The invention relates to a drive control for a vehicle of the type
as outlined in the preamble of claim 1.
A drive control of this type is described in US-A-4 113 042. The
known drive control includes a potentiometer which is to be actuated by the operator
for preselecting the speed of the vehicle. A trigger is provided to be squeezed
by the operator for actuating the potentiometer. The more the trigger is squeezed
the faster the vehicle will be driven, starting at a voltage output of 0 from the
potentiometer representative for 0 speed until the maximum voltage output of the
potentiometer representative for the speed maximum. For preselecting the direction
of movement of the vehicle the operator has to push or to pull (lower or elevate)
the handle in addition to squeezing the trigger for speed selection. The handle
is connected to an actuating mechanism which will close a switch when the operator
is pulling the handle towards himself. If the switch is closed the vehicle will
move in forward direction and will be driven by a speed preselected by positioning
the potentiometer to cause an output between 0 and the maximum of the voltage
range. If reverse movement is desired the handle has to be pushed which will open
the switch. Again, the speed of reverse movement may be preselected by varying
the output of the potentiometer between 0 and the maximum of its voltage range.
Thus, two different motions are required to be performed by the operator for operating
the known vehicle. In addition, an unskilled operator may be tempted to pull the
handle towards him, causing forward movement, if he really intends to stop the
vehicle in front of a sudden obstacle.
It will therefore be appreciated that there has been a significant
need for a drive control easy in design and easy to be handled even by unskilled
This need will be fulfilled by a drive control containing the features
of claim 1.
The drive control of the present invention eliminates the cost and
complexity of a separate switching means for commanding forward and reverse movement.
In addition, only one kind of motion of the handle changes the speed as well as
forward and reverse direction of the movement.
Developments of the drive control of the present invention are contained
in claims 3 to 11.
The use of a proximity sensor for sensing the presence of an operator
closely adjacent the rear of the vehicle, and for inhibiting the reverse movement
of the vehicle if such a presence will be sensed, provides a further help for
an unskilled operator. Known measures provided for this purpose, like the safety
cap of US-A-4 444 284, after being actuated, will simply stop the engine and may
leave an unskilled operator helpless of what has to be done. The proximity sensor
of the present invention, however, may be adapted to automatically operate the
vehicle in a suitable manner.
The invention is illustrated diagrammatically in the following drawings
- Figure 1 is a perspective of a vehicle of the type described in the form of
a floor maintenance machine, specifically a scrubber,
- Figure 2 is a top view of the operator controls,
- Figures 3A and 3B together provide a block diagram of the drive control for
the vehicle of Figure 1, and
- Figure 4 is a side view of a vehicle of the type shwon in Figure 1 with an
articulated sulky for supporting the operator.
In Figure 1, a vehicle typified as a scrubber is indicated generally
at 10 and may be of the type manufactured by Tennant Company, of Minneapolis, Minnesota,
assignee of the present invention, or a subsidiary, Tennant Trend, Inc. of Niagara
Falls, N.Y. The scrubber may include a housing 12, and rear operating control
14 which is used by the operator to control speed and direction. There may be a
pair of rotating brushes, one of which is indicated at 16, and one of the two drive
wheels for the vehicle is indicated at 18. A squeegee 20 is normally positioned
at the rear of the vehicle and is effective, as is known in the art, to squeegee
the floor and remove any standing water. Normally, there will be a vacuum device
attached to the squeegee which will apply suction to standing water collected by
the squeegee. The vacuum hose is indicated at 22. A proximity sensor 68 is positioned
at the rear of housing 12 and may be of a capacitance type which will sense the
presence of the operator if the operator comes too close to the machine. This
will be described in more detail hereinafter.
Although the invention will be described in connection with a scrubber,
it should be clear that the control has application to other types of vehicles that
are controlled by an operator walking or riding behind the machine and are propelled
by two electric motors, such as battery powered pallet trucks and sweepers and
so should not be limited to a scrubber.
Figure 2 illustrates an operator control 14 which is positioned at
the rear of the machine and used by the operator to control speed and direction.
A bracket 30 is suitably attached to the rear of the machine at a comfortable height
for the operator and has rearwardly extending arms 32 which support a rotatable
shaft 34 having hand grips 36 on the outside ends thereof. Positioned on shaft
34 between the bracket arms 32 is a gear 38 which is in mesh with a smaller gear
40 fastened to a shaft 42 extending outwardly from potentiometer 44. Potentiometer
44 may be mechanically held in position on bracket 30 by means of an angle support
46. A dual throw coil spring 48, similar to those used in door knobs, is mounted
about shaft 34 and is arranged to always return it to a predetermined stationary
position which, as will be described hereinafter, effectively places the machine
drive in neutral.
