CA2148159A1 - Wheel balancer digital output force transducer - Google Patents
Wheel balancer digital output force transducerInfo
- Publication number
- CA2148159A1 CA2148159A1 CA002148159A CA2148159A CA2148159A1 CA 2148159 A1 CA2148159 A1 CA 2148159A1 CA 002148159 A CA002148159 A CA 002148159A CA 2148159 A CA2148159 A CA 2148159A CA 2148159 A1 CA2148159 A1 CA 2148159A1
- Authority
- CA
- Canada
- Prior art keywords
- enclosure
- force transducer
- analog
- wheel
- digital converter
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
- 239000007769 metal material Substances 0.000 claims description 5
- 230000000712 assembly Effects 0.000 description 12
- 238000000429 assembly Methods 0.000 description 12
- 239000000725 suspension Substances 0.000 description 5
- 238000001914 filtration Methods 0.000 description 3
- 239000012212 insulator Substances 0.000 description 3
- 230000035945 sensitivity Effects 0.000 description 3
- 230000003321 amplification Effects 0.000 description 2
- 239000013078 crystal Substances 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 description 1
- BQCADISMDOOEFD-UHFFFAOYSA-N Silver Chemical compound [Ag] BQCADISMDOOEFD-UHFFFAOYSA-N 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000004891 communication Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 239000000356 contaminant Substances 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 229920006332 epoxy adhesive Polymers 0.000 description 1
- 239000011810 insulating material Substances 0.000 description 1
- HFGPZNIAWCZYJU-UHFFFAOYSA-N lead zirconate titanate Chemical compound [O-2].[O-2].[O-2].[O-2].[O-2].[Ti+4].[Zr+4].[Pb+2] HFGPZNIAWCZYJU-UHFFFAOYSA-N 0.000 description 1
- 229910052451 lead zirconate titanate Inorganic materials 0.000 description 1
- 239000000565 sealant Substances 0.000 description 1
- 229910052710 silicon Inorganic materials 0.000 description 1
- 239000010703 silicon Substances 0.000 description 1
- 229910052709 silver Inorganic materials 0.000 description 1
- 239000004332 silver Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 230000000007 visual effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01M—TESTING STATIC OR DYNAMIC BALANCE OF MACHINES OR STRUCTURES; TESTING OF STRUCTURES OR APPARATUS, NOT OTHERWISE PROVIDED FOR
- G01M1/00—Testing static or dynamic balance of machines or structures
- G01M1/14—Determining imbalance
- G01M1/16—Determining imbalance by oscillating or rotating the body to be tested
- G01M1/22—Determining imbalance by oscillating or rotating the body to be tested and converting vibrations due to imbalance into electric variables
- G01M1/225—Determining imbalance by oscillating or rotating the body to be tested and converting vibrations due to imbalance into electric variables for vehicle wheels
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L1/00—Measuring force or stress, in general
- G01L1/16—Measuring force or stress, in general using properties of piezoelectric devices
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Testing Of Balance (AREA)
- Arrangements For Transmission Of Measured Signals (AREA)
- Force Measurement Appropriate To Specific Purposes (AREA)
- Casings For Electric Apparatus (AREA)
Abstract
A device for converting the analog output from a force transducer element into a digital signal which characterized by: an enclosure for housing the force transducer element; and an analog-to-digital converter located within the enclosure and connected to the force transducer element; wherein the analog to digital converter outputs a digital signal from the enclosure.
Description
21481~9 WHEEL BALANCER DIGITAL OUTPUT FORCE TRANSDUCER
This invention relates to an apparatus for balancing rotary bodies, 5 such as the wheels of a motor vehicle, which is commonly referred to as a wheel balancer. More particularly, the invention relates to a force transducer assembly for use in such an apparatus which converts the analog signal generated by the force transducer into a digital signal within a shielded environment which is relatively impervious to electrical 1 0 interference.
Wheel balancers of both the motorized and hand-spun types are well known in the automotive service equipment art. For example, U.S. Patent No. 4,046,017, which issued to Hill and is owned by the assignee hereof, 15 discloses a motorized wheel balancer comprising a rotatable shaft upon which the wheel to be balanced is mounted and a pair of force transducers positioned adjacent the shaft for providing signals representative of the imbalance forces on both the inner and outer rims of the wheel. The force transducers employed in prior art wheel balancers are typically analog 20 devices, such as piezoelectric crystal load cells, which generate analog signals which must then be transmitted to a central processor remote from the transducers.
