The present invention relates to screeds for leveling concrete, and more particularly to vibrating screeds.
Vibrating screeds include a blade and a vibration mechanism to impart vibration to the blade to facilitate smoothing and leveling a poured viscous material, such as concrete.
The present invention provides, in one aspect, a vibrating screed comprising a screed member, a motor, and an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft. The exciter assembly includes a first eccentric mass fixed on the driveshaft and a second eccentric mass axially and rotationally moveable along the driveshaft between a first position and a second position in which the second eccentric mass is axially closer to the first eccentric mass than in the first position. The vibrating screed further comprises a mode selection member to switch the exciter assembly between a first, low vibration mode, in which the second eccentric mass is in the first position, and a second, high vibration mode, in which the second eccentric mass is in the second position.
The present invention provides, in another aspect, a vibrating screed comprising a screed member, a motor, and an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft. The exciter assembly includes a first eccentric mass fixed on the driveshaft and a second eccentric mass axially and rotationally moveable along driveshaft between a first position and a second position. In the first position, the second eccentric mass is 180 degrees about the drive shaft from the first eccentric mass. In the second position, the second eccentric mass is axially closer to the first eccentric mass than in the first position and is less than 180 degrees about the drive shaft from the first eccentric mass. The vibrating screed further comprises a mode selection member to switch the exciter assembly between a first low vibration mode and a second, high vibration mode. In the first, low vibration mode, the second eccentric mass is in the first position. In the second, high vibration mode, the second eccentric mass is in the second position.
The present invention provides, in another aspect, a vibrating screed comprising a screed member, a motor, and an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft. The exciter assembly includes a first eccentric mass, a second eccentric mass, and a third eccentric mass. The first eccentric mass is fixed on the driveshaft, the second eccentric mass is axially movable along and rotatable relative to the drive shaft, the second eccentric mass having an eccentric weight portion, and the third eccentric mass is axially movable along and rotatable relative to the drive shaft, the third eccentric mass having an eccentric weight portion. The vibrating screed further comprises a mode selection member to switch the exciter assembly between a first low vibration mode, a second medium vibration mode, and a third high vibration mode. In the first, low vibration mode, the second eccentric mass is mated for rotation with the first eccentric mass on the driveshaft such that the eccentric weight portion of the second eccentric mass is 180 degrees from the first eccentric mass about the driveshaft, and the third eccentric mass is axially spaced from and not rotatable with the first eccentric mass. In the second, medium vibration mode, the second and third eccentric masses are both axially spaced from and not rotatable with the first eccentric mass. In the third, high vibration mode, the third eccentric mass is mated for rotation with the first eccentric mass on the driveshaft such that the eccentric weight portion of the third eccentric mass is rotationally aligned with the first eccentric mass on the driveshaft, and the second eccentric mass is axially spaced from and not rotatable with the first eccentric mass.
The present invention provides, in another aspect, a vibrating screed comprising a screed member, a motor, an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft, a frame coupled to the screed via a first plurality of vibration dampers configured to attenuate a transfer of vibration from the screed member to the frame, and a housing in which control electronics for the motor are located, the housing coupled to the frame via a second plurality of vibration dampers configured to attenuate a transfer of vibration from the frame to the housing.
The present invention provides, in another aspect, a vibrating screed comprising a screed member, a brushless direct-current motor, a power switching network coupled between a power source and the brushless direct-current motor, and an exciter assembly configured to vibrate the screed member in response to receiving torque from the motor via a driveshaft, and an electric processor. The electric processor is electrically coupled to the motor and the power switching network and is configured to operate the brushless direct-current motor at a selected speed by providing pulse-width modulated signals to the power switching network, the pulse-width modulated signals having a duty ratio, determine a current speed of the brushless direct-current motor, determine whether a difference between the selected speed and the current speed is above a threshold amount, and modify the duty ratio by a predetermined amount when the difference between the selected speed and the current speed is above the threshold amount to continue operating the motor at the selected speed.
Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting.
