Background Batteries or accumulators are useful in many different applications due to their ability to store electrical charge or energy. Batteries are divided into mainly two groups, primary batteries and secondary batteries. Primary batteries chemistries are e.g. zinc-carbon, zinc- chloride, alkaline, lithium, lithium-copper oxide and lithium-manganese dioxide, and secondary batteries chemistries are e.g. NiCd, Lead Acid, NiMH NiZn and lithium ion. Secondary batteries are also characterized in that they are rechargeable. Wet cell batteries, acid or lead batteries are preferable used in vehicles such as cars, trucks, ships etc, due to their ability to store large amount of energy and to supply high surge currents. This is especially important for traction batteries, i.e. batteries used in e.g. electrical trucks and forklifts - impossible to manage without in logistics enterprises such as e.g. furniture, or food storage warehouses, which are reused almost every day; or in important community functions such as stationary batteries for hospitals and telecom stations, as well as start batteries for trains, lorries, busses, etc.

In short, a battery can be described as a device that converts chemical energy directly to electrical energy and the energy amount contained in a battery is typically measured in ampere-hours - Ah. If a battery for example has a capacity of 75 Ah, it could be seen as the total amount of charge that could, in the ideal case, be delivered as a 1 A current during 75 hours, a 3 ampere current during 25 hours or a 75 ampere current during 1 hour. Normally, the minimum and maximum current that could be delivered is constrained for the battery type.

A wet cell battery consists of a number of cells (voltaic cells), and in order to create a higher potential in the wet cell batteries, the cells are connected to each other and ends in the positive and negative terminals, or poles, of the battery. There also exist sealed batteries, wherein the electrolyte is in the form of a gel. Each cell consists of two electrodes (anode and cathode), which are submerged in a conductive dissociated liquid, or solution, containing ions (anions and cations). The liquid, which typically consists of sulphuric acid (H ₂ SO ₄ ) dissolved in water, is called an electrolyte, and the determining factor of its electrical conductivity is the access to free charge carriers, just as in good metal conductors (e.g. copper). One difference to metals is that in the electrolyte there exist both positive and negative charge carriers, where the charges are carried by the movable positive and negative ions (dissolved molecules). In metal conductors free charge carriers only exist in the form of electrons (negative charge). Each molecule of the sulphuric acid (H ₂ SO ₄ ) is dissolved into two positive hydrogen ions (H ⁺ ), which lacks an electron each, and a sulphate ion (SO ₄ ² ) which has two free electrons (two electrons too much). The sulphate ions and the hydrogen ions are combined with the substances of the electrodes (e.g. different compounds of e.g. copper, lead, zinc, etc) at which electrons, and their charge, are set free or said to be absorbed. The electrical current in the external circuit connected to the electrodes (terminals or poles) of the battery is carried by electrons (i.e. the free electrons in e.g. copper wires), and the electrodes (here each part of them not submerged in the electrolyte - i.e. poles) provide the physical interface between the battery and a device using current from the battery (e.g. a start engine to a car, a generator, a traction engine etc). One of the most used wet cell battery types is the lead acid accumulator, or lead accumulator. Its structure and functionality will here be described in more detail in order to illustrate the need of the invention more clearly and to define important concepts, although these kinds of batteries are well known by the person skilled in the art. This illustration is nevertheless convenient, since the battery's principal functionality is similar to the most rechargeable battery types and therefore constitutes an important fundament in explaining the difference between various reconditioning and recharging methods.

The electrodes of a lead acid accumulator cell consist of two solid lead plates (i.e. anode and cathode). The cathode, or the negative plate typically consists of amorphous lead, or spongy metallic lead, and the anode, or the positive plate typically consists of lead oxide (peroxide Pb0 ₂ ).