One problem with typical prior art analog force transducers is that they are high impedance devices which output a low level analog signal that 25 is then transmitted to a converting and digitizing circuit connected to the central processor. The converting and diyili~ g circuit presents a high impedance load, and when the converting and digitizing circuit is located remote from the transducers, the transducer signal becomes highly susceptible to the electrical interference or noise commonly experienced in 30 the wheel balancer environment. This noise is usually eliminated using either analog or digital filtering techniques. Also, if the high impedance load results from the use of large values of resistance, DC drift due to temperature and humidity become a problem.
These and other problems are overcome by providing a force 35 transducer assembly comprising a piezoelectric crystal transducer and a 21~81S9 transducer circuit board located within an electrically shielded housing. The transducer circuit board comprises a operational-amplifier ("op-amp") circuit and an analog-to-digital ('WD") converter. Thus, the force transducer assembly is capable of generating a digital signal which is relatively impervious to electrical interference, thereby eliminating the need for any further filtering at the central processor. Preferably, the A/D converter is a high resolution sigma/delta-type converter with a built-in low-pass filter which guarantees 16 bits of monotonic data and effectively reduces the transducer bandwidth to just above the expected shaft frequency to further reduce system noise and allow the digital signal to more accurately represent the actual analog force being measured. In addition, the op-amp circuit preferably has a high input impedance. The use of the high resolution A/D converter with the high input impedance op-amp requires only one stage of analog amplification and no need for analog gain adjustments. This greatly reduces errors due to DC drift with temperature and humidity.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.
Figure 1 is a perspective view, partially broken away, of a wheel balancer incorporating the transducer assemblies of the present invention;
Figure 2 is an exploded perspective view of the transducer assembly of the present invention;
Figure 3 is a diagrammatic view of the transducer circuit of the present invention; and Figure 4 is a diagrammatic view of a second embodiment of a portion of the circuit depicted in Figure 3.
While the force transducer assembly of the present invention may be adapted for use in a variety of applications, it is particularly suitable for use in vehicle wheel balancers. Referring to Figure 1, two force transducer assemblies 10 according to the present invention are shown incorporated in a representative vehicle wheel balancer 12. The particular wheel balancer depicted in Figure 1 comprises a bearing tube 14 which is supported on two 2148i59 suspension brackets 16. In a manner known to those skilled in the art, bearing tube 14 is adapted to receive a rotatable mounting shaft 18 to which a wheel W is mounted for correction of unbalance. Suspension brackets 16 are designed to yield in a direction transverse to the axis of 5 bearing tube 14, and force transducer assemblies 10 are mounted at appropriate locations on suspension brackets 14 such that the forces generated by the unbalance in wheel W as wheel W rotates are transmitted through bearing tube 14 to force transducer assemblies 10. A more complete description of the structure in which force transducer assemblies t 0 10 are mounted is not critical to an understanding of the invention.
The digital signals generated by force transducer assemblies 10, which will be described more fully hereafter, are transmitted to a central processing circuit 20, which comprises a suitable microprocessor for processing the digital signals and generating data indicative of the 15 magnitudes and locations of the wei~l ,ts required to be applied to wheel W
to correct the imbalance in wheel W. This data is transmitted to a suitable display circuit 22 located in a console 24. Display circuit 22 controls the presentation of the data on a visual display 26. Force transducer assemblies 10, central processing circuit 20, display circuit 22 and a motor 20 control circuit (not shown) are preferably located remote from each other on individual circuit boards to prevent any electrical interference generated by each circuit board from affecting the other boards or force transducer assemblies 10.
Referring to Figure 2, each force transducer assembly 10 comprises 25 a piezoelectric transducer element 28. In a preferred embodiment of the invention, transducer element 28 is manufactured from a piezoceramic material such as lead zirconate titanate equivalent to Channelite 5500 or Navy Type ll (mil standard .1376 (ship)), which is silvered on both sides, poled for compression loading parallel to its axis and has a diameter of .630 30 inch and a width of .042 inch to produce an output of 400 coulombs per Newton of force with a capacitance of 2900 picofarads. Such a transducer element can be obtained from a number of manufacturers of piezoelectric devices, one of which is Piezo Kinetics Incorporated of Bellefonte, Pennsylvania. Transducer element 28 is sandwiched between two contact 35 plates 30, each of which comprises a contact 32 which is soldered to an -- 21~815~
appropriate junction on a transducer circuit board 34, which will be described more fully hereafter.
