistance of each print element, as well as other parameters. The monitoring of the resistances of the print elements provide a way to detect an open or a shorted print element, and permits the amount of power being applied to the various print elements to be calculated.The battery voltage sensing permits a defective cell in the battery to be detected, and permits the length of time that each print element is energized to be adjusted as a function of battery voltage, and if desired, as a function of print element resistance in order to assure uniform density of printing. In addition, the length of time that the elements are energized is adjusted as a function of how recently the elements were previously energized to compensate for the heating and cooling characteristics of the elements.

When repetitive characters, such as, for example, the guard bars of the Universal Product Code are printed, the microprocessor staggers the code symbols so that the guard bars are printed by different print elements on different labels. This prevents the guard bar printing from being energized substantially continuously and failing prematurely. A keyboard as well as a computer interface is provided for entering data into the device, and a microprocessor controlled D.C. motor is used to advance the web past the print head.

These and other objects and advantages of the present invention will become readily apparent upon consideration of the following detailed description and attached drawing wherein: Figure lisa perspective view of a hand-held labeler constructed in accordance with the principles of the present invention; Figure2 is a system block diagram of the logic circuitry controlling the thermographic printing apparatus according to the invention; Figure 3 is a plan view of a thermographic print head usable with the printing apparatus according to the present invention; Figure 4 is a block diagram illustrating one embodiment of the print head driving circuitry; Figure 5 is a block diagram of an alternative embodiment of the print head driving circuitry;; Figure 6 is a graph illustrating the time-versus-voltage relationship necessary to obtain substantially constant density printing; Figure 7 is a graph illustrating the heating and cooling characteristics of a print element as a function of elapsed time between successive energizations; Figure 8 is a plan view of the print head and a label indicating the printing of a bar code as well as the staggering of the bar code in order to reduce the probability of premature print head failure; Figure 9 is another block diagram of a hand-held thermographic labeler according to the invention illustrating the control of the web advance motor; and Figure 10 illustrates the use of the labeler according to the invention used in a data retrieval and remote programming system.

Referring now to the drawing, with particular attention to Figure 1, there is shown a thermographic microprocessor controlled hand-held labeler according to the invention, generally designated by the reference numeral 10. The labeler 10 includes a housing 12 that supports a roll 14 of adhesive backed labels 16 that are supported on a backing web 18. A keyboard 20 is disposed on the housing 12 and contains a plurality of individually operable key switches 22 for entering data into the labeler. A display 24, which may be a liquid crystal or light emitting diode display, is also disposed on the housing to permit the entered data and microprocessor-generated prompting instructions to be viewed by the operator.A battery pack, which may be contained in a removable battery pack-handle unit 25 containing a battery 26 having an internal resistance 27, provides electrical power for the labeler 10. A trigger 28 is provided to initiate the label printing operation, and a label applying roller 30 is used to apply pressure to the adhesive backed label 16 when the label 16 is being applied to an article of merchandise. A label stripper (not shown) is contained within the housing 12 to separate the labels 16 from the backing strip 18. A plurality of guide rollers are provided to guide the separated labels 16 to the forward portion of the housing beneath the label applying roller 30, and to guide the backing strip to the rear of the housing beneath the roll 14.

As previously stated, the labeler according to the invention is quite versatile and is capable of printing alphanumerics, as well as bar codes including the Universal Product Code (UPC) and the European Article Number (EAN). The type of format, whether alphanumeric or bar code, is readily selected by entering the appropriate format and fonts defining data via the keyboard 20. The data to be printed, for example, price, product defining data and other information about the product such as the size, color, etc. is also entered via the keyboard 20. In addition, the number of labels to be printed may be entered. Also, a data input/output connector 32, may be provided on the housing to permit data to be entered into the labeler by an external source, such as, a remotely-located computer, and to permit the battery 26 to be charged.

Referring to Figure 2, the keyboard 20 is coupled to a peripheral interface adapter (PIA) 40 which provides an interface between various input and output devices and a microprocessor 42. Also coupled to the peripheral interface adapter 40 are a sensor 44 that senses a notch or other index indicating a separation between tags, a trigger switch 46 that is controlled by the trigger 28, and a motor control circuit 48.

Alternatively, the top of form sensor 44 may sense a mark or index on a web advancing wheel 49 that is driven by a web advancing motor 50. The motor control circuit responds to data received from the microprocessor 42 through the peripheral interface adapter 40, and controls the operation of the web advancing motor 50, which may be a stepping motor or a D.C. motor, the latter being preferable because of its low speed torque characteristics. An audible alarm 52 is also connected to the peripheral interface adapter 40 and is useful for indicating to the operator that a problem or potential problem exits. For example, the audible alarm 52 may be used to indicate a discharged orfaulty battery, a faulty print head, that the labeler is out of labels, or may simply be used to indicate that data entered into the device has been received. In the latter case, the audible alarm 52, can be used to provide an audible indication each time one of the key switches 22 on the keyboard 20 is depressed.

The display 24 is coupled to the microprocessor 42 via a display driver 54. The display 24 is used to display data being inputted into the microprocessor as well as other messages such, for example, prompting and diagnostic messages generated by the microprocessor. A read-only memory (ROM) 56 is provided for storing permanent data, such as the program defining operation of the device. The read-only memory 56 may either be permanently installed in the labeler 10, or may be removably installed in a socket or the like to permit the font and/or format to be changed by changing the memory 56. In addition, a random access memory (RAM) 58, usable for storing short term data, such as data entered via the keyboard 20, is provided, as is a non-volatile random-access memory (NVRAM) 60, suitable for storing data such as format data.The input/output connector 32 provides communications between the device and an external computer. Printing is accomplished by a print head assembly 64 that contains a print head 66 and print head driver 68 coupled to the peripheral interface adapter 40. An analog-to-digital converter 70 coupled to the peripheral interface adapter 40 senses the battery voltage or the voltage applied to the print head assembly 64, and provides a digital indication of that voltage to the peripheral interface adapter 40 so that the microprocessor may adjust the time that the print head is energized to compensate for variations in battery or print head voltage.

One example of the print head assembly 64 is ilustrated in simplified form in Figure 3. In the illustrated embodiment, the print head assembly 64 contains the print head driver 68 and the print head 66 disposed on a thin film substrate. A suitable print head assembly usable as the print head assembly 64 is a Kyocera print head manufactured by Kyoto Ceramic Company Ltd. of Japan. The Kyocera print head has a single line of print elements disposed transverse to the direction of travel of the web 14, and is particularly suitable for use in a hand-held labeler because of the high density of the print elements that make up the print head 66, particularly if both alphanumerics and bar codes are to be printed. One print head assembly particularly usable as the print head assembly 66 employs 224 printing elements that are each 10 mils long and 4.4 mils wide, and spaced on 5.2 mil centers.Such a configuration permits a virtually continuous line to be printed.