Mounted ahead of bracket 30 is a support member 50 which has a pair
of proximity switches 52 and 54 mounted on opposite sides of a central pivotal
support 56 and directly ahead of and spaced slightly away from the forward side
of bracket 30. Adjacent each of the proximity switches there is a rubber mounting
58 which provides a light resistance to pivotal movement of the hand grips. These
center the control when no force is being applied and provide a "feel" to the steering.
Two fixed stops 59 limit the degree of pivotal movement of bracket 30.
The proximity switches 52 and 54 may advantageously be eddy current
switches, which are economical and reliable. However, a person versed in the art
will recognize that these switches could be any of several other types of non-contact
switches, and also that mechanical switches requiring contact to operate them
could be used. The latter are less reliable and not preferred. However, the invention
is broad enough to envision using any suitable type of switch giving an on-off
In operation, shaft 34 through its hand grips 36 will be rotated
in the forward direction to cause the machine to move forward with the degree of
rotation providing an output voltage from potentiometer 44 consistent with rotation
of the shaft. Rotation of shaft 34 in the reverse direction will cause the machine
to move in a backward direction. When the operator wishes to turn to the right
or left, he pivots bracket 30 about its pivotal connection 56 to support 50 so as
to move the front of the support bracket toward one or the other of the proximity
switches 52 and 54, depending upon the desired direction of turn. There is no
contact between the bracket and the proximity switches, but rather a slight lessening
of the distance between a switch and the bracket will cause the proximity switch
to close sending out an electrical turn signal described in connection with the
circuit of Figures 3A and 3B. Thus the operator, by using one or both hands, may
simply rotate shaft 34 in the forward or reverse direction or pivot the shaft about
its central pivot point to provide all of the necessary speed and direction controls
for the vehicle.
In Figures 3A and 3B, potentiometer 44 is illustrated at the upper
left-hand portion of the drawing and provides a voltage output which is dependent
upon the amount and direction of rotation of shaft 34. Although a potentiometer
is described as the means for providing a variable voltage responsive to handle
rotation, devices such as a Hall effect transducer or a photoelectric device may
also be acceptable. The potentiometer does not provide a voltage output of different
polarity depending upon the direction of rotation of shaft 34, but rather provides
an output voltage which differs in magnitude. Specifically, that portion of the
potentiometer range having an output voltage of from 0 to approximately 4 volts
is indicative of movement in the reverse direction, with the highest voltage being
indicative of the lowest reverse speed. There is a deadband between 4 and approximately
4. 2 volts which is the neutral position of the machine drive. When the potentiometer
is so positioned, shaft 34 is at rest and the machine will be stationary. An output
voltage from potentiometer 44 of from approximately 4.2 to 8 volts is indicative
of movement in the forward direction, with the greater the voltage the faster the
Connected to potentiometer 44 is a reverse speed limit adjust circuit
60 which is a variable resistance, normally ad justed at the factory, to limit
speed in the reverse direction. The output from reverse speed limit circuit 60
is connected to a sensor cutoff circuit 62 which also has an input directly from
potentiometer 44. Thus, the sensor cut-off circuit 62 receives both an analog
signal representative of reverse speed, as limited by circuit 60, and a similar
signal representative of forward speed limited only by the maximum voltage output
of the potentiometer. Sensor cut-off 62 also receives inputs from a temperature
probe cut-off circuit 64 which is responsive to a temperature probe 66 effective
to sense overheating of any of the drive elements of the machine. A second input
to sensor cut-off 62 is provided by backup sensor 68 positioned on the rear of the
machine. The third input for sensor cut-off 62 is provided by a pair of current
limit cutoff switches indicated at 70 and 72 which function to shut the machine
down in the event that motor current exceeds a predetermined limit. Any one of the
cut-off inputs, if indicating an improper condition, will cause circuit 62 to inhibit
machine movement. Assuming that no inhibit signal is provided by the current limit
switches or the temperature probe or the backup sensor, sensor cut-off 62 will
provide one output on line 74 representative of forward speed and a second output
on line 76 representative of speed in the reverse direction. It may also provide
no output, representative of a neutral speed condition. The speed signals are
differentiated by their analog voltage amplitudes.
A cutout switch 78, forming a part of the backup sensor control,
is connected between output line 74 of sensor cut-off 62 and a forward inverter
80 which functions in a manner similar to a reverse inverter 82 which is connected
to line 76. The input to forward inverter 80 will be an analog voltage between
4.2 and 8 volts, depending upon the degree of rotation of shaft 34 in a forward
direction. This voltage is converted by the forward inverter to a voltage in the
range of .9 to 4.55 volts, with the .9 volt limit being equivalent to an 8 volt
input and the 4.55 volt limit being equivalent to a 4.2 volt input. Similarly,
reverse inverter 82 will convert the input analog voltage of 0 to 4 volts, representative
of rotation of shaft 34 in the reverse direction, to the same output range of .9
to 4.55 volts. Again, the maximum speed will be represented by the lower voltage.