Force transducer assembly 10 further comprises two insulator disks 36, which are manufactured from the same piezoceramic material as 5 transducer element 28, but not silvered or poled. Insulator discs 36 insulate contact plates 30 from electrical contact with the respective raised bosses 38 of a top thrust plate 40 and a bottom thrust plate 42, both of which thrust plates are manufactured of a metallic material such as steel. Transducer element 28, contact plates 30 and insulator discs 36 are held together 10 between bosses 38 by a sleeve 44 manufactured from an appropriate insulating material. Sleeve 44 comprises two slots 46 which are adapted to receive contacts 32 to thereby allow sleeve 44 to be positioned around contact plates 30. Transducer circuit board 34 is fastened to bottom thrust plate 42 by screws 48. The appropriate spacing between transducer circuit 15 board 34 and bottom thrust plate 42 is maintained by standoffs 50. Screws 48 and standoffs 50 also serve to ground transducer circuit board 34 to bottom thrust plate 42. A cable 52 comprising a number of wires 54 soldered to appropriate junctions on transducer circuit board 34 and having a connector 56 attached to the distal ends of wires 54 provides for electrical 20 communication between transducer circuit board 34 and the central processing circuit board 20. Cable 52 extends through an aperture 58 on top thrust plate 40 and is secured to transducer circuit board 34 with a tie wrap 60 Force transducer assembly 10 also comprises a cylindrical housing 25 62 into which top thrust plate 40 and bottom thrust plate 42 are slideably received to thereby form a complete enclosure for the other components of transducer assembly 10 described above. Housing 62 is preferably made of the same metallic material as top and bottom thrust plates 40 and 42 to provide an electrical shield for transducer circuit board 34. In addition, a 30 conductive silver epoxy adhesive is preferably applied to the seams between housing 62 and top and bottom thrust plates 40 and 42. In this manner, the entire enclosure formed by housing 62 and top and bottom thrust plates 40 and 42 are maintained at ground potential to electrically shield transducer circuit board 34 from electrical interference generated by 35 wheel balancer 12. Furthermore, elastomeric O-rings 64 are positioned -~ 21481~9 around the circumferences of top and bottom thrust plates 40 and 42 before these elements are assembled in housing 62 to provide a sealed enclosure for transducer circuit board 34 and the remainder of the components of force transducer assembly 10. A hermetically sealed environment is fully 5 created by applying a silicon sealant between cable 52 and aperture 58. In this manner, transducer circuit board 34 and the other components of force transducer element 10 are protected from moisture and environmental contaminants.
Transducer circuit board 34 is described more fully with reference to 10 Figure 3. In operation of force transducer assembly 10, transducer element 28 outputs a charge in response to the changes in force imparted on top and bottom thrust plates 40 and 42. The forces are created by the imbalance loads on rotating wheel W and are transmitted to top and bottom thrust plates 40 and 42 through bearing tube 14 and suspension brackets 15 16. The charge is communicated through contact plates 30 and their respective contacts 32 to a high impedance operational-amplifier ("op-amp") circuit 66, where it is converted to a voltage. The output voltage of op-amp circuit 66 is dependent on the amount of charge output by transducer element 28 and the input impedance of op-amp circuit 66. The required 20 input impedance depends upon the sensitivity of the support assembly for mounting shaft 18, i.e., the ability of bearing tube 14 and suspension brackets 16 to transmit the imbalance loads of rotating wheel W to force transducer assemblies 10. The higher the sensitivity of the support assembly, the higher the charge that is output by transducer element 28 25 and, consequently, the lower the input impedance that is required to avoid saturation of op-amp U2. For relatively sensitive support assemblies, the impedance of op-amp circuit 66 is determined by input resistor R1, which in this embodiment is 1 mega-ohm as shown in Figure 3. The op-amp U2 is a low noise, low drift amplifier, such as the OP77GS op-amp available from 30 the company Analog Devices. The input offset current drift and input offset voltage drift of op-amp U2 are such that no significant error is introduced over the normal operating temperature range of wheel balancer 12.