Each of the printing elements constitutes a resistive heating element 80 (Figure 4) that is individually energizable by the print head driver circuitry 68 which contains a heater driver transistor 82 for each of the printing elements 80. A gate 84 controls each of the heater driver transistors 82, and an input register 86 and a data register 88 control the operation of the gates 84. Thus, if a 224-element head is used as the print head 66, 224 driver transistors 82 and 224 gates 84 must be provided, and the input register 86 and the data register 88 must each have at least 224 stages.

The input register 86 receives data serially from a data input line 90 under the control of clock signals applied to a clock line 92. When the input register 86 is full, the data is transferred in parallel to the data register 88 under the control of a latch signal applied to the data register 88 by a line 94. The input register 86 is then reset by a reset pulse applied to the reset line 96, and new data is supplied to the input register.

Because the resistive heating elements 80 draw a substantial amount of current, for example, approximately 50 milliamps per element, and because of the extreme density of the elements, for example, approximately 200 elements per inch, the current drain on the battery 26 would be excessive if all of the elements 80 were turned on simultaneously. For this reason, the heater driver transistors 82 are strobed by the gates 84 so that no more than one-fourth of the heater drivers 82 may be energized at any one time.

In the embodiment, illustrated in Figure 4, the strobing is accomplished by utilizing three input AND gates as the gates 84, and by enabling the gates 84 in blocks. This is accomplished by providing two block enable signals BE1 and BE2 on lines 100 and 102, respectively, and strobes ST1 and ST2 on lines 104 and 106, respectively. Each of the block enable signals is connected to one-half of the gates 84 so that one-half of the gates 84 are enabled when the BE1 signal is high, and the other half are enabled when the BE2 signal is high.

The ST1 signal is applied to one-half of the gates 84 receiving the BE1 signal and to one half of the gates 84 receiving the BE2 signal. Similarly, the ST2 signal is applied to the gates 84 not receiving the ST1 signal.

Thus, since it is necessary for each gate to receive one of the block enable signals and one of the strobe signals in order to be fully enabled, only one-fourth of the gates 84 are enabled at any given time. Thus, the data from the data register 88 is applied to the heater driver transistors 82 in four steps, so that no more than one-fourth of the transistors 82 may be energized at a given time.

An alternative embodiment of the print head driving mechanism is illustrated in Figure 5. The embodiment illustrated in Figure 5 is similar to the one illustrated in Figure 4, except that the input register 86 is broken up into a plurality of smaller registers, for example, seven 32-stage shift registers 86' in the illustrated embodiment. Such an arrangement has the advantage that it permits data to be entered more rapidly into the system, thereby permitting a faster printing speed. This occurs because each of the seven shift registers 86' can be fed in parallel from said seven separate data lines 90'. Consequently, the data need be shifted only 32 times to load the registers 86', as opposed to the 224 shift required to load the input register 86.However, when loading the shift registers 86' the 224 bits defining each line cannot be fed serially into the shift registers 86', but the bits must be grouped so that they may be applied to the appropriate registers. This is accomplished by taking every 32nd bit from the data defining a line, and applying it to the appropriate one of the shift registers 86'. For example, if 224 bits are used to define a line, the 32nd, 64th, 96th, 1 28th, 1 60th, 192nd and 224th bits are selected and applied to seven stages of a buffer 108 (Fig u re 5). These bits are then applied in parallel to the shift registers 86'. Next, the 31st, 63rd, 95th, 127th, 159th, 191st and 223rd bits are applied to the buffer 108 and shifted to the registers 86'. The process is repeated until the first, 33rd, 65th, 97th, 129th, 161stand 193rd bits are loaded into the buffer 108 and supplied to the registers 86'. At this point, the seven registers 86' contain the bits 1-32, 33-64, 65-96, 97-128, 129-160, 161-192 and 193-224. Since this data completely defines a line, the data from the registers 86' can be transferred to a data register, such as the data register 88 (Figure 4), or to a plurality of individual data registers 88' (Figure 5). The output of the latches 88' can be applied to a plurality of three-input AND gates 84, orto any suitable device for limiting the number of individual elements that can be simultaneously energized.

In the embodiment illustrated in Figure 5, the strobe function that limits the number of elements that can be simultaneously energized is provided by a plurality of circuits 83. Each of the circuits 83 contains 32 two-input AND gates and appropriate driving circuitry for driving the print head 66. Such a system is somewhat simpler than the system illustrated in Figure 4 because only two-input AND gates, rather than three-input AND gates, are required. By providing three strobe signals S1, S2 and S3, the number of printing elements that can be simultaneously energized is restricted approximately one-third of the total number of print elements.

In the embodiment illustrated in Figure 5, the strobe signal S1 is applied to the first two and the last one of the circuits 83. The strobe signal S2 is applied to the third and fourth ones of the circuits 83, and the strobe signal S3 is applied to the fifth and sixth ones of the circuits 83. Consequently, no more than two out of seven printing elements may be simultaneously energized when either the strobe signal S2 or the strobe signal S3 is present. Theoretically, as many as three out of seven elements may be energized when the strobe signal S1 is present, but in practice, the line of print is seldom as wide as the width of the print head 66, and consequently, it is unlikely that more than one-half of the total elements in the first and last ones of the circuits 83 would be energized.

Even though the number of resistive heater elements 80 that can be energized simultaneously is limited, there is some fluctuation in battery voltage as a function of the number of resistive heater elements that are energized because of the internal resistance of the battery. For this reason, the analog-to-digital converter 70 (Figure 2) is used in combination with the peripheral interface adapter 40 and the microprocessor 42 to adjust the length of time that each of the resistive heater elements 80 is energized as a function of battery voltage.

In order to maintain constant density printing, the amount of Joule heating applied to the resistive printing elements must remain substantially constant as the voltage varies. The amount of Joule heating generated in each resistive heating element is defined by the following formula: v2 x t R where J is the Joule heat generated by each resistive heating element, v is the voltage applied to the resistive heating element, R is the resistance of the resistive heating element, andt represents the length of time that the resistive heating element is energized.

As previously discussed, it is desirable to maintain the Joule heating substantially constant in order to maintain substantially constant print density. Constant Joule heating is thus given by the following formula: v2 x t - K R where K is a constant.

Solving the above equation for time, t, the following relationship is obtained: KR v2 This relationship is illustrated bythe curve 110 in Figure 6.

The above-described relationship is suitable for thermog raphic printing heads formed on relatively insulated substrates, such as, for example, on glass or ceramic substrates. However, for print heads that are not so well insulated, or for those that may be used in relatively low temperature ambient conditions, the constant Joule heating input does not always provide optimum results, because the head cools relatively rapidly during the extended heating time. For example, in the graph illustrated in Figure 6, when the voltage is V2, a time equal to T1 is required to provide the desired Joule heating input. If the voltage drops to V1, then a longer time, T2, is required to provide the same amount of Joule heating. If the head is well insulated, and little or no heat is lost in a time interval between T1 and T2, the print density will be unaffected.However, if appreciable heat is lost in the time interval between T1 and T2, additidnal heat must be provided to compensate for that heat loss. Consequently, in such cases it is necessary to increase the Joule heat input when the print head voltage drops to compensate for such additional heat loss.