As shown in
With continued reference to
As shown in
In operation of the exciter assembly 68 of
If the operator desires to increase the magnitude of vibration transferred to the screed member 14, the operator manipulates a mode selector 100, such as a knob or sliding actuator, on the exterior of the exciter housing 62. The mode selector 100 is operably coupled to the shift collar 94 via a shift pin 104 arranged between parallel flanges 105 of the shift collar 94. Manipulation of the mode selector 100 causes the shift collar 94, and thus the second eccentric mass 74, to move towards the first eccentric mass 70 along the driveshaft 50 to a second position (
If the operator thereafter wants to adjust the exciter assembly 68 back to the first, low vibration mode, the operator manipulates the mode selector 100, shifting the shift collar 94 away from the first eccentric mass 70, thus allowing the spring 78 to bias the second eccentric mass 74 back to the first position shown in
As shown in
The second eccentric mass 114 includes an eccentric weight portion 138 and the third eccentric mass 118 also includes an eccentric weight portion 142. A mode selector, such as knob 146 on the exterior of the exciter housing 62, includes a first arm 148 and a second arm 150 that are engageable, respectively or simultaneously, with the second and third eccentric masses 114, 118, as explained in further detail below.
As shown in
As shown in
In operation of the exciter assembly 106 of
If the operator desires to increase vibration of the exciter assembly 106, the knob 146 is moveable to a second position (
If the operator desires to further increase vibration of the exciter assembly 106, the knob 146 is moveable to a third position (
Typical vibrating screeds limit or do not give the operator the ability to adjust the magnitude of vibration that is delivered to the screed member 14, independent of adjusting the speed of the motor 18 (and thus the frequency, but not magnitude, of vibration). Even if the operator can change the magnitude of vibration on typical vibrating screeds, such magnitude changes involve manually removing a nut or bolt from the driveshaft to adjust the position of the eccentric mass to a desired position, which is time consuming, difficult, and can undesirably expose the exciter assembly to concrete.
In contrast to typical vibrating screeds, the exciter assemblies 68, 106 are both arranged in the sealed exciter housing 62, and changing the magnitude of vibration delivered to the screed member 14 is as simple as adjusting the mode selection members 146. This allows the operator to quickly and efficiently change vibration modes for new pour conditions in a screed operation, while simultaneously providing better protection to the exciter assemblies 68, 106, thus increasing their longevity.
The motor 218 is configured to drive an exciter assembly 234 including an exciter housing 238 (
As shown in
As shown in
As shown in
The power switching network 316 enables the electronic processor 308 to control the operation of the motor 218. Generally, when the trigger 324 is depressed, electrical current is supplied from the battery pack 222 to the motor 218, via the power switching network 316. When the trigger 324 is not depressed, electrical current is not supplied from the battery pack 222 to the motor 218. In some embodiments, the amount in which the trigger 324 is depressed is related to or corresponds to a desired speed of rotation of the motor 218 (that is, closed loop speed control). In other embodiments, the amount in which the trigger 324 is depressed is related to or corresponds to a desired torque (that is, open loop speed control, or “direct drive”).
In response to the electronic processor 308 receiving a drive request signal from the trigger 324, the electronic processor 308 activates the power switching network 316 to provide power to the motor 218. Through the power switching network 316, the electronic processor 308 controls the amount of current available to the motor 218 and thereby controls the speed and torque output of the motor 218. The power switching network 316 includes a plurality of FETs, for example, a six-FET bridge that receives pulse-width modulated (PWM) signals from the electronic processor 308.
The rotor position sensor 320 is coupled to the electronic processor 308. The rotor position sensor 320 includes, for example, a plurality of Hall-effect sensors, a quadrature encoder, or the like attached to the motor 18. The rotor position sensor 320 outputs motor feedback information to the electronic processor 308, such as an indication (e.g., a pulse) when a magnet of a rotor of the motor 218 rotates across the face of a Hall sensor. Based on the motor feedback information from the rotor position sensor 320, the electronic processor 308 can determine the position, velocity, and acceleration of the rotor 218a. In response to the motor feedback information and the signals from the trigger 324, the electronic processor 308 transmits control signals to control the power switching network 316 to drive the motor 18. For instance, by selectively enabling and disabling the FETs of the power switching network 316, power received from the battery pack 222 is selectively applied to the stator windings of the motor 218 in a cyclic manner to cause rotation of the rotor of the motor 18.
In some embodiments, the motor 218 is a sensorless motor that does not include the Hall-effect sensors. Removing the Hall-effect sensors provides the advantage of further reducing the size of the motor package. In these embodiments, the rotor position is detected based on the detecting the current, back electro-motive force (EMF), and/or the like in the inactive phases of the motor 218. Specifically, rather than the Hall sensors, current sensors, voltage sensors, or the like are provided outside the motor 18, for example, in the power switching network 316 or on a current path between the power switching network 316 and the motor 218. The permanent magnets of the rotor 218a generate a back EMF in the inactive phases as the rotor 218a moves past the stator phase coils. The electronic processor 308 detects the back EMF (e.g., using a voltage sensor) or the corresponding current (e.g., using a current sensor) generated in the inactive phase to determine the position of the rotor 218a. The motor 218 is then commutated similarly as described above based on the position information of the rotor 218a. Such a sensorless motor 218 may function without hall sensors acting as a quadrature encoder to output motor speed. Alternatively, constant power control circuitry may be used to minimize the impact in speed as the battery 222 state of charge diminishes. Such a sensorless motor 218 may include an initialization rotor alignment routine which is performed when starting the rotor 218a to determine the position of the rotor 218a before commutating.