For less sensitive support assemblies, another embodiment of op-35 amp circuit 66 may be required. Such an op-amp circuit is shown in Figure 21481`5~
4 and is designated by reference number 68. Op-amp circuit 68 achieves a high input impedance without using large values of resistance by the known method commonly referred to as "bootstrappingn. In op-amp circuit 68, resistors R3, R4 and R5 have respective values of 20,000, 200,000 and 5 200 ohms. The advantages of using these smaller resistors are that lower output errors due to input bias current drift with temperature and input offset voltage drift with temperature are achieved. Also, the circuit's sensitivity to humidity is greatly reduced. Op-amp circuit 68 has an input impedance of about 20 mega-ohms. The op-amp U6 is preferably an OP77GS op-amp, 10 the same as op-amp U2 in Figure 3.
Regardless of which op-amp circuit is used, the output voltage is fed directly into a 16-bit sigma/delta analog-to-digital ("A/D") converter U1, which preferably includes a built-in 6-pole,10 hertz low pass filter. A
suitable A/D converter U1 is the AD7701 available from Analog Devices.
15 The output of A/D converter U1 is a 16-bit stream of serial information. A/D
converter U1 guarantees 16 bits of monotonic data and effectively reduces the bandwidth of transducer element 28 to just above the expected frequency of mounting shaft 18. This will reduce system noise and allow the digital signal to more accurately represent the analog force being 20 measured. The output of A/D converter U1 is communicated by cable 52 to central processing circuit board 20 for further processing.
An appropriate power supply is applied to transducer circuit board 34 at junctions 70 and 72, and power regulators U4 and U5 ensure a constant +5V and -5V voltage at junctions 74 and 76, respectively. Furthermore, a 25 constant 2.5V reference voltage is supplied to A/D converter U1 by element U3.
Force transducer assemblies 10 therefore convert the analog output from transducer element 28 into a digital signal within the shielded enclosure formed by housing 62 and top and bottom thrust plates 40 and 30 42. This greatly reduces the effects of electrical interference on the signaland eliminates the need for any further filtering at the central processing circuit board 20. Also, using a high resolution A/D converter U1, along with a high input impedance op-amp circuit requires only one stage of analog amplification and eliminates the need for analog gain adjustments. This 35 greatly reduces errors due to DC drift with temperature.
This invention relates to an apparatus for balancing rotary bodies, 5 such as the wheels of a motor vehicle, which is commonly referred to as a wheel balancer. More particularly, the invention relates to a force transducer assembly for use in such an apparatus which converts the analog signal generated by the force transducer into a digital signal within a shielded environment which is relatively impervious to electrical 1 0 interference.
Wheel balancers of both the motorized and hand-spun types are well known in the automotive service equipment art. For example, U.S. Patent No. 4,046,017, which issued to Hill and is owned by the assignee hereof, 15 discloses a motorized wheel balancer comprising a rotatable shaft upon which the wheel to be balanced is mounted and a pair of force transducers positioned adjacent the shaft for providing signals representative of the imbalance forces on both the inner and outer rims of the wheel. The force transducers employed in prior art wheel balancers are typically analog 20 devices, such as piezoelectric crystal load cells, which generate analog signals which must then be transmitted to a central processor remote from the transducers.
One problem with typical prior art analog force transducers is that they are high impedance devices which output a low level analog signal that 25 is then transmitted to a converting and digitizing circuit connected to the central processor. The converting and diyili~ g circuit presents a high impedance load, and when the converting and digitizing circuit is located remote from the transducers, the transducer signal becomes highly susceptible to the electrical interference or noise commonly experienced in 30 the wheel balancer environment. This noise is usually eliminated using either analog or digital filtering techniques. Also, if the high impedance load results from the use of large values of resistance, DC drift due to temperature and humidity become a problem.