One relation that linearly increases the Joule heat input as a function of time is given by the following relation: v2 R x t K + Ct R x t where C is a constant proportional to the cooling characteristics of the print head. As is apparent from the above equation, it is similar to the constant Joule heat equation except that the term Ct has been added so that the amount of Joule heat added is a function of the time that the print head must be energized in order to compensate for any additional heat loss occurring during the additional time that the head is energized.

When this equation is solved fort, the following result occurs: KR v - CR This relationship is illustrated in the curve 112 of FigureS, and as is apparent from Figure 6, if a head having appreciable heat loss is used, the energization time must be extended from T2 toT3 to compensate for the additional heat loss.

Another factor that must be compensated for is the increase in the temperature of a printing element that occurs when the printing element is successively energized. For example, when a voltage, V, (Figure 7) is applied to a printing element, the temperature of the printing element rises from the ambient temperature (Tamb) to a temperature sufficient to cause printing to occur, as is shown by the curve 120. When the application of voltage to the printing element is terminated, the printing element cools exponentially as is shown by the curve 122. When power is reapplied to the printing element, the temperature of the element again rises, as is illustrated by the curve 124.However, if the head is reenergized before the printing element has sufficient time to cool to the ambient temperature, the peak temperature that will be reached the next time the head is energized will be higher than the previous peak temperature. This phenomenon is cumulative, as is illustrated by the cooling and heating curves 126 and 128, with the peak temperature reached during each heating cycle being higher than the peak temperature reached during the previous heating cycle. If no compensation is provided, the peak temperature can exceed the maximum temperature rating of the printing element (Tpmax), and cause damage to the printing elements.If the power applied to the elements is reduced, the temperature of the heads may fail to reach the minimum temperature required for printing (Tpmjn). In addition, it is apparent that as the ambient temperature (Tamb) changes, the peak temperature reached by the printing element will also change. Consequently, it is desirable to adjust the energization time of the print elements as a function of the elapsed time between successive energizations, and for ambient temperature in order to compensate for these factors. Such compensation techniques will be discussed in a subsequent portion of this discussion.

As is apparent from the previous discussion, the factors or elements affecting the density of printing can be separated into two general categories. The first category includes those elements relating to the environment in which the printer is operated, and includes such elements as battery condition, ambient temperature, the characteristics of the paper, the speed at which the paper is moved past the head, the intimacy of contact between the paper and the head, and other elements. The second category includes elements that are related to the characters being printed, insofar as the characters determine the energizing sequence of the elements, and how frequently the elements are energized. Some elements may fall into both the environmental dependent category and the character dependent category.An example of such an element is voltage, which is both a function of the condition of the battery (environmental) and a function of the number of printing elements that are simultaneously energized (character related).

Although the amount of compensation required to compensate for the various elements may be continuously calculated to maintain the print density constant, it has been found convenient to determine the required compensation factors for the various elements in advance and to store them in a look-up table.

The compensation factors can be stored in a multidimensional look-up table and the appropriate compensation factor retrieved as a function of the various elements to be considered. Alternatively, the compensation factors may be stored in a series of single variable look-up tables, each containing compensation factors for a single element. In this case overall compensation would be achieved through a series of individual steps.

For example, with respect to voltage compensation, the times required to obtain satisfactory printing at various voltages may be either calculated or determined empirically. Because of the large number of factors affecting the heating and cooling characteristic of a print head, the empirical approach is more straighfforward since the printing characteristics can readily be measured and stored.

Because of the fact that various elements that control printing density can be separated into character dependent and environment dependent elements, they can be treated separately so that the character generation circuitry can operate independently of the environmental compensation circuitry, and vice versa.

This is advantageous because it permits changes to be made to the character generation circuitry without affecting the environment compensating circuitry and vice versa. In addition, separate circuitry may be provided for controlling the web advancing motor 50 to make the motor control function independent of the print control and environmental compensating circuitry.

Thus, it is desirable to generate the data defining the characters to be printed prior to the actual printing of the characters, because this permits all of the character dependent compensating factors to be defined prior to the actual printing of a character of group of characters. For example, for the type of print head used in the illustrated embodiment, the printing on a typical label may be defined by 100 rows of 224 dots each. Thus, to define the information to be printed, data defining the individual characters to be printed is retrieved from a look-up table defining the various characters. The data thus retrieved defines which (if any) of the 224 elements must be be energized for each of the 100 rows two be printed. In addition to defining which of the 224 elements must be energized in each of the 100 rows, it is necessary to define the length of time that the elements are to be energized. Typically, this length of time is a function of how recently each of the energized elements had been previously energized, and the number of elements that are to be simulataneously energized for each row. Based on these factors, data defining the energization time, or burn time, for each row of dots is stored. Typically, one byte in storage is sufficient to define the burn time for each row, particularly when bar codes are being printed, because the same elements are always energized during the printing of the bar code, and consequently, the main parameter affecting the energization time is the number of elements that are simultaneously energized.For alphanumerics, where different ones of the printing elements are energized as different portions of the character are being printed, past history, or the elapsed time since each element was last energized, becomes more important, and additional information may be necessary to define the energization time. For example, different portions of a line may have different burn times resulting from different past histories, and this would require additional information to define the various burn times. Also, the circuitry would have to be more complex than that shown in Figures 4 and 5 if more than three or four different burn times are required per line. In the extreme, individual control of each of the print elements may be necessary.

With respect to environmental conditions that affect the printing characteristics, the condition of the battery is one of the most critical conditions. Consequently, the battery voltage is monitored by the analog-to-digital converter 70 under various conditions. For example, the battery voltage may be monitored under open circuit conditions, under load, or both. A suitable load for voltage monitoring puposes is the web advancing motor 50 because it presents a more constant load to the battery than does the print head 64.

Based on the condition of the battery, time correction factors proportional to the battery voltage may be obtained by solving one of the Joule heating equations previously discussed or determined empirically.

Once obtained, the correction factors may be stored in a look-up table as a function of open circuit battery voltage or battery voltage under load to provide the burn time corrections required for variations in battery condition.