The outputs of inverters 80 and 82 are connected to a selector circuit
84 which receives the same range of input voltage from each of the inverters. The
selector will select the lowest input voltage which is indicative of the highest
speed and in this way differentiates between desired movement in the forward or
reverse directions. For example, a signal of .9 volt from forward inverter 80 means
maximum speed in the forward direction. At the same time, the voltage from reverse
inverter 82 would be 4.55 volts indicative of zero speed in the reverse direction
and thus selector 84, having selected the lowest input voltage, would provide an
output voltage indicative of maximum forward speed.
The output from selector 84 is connected to a motor balance adjustment
86 which may be a factory adjustment to take into account variations in the parameters
between the two drive motors. The output from motor balance adjustment 86 is connected
to a left motor ramp control 88 and a right motor ramp control 90.
Proximity switches 52 and 54 are indicated in Figure 3A and the proximity
switches provide either an on or off signal to proximity sensor inverter 92. If
the vehicle is moving in the forward direction and a steering command is given,
that command will be passed directly through inverter 92 to one or the other of
the two ramp control circuits. On the other hand, if machine travel is in the reverse
direction, it is necessary to invert the control information provided by the two
proximity sensors. Whereas, normally a closing of left sensor 52 would provide an
on signal to left ramp control 88, when the machine is in the reverse direction,
a closure of left senser 52 will provide an on signal to right ramp control 90.
The proximity sensor inverter 92 is controlled by a reverse detector 94 which is
connected to potentiometer 44 and is effective to determine whether the potentiometer
output signal is indicative of forward or reverse movement. Thus, the proximity
sensor inverter will either invert or not invert, depending upon whether movement
of the vehicle is in the forward or reverse direction.
Ramp control circuit 88 includes a resistance 88a and the parallel
combination of a capacitor 88b and a variable resistance 88c. Resistance 88a and
capacitor 88b provide a conventional RC (resistance-capacitance) time constant
circuit which controls the time and rate by which a signal indicative of motor
speed from balance adjust 86 is reduced from a particular speed down to zero,
with this reduction being triggered by the closure of a proximity switch and being
used in controlling steering of the vehicle to the right or to the left. Resistance
88c controls the rate at which capacitor 88b charges after the proximity switches
both return to the normally open position. Thus, return to speed of the wheel
slowed during turning is not abrupt, but gradual. Resistance 88c is an adjustable
resistor which can be used to factory adjust the rate at which the wheel returns
to speed. Ramp control 90 has the same set of resistance and capacitive elements,
given like numbers. The input voltage to a ramp control will be low for high speed
and gradually increased toward a high voltage representative of zero speed.
The output from ramp control circuits 88 and 90 is an analog signal
indicative of the desired motor speed for the left and right vehicle wheels. If
no turn is indicated, the two motor speed signals will be equal. If a turn has
been required by the closing of one of the proximity switches, the analog signal
at the output of one or the other of the ramp control circuits will be gradually
ramped toward a voltage indicative of no speed. Both output signals are connected
to analog to digital converters 96 and 98, respectively, which will take the analog
input voltages and will provide a digital output representative thereof. The analog
to digital conversion rate is controlled by a 220 kHz clock 100 connected to both
converters 96 and 98.
The output from the two converters is connected to a current amplifier
102 with the output from current amplifier 102 being connected to left and right
power amplifiers 104 and 106. The current limit to which cutoff switches 70 and
72 respond are determined in power amplifiers 104 and 106. The output from the
two power amplifiers is connected to a reversing circuit 108 receiving its operating
condition signal from reverse detector 94. If speed of the vehicle is to be in
the forward direction, the outputs of the two power amplifiers will pass directly
through the reversing circuit and the dynamic brake 110 and then to the left drive
motor 112 and the right drive motor 114. On the other hand, if the machine is to
be moved in the reverse direction, the output of the reversing circuit will be
of opposite polarity from the input so as to drive the drive motors in the opposite
direction. Both drive motors respond to pulse width modulation for speed control.
It should be noted that the inputs to the two ramp control circuits
is the same voltage indicative of speed in either a forward or a reverse direction.
If no steering control is provided, these voltages will be passed directly to the
analog to digital converters for subsequent application of the same drive signals
to each of the vehicle motors. In the event that a turning movement is indicated,
one or the other of the ramp control circuits will start its voltage ramp at the
existing speed of the wheel whose speed will be reduced to effect the turn. The
reduction in speed and return to speed upon completion of a turn are gradual, which
provides smooth easy control for the operator.