These and other problems are overcome by providing a force 35 transducer assembly comprising a piezoelectric crystal transducer and a 21~81S9 transducer circuit board located within an electrically shielded housing. The transducer circuit board comprises a operational-amplifier ("op-amp") circuit and an analog-to-digital ('WD") converter. Thus, the force transducer assembly is capable of generating a digital signal which is relatively impervious to electrical interference, thereby eliminating the need for any further filtering at the central processor. Preferably, the A/D converter is a high resolution sigma/delta-type converter with a built-in low-pass filter which guarantees 16 bits of monotonic data and effectively reduces the transducer bandwidth to just above the expected shaft frequency to further reduce system noise and allow the digital signal to more accurately represent the actual analog force being measured. In addition, the op-amp circuit preferably has a high input impedance. The use of the high resolution A/D converter with the high input impedance op-amp requires only one stage of analog amplification and no need for analog gain adjustments. This greatly reduces errors due to DC drift with temperature and humidity.
These and other objects and advantages of the present invention will be made apparent from the following detailed description, with reference to the accompanying drawings.
Figure 1 is a perspective view, partially broken away, of a wheel balancer incorporating the transducer assemblies of the present invention;
Figure 2 is an exploded perspective view of the transducer assembly of the present invention;
Figure 3 is a diagrammatic view of the transducer circuit of the present invention; and Figure 4 is a diagrammatic view of a second embodiment of a portion of the circuit depicted in Figure 3.
While the force transducer assembly of the present invention may be adapted for use in a variety of applications, it is particularly suitable for use in vehicle wheel balancers. Referring to Figure 1, two force transducer assemblies 10 according to the present invention are shown incorporated in a representative vehicle wheel balancer 12. The particular wheel balancer depicted in Figure 1 comprises a bearing tube 14 which is supported on two 2148i59 suspension brackets 16. In a manner known to those skilled in the art, bearing tube 14 is adapted to receive a rotatable mounting shaft 18 to which a wheel W is mounted for correction of unbalance. Suspension brackets 16 are designed to yield in a direction transverse to the axis of 5 bearing tube 14, and force transducer assemblies 10 are mounted at appropriate locations on suspension brackets 14 such that the forces generated by the unbalance in wheel W as wheel W rotates are transmitted through bearing tube 14 to force transducer assemblies 10. A more complete description of the structure in which force transducer assemblies t 0 10 are mounted is not critical to an understanding of the invention.
The digital signals generated by force transducer assemblies 10, which will be described more fully hereafter, are transmitted to a central processing circuit 20, which comprises a suitable microprocessor for processing the digital signals and generating data indicative of the 15 magnitudes and locations of the wei~l ,ts required to be applied to wheel W
to correct the imbalance in wheel W. This data is transmitted to a suitable display circuit 22 located in a console 24. Display circuit 22 controls the presentation of the data on a visual display 26. Force transducer assemblies 10, central processing circuit 20, display circuit 22 and a motor 20 control circuit (not shown) are preferably located remote from each other on individual circuit boards to prevent any electrical interference generated by each circuit board from affecting the other boards or force transducer assemblies 10.
Referring to Figure 2, each force transducer assembly 10 comprises 25 a piezoelectric transducer element 28. In a preferred embodiment of the invention, transducer element 28 is manufactured from a piezoceramic material such as lead zirconate titanate equivalent to Channelite 5500 or Navy Type ll (mil standard .1376 (ship)), which is silvered on both sides, poled for compression loading parallel to its axis and has a diameter of .630 30 inch and a width of .042 inch to produce an output of 400 coulombs per Newton of force with a capacitance of 2900 picofarads. Such a transducer element can be obtained from a number of manufacturers of piezoelectric devices, one of which is Piezo Kinetics Incorporated of Bellefonte, Pennsylvania. Transducer element 28 is sandwiched between two contact 35 plates 30, each of which comprises a contact 32 which is soldered to an -- 21~815~
appropriate junction on a transducer circuit board 34, which will be described more fully hereafter.