As a battery discharges, the voltage developed by the battery 26 does not change substantially, but rather, the value of the internal resistance 27 increases. This value can vary from a value of a fraction of an ohm for a fully charged battery to a value on the order of a few ohms for a battery that is approaching its discharged state. It has been found that the value of the internal resistance 27 can be readily measured, and that this value provides a convenient way of compensating the burn time as a function of battery condition. For example, the value of the internal resistance 27 may be obtained by measuring the voltage across the terminals of the battery pack 25 under no load, or a light load such as the microprocessor 42 and associated equipment, and also under a heavy load, such as the motor 50 or the print head 64, or both.By knowing the currents drawn during the light load condition and during the heavy load condition, and by knowing the difference in the terminal voltage across the battery pack 25 under the light load conditions, the value of the internal resistance 27 can be readily calculated. For example, if the battery current under the light load condition is 100 milliamps and the voltage across the terminals of the battery pack 25 is 12.6 volts, and if the terminal voltage drops to 10.6 volts when the current is increased to 1.1 amps under the heavy load condition, the 2-volt drop caused by the 1-amp increase in current indicates that the value of the internal resistance 27 is 2 ohms.

Once the range of values of the internal resistance 27 for the type of battery used in the labeler 10 is known, the required burn time can be calculated as a function of the value of the resistance 27, or can be empirically determined. Once determined, burn time correction factors based on the value of the resistance 27 can be stored in a look-up table and used to compensate the burn times as a function of battery condition.

In addition to providing information for determining time correction factors, monitoring the battery permits a defective cell in a multi-cell battery to be readily detected. For example, by knowing the voltage per cell and the number of cells in the multi-cell battery, the voltage of the battery, when properly functioning, is known. Consequently, if a cell should fail, the voltage of the battery will drop by the voltage of one cell, and the change readily detected and a defective cell warning given. For example, in a nickel cadmium battery, the voltage is approximately 1.25 volts per cell. Thus, if a cell becomes completely discharged to the point of being reversed, the drop can be readily detected and the operator informed before the battery is damaged.

Typically, the voltage measurement made to detect a reversed cell is made under open circuit conditions, or with the microprocessor 42 and associated components as the only load, since the microprocessor load is so low that it approximates open circuit conditions.

Because the resistance of the individual print elements is also important in determining the amount of Joule heating that occurs during energization, it is desirable to know the resistance of each of the print elements. The resistance can readily be measured by passing a small current that is below the current required to cause printing through each of the print elements to measure the resistance of each element. The measurement can be achieved either by passing a known current through each element and measuring the voltage across the element in order to calculate its resistance, or by placing a known resistance in series with one of the power leads to the print head and measuring the voltage across the known resistance as each element is energized. Such a measurement serves two functions.It provides values of resistance for use in the Joule heating equation or in the burn time value or burn time correction look-up table. If extreme accuracy is required, the individual resistances of each element may be used, but if not, an average resistance of all of the elements may be used instead. Secondly, by placing maximum and minimum limits on the resistance of each print element, it becomes possible to isolate at open circuited or a short circuited element, and to inform the operator when such an element is found.

Other factors that affect print density include the ambient or substrate temperature, the characteristics of the thermographic paper being used for the web, the speed of paper moving past the printing head and the pressure between the printing head and paper. These factors can also be compensated for if desired. For example, the substrate temperature can be measured with a thermistor whose output is applied to an analog-to-digital converter, which in turn can be used to address appropriate locations in a substrate temperature look-up table containing appropriate burn time values or correction factors as a function of substrate temperature. If necessary, a shut off feature can be provided to terminate the printing function if the print head becomes excessively hot.Paper speed and contact pressure between the print head and the paper can also be measured, and appropriate corrections extracted from look-up tables. The characteristics of various types of thermal paper can also be stored in a look-up table, and accessed manually by entering the type of paper that is being used via the keyboard 20, or otherwise.

As previously stated, the labeler according to the invention is capable of printing bar codes as well as alphanumeric characters. When printing bar codes, the bars forming the bar code are preferably printed longitudinally along the web in a direction transverse or perpendicular to the direction of elongation of the printing head 66 (Figure 8). The code illustrated in Figure 8 is the Universal Product Code, but the device according to the invention is capable of printing any bar code including the European Article Number, or other codes. However, because the Universal Product Code is a common code, it will be used for purposes of illustration.

The Universal Product Code contains both bar codes and numerics (Figure 8). The zero to the left of the bar code indicates that the item to which the code is affixed is a product (as opposed to a coupon which normally bears the numeral 5). Ten human readable digits are disposed beneath the bar code and represent the value of the coded bars directly above the digits. Typically, the first five digits identify a manufacturer, and the last five digits identify a product. A series of guard bars, which are longer than the bars identifying the manufacturer and product, are disposed to the left and right of the manufacturer and product identifying digits and serve to indicate to the scanning circuitry the beginning and end of the code. These guard bars are always the same for a Universal Product Code regardless of the manufacturer and product identification information contained in the code.

Because the guard bars are always the same, when a series of labels is printed, the printing of the guard bars requires that the same elements always be energized. This causes the elements printing the guard bars to wear out more rapidly than the elements printing the manufacturer and product identification codes because the identification codes are variable. Consequently, in accordance with another important aspect of the invention, the position with respect to the print head 66 that the code is printed is varied periodically so that different ones of the print elements 80 of the head 66 are used to print the guard bars. Such a shift is indicated by the dashed arrows of Figure 8, and can be implemented in a number of ways.For example, the shift can be accomplished by loading additional zeros before or after the information loaded into the input registers 86 (Figure 4) or 86' (Figure 5). The shift can be accomplished at various times, such as, for example, after every batch of labels is printed, each time the labeler is turned on, after each tag is printed, or even at random. Of the various possible times to shift the code, shifting the code after every batch, or each time the machine is turned on, appear to be preferable.

Although various types of motors, including stepping motors, are usable as the web advancing motor 50, it has been found that a D.C. motor is particularly useful as the web advancing motor 50, partly because of its good low speed torque characteristics. However, when a D.C. motor is used, it is necessary to provide circuitry for controlling the speed and position of the D.C. motor shaft. To this end it has been found advantageous to utilize a separate microprocessor, such as a motor control processor 130 (Figure 9), within the motor control circuitry 48. Such an arrangement has two advantages. Firstly, it frees up the microprocessor 42 to carry out its print control and environmental compensation functions, and secondly provides greater flexibility of design and function by making the motor control function independent of the print control and environmental compensation functions.The various components necessary to carry out the print control and compensation functions are not shown in Figure 9 for purposes of clarity; however, it should be understood that the microprocessor 42 of Figure 9 must be coupled to components that are the same or analogous to the components shown in Figure 2 to provide the printing function.

The control of the D.C. motor 50 can be accomplished either by an open loop or a closed loop control system. However, in either case, because of the digital nature of the motor control processor 130, it is convenient to control the speed and torque of the motor 50 by applying a pulse width modulated signal to the motor 50. For example, the motor control processor 130 can supply motor driving pulses to the motor 50 at a constant frequency, and vary the width of the pulses to vary the speed or torque of the motor.