When charging a rechargeable battery, the electrical energy is instead converted into chemical energy by a supplied voltage and/or current at the terminals of the battery from an external source. In the lead acid battery, the electro-chemical reactions that take place at the positive and negative electrode plates during charge are:

Positive plates: PbS0 ₄ + 2H ₂ 0→ Pb0 ₂ + 4H ⁺ + SO ₄ +2e ^~

Negative plates: PbS0 ₄ + 2e ^" → Pb + S0 ^2" ₄

Over all reaction: 2PbS0 ₄ + 2 H ₂ 0→ Pb0 ₂ + Pb + 2H ₂ S0 ₄

During discharge of the lead acid battery, electrons are emitted by reaction with the sulphuric acid (H ₂ S0 ₄ ), whereby lead sulphate (PbS0 ₄ ) is formed, and the current is taken from the cell in the direction from the positive plate to the negative plate in the outside circuit. The electro-chemical reactions that take place at the positive and negative electrode plates during discharge inside the battery are:

Positive plates: Pb0 ₂ + 4H ⁺ + SO ₄ +2e ^" → PbS0 ₄ + 2H ₂ 0

Negative plates: Pb + S0 ² - ₄ → PbS0 ₄ + 2e

Over all reaction: Pb0 ₂ + Pb + 2H ₂ S0 ₄ → 2PbS0 ₄ + 2H ₂ 0

That is, lead sulphate (PbS0 ₄ ) is formed in connection with the discharge and the chemical reactions turn both the plates, or electrodes, into lead sulphate (PbS0 ₄ ). Moreover, the electrolyte loses its dissolved sulphuric acid and becomes primarily water, which has the effect that the acid density decreases.

If the lead sulphate (PbS0 ₄ ) becomes more and more crystallized, it is very hard to dissolve and will adhere at the electrodes. During the battery's numerous discharges and charges the lead sulphate will inevitably transform into a stable crystalline form that no longer dissolves during recharge, and since not all the lead is absorbed back to the battery plates, the amount of active material for use in generating electricity declines over time.

This process is called sulfation, or sulphating, and since the lead plates are covered with larger and larger lead sulphate (PbS0 ₄ ) crystals one of the problems with sulphating, except from the fact that this might spoil the plates since it is conducive to buckling, which in itself will considerably shorten the life of a cell, is that these crystals impedes recharging by physically block the fluid of the electrolyte from entering the pores in the amorphous lead at the plates by large adhered crystals. The hard lead sulphate is also a non-conductive material and when it coats the electrode plates it causes a reduction in the area needed for the electro-chemical reactions.

Typically, a normal three phase charger starts with a fixed current charge. When the voltage has reached a predetermined voltage it switches over to this predetermined voltage and after a while the current normally drops below the fixed current. When the maintenance current for this type of battery has been achieved the charger terminates the operation. By doing this the charger could always start charging independent of the status of the battery. However, for heavily sulfated batteries the charger is not working.

In theory there are typically three types of lead sulphate. One is soft lead sulphate that decomposes with a regular charge. The second is hard lead sulphate that normally only decomposes during an equalization charge (controlled over-charge done in industrial battery maintenance). The last is a very hard lead sulphate that fails to decompose even during equalization charging.

The purpose with almost all reconditioning methods is to try to decompose the sulphate crystals and restore the battery plates to an amorphous condition in the lead acid batteries. A problem with methods used in prior art in order to reverse sulphating is the risk of excessive charging, which typically results in "gassing" (i.e. gassing- voltage) the battery. Gassing- voltage is normally a condition methods in prior art tries to avoid due to the risk of breaking down the battery and shorten its life time by gas development and increased heat. Due to the risk of excessive charging and gassing, the current supply is typically reduced, and the reconditioning of the battery will in many cases be incomplete.

Summary

It is therefore an objective of the present invention to provide a method and a device to recondition batteries, by which it will be possible to maintain high voltage and current during gassing-voltage without breaking down the battery, and by using the understanding that an energy balanced supply of constant rectifying power and pulsed rectifying power has better effect than previously known methods and devices for reconditioning in prior art. According to an aspect of the invention, the invention relates to a method for reconditioning batteries, preferably lead acid batteries having at least one cell, comprising the steps of connecting a device to a battery; and determining a battery type; characterized by the steps of calculating an energy balance; supplying a constant rectifying power and a pulsed rectifying power during intermittent time intervals to the at least one cell; and determining an end criterion.

According to another aspect of the invention, the invention relates to a device for reconditioning batteries, preferably lead acid batteries having at least one cell, comprising wires arranged to connect the device to a battery; voltage and current measurement means arranged to measure voltage and current, and logical circuit means arranged to determining a battery type; characterized in that the logical circuit means is further arranged to calculate an energy balance; and in that the device comprises supply-switching means arranged to supply a constant rectifying power and a pulsed rectifying power during intermittent time intervals to the at least one cell; and in that the logical circuit means is further arranged to determine an end criterion.

The invention further relates to a method for reconditioning batteries wherein the constant rectifying power and the pulsed rectifying power are supplied in a predetermined order and ratio to the at least one cell, wherein the supplied energy amount in the pulsed rectifying power is up to five times the supplied energy amount in the constant rectifying power, and in accordance with the energy balance, and wherein the constant rectifying voltage of the constant rectifying power has a potential equal to the gassing voltage, and wherein the pulsed rectifying voltage of the pulsed rectifying power has a potential above gassing- voltage, wherein the time the constant rectifying power is supplied during intermittent time intervals typically range from 0.8 to 7 seconds, and wherein the time the pulsed rectifying power is supplied during intermittent time intervals typically range from 100 ms to 500 ms, wherein determining the end criterion comprises the step of terminating the supply when the calculated, or estimated, energy balance has been supplied to the battery, and wherein determining the end criterion comprises the steps of measuring a rest voltage; and terminating the supply of constant and pulsed rectifying power to the battery when the rest voltage has achieved a certain value, wherein the certain value lies slightly above gassing- voltage. The invention also further relates to a device for reconditioning batteries, wherein the supply-switching means comprises means to supply the constant rectifying power and the pulsed rectifying power in a predetermined order and ratio, wherein the supplied energy amount in the pulsed rectifying power is up to five times the supplied energy amount in the constant rectifying power, and in accordance with the energy balance calculated by the logical circuit means, wherein the supply-switching means comprises means to supply the constant rectifying voltage of the constant rectifying power such that it has a potential equal to the gassing voltage, and the pulsed rectifying voltage of the pulsed rectifying power such that it has a potential above gassing- voltage, wherein the time the constant rectifying power is supplied by the supply-switching means during intermittent time intervals typically range from 0.8 to 7 seconds, and wherein the time the pulsed rectifying power is supplied by the supply-switching means during intermittent time intervals typically range from 100 ms to 500 ms, wherein the logical circuit means comprises means to determine the end criterion comprising the step of terminating the supply when the calculated, or estimated, energy balance has been supplied to the battery, wherein a voltage and current measurement means the logical circuit means comprises means to measure a rest voltage; and the logical circuit means comprises means to terminate the supply of constant and pulsed rectifying power to the battery when the rest voltage has achieved a certain value, wherein the certain value lies slightly above gassing-voltage.

Brief Description of the Drawings

The invention will be further described with reference to attached drawings, where: Fig.l illustrates schematically a device for reconditioning of batteries according to an embodiment of the invention,

Fig.2 illustrates schematically another embodiment of the device for reconditioning of batteries according to the invention,

Fig.3 illustrates a flowchart which describes the method according to an embodiment of the invention,

Detailed Description

In the following a preferred embodiment of the invention is described with reference to fig. 1. A reconditioning device 100 comprises logical circuit means 160, supply-switching means 130 comprising at least one switch, voltage and current measurement means 170, a transformer 150, and an AC/DC-converter 140. The reconditioning device 100 also comprises positive and negative wires (110, 111), which are connected to a positive 310 and a negative 311 terminal, or poles, of a battery 300, respectively; and temperature measurement means 112 which is also connected to the battery 300. To the reconditioning device 100 are power supply wires 50 connected to a power supply device 10.

The reconditioning device 100 could also comprise logical circuit means 160, which also comprises at least a readable and writeable memory storage means 161 as well as a communication interface unit 181 such as a keyboard or any wire, wire-less interface, and a presentation unit 182, i.e. a display. Such an embodiment of the invention is shown in fig. 2.

By the transformer 150 the voltage is transformed to a preferred value which is supplied to the AC/DC-converter 140 and to the supply-switching means 130. The AC/DC-converter also supply power to all the components comprised in the reconditioning device 100 .

The main control is achieved by the logical circuit means 160 (i.e. a control device), for example an appropriate programmed digital microprocessor with circuits, or a regulator comprising analogue circuits. The logical circuit means 160 controls the supply-switching means 130 to open and close the power supply through the positive 110 and negative 111 wires to the battery 300. The logical circuit means 160 could also be arranged to control the power supply to the supply-switching means 130 in dependence of the voltage and/or current readings, which is monitored by the voltage and current measurement means 170 (a monitoring circuit) or through the communication interface 181.