Force transducer assembly 10 further comprises two insulator disks 36, which are manufactured from the same piezoceramic material as 5 transducer element 28, but not silvered or poled. Insulator discs 36 insulate contact plates 30 from electrical contact with the respective raised bosses 38 of a top thrust plate 40 and a bottom thrust plate 42, both of which thrust plates are manufactured of a metallic material such as steel. Transducer element 28, contact plates 30 and insulator discs 36 are held together 10 between bosses 38 by a sleeve 44 manufactured from an appropriate insulating material. Sleeve 44 comprises two slots 46 which are adapted to receive contacts 32 to thereby allow sleeve 44 to be positioned around contact plates 30. Transducer circuit board 34 is fastened to bottom thrust plate 42 by screws 48. The appropriate spacing between transducer circuit 15 board 34 and bottom thrust plate 42 is maintained by standoffs 50. Screws 48 and standoffs 50 also serve to ground transducer circuit board 34 to bottom thrust plate 42. A cable 52 comprising a number of wires 54 soldered to appropriate junctions on transducer circuit board 34 and having a connector 56 attached to the distal ends of wires 54 provides for electrical 20 communication between transducer circuit board 34 and the central processing circuit board 20. Cable 52 extends through an aperture 58 on top thrust plate 40 and is secured to transducer circuit board 34 with a tie wrap 60 Force transducer assembly 10 also comprises a cylindrical housing 25 62 into which top thrust plate 40 and bottom thrust plate 42 are slideably received to thereby form a complete enclosure for the other components of transducer assembly 10 described above. Housing 62 is preferably made of the same metallic material as top and bottom thrust plates 40 and 42 to provide an electrical shield for transducer circuit board 34. In addition, a 30 conductive silver epoxy adhesive is preferably applied to the seams between housing 62 and top and bottom thrust plates 40 and 42. In this manner, the entire enclosure formed by housing 62 and top and bottom thrust plates 40 and 42 are maintained at ground potential to electrically shield transducer circuit board 34 from electrical interference generated by 35 wheel balancer 12. Furthermore, elastomeric O-rings 64 are positioned -~ 21481~9 around the circumferences of top and bottom thrust plates 40 and 42 before these elements are assembled in housing 62 to provide a sealed enclosure for transducer circuit board 34 and the remainder of the components of force transducer assembly 10. A hermetically sealed environment is fully 5 created by applying a silicon sealant between cable 52 and aperture 58. In this manner, transducer circuit board 34 and the other components of force transducer element 10 are protected from moisture and environmental contaminants.
Transducer circuit board 34 is described more fully with reference to 10 Figure 3. In operation of force transducer assembly 10, transducer element 28 outputs a charge in response to the changes in force imparted on top and bottom thrust plates 40 and 42. The forces are created by the imbalance loads on rotating wheel W and are transmitted to top and bottom thrust plates 40 and 42 through bearing tube 14 and suspension brackets 15 16. The charge is communicated through contact plates 30 and their respective contacts 32 to a high impedance operational-amplifier ("op-amp") circuit 66, where it is converted to a voltage. The output voltage of op-amp circuit 66 is dependent on the amount of charge output by transducer element 28 and the input impedance of op-amp circuit 66. The required 20 input impedance depends upon the sensitivity of the support assembly for mounting shaft 18, i.e., the ability of bearing tube 14 and suspension brackets 16 to transmit the imbalance loads of rotating wheel W to force transducer assemblies 10. The higher the sensitivity of the support assembly, the higher the charge that is output by transducer element 28 25 and, consequently, the lower the input impedance that is required to avoid saturation of op-amp U2. For relatively sensitive support assemblies, the impedance of op-amp circuit 66 is determined by input resistor R1, which in this embodiment is 1 mega-ohm as shown in Figure 3. The op-amp U2 is a low noise, low drift amplifier, such as the OP77GS op-amp available from 30 the company Analog Devices. The input offset current drift and input offset voltage drift of op-amp U2 are such that no significant error is introduced over the normal operating temperature range of wheel balancer 12.
For less sensitive support assemblies, another embodiment of op-35 amp circuit 66 may be required. Such an op-amp circuit is shown in Figure 21481`5~
4 and is designated by reference number 68. Op-amp circuit 68 achieves a high input impedance without using large values of resistance by the known method commonly referred to as "bootstrappingn. In op-amp circuit 68, resistors R3, R4 and R5 have respective values of 20,000, 200,000 and 5 200 ohms. The advantages of using these smaller resistors are that lower output errors due to input bias current drift with temperature and input offset voltage drift with temperature are achieved. Also, the circuit's sensitivity to humidity is greatly reduced. Op-amp circuit 68 has an input impedance of about 20 mega-ohms. The op-amp U6 is preferably an OP77GS op-amp, 10 the same as op-amp U2 in Figure 3.