A neutral detector 116 is connected to the output of potentiometer
44 through the sensor cut-off 62 and cut-off switch 78, with the input to the neutral
detector, in the example de scribed, being a voltage of between 4 to 4.2 volts
when shaft 34 is in the neutral position indicative of no movement for the vehicle.
Connected to the neutral detector is a timer 118 and a vacuum fan shut-off 120.
Thus, after a short interval of time necessary to remove any standing water, when
the machine is in the neutral or non-moving position the vacuum fan does not operate.
Also connected to the neutral detector is a water valve shutoff 122
whereby the water valve used to supply the cleaning solution will be shut off when
the machine is not moving. Similarly, an automatic squeegee lift circuit 124 is
connected to reversing circuit 108 whereby the squeegee is automatically lifted
whenever the machine moves backward, as otherwise there is the possibility of
damage to the squeegee.
Also connected to the neutral detector 116 is an LED (light-emitting
diode) 117 for facilitating installation of potentiometer 44. The LED will light
when the voltage range is in the neutral deadband of 4.0 to 4.2 volts. An installer
can thus readily position potentiometer 44 so its neutral corresponds to the neutral
position of spring 48.
Dynamic brake 110 is also connected to neutral detector 116 whereby
the machine is automatically braked when there is no indication from the operator
to move in the forward or reverse direction. When the machine is in neutral, the
motors are effectively functioning as generators with the result that although the
machine may move, such movement will be slowed down. This is a useful feature
to aid in controlling the vehicle speed when traveling down a ramp. The dynamic
brake will also be applied in a turn to the motor which is on the inside of the
turn when its voltage reaches zero. This functions to further tighten the turn
and thus increases the maneuverability of the vehicle. This is especially useful
in a vehicle having a high polar moment of inertia about the turning axis.
Backup sensor 68 is positioned at the rear of housing and is mounted
on a strap attached to bracket 30. It is a capacitance type sensor effective to
react to the presence of a human body closely adjacent to it. The backup sensor
functions to stop reverse movement in the event that the operator has come too
close to the machine when it is moving ina reverse direction as might come about
if the operator was against a wall and the machine was moving backward toward him.
Connected to the backup sensor, in addition to the connection with sensor cut-off
62, is a timer 126, for example a .4 second timer, which in turn is connected to
a 6 volt supply indicated at 128. Voltage source 128 is connected to the output
side of cut-off switch 78. The result of this combination of elements and circuits
is that when the backup sensor indicates the presence of the operator too close
to the rear of the machine, sensor cut-off 62 stops reverse movement of the machine.
Timer 126 will cause source 128 to supply a 6 volt signal for approximately . 4
second to forward inverter 80 with the result that there will be a forward movement
of the machine for that period of time which will cause the machine to move away
from the operator. Backup sensor set point adjust 69 acts when the vehicle is
in reverse. It monitors the reverse speed and when that speed exceeds a predetermined
value, it will allow the backup sensor 68 to activate the sensor cut-off 62. This
provides the operator will full maneuverability at slow reverse speeds, but prevents
higher speeds where injury to the operator might occur. The predetermined set point
value can be pre-set at the factory.
Although the backup sensor has been described in connection with a
vehicle having steering control, it should be understood that it may be utilized
in a machine without accompanying steering, or there may be steering in some other
The effect of the temperature probe cut-off 64 and the current limit
cut-offs 70 and 72, as well as the backup sensor 68, is to return the machine control
to a neutral condition. The most likely cause of an overload, which might be recognized
either by the current limit sensor or by the temperature probe, is if the machine
was going up a steep ramp such that there would be an overload on the motors. Although
the operator may hold the machine in an operating condition, the sensor cut-off
will return the machine to an effective neutral condition because it will not
permit operation of the drive motors when any of the sensors indicate a malfunctioning
condition. When the machine returns to neutral, the dynamic brake operates to keep
it from rolling rapidly back down the ramp.
The effect of the drive control circuit described on a walk-behind
vehicle is to provide power control for the machine such that the effort required
by the operator is essentially similar to that required to move a conventional shopping
cart. The operator walks behind the machine and by simple rotation of the twist
grip controls direction and speed, that is either moving in the forward or reverse
direction at a desired speed.
Figure 4 illustrates a scrubber or other type of floor or surface
maintenance vehicle which provides an articulated sulky to support the operator.
A vehicle 130, which again is shown as a scrubber, has drive wheels 132, rotating
scrubbing brushes 134 and a squeegee 136, as in the embodiment of Figure 1. A sulky
138 having a pair of wheels, one of which is shown at 140, provides a seat 142
for an operator. Seat 142 is supported on a bracket 144 which may include a forwardly-extending
yoke 146. Yoke 146 is pivoted at 148 to a hook 150 or any type of support which
will loprovide an articulated