Geometrical instruments – Distance measuring – Single contact with a work engaging support
Reexamination Certificate
2000-09-28
2002-06-11
Bennett, G. Bradley (Department: 2859)
Geometrical instruments
Distance measuring
Single contact with a work engaging support
C033S703000
Reexamination Certificate
active
06401352
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a linear measuring machine having a probe movable vertically, the probe being in contact with a target portion of a workpiece to measure a workpiece dimension such as height, level difference, hole and shaft.
2. Description of Related Art
Conventionally, a linear measuring machine having a probe movable vertically, the probe being in contact with a target portion of a workpiece to measure a workpiece dimension such as height, level difference, hole and shaft, has been known in, for example, a linear distance measuring machine disclosed in Japanese Patent Application Laid-Open Publication No. Hei 6-123602.
The linear measuring machine has a base, a column mounted on the base, a first slider vertically ascendable and descendable along the column and having a probe to be in contact with a workpiece, a displacement sensor for detecting a height position of the first slider, a second slider provided to the first slider movable in the same direction as a moving direction of the first slider, a constant-pressure mechanism for holding the first slider relative to the second slider, the constant-pressure mechanism relatively moving the second slider relative to the first slider when a more than predetermined load is applied between the sliders and returning the first slider and the second slider to a rest position when the load is released, a drive mechanism connected to the second slider for lifting and lowering the first and the second slider along the column upwardly and downwardly, and a switch actuated when the second slider moves relative to the first slider to capture a detection value of the displacement sensor.
In initiating measurement, the drive mechanism is actuated to lift and lower the first and the second slider vertically along the column. When the probe is in contact with the workpiece, since the first slider cannot move further, the second slider moves relative to the first slider. Then, the switch is actuated to capture the detection value of the displacement sensor. In other words, a height position of the first slider when the probe touches the workpiece is detected. Accordingly, the dimension of the workpiece can be measured by sequentially measuring a target portion of the workpiece.
[First Problem]
In the above-described measuring machine, since the detection value of the displacement sensor is captured by actuating the switch when the second slider moves relative to the first slider after the probe touches the workpiece, the detection value of the displacement sensor can be captured while impulse or vibration caused when the probe touches the workpiece is not stilled.
When the detection value is captured during the above condition, the detection value of the displacement sensor is unstable on account of influence of the impulse of the vibration, which can be observed as a measurement error.
[Second Problem]
As the switch of the measuring machine, an arrangement having a resistance band provided on the first slider along the moving direction thereof and a plate spring provided on the second slider with an end thereof sliding on the resistance band has been known, where the switch is actuated when a resistance value of the resistance band up to a position where the plate spring touches the resistance band reaches a predetermined value, thereby capturing the detection value of the displacement sensor.
However, since the plate spring slides on the resistance band according to the switch arrangement, the resistance value is likely to be fluctuated on account of the slide movement. In other words, such arrangement is likely to be influenced by age deterioration.
[Third Problem]
Since the constant-pressure mechanism of the aforesaid linear distance measuring machine is composed of three coil springs, more specifically, first extension coil spring for balancing weight of the first slider itself and two mutually parallel second extension coil springs opposing in motion for maintaining constant measuring pressure on both moving directions of the second slider, a space for disposing the coil springs in mutually parallel manner has to be secured in width direction of the slider. Further, since the extension coil spring requires considerable longitudinal space, the size of the slide portion can be increased.
Further, when two extension coil springs are used for maintaining the constant measuring pressure, extension coil springs are actuated when the second slider is lifted and when the second slider is lowered. Accordingly, since the measurement pressure when the second slider is lifted and the measurement pressure when the second slider is lowered become different if the spring pressures of the two extension coil springs are identical, so that the measuring pressure can be different according to measurement direction.
[Fourth Problem]
Since the constant-pressure mechanism of the aforesaid linear distance measuring machine is composed of three coil springs, more specifically, first extension coil spring for balancing weight of the first slider itself and two mutually parallel second extension coil springs opposing in motion for maintaining constant measuring pressure on both moving directions of the second slider, the first slider having the probe is likely to move along the column when an outside force is applied to the probe. Therefore, it is difficult to conduct marking-off work with the conventional linear distance-measuring machine.
Further, when impulse or vibration is applied during transportation, the first slider moves along the column, so that the three coil springs can be excessively stretched.
SUMMARY OF THE INVENTION
[First Aspect]
For solving the aforesaid first problem, first aspect of the present invention includes following arrangement including: a base; a column mounted on the base; a first slider movable vertically along the column and having a probe to be in contact with a workpiece; a displacement sensor for detecting height position of the first slider; a second slider provided on the first slider, the second slider being movable in the same direction as a moving direction of the first slider; a constant-pressure mechanism for holding the first slider against the second slider, the constant-pressure mechanism moving the second slider relative to the first slider when a more than predetermined load is applied between the sliders and returning the first slider and the second slider to a rest position when the load is released; a drive mechanism connected to the second slider for vertically moving the second slider along the column; and a switch being actuated when the second slider moves relative to the first slider to capture a detection value of the displacement sensor, the linear measuring machine being characterized in that an allowable relative movement amount of the first slider and the second slider is not less than 3 mm, and that the switch is actuated to capture the detection value of the displacement sensor when the first slider and the second slider relatively move not less than 3 mm.
According to the above arrangement, when the second slider is vertically lifted and lowered along the column, lowered for instance, the first slider is also lowered together in the same direction by the constant-pressure mechanism. Then, when the second slider is further lowered after the probe touches the workpiece, since the first slider cannot be further lowered, the second slider is moved (lowered) relative to the first slider by the constant-pressure mechanism when the more than predetermined load is applied between the first and the second sliders. When the relative movement amount is not less than 3 mm, the switch is actuated to capture the detection value of the displacement sensor. In other words, the height dimension of the measurement surface of the workpiece in contact with the probe is measured (basic movement).
Accordingly, since the detection value of the displacement sensor is captured when the second slider is
Kimura Kazuhiko
Kojima Kenji
Shoganji Tadashi
Bennett G. Bradley
Mitutoyo Corporation
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