Alternatively, constant width, variable frequency pulses may be employed, but the use of constant frequency, variable width pulses has been found to be preferable in the illustrated embodiment; however, this may not be the case in every instance.

In a typical system, the microprocessor 42 issues a command to the motor control processor 130 indicating to the motor control processor 130 that the motor is to be started. When this occurs, the motor control processor 130 applies the appropriate width pulses to the motor 50. The motor 50 drives a tachometer 132 which generates pulses having a frequency proportional to the speed of the motor 50.

Although various types of tachometers may be used as the tachometer 132, such as, for example, magnetic tachometers, it has been found convenient to utilize a light-chopper type tachometer that utilizes a slit or perforated wheel interposed between a light source, such as a light emitting diode, and a light sensor to generate the tachometer pulses. These pulses are applied to the motor control processor 130, preferably via a peripheral interface adapter such as the peripheral interface adapter 40. The pulses are processed by the motor control processor 130 which then generates a label position signal and applies itto the microprocessor 42 to indicate the position of the tag relative to the print head.A start-print signal, which indicates to the microprocessor 42 that a printable area of the label is positioned beneath the print head, is also generated by the motor control processor 130 in response to the tachometer pulses. The start print signal may be a two-level signal that is, for example, high when a printable area is present beneath the print head, and low when a non-printable area is present. The paper position signal may be simply a squared up facsimile of the output signal from the tachometer 132, or a multiple or submultiple of the frequency of the tachometer signal. Alternatively, the motor control processor 130 can countthe tachometer pulses and provide a paper position signal that is representative of the number of tachometer pulses that have been counted during the advancement of a particular label.To determine the position of the top of the label, the motor control processor 130 also cooperates with the top of the form sensor 44 which detects an index such as a notch or printed mark on the web 14 that indicates the separations between individual labels 16 to thereby provide a position reference for the system.

As discussed, the control of the motor 50 may be either open loop or closed loop. In the open loop case, the characteristics of the motor 50 must be empirically or otherwise determined to determine the width of the driving pulses that must be applied to the motor 50 to obtain the desired speed or torque characteristic.

These values of pulse width may be stored in a look-up table, for example, in a read-only memory 134 that may be either internal or external to the motor control processor 130. A great deal of pulse width information can be stored in the memory 134 to permit rather sophisticated motor control. Such data may include data that permits a ramping up of the motor speed when the motor is initially started, maintains a constant printing speed, and subsequently ramps down the motor speed when the printing has been completed.

Thus, information defining the pulse width that provides the required printing speed must be stored, as must the sequence of pulse widths that provides the initial ramp up and subsequent ramp down when the printing is terminated.

In the open loop case discussed above, the tachometer pulses from the tachometer 132 are used simply to provide position information, but in the closed loop system they are also used to control motor speed. In the closed loop system, rather than storing pulse width information for speed control purposes, the frequencies of the tachometer pulses that correspond to various motor speeds are stored in the memory 134. To control motor speed, the frequency of the tachometer pulses is ascertained, and compared with the frequency corresponding to the desired speed stored in the read-only memory 134. Based on this comparison, the motor control processor 130 adjusts the width of the driving pulses to the motor 50 until the frequency of the tachometer pulses from the tachometer 132 corresponds to the frequency stored in the read-only memory 134.As in the open loop case, ramp up, running speed and ramp down can be achieved by storing the frequencies for the various phases of operation in the read-only memory 134.

Because the motor 50 is pulsed with voltage pulses as is illustrated in Figure 7, it is possible to determine the speed of the motor 50 by measuring the voltage or back EMF generated by the motor between voltage pulses. This may be accomplished by an analog-to-digital converter, such as an analog-to-digital converter 136, which is used to sample the voltage (back EMF) generated by the motor 50 between voltage pulses applied to the motor 50. Because the back EMF of a motor is related to the speed at which the motor is rotating, it provides an indication of the speed of the motor 50, and eliminates the need for a tachometer, such as the tachometer 132, in a closed loop system.When back EMF is used to control motor speed in a closed loop system, the analog-to-digital converter 136 samples the back EMF generated by the motor 50 at periodic intervals and provides a digital representation of the sampled voltage to the motor control processor 130 (or to another microprocesor such as the microprocessor 42 when no motor control processor is employed as is the case of Figure 2). This digital representation is then compared with stored digital representations of voltage corresponding to various desired operating speeds, and the width (or frequency) of the pulse applied to the motor 50 is adjusted until the back EMF generated by the motor 50 corresponds to one of the stored digital representations of voltage.As in the previously discussed closed loop case, ramp up, running speed and ramp down can be achieved by storing digital representations of the various voltages (back EMFs) required for the various phases of operation in the read-only memory 134.

Because the labeler according to the invention includes data processing capability, it can be used for data collection and for receiving data from a remotely-located source, such as a central computer 138 (Figure 10) which may be coupled to the labeler 10 by a suitable interface 140. For example, one way in which the labeler according to the invention can be used for data collection is for the labeler to store in memory the number of labels of various types that were printed when the labels were being applied to merchandise. This information could later be read out by a computer 138 via the data interface 140 coupled to the connector 32.

Such information would be an aid in inventory control by indicating to the central computer 138 the type and quantity of merchandise that was labeled and placed on the sales floor. In addition, an operator taking inventory could manually enter data defining the type and quantity of merchandise in stock into the labeler according to the invention in order to collect inventory data which would subsequently be transmitted to the central computer 138. In addition, the central computer 138 could be used to supply data to the labeler 10 defining the information to be printed on the labels, as well as the number of labels to be printed. This would reduce the probability of errors caused by incorrect data entry by an operator, and would permit the operator to apply the labels to articles of merchandise without having to enter any data at all. Such a system would eliminate the need for preprinting the labels, as is sometimes done by a stationary table-top printer, and avoid the need to transport the tags physically from the printer to the merchandise, thus reducing the possibility of applying the labels to the wrong merchandise items.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.

Claims (80)

1. A hand-held labelling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to the backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually energizable printing elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means for selectively energizing the predetermined ones of said print elements, means for sensing the voltage applied to said print head, means for determining the resistance of the print elements in said print head, and means responsive to the voltage applied to said print head and the resistance of said print elements for altering the length of time the various print elements are energized as a function of print element resistance and print head voltage.

2. A hand-held labeling machine as recited in claim 1 wherein said length of time altering means is responsive to the voltage applied to the individual print elements.

3. A hand-held labeling machine as recited in claim 2 wherein said source of electrical energy is a battery, and wherein said time altering means includes means for determining the internal resistance of the battery.

4. A hand-held labeling machine as recited in claim 1 wherein the length of time altering means is further responsive to one of substrate and ambient temperature.

5. A hand-held labeling machine as recited in claim 1 further including means for determining the time interval between successive energizations of each print element and altering the length of time each print element is energized as a function of the time interval between successive energizations thereof.

6. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel the printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually energizable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means for selectively energizing predetermined ones of said print elements for predetermined time intervals, means for providing a digital indication representative of the energization sequence of each of said print elements, means for storing said digital indication, and digital means responsive to stored digital indications for altering the predetermined time intervals as a function of said stored digital indication.

7. A hand-held labeling machine as recited in claim 6 wherein said altering means includes means for determining the predetermined time interval for each print element as a function of the elapsed time since that element was last energized.

8. A hand-held labeling machine as recited in claim 7 wherein said determining means includes means for storing representations of the predetermined time intervals as a function of elapsed time.

9. A hand-held labeling machine as recited in claim 7 wherein said determining means includes means for computing the predetermined time intervals as a function of elapsed time.

10. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing station, means for peeling the printed labels from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into applying relationship with the label applying means and to advance another label into the printing station, means for entering selected data to be printed, the printing means including a thermographic print head located at said printing station, said print head having a plurality of individually energizable thermographic print elements arranged in a straight line array disposed transverse to the direction of travel of the web and powered by the source of electrical energy for printing on a thermographic label at the printing station, means for selectively energizing predetermined ones of said elements having a predetermined spatial relationship with respect to each other to generate a predetermined bar code pattern, and means for selectively energizing different predetermined ones of said elements having the same predetermined spatial relationship with respect to each other to generate the same bar code pattern on said web at a location spaced laterally from said predetermined bar code pattern.

11. A hand-held labeling machine comprising; a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually selectable print elements powered by the source of electrical energy for printing on a thermographic label at the printing means, means for applying an energizing voltage from said source of electrical energy to said print head, means for selectively energizing predetermined ones of said predetermined print elements, means for sensing the voltage applied to said print head and providing a digital representation thereof, and digital means responsive to the digital representation generated by said voltage sensing means for determining the length of time that the various print elements are to be energized as a function of the voltage applied to the print head.

12. A hand-held labeling machine as recited in claim 11 wherein said digital means includes means responsive to the digital representation for altering the length of time that the individual print elements are energized as an inverse function of the voltage applied to the print head.

13. A hand-held labeling machine as recited in claim 11 wherein said digital means includes memory means for storing data representative of print element energization time as a function of the voltage applied to the print head, and wherein said digital means includes means responsive to the digital representation of voltage for retrieving a time corresponding to the digital representation of voltage and for energizing the individual print elements for that corresponding time.

14. A hand-held labeling machine as recited in claim 11 wherein said source of electrical energy is a battery, and wherein said digital means includes means responsive to the digital representations of voltage for determining the internal resistance of the battery, and includes means for storing data representative of print element energization time as a function of internal resistance, and wherein said digital means includes means responsive to the internal resistance for retrieving a time corresponding to the internal resistance and for energizing the individual print elements forthat corresponding time.

15. A hand-held labeling machine as recited in claim 11 wherein said digital means includes means for energizing each of said print elements for a predetermined time period, and further including memory means for storing time adjustments as a function of voltage, said digital means further including means responsive to the digital representation of the voltage for retrieving the time adjustment corresponding to the digital representation of the voltage and adjusting the predetermined time period in response to the time adjustment.

16. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent to the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually energizable elements powered by the source of electrical energy for printing on a thermographic label at the printing position, wherein said source of electrical energy includes a multi-cell battery, said labeling machine further including means for applying an energizing voltage from said multi-cell battery to said print head, means for selectively energizing predetermined ones of said print elements, and means for sensing the voltage produced by the multi-cell battery and producing an indication if the voltage of the multi-cell battery drops below a predetermined level.

17. A hand-held labeling machine as recited in claim 16 wherein said voltage sensing means includes means for providing an indication when not all of the cells of the multi-cell battery are operative.

18. A hand-held labeling machine as recited in claim 17 wherein said multi-cell battery is a nickel cadmium battery, and wherein said sensing means includes means for detecting a reversed cell in said nickel cadmium battery.

19. A hand-held labeling machine as recited in claim 18 wherein each cell of said nickel cadmium battery produces a predetermined voltage, and wherein said sensing means detects said reversed cell if the voltage of said battery is not substantially equal to said predetermined voltage multiplied by the number of cells in the nickel cadmium battery.

20. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually selectable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means for applying an energizing voltage from said source of said electrical energy to said print head, means responsive to said selected data for selectively energizing predetermined ones of said print elements in response to said data, means for providing an indication that is a function of the number of said individually energizable print elements that are to be simultaneously energized at a given time, and means for determining the length of time that the individually energizable print elements are to be energized, said length of time determining means being responsive to said indication for adjusting the length of time that the print elements are to be energized as a function of the number of print elements that are simultaneously energized.

21. A hand-held labeling machine as recited in claim 20 wherein said source of electrical energy is a battery, and wherein said length of time determining means includes means for determining the internal resistance of the battery and adjusting the length of time that the print elements are to be energized as a function of internal resistance.

22. A hand-held labeling maching as recited in claim 20 wherein said length of time determining means includes means for increasing the length of time that the print elements are energized when the number of simultaneously energized print elements is increased.

23. A hand-held labeling machine as recited in claim 20 further including means responsive to the voltage applied to said print head for altering the length of time the print elements are energized as a function of the voltage applied to the print head.

24. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually energizable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means for applying an energizing voltage from said source of electrical energy to said print head, means for selectively energizing predetermined ones of said print elements in response to said selected data, means for individually determining the resistance of each of the individual print elements in said print head, and means for providing an indication if the resistance of any one of said print elements is not within a predetermined range of resistances.

25. A hand-held labeling machine as recited in claim 24 wherein said indication providing means includes means for providing an indication of a short circuited print element.

26. A hand-held labeling machine as recited in claim 24 wherein said indication providing means includes means for providing an indication of an open circuited print element.

27. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually selectable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means coupled to said data entering means for electrically processing the selected data and energizing the individual print elements in a predetermined sequence determined by the selected data to print data on the label, wherein said advancing means includes a D.C. motor electrically coupled to said processing means, a tachometer coupled to the D.C. motor and to the processing means for providing atachometersignal representative of the speed ofthe D.C. motortothe processing means, wherein said processing means included means for applying electrical pulses to said D.C.

motor to cause said D.C. motor to advance said web.

28. A hand-held labeling machine as recited in claim 27 wherein said labeling machine further includes means for sensing indices on said web and supplying an index signal to said processing means whenever one of the indices is sensed, said processing means being responsive to said index signal and to said tachometer signal for determining the relative position between the print head and a label.

29. A hand-held labeling machine as recited in claim 28 wherein said processing means includes means for adjusting the width of the pulses applied to said D.C. motor in order to control the speed of the D.C.

motor.

30. A hand-held labeling machine as recited in claim 29 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the tachometer signal and adjusting the width of the pulses applied to the D.C. motor until the tachometer signal corresponds to the stored speed representative data defining the desired speed.