The temperature measurement means 112, such as a thermometer, thermostat, thermoelement etc, is connected to the reconditioning device 100 and placed in, or at, the battery 300 in order to give temperature readings of the battery 300 during the reconditioning, or send a signal if a temperature threshold is exceeded or if the temperature is increased to rapidly. In either way the reconditioning device 100 could be paused, or set to alter its power supply, as well as to perform an emergency stop of the reconditioning. In figure 3, steps S100-S500 for reconditioning the battery 300 according to an embodiment of the invention are shown. The steps S100-S500 are explained thoroughly in relation to the reconditioning device 100 in the following. In the first step SI 00 the reconditioning device 100 (i.e. the device used for reconditioning) is connected to the battery 300, preferably by connecting the positive and negative wires 110, 111 to the positive and negative terminals 310, 311 of the battery 300, respectively, but the wires 110, 111 of the reconditioning device 100 could also be connected to separate cells if necessary. The reconditioning device 100 is also connected to the power supply wires 50 which in turn is connected to the power supply device 10, such as an electrical distribution net (i.e. the electrical mains), although the power supply 10 could be provided by any suitable power source.

Typically the battery 300 is discharged before the reconditioning starts according to standard discharge proceedings for that specific battery type (e.g. traction, stationary or start batteries). It is also possible to measure a rest voltage, the temperature and the specific gravity (i.e. relative acid density - typically g (H ₂ SO ₄ ) per cm ³ (H ₂ 0)), or the resistance instead, if it is hard to access the interior of the battery (for example in closed battery types), before the reconditioning starts. These measurements could be stored, processed and evaluated as measurement data. This measurement data could be used when calculating, or estimating, an energy balance for the specific battery.

As an illustrative example, the relationship between typical values of battery voltages, approximate charge and relative acid density could be seen in table 1 below:

Approximate Approximate

Approximate Approximate relative Open Circuit Voltage Open Circuit Voltage

charge acid density (12 V (6 cells)) (6 V (3 cells))

12.65 V 6.32 V 100% 1.265 g/cm ³

12.45 V 6.22 V 75% 1.225 g/cm ³

12.24 V 6.12 V 50% 1.190 g/cm ³

12.06 V 6.03 V 25% 1.155 g/cm ³

11.89 V 6.00 V 0% 1.120 g/cm ³

Table 1 ; Normally, and as can be seen in table 1, the voltages and the relative acid density (i.e. the specific gravity) follow each other, wherein maximum and minimum values could be seen for six and three cells wet cell battery types. Such a battery is typically (by persons skilled in the art) seen as "charged" when the specific gravity ranges from 1.205 to 1.215 g/cm ³ , and "discharged", when the specific gravity typically ranges from 1.17 to 1.19 g/cm ³ . Deviations could of course occur, for example, between battery types and due to the temperature of the surrounding environment, and it is from the measurement data possible to determine the degree of sulfation, and if the battery for example is: 1) discharged and softly sulfated,

2) fully charged but heavily sulfated,

or

3) fully charged and not sulfated, Although the measurement data mentioned above is to be preferred, it is not necessary for the invention to work. By the invention it is possible to recondition batteries regardless of detailed information about the battery's charge status and its degree of sulfation.

It is also important to emphasize that it is not always necessary, or even possible, to charge a battery to its maximum standard capacity, but even a battery of lower performance (for example an old or damaged battery) will also be improved when subjected to the invention, and could be used thereafter. The cell voltages typically range between 1.5 to 2.4 volt.

In the next step S200, after the reconditioning device 100 has been physically connected to the battery 300, a battery type could either be automatically derived (e.g. by measuring the voltage), or set at the reconditioning device 100 by an operator, for example according to the number of cells and the type of battery (e.g. traction, stationary, start).

In the following step S300 the energy balance of the battery 300 is calculated or estimated from the battery's individual measurement data, or the standard settings for that specific battery type. The energy supply to the battery 300 is scheduled in accordance to the calculated or estimated energy balance during the whole reconditioning process. It is important not to transfer too much of the battery's maximum energy capacity to the battery 300 too early in the process, and by determining how much energy it is suitable, or even possible, to provide the battery with for each moment in time excess charging is avoided and the reconditioning more efficient.