Regardless of which op-amp circuit is used, the output voltage is fed directly into a 16-bit sigma/delta analog-to-digital ("A/D") converter U1, which preferably includes a built-in 6-pole,10 hertz low pass filter. A
suitable A/D converter U1 is the AD7701 available from Analog Devices.
15 The output of A/D converter U1 is a 16-bit stream of serial information. A/D
converter U1 guarantees 16 bits of monotonic data and effectively reduces the bandwidth of transducer element 28 to just above the expected frequency of mounting shaft 18. This will reduce system noise and allow the digital signal to more accurately represent the analog force being 20 measured. The output of A/D converter U1 is communicated by cable 52 to central processing circuit board 20 for further processing.
An appropriate power supply is applied to transducer circuit board 34 at junctions 70 and 72, and power regulators U4 and U5 ensure a constant +5V and -5V voltage at junctions 74 and 76, respectively. Furthermore, a 25 constant 2.5V reference voltage is supplied to A/D converter U1 by element U3.
Force transducer assemblies 10 therefore convert the analog output from transducer element 28 into a digital signal within the shielded enclosure formed by housing 62 and top and bottom thrust plates 40 and 30 42. This greatly reduces the effects of electrical interference on the signaland eliminates the need for any further filtering at the central processing circuit board 20. Also, using a high resolution A/D converter U1, along with a high input impedance op-amp circuit requires only one stage of analog amplification and eliminates the need for analog gain adjustments. This 35 greatly reduces errors due to DC drift with temperature.
Claims (9)
1. A device for converting the analog output from a force transducer element into a digital signal which characterized by:
an enclosure for housing the force transducer element; and an analog-to-digital converter located within the enclosure and connected to the force transducer element;
wherein the analog to digital converter outputs a digital signal from the enclosure.
an enclosure for housing the force transducer element; and an analog-to-digital converter located within the enclosure and connected to the force transducer element;
wherein the analog to digital converter outputs a digital signal from the enclosure.
2. The device of claim 1, characterized in that the enclosure is manufactured from a metallic material and is grounded to provide electrical shielding for the force transducer element and the analog-to-digital converter.
3. The device of claim 1, characterized in that the enclosure is sealed to prevent the entry of moisture.
4. In a vehicle wheel balancer comprising a rotatable shaft upon which a wheel to be balanced is mountable, at least one force transducer means for generating an output representative of the forces imparted to the shaft by imbalance in the rotating wheel, and processor means for determining magnitudes and positions of imbalance in the wheel from the output generated by the force transducer means, characterized by:
an enclosure in which the force transducer means is located;
analog-to-digital converter means for converting the output of the force transducer means into a digital signal representative of the forces imparted to the shaft by imbalance in the rotating wheel;
the analog-to-digital converter means being located in the enclosure; and means for communicating the digital signal to the processor means.
an enclosure in which the force transducer means is located;
analog-to-digital converter means for converting the output of the force transducer means into a digital signal representative of the forces imparted to the shaft by imbalance in the rotating wheel;
the analog-to-digital converter means being located in the enclosure; and means for communicating the digital signal to the processor means.
5. The wheel balancer of claim 4, characterized in that the enclosure comprises:
at least one thrust plate through which the forces imparted to the shaft are transferred to the force transducer means; and a housing which, together with the thrust plate, forms a complete enclosure for the force transducer means and the analog-to-digital converter means.
at least one thrust plate through which the forces imparted to the shaft are transferred to the force transducer means; and a housing which, together with the thrust plate, forms a complete enclosure for the force transducer means and the analog-to-digital converter means.
6. The wheel balancer of claim 5, characterized in that the enclosure is constructed of a metallic material.
7. The wheel balancer of claim 6, characterixed in that the enclosure is grounded to provide electrical shielding for the force transducer means and the analog-to-digital converter means.