The motor feedback information is used by the electronic processor 308 to ensure proper timing of control signals to the power switching network 316 and to provide closed-loop feedback to control the speed of the motor 218 to be at a desired level (i.e., at a constant speed). Specifically, the electronic processor 308 increases and decreases the duty ratio of the PWM signals provided to the power switching network 316 to maintain the speed of the motor 218 at a speed selected by the trigger 324. For example, as the load on the motor 218 increases, the speed of the motor 218 may decrease. The electronic processor 308 detects the decrease in speed using the rotor position sensor 320 or the back EMF sensors and proportionally increases the duty ratio of the PWM signals provided to the power switching network 316 (and thereby, the electrical power provided to the motor 218) to increase the speed back up to the selected speed. Similarly, when the load on the motor 218 decreases, the speed of the motor 218 may increase. The electronic processor 308 detects the increase in speed using the rotor position sensor 320 or the back EMF sensors and proportionally decreases the duty ratio of the PWM signals provided to the power switching network 316 (and thereby, the electrical power provided to the motor 218) to decrease the speed back down to the selected speed. Such operation of the electronic processor 308 may be continuous when the vibrating screed 210 is operated.
In open loop speed control, the electronic processor 308 maintains a constant duty ratio of the PWM signals (and thereby, constant electrical power provided to the motor 218) corresponding to the position of the trigger 324.
The electronic processor 308 is operable to receive the sensed position of the rotor 218a and to commutate the electric motor 18 according to the sensed position. Additionally or alternatively, the electronic processor 308 is operable to receive the sensed speed of the rotor 218a and to adjust the amount of power provided to the electric motor 218 in the manner described above such that the motor 218 is driven at a desired speed. In the illustrated embodiment, the desired speed is a speed above 9,000 revolutions per minute. For example, the desired speed may be 10,000 revolutions per minute. As the speed of the electric motor 218 is maintained at the desired speed, a vibration frequency of the screed blade 214 is also maintained.
It is desired to maintain the vibration frequency of the screed blade 214 during operation of the vibrating screed 210. While passing the screed blade along wet concrete, it is important to vibrate the screed blade 214 at a speed high enough for proper concrete consolidation. If the speed of the motor 218 drops below a threshold, for example, 9,000 revolutions per minute, the concrete may not consolidate properly. Additionally, if the speed of the motor 218 rises above a threshold, for example, 15,000 revolutions per minute, the concrete may not consolidate properly. Thus, the integrity and appearance of the vibrated concrete will be negatively affected if the vibration frequency falls outside a threshold range.
By sensing the speed of the rotor 218a and commutating the electric motor 218 according to the sensed speed, the motor 218 can circumvent any speed discrepancies due to changes in the state of charge of the battery pack 222. As the vibrating screed 210 is used, the battery pack 222 state of charge becomes depleted. The electronic processor 308 is operable to receive sensed speed of the rotor 218a from the rotor position sensor 320 or the back EMF sensors, and operate commutation of the motor 218 independent of the state of charge of the battery pack 222.
By utilizing the electronic processor 308 and rotor position sensor 320 of the BLDC motor 218, the vibrating screed 210 has numerous other advantages over other known vibrating screeds. The vibrating screed 210 is capable of operating at a higher efficiency when compared to known vibrating screeds. By commutating the motor 218 based on the sensed rotor 218a speed, mechanical drag and friction between components is eliminated. By commutating the motor 218 based on the sensed rotor 218a position, a constant phase advance can be optimized for relatively consistent loading of the tool. This is not possible with brushed DC electric motors. In brushed DC electric motors, brushes wear and the phase advance changes with the brush geometry. As such, the efficiency remains high because the brushless DC motor 218 phase advance is optimized and does not change throughout use.
Various features of the invention are set forth in the following claims.
This application claims priority to U.S. Provisional Patent Application No. 63/166,617 filed on Mar. 26, 2021 and U.S. Provisional Patent Application No. 63/064,089 filed on Aug. 11, 2020, the entire contents of both of which are incorporated herein by reference.
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