In order to determine the energy balance, a relationship between the energy amount contained in a constant rectifying power and a pulsed rectifying power, which are to be supplied to the battery 300, is determined. This relationship is determined by a ratio of the energy amount supplied to the battery 300 in the constant rectifying power and the energy amount supplied to the battery 300 in the pulsed rectifying power, and typically range from 1 :1 to 1 :5 - i.e. the supplied energy in the pulsed rectifying power could be 5 times the supplied energy in the constant rectifying power during the whole reconditioning process.

Here it is also important to take into consideration the energy efficiency between these two different types of power supply. During the relatively short periods of time the pulsed rectified power is exposed at the terminals 310, 311 (and hence the plates) the amount of charge that is absorbed in the electrolyte and used in actually charging the battery could differ a lot from the amount of charge absorbed in the electrolyte during the time the constant rectifying power is applied at the terminals 310, 311. This difference is due to the fact that there naturally exists a time lag between the charge absorbed and transferred by the ions in the electrolyte and the charge supplied to the terminals, especially during the rapid pulsing phases. This time lag is due to the relatively slow motions of the positive and negative ions between the electrical field present in the electrolyte and which emanates from the positive to the negative plate, and the comparatively fast process of supplying energy through the reconditioning 100 device's wires 1 10, 111 at the terminals 310, 311 of the battery. The most part of the excess energy is transformed into energy states that will not be directly transformed into charge, and hence the total amount of energy delivered to the battery 300 could easily exceed the maximum energy capacity of the battery 300, especially since only a percentage of the energy in the pulsed rectifying power is typically absorbed by the electrolyte. Another important parameter is the battery's resistance. The resistance is proportional to the degree of sulfation of the battery 300. Typically, a battery's resistance (i.e. the real part of the impedance of the battery) is determined by the resistance of the plates. The impedance of the battery also comprises an additional inductive part, and in the battery it mainly corresponds to the response time of the ions.

In the next step S400 electrical power is supplied to the battery 300 according to the calculated, and scheduled energy balance supply described in step S300 above. Electrical power is the electrical energy supply [Nm] for each moment in time [s] (i.e. W, watt, or [Nm/s]), and is here supplied in the form of the constant rectifying power and the pulsed rectifying power during intermittent time intervals through the wires 110, 111. Both the constant and pulsed power is the product of a constant and pulsed voltage (V, volt or

[Nm/As]) and current [A] (i.e. supplied amount of charge [As] at each moment in time [s] - i.e. Coulomb, C), respectively. During the initial phase, the current is the dominant part of the power, i.e. current controlled. After a while this changes to a supply wherein the constant rectifying voltage and the pulsed rectifying voltage is the dominant part of the supplied power.

The voltage of the battery cells is measured during time intervals; moreover, current could also be measured, as well as the supplied voltage and current from the reconditioning device 100 to the battery 300 by the voltage and current measurement means 170. The supplied voltage and current are either regulated automatically by the logical circuit means 160 comprised in the reconditioning device 100 according to a standard program, or procedure, or manually by an operator. In order to correctly determine the rest voltage, or rest voltages of each cell, the power supply must be paused such that the voltage of the battery can become stationary (i.e. the battery's rest voltage,). In order to achieve a reliable measurement such a pause length should typically last between 15-30 minutes.

The constant rectifying power and the pulsed rectifying power are supplied repeatedly in a predetermined order and ratio to the battery (or a cell) during a time interval, wherein the constant rectifying voltage of the power supply has a potential equal to, or below, gassing voltage and the pulsed rectifying voltage of the power supply has a potential above gassing voltage. This is governed by the logical circuit means 160, which controls the supply- switching means 130 whereby the reconditioning process is switched into a gas-loop procedure or a partial gas-loop procedure. The gas-loop procedure is defined as a process where both the pulsed rectifying voltage and the constant rectifying voltage of the power supply achieve gassing voltage, and the partial gas-loop procedure is defined as a process where only the pulsed rectifying voltage achieves gassing voltage. Hence - the constant rectifying voltage does not achieve gassing voltage during the partial gas-loop procedure. If gassing voltage has been achieved or when the charge current is less than 400 % of the marked current of the battery, the criterion for switching between gas-loop and partial gas- loop has been achieved and there is a switch between the gas-loop procedure and the partial gas- loop procedure. The time the constant rectifying power is supplied during intermittent time intervals typically range from 0.8 to 7 seconds, and the time the pulsed rectifying power is supplied during intermittent time intervals typically range from 100 ms to 500 ms. When the supplied voltage does exceed gassing-voltage (i.e. typically above 2.7-2.8 volt/cell), the voltage at each cell does not exceed 3.8 volt/cell.