8. The wheel balancer of claim 5, characterized by the enclosure is sealed to prevent the entry of moisture.
9. In a vehicle wheel balancer characterized in that a rotatable shaft upon which a wheel to be balanced is mountable, at least one force transducer means for generating an output representative of the forces imparted to the shaft by imbalance in the rotating wheel, and processor means for determining magnitudes and positions of imbalance in the wheel from the output generated by the force transducer means, the improvement comprising:
an enclosure in which the force transducer means is located;
analog-to-digital converter means for converting the output of the force transducer means into a digital signal representative of the forces imparted to the shaft by imbalance in the rotating wheel;
the analog-to-digital converter means being located in the enclosure;
the enclosure comprising a top thrust plate, a bottom thrust plate and a housing forming the sides of the enclosure;
the top thrust plate and the bottom thrust plate being slideably received in the housing to thereby form a complete enclosure; and means for communicating the digital signal to the processor means;
wherein the enclosure is constructed of a metallic material, is grounded to provide electrical shielding for the force transducer means and the analog-to-digital converter means, and is sealed to prevent the entry of moisture.
an enclosure in which the force transducer means is located;
analog-to-digital converter means for converting the output of the force transducer means into a digital signal representative of the forces imparted to the shaft by imbalance in the rotating wheel;
the analog-to-digital converter means being located in the enclosure;
the enclosure comprising a top thrust plate, a bottom thrust plate and a housing forming the sides of the enclosure;
the top thrust plate and the bottom thrust plate being slideably received in the housing to thereby form a complete enclosure; and means for communicating the digital signal to the processor means;
wherein the enclosure is constructed of a metallic material, is grounded to provide electrical shielding for the force transducer means and the analog-to-digital converter means, and is sealed to prevent the entry of moisture.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US23558794A | 1994-04-29 | 1994-04-29 | |
| US08/235,587 | 1994-04-29 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2148159A1 true CA2148159A1 (en) | 1995-10-30 |
Family
ID=22886133
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002148159A Abandoned CA2148159A1 (en) | 1994-04-29 | 1995-04-28 | Wheel balancer digital output force transducer |
Country Status (6)
| Country | Link |
|---|---|
| JP (1) | JPH0862084A (en) |
| KR (1) | KR950033448A (en) |
| CA (1) | CA2148159A1 (en) |
| DE (1) | DE19515654A1 (en) |
| FR (1) | FR2719408B1 (en) |
| IT (1) | IT1274404B (en) |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2886732B1 (en) * | 2005-06-01 | 2007-10-05 | Jeumont Sa Sa | METHOD FOR CONTROLLING THE STATE OF A ROTATING MACHINE DRIVE SHAFT |
| JP5489697B2 (en) * | 2009-12-21 | 2014-05-14 | 大和製衡株式会社 | Dynamic balance inspection system for tires |
Family Cites Families (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1573842A1 (en) * | 1965-01-08 | 1970-04-16 | Schladitz Hermann J | Micro shredding machine |
| US4507964A (en) * | 1982-11-29 | 1985-04-02 | Willy Borner | Slow speed dynamic wheel balancer |
| DE3645209C2 (en) * | 1986-08-27 | 1995-11-02 | Jagenberg Ag | Web winding machine winding sleeve inserter |
| US4815547A (en) * | 1987-11-30 | 1989-03-28 | Toledo Scale Corporation | Load cell |
| CH682182A5 (en) * | 1990-05-31 | 1993-07-30 | Kk Holding Ag | |
| CH681406A5 (en) * | 1990-05-31 | 1993-03-15 | Kk Holding Ag | |
| FR2686412B1 (en) * | 1992-01-16 | 1997-05-09 | Univ Joseph Fourier | TEMPERATURE COMPENSATED PIEZOELECTRIC SENSOR. |
-
1995
- 1995-04-28 IT ITMI950863A patent/IT1274404B/en active IP Right Grant
- 1995-04-28 DE DE19515654A patent/DE19515654A1/en not_active Withdrawn
- 1995-04-28 FR FR9505132A patent/FR2719408B1/en not_active Expired - Fee Related
- 1995-04-28 CA CA002148159A patent/CA2148159A1/en not_active Abandoned
- 1995-04-29 KR KR1019950010893A patent/KR950033448A/en not_active Application Discontinuation
- 1995-05-01 JP JP7131021A patent/JPH0862084A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| FR2719408B1 (en) | 1998-05-07 |
| DE19515654A1 (en) | 1995-11-02 |
| FR2719408A1 (en) | 1995-11-03 |
| KR950033448A (en) | 1995-12-26 |
| ITMI950863A1 (en) | 1996-10-28 |
| JPH0862084A (en) | 1996-03-08 |
| ITMI950863A0 (en) | 1995-04-28 |
| IT1274404B (en) | 1997-07-17 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |