SPECIFICATIONWeighing apparatusThis invention relates to weighing apparatus, and is concerned particularly although not exclusively with portable apparatus for weighing babies.
At the present time, it is common practice for visiting midwives and health visitors to weight babies at home. For this purpose, various mechanical scales are used - for example, spring balances, steelyard balances, etc.
These can be reasonably accurate, but are prone to breakage, and require a significant amount of time to set up and repack.
Preferred embodiments of the present invention aim to provide fully electronic scales which are both portable and. simple to use.
Other special factors have to be taken into consideration, in providing scales for weighing babies. For the scales to be portable, they must be of modest size and weight, but nevertheless sufficiently robust to cope with a wriggling baby. In contrast to the small size required for portability, the weight platform must be of sufficiently large size, to easily accommodate a baby.
Apart from giving a certain requirement as to robustness of the equipment, the wriggling of a baby can also introduce momentary variations in a weighing measurement. Also, one has to be able to deal with the weight of paper towels, terry nappies, etc., which are almost always used on the weighing platform.
It is important also to be able to clean, and preferably sterilize, the weighing platform.
A further desirable feature is to provide simple calibration of such scales. Moreover, being portable, they should require a relatively low power consumption.
Preferred embodiments of the invention aim to meet the above objectives.
More generally, according to a first aspect of the present invention, there is provided weighing apparatus comprising:a load cell arranged- to receive a load and to output an electrical signal proportional to the load;a weighing platform which is arranged to support an article to be weighed and is connected to the load cell to transmit thereto a load representing the weight of an article supported on the platform;electronic measurement circuitry connected to receive an output signal from the load cell and to arrange to generate from said output signal a measurement signal representing the weight of an article supported on the platform; anddisplay means connected to receive said measurement signal and arranged to display a weight value proportional to the measurement signal.
Preferably, the measurement signal comprises a pulse train, the frequency of which is proportional to said output signal. The output signal may advantageously be an analogue voltage, and the apparatus may include an amplifier for amplifying the output signal, and temperature compensation means for compensating the gain of the amplifier for changes in ambient temperature.
The apparatus preferably includes logic means arranged to receive said measurement signal and to control said display means in dependence upon the value of said measurement signal.
The logic means is preferably arranged to average said measurement signal over a predetermined time period.
The logic means may be arranged to cause a zero value to be displayed by the display means, if the measurement signal represents a measured weight of less than a predetermined limit value - e.g. 500 grams.
The logic means may be arranged to perform a calibration operation, whereby a value of said measurement signal is stored by the logic means as a reference value, corresponding to a standard reference weight placed upon the weighing platform.
The logic means may be arranged to lock the weight value displayed by the display means, upon completion of a weight measurement. The apparatus may further include power-off means for turning off the power supply of the apparatus a predetermined time after the power supply has been turned on.
The apparatus is preferably portable weighing apparatus, and may be battery powered.
In an advantageous arrangement, the apparatus is contained within a case having a body and a iid. The apparatus may comprise a substantially flat cover which is fitted in said body in a substantially fluid-tight manner, the weighing platform being disposed above said cover and the remainder of the apparatus being housed below said cover, the weighing platform including a support which passes through said cover to connect the weighing platform with said load cell.
The weighing platform may be mounted on a first frame above said cover, and the load cell mounted on a second frame below said cover. Each frame may be of steel, and preferably of angle-section members. The first and second frames may be substantially identical.
The load cell is preferably adapted to receive off-centre loadings.
The weighing platform preferably comprises a plurality of hinged parts which may be folded onto one another for storage. The weighing platform may be detachable from the apparatus, and/or may be of a plastics material.
For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings, in which:Figure 1 is a perspective view of a portable baby scale, embodying the invention;Figure 2 is a block schematic diagram of the electronic circuitry thereof; andFigure 3 is a perspective view of a support frame of the baby scale.
The illustrated baby scale 1 is housed within a case 2 comprising a body 3 and removable lid 4. A substantially flat cover 5 of washable plastics material is fitted in the body 3 in a substantially fluid-tight manner. As may be seen in Fig. 1, the cover 5 is disposed at the top of the body 3, and a sealing compound 6 is provided around the edge of the cover 5, to seal between the cover 5 and the body 3.
Disposed above the cover 5 is a weighing platform 7 which comprises a centre portion 8 and two end portions 9. The weighing platform 7 is of a sterilizable plastics material (e.g. polyethylene), and is detachably mounted on a support frame 50 (Fig. 3). The centre portion 8 of the weighing platform has a pair of upstanding sides 10. The end portions 9 are connected at hinges 11 to the centre portion 8, so that they may be folded substantially flat upon the centre portion 8, for storage and transportation or, as shown in Fig.
1, unfolded to extended positions, to provide an extended weighing platform 7 of sufficient size to accommodate a baby.
Mounted on the upper face of the cover 5, substantially flush therewith, are a control button 12, and a visual display 13.
The support frame 50 for the weighing platform 7 is shown in somewhat more detail, inFig. 3. It comprises a pair of parallel members 51 of angle-section steel, connected (e.g. by welding) by a steel cross-member 52. A substantially identical lower frame 60 is disposed under the cover 5, and comprises a pair of parallel steel members of angle section. interconnected by a steel cross-member 62.
The two steel cross-members 52 and 62 are not disposed immediately above one another. The lower cross-member 62 is connected to one end of a transducer or load cell 20, whilst the upper cross-member 52 is connected by connecting rods 53 to the other end of the load cell 20.