Typically a high energy amount in each pulse during a short time interval is preferred because this helps in separating the sulphate crystals into smaller parts. It is also possible to increase the voltage or the current, and at the same time decrease the pulse lengths, in that way the same energy amount is supplied during a shorter period of time. By the pause lengths the risk of overheating is reduced, and by the temperature measurement means 112 (i.e. a temperature watch) the reconditioning device 100, or the regenerating machine, stops the procedure if the temperature exceeds a certain temperature value/threshold.

It is also possible to superimpose high frequency pulses over the pulsed rectifying power supply. The frequency of such superimposed high frequency pulses is determined in relation to the eigenfrequency of the sulphate molecule bounding. The underlying physical cause to that this type of power supply is effective is that the individual sulphate crystal molecules in the crystal structure will take up the high frequency energy transferred by the superimposed high frequency pulses and thereby further separate the molecule bounds in the crystal. In this ways the sulphur molecules can return to the solution and again contribute in the active electrolyte.

Depending on the time one has on one's disposal and the degree of the battery's sulfation - if needed, it is also possible to shorten the regeneration process by reducing the pulsed rectifying power.

In step S500 an end criterion is determined, that is when the regeneration process should be stopped, or halted. The end criterion could be either of the following: the reconditioning stops when the calculated, or estimated, energy balance has been supplied to the battery 300 from the reconditioning device 100; when the charging exceeds one prefixed charge voltage; when the rest voltage, or any other voltage, has achieved a value (for example a potential slightly above gassing-voltage) and then terminate the power to the battery. Another end criterion could of course be a certain time period, and after that time period has elapsed, the reconditioning stops. It is essential to distinguish between end of one regeneration process and termination of the whole regeneration process. End of one regeneration process is either when the battery is fully charged or the time limit for the regeneration process is ended. Typically, by determination of the energy required you will have a battery fully charged according to the criteria fully charged according to this invention - that is if the process stops without being fully charged then you charge the battery until its fully charged. The only way to state if the desulfatating has been successful is to have a fully charged battery both before and after. There are various instruments which could be used to establish the capacity of the battery. Here follows some examples, which are not limiting the scope of the invention, but should instead be seen as a further illustration of the inventive concept.

In a first example, the objective was to ensure that a 48 volt 600 Ah traction battery, which had been in use daily during 4 years, was fully charged. The voltage and density were measured and is named "before" in table 2.

The procedure started by discharging the traction battery to 1,7 volt per cell. This was done by using a discharge current equal to the standard 600 Ah/5= 120 A. After 2,95 hours the battery reached the stipulated voltage per cell.

After this a mixture of pulsed and constant power were supplied in order to take away the hard crystal of sulphate. The pulse current was set to 300 A with a pulse length of 200 ms and repeatedly supplied with a pause of 3 sec. These values remained the same during the regeneration.

The pulsed power was adopted to exceed gas voltage but not to exceed 3,8 volt/cell, and the pause length was set to 3 sec in order to avoid overheating. The temperature measurement means 112 (i.e. a temperature watch) would stop the regenerator (or the regenerating machine) if the temperature exceeds a certain temperature.

The time the pulses were supplied was set to 11 hours. After that a constant charge during one hour with current value of 60 A was implemented. This procedure was repeated 3 times and the total time for that was 18 hours. After these three loops the parameter for constant charge was changed to gas voltage but the duration of one hour was the same. The latter process was repeated 5 times, which gives the regeneration a total time of 96 hours. By this time the battery was fully charged and the voltage and density were measured, see "After".

The results are given in table 2 below:

Table 2, In a second example, the period is two days with a more reduced effect on desulfatation. Here we had 8 periods of pulse charge (5 hours) and constant charge 1 (hours). During the first three hours of constant charge the current value was set to 120 Amp. The other parameters were the same as in first example but with less density and following less voltage as an end result.

The description is not intended to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be ascertained with reference to the issued claims.