31. A hand-held labeling machine as recited in claim 30 wherein said desired speed representative data storing means includes means for storing indications representative of a ramping up of the speed of the D.C.

motor, indications representative of the printing speed of the D.C. motor and indications representative of the ramping down of the speed of the D.C. motor.

32. A hand-held labeling machine as recited in claim 29 wherein said processing means includes means for storing representations of pulse widths that correspond to various motor speeds.

33. A hand-held labeling machine as recited in claim 22 wherein said processing means includes means for selecting the pulse widths selectively to provide a ramp up of motor speed, to maintain a substantially constant speed during printing, and to provide a ramp down of motor speed.

34. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to the backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually selectable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means coupled to said data entering means for electrically processing the selected data and energizing the individual print elements in a predetermined sequence determined by the selected data to print data on the label, wherein said advancing means includes a D.C. motor electrically coupled to said processing means, wherein said processing means includes means for applying electrical pulses to said D.C. motor to cause said D.C. motor to advance said web, and means coupled to said D.C. motor and to said processing means for determining the back EMF generated by said D.C. motor between the electrical pulses applied thereto and for providing a signal representative of the speed of the D.C. motor to the microprocessor in response to the back EMF.

35. A hand-held labeling machine as recited in claim 34 wherein said processing means includes means for adjusting the width of the pulses applied to the D.C. motor in order to control the speed of the D.C. motor.

36. A hand-held labeling machine as recited in claim 35 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the speed representative signal received from the back EMF determining means, and adjusting the width of the pulses applied to the D.C. motor until the speed representative signal corresponds to the stored speed representative data defining the desired speed.

37. A hand-held labeling machine as recited in claim 36 wherein said desired speed representative storing means includes means for storing data representative of a ramping up of the speed of the D.C. motor, data representative of the printing speed of the D.C. motor and data representative of the ramping down of the D.C. motor.

38. A thermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing predetermined ones of said print elements; means for sensing the voltage applied to said print head; means for determining the resistance of the print elements in said print head; and means responsive to the voltage and resistance determining means for altering the length of time the various print elements are energized as a function of print element resistance and print head voltage.

39. A thermographic printer as recited in claim 38 wherein said length of time altering means is responsive to the voltage applied to the individual print elements.

40. Athermographic printer as recited in claim 38 wherein said length of time altering means is further responsive to one of substrate and ambient temperature.

41. Athermographic printer as recited in claim 38 further including means for determining the time interval between successive energizations for each print element and altering the length of time each print element is energized as a function of the time interval between successive energizations thereof.

42. Athermographic printercomprising: a thermographic print head having a plurality of individually energizable print elements; means for selectively energizing predetermined ones of said print elements for predetermined time intervals; means for providing a digital indication representative of the energization sequence of each of said print elements; means for storing said digital indication; and digital means responsive to said stored digital indication for altering said predetermined time intervals as a function of said stored digital indication.

43. A thermographic printer as recited in claim 42 wherein said altering means includes means for determining the predetermined time interval for each print element as a function of the elapsed time since that element was last energized.

44. A thermographic printer as recited in claim 43 wherein said determining means include means for storing representations of the predetermined time intervals as a function of elapsed time.

45. A thermographic printer as recited in claim 44 wherein said determining means includes means for computing said predetermined time intervals as a function of elapsed time.

46. A thermographic printer for printing bar codes onto a web of thermally sensitive stock, comprising: a printing station; meansforfeeding said web past the printing station; a thermographic print head located at said printing station, said print head having a plurality of individually energizable thermographic print elements arranged in a straight line array disposed transverse the direction the travel of said web; means for selectively energizing predetermined ones of said elements having a predetermined spatial relationship with respect to each other to generate a predetermined bar code pattern; and means for selectively energizing different predetermined ones of said elements having the same predetermined spatial relationship with respect to each other to generate the same bar code pattern on said web at a location spaced laterally from said predetermined bar code pattern.

47. Athermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing predetermined ones of said print elements; means for sensing the voltage applied to said print head and providing a digital representation in response thereto; and digital means responsive to the digital representation generated by said voltage sensing means for determining the length of time that the various print elements are to be energized as a function of print head voltage.

48. Athermograhic printer as recited in claim 47 wherein said digital means includes means responsive to the digital representation for altering the length of time that the individual print elements are energized as an inverse function of the voltage applied to the print head.

49. A thermographic printer as recited in claim 48 wherein said length of time altering means includes digital computing means for determining the length of time that the individual print elements are energized according to the following relationship: KR t= 2 V wherein t is the length of time that the individual print elements are energized, K is a constant, R is a function of the resistance of the individual print elements and v is the voltage applied to the print head.

50. A thermographic printer as recited in claim 48 wherein said length of time determining means includes digital computing means for determining the length of time that the individual print elements are energized according to the following relationship: t= v2KR - v2 - CR wherein t is the length of time that the individual print elements are energized, K and C are constants, R is a function of the resistance of the individual print elements and v is the voltage applied to the print head.

51. A thermographic printer as recited in claim 47 wherein said digital means includes memory means for storing print element energization times as a function of print head voltage, and said digital means includes means responsive to the digital representation of voltage for retrieving a time corresponding to the digital representation of voltage and for energizing the individual print elements for that corresponding time.

52. Athermographic printer as recited in claim 47 wherein said digital means includes means for energizing each of said print elements for a predetermined time period, and further including memory means for storing time adjustments as a function of voltage, said digital means further including means responsive to the digital representation of voltage for retrieving the time adjustment corresponding to the digital representation of voltage and adjusting the predetermined time period in response to the time adjustment.

53. A thermographic printer operable from a multi-cell battery comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage from said multi-cell battery to said print head; means for selectively energizing predetermined ones of said print elements; and means for sensing the voltage produced by the multi-cell battery and producing an indication if the voltage of the multi-cell battery drops below a predetermined level.

54. Athermographic printer as recited in claim 53 wherein said voltage sensing means includes means for providing an indication when not all of the cells of the multi-cell battery are operative.

55. A thermographic printer as recited in claim 54 wherein said printer is operable from a nickel cadmium battery, and wherein said sensing means includes means for detecting a reversed cell in said nickel cadmium battery.

56. A thermographic printer as recited in claim 55 wherein each cell of said nickel cadmium battery produces a predetermined voltage, and wherein said sensing means detects said reversed cell if the voltage of said battery is not substantially equal to said predetermined voltage multiplied by the number of cells in the nickel cadmium battery.

57. A thermographic printer as recited in claim 56 wherein said predetermined voltage is approximately on the order of 1.25 volts.