The nature of the load cell 20, and the configuration of the upper and lower frames 50, 60 are such that the load cell 20 may respond accurately to off-centre loadings. The load cell 20 is a centre cell transducer which accommodates any loading direction. It will be appreciated that a load placed upon the weighing platform 7 will be transmitted to the load cell 20, and this is arranged to emit an electrical signal proportional to the load.
The configuration of the upper and lower support frames 50, 60 affords great strength and robustness to the scale, whilst not being unduly heavy or cumbersome.
Turning now to Fig. 2, the load cell 20 responds to the weight of a mass 15 placed upon the weighing platform, and emits an output signal Vic (e.g. of the order of 5mV), proportional to the load. The signal Vic is passed to a signal amplifier 21, which emits a corresponding signal Via of greater amplitude (e.g. of the order of 2 volts), which is then passed to a temperature compensation circuit 22, which detects ambient temperature, and compensates the gain of the signal amplifier 21, via a feedback path 23, for any temperature-dependent changes in the gain of the amplifier 21.The temperature compensated signal Vit is then passed to an analogue to digital (A/D) converter 24, which converts the analogue signal Vit to a digital output signal f1 which comprises a train of digital pulses, the repetition frequency of which is proportional to the analogue input voltage Vit, and may be of the order of, for example, 20 KHz.
The digital signal f1 is passed to a logic circuit 25, which carries out a measurement function. To this end, the logic circuit 25 counts the number of pulses over a predetermined time period, which number is proportional to the measured weight. The logic circuit 25 emits a control signal Vc to the visual display unit 13, to display thereon a measured weight value.
Because the logic circuit 25 measures the pulses of the signals f1 over the predetermined time period, it performs an averaging function, over that time period. This compensates for variations in the instantaneous value of measured load, which may be particularly prevalent due to the movement of a baby on the weighing platform 7. The predetermined time period over which averaging takes place may be pre-set at the manufacturing stage.
However, if desired, means may be provided for adjusting the predetermined period.
The logic circuit is adapted to ignore all weights placed on the weighing platform 7, below a predetermined value (which may also be adjustable, if desired). For example, such a predetermined value may be of the order of 500 grams, and this allows the weighing circuitry effectively to "Ignore" any relatively lightweight items, such as paper towels, terry nappies, etc., which may be placed on the weighing platform 7, prior to placing a baby thereon.
The logic circuit 25 is also effective to lock the control signal Vc at its calculated value, and thereby also lock the display 13, immediately a weight calculation is completed. This avoids a constantly varying display, which may otherwise occur, as a baby on the platform continues to move about.
The logic circuit 25 is also advantageously arranged to turn off the (preferably) battery powered electronic circuitry, a predetermined time after a weighing cycle has been initiated.
It is preferably also arranged only to carry out a single weighing cycle, each time it is powered on.
Operation of the iliustrated baby scale 1 is therefore extremely simple.
Firstly, the user can readily transport the scale from one location to another, with the lid 4 fitted to the body 3, and the case 2 carried by a carrying handle 14. The lid 4 may co-operate with the weighing platform 7 to prevent significant movement thereof, during transport.
At a desired point of use, the body 3 is placed on a reasonably flat, horizontal surface, and the lid 4 raised and, optionally, removed.
The end portions 9 of the weighing platform 7 are folded out, to extend the platform.
Any desired paper towel, terry nappy, etc, is placed on the weighing platform 7, which is then switched on, by depressing or touching the button 12. Provided that the paper towel, nappy, etc., weighs less than 500 grams, the weight of this is ignored, and the logic circuitry 25 assumes that the current weight value is zero.
The baby is then placed upon the weighing platform 7, whereupon the load cell emits its appropriate voltage, which is processed by the subsequent electronic circuitry, and the logic circuit 25 causes the averaged control signalVc to be passed to the display 13, which shown an appropriate weight value. This value is continued to be displayed for a predetermined time (e.g. between 10 and 20 seconds), whereafter the logic circuit 25 causes the electronic circuit to be switched off.
The operation may then be repeated, as often as desired.
It is not essential for the automatic poweroff facility to be provided, in which case a weighing cycle may- be initiated, each time the button 12 is actuated.
After use, the user simply folds the end portions 9 back over the centre portion 8. of the weighing platform 7, replaces and fastens the lid 4, and the baby scale 1 is again ready for transport to the next iocation.
To clean the scale 1, the weighing platform 7 may readily be detached from the support frame 50 (e.g. by snap-engaging resilient catches) and then thoroughly cleaned or, if desired, sterilized. The flat upper surface of the cover 5 may also be readily cleaned, disinfected or sterilized. In addition to the seal 6 provided around the edge of the cover 5, seals are also provided around the control button 12, display 13, and connecting rods 53 to the load cell 20.
From time to time, it will be desired to recalibrate the scale 1. This may be effected, under control of the logic circuit 25, in a very straightforward manner, as follows.
Upon actuating the operation button 12 for, say, five seconds, the logic circuit 25 detects that a calibration is to be carried out. A standard mass (e.g. 10 kg) is placed upon the weighing platform 7. The logic circuit 25 computes the appropriate number of digital pulses emitted during the predetermined averaging time period, and then stores the corresponding values, both for zero and 10 kg measurements, within a non-volatile memory 26. The stored values are then used as reference calibration values, until the next calibration takes place.
Thus, from the users point of view, all that is required to effect calibration is to actuate the button 12 for five seconds, and then place the standard mass upon the weighing platform 7. An appropriate signal on the display unit 13 may indicate when the scale is in calibration mode, and/or when calibration has been completed.
The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification and/or drawings, or to any novel one, or any novel combination, of the steps of any method or process disclosed herein.