58. A thermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing predetermined ones of said print elements; means for providing an indication that is a function of the number of said individually energizable print elements that are to be simultaneously energized at a given time; and means for determining the length of time that the individually energizable print elements are to be energized, said length of time determining means being responsive to said indication for adjusting the length of time that the print elements are to be energized as a function of the number of print elements that are simultaneously energized.

59. Athermographic printer as recited in claim 58 wherein said printer is powered by a battery, and wherein said length of time determining means includes means for determining the internal resistance of the battery and for altering the length of time the print elements are to be energized as a function of internal resistance.

60. A thermographic printer as recited in claim 58 wherein said length of time determining means includes means for increasing the length of time that the print elements are energized when the number of simultaneously energized print elements is increased.

61. A thermographic printer as recited in claim 58 further including means responsive to the voltage applied to said print head for altering the length of time the print elements are energized as a function of the voltage applied to the print head.

62. A thermographic printer as recited in claim 61 wherein said altering means includes means for increasing the length of time the print elements are energized as the battery voltage decreases.

63. A thermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing predetermined ones of said print elements; means for individually determining the resistance of each of the individual print elements in said print head; and means for providing an indication if the resistance of any one of said print elements is not within a predetermined range of resistances.

64. A thermographic printer as recited in claim 63 wherein said indication providing means includes means for providing an indication of a short circuited print element.

65. A thermographic printer as recited in claim 63 wherein said indication providing means includes means for providing an indication of an open circuited print element.

66. A thermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing prdetermined ones of said print elements; means for entering data representative of the information to be printed; means coupled to said data entering means for electrically processing the entered data and energizing the individual print elements in a predetermined sequence determined by the entered data to print data on a web; and means for advancing the web past the print head, wherein said advancing means includes a D.C. motor electrically coupled to said processing means, a tachometer coupled to the D.C. motor and to the processing means for providing a tachometer signal representative of the speed of the D.C. motor to the processing means, wherein said processing means includes means for applying electrical pulses to said D.C. motor to cause said D.C. motor to advance said web, said processing means including means for adjusting the width of the pulses applied to said D.C. motor to varythe speed of the D.C. motor.

67. A thermographic printer as recited claim 66 wherein said printer further includes means for sensing indices indicative of the position of said web and supplying an index signal to said processing means whenever one of said indices is sensed, said processing means being responsive to said index signal and to said tachometer signal for determining the relative position between said print head and the web.

68. A thermographic printer as recited in claim 66 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the tachometer signal and adjusting the width of the pulses applied to the D.C motor until the tachometer signal corresponds to the stored speed representative data defining the desired speed.

69. A thermographic printer as recited in claim 68 wherein said desired speed representative data storing means includes means for storing indications representative of a ramping up of the speed of the D.C. motor, indications representative of the printing speed of the D.C. motor and indications representative of the ramping down of the speed of the D.C. motor.

70. A thermogrphic printer as recited in claim 66 wherein said processing means includes means for storing representations of pulse widths that correspond to various motor speeds.

71. Athermographic printer as recited in claim 70 wherein said processing means includes means for selecting the pulse width selectively to provide a ramp up of motor speed, to maintain a substantially constant speed during printing, and to provide a ramp down of motor speed.

72. Athermographic printer comprising: a thermographic print head having a plurality of individually energizable print elements; means for applying an energizing voltage to said print head; means for selectively energizing predetermined ones of said print elements; means for entering data representative of the information to be printed; means coupled to said data entering means for electrically processing the entered data and energizing the individual print elements in a predetermined sequence determined by the entered data to print data on a web;; means for advancing the web past the print head, wherein said advancing means includings a D.C. motor electrically coupled to said processing means, wherein said processing means includes means for applying electrical pulses to said D.C. motor to cause said D.C. motor to advance said web, said processing means includes means for adjusting the width of the pulses applied to said D.C. motor to vary the speed of the D.C.

motor; and means coupled to said D.C. motor and to said processing means for sensing the back EMF generated by the D.C. motor between pulses, and for applying a signal representative of the speed of the D.C. motor to the microprocessor in response to the amplitude of the back EMF.

73. Athermographic printer as recited in claim 72 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the speed representative signal and adjusting the width of the pulses applied to the D.C. motor until the speed representative signal corresponds to the stored speed representative data defining the desired speed.

74. A thermographic printer as recited in claim 73 wherein said desired speed representative data storing means includes means for storing data representative of a ramping up of the speed of the D.C. motor, data representative of the printing speed of the D.C. motor and data representative of the ramping down of the speed of the D.C. motor.

75. A thermographic printer as recited in claim 72 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the speed representative signal and adjusting the frequency of the pulses applied to the D.C. motor until the speed representative signal corresponds to the stored speed representative data defining the desired speed.

76. A thermographic printer as recited in claim 75 wherein said processing means includes means for storing data representative of the desired speed of the D.C. motor, and wherein said processing means includes means for comparing the stored desired speed representative data with the speed representative signal and adjusting the frequency of the pulses applied to the D.C. motor until the speed representative signal corresponds to the stored speed representative data defining the desired speed.

77. A labeling system comprising: a hand-held labeling machine having a manually engageable handle, the housing having means for holding a label supply, means for printing on a label at a printing position, means for advancing the labels into the printing position, data entering and transmitting means including a keyboard mounted on the housing for entering data including selected data to be printed into the labeling machine, the printing means including a print head having a plurality of individually energizeable printing elements powered by the source of electrical energy for printing on a label at the printing position, means coupled to the entering means for electrically processing the data entered by the entering means, means electrically coupling the data processing means and the printing head for causing the data processing means to operate the printing head to print the selected data on the label, and memory means for storing data; and interface means connectable to said data entering means for receiving data including selected data from a centrally located computer and applying it to the hand-held labeling machine, and for receiving data stored in the memory means from the hand-held labeling machine and transmitting it to the central computer.

78. A hand-held labeling machine comprising: a housing having a manually engageable handle, the housing having means for holding a label supply roll of a composite web having labels releasably adhered to a backing strip, means for printing on a label at a printing position, means for peeling the printed label from the backing strip, label applying means disposed adjacent the peeling means, means for advancing the web to peel a printed label from the backing strip at the peeling means and advance the printed label into label applying relationship with the label applying means and to advance another label into the printing position, means for entering selected data to be printed, the printing means including a thermographic print head having a plurality of individually selectable print elements powered by the source of electrical energy for printing on a thermographic label at the printing position, means coupled to said data entering means for electrically processing the selected data and energizing the individual print elements in a predetermined sequency determined by the selected data to print data on the label, wherein said advancing means includes signaling means electrically coupled to said processing means for providing a signal representative of the position of the label, said signaling means including means for providing a signal representative of a printable area on the label, said processing means including means responsive to said printable area signal providing means for rendering said print head operative to place the data on the label.

79. A thermographic printer substantially as described with reference to Figures 2 to 9 of the drawings.

80. A hand-held labeler substantially as described with reference to the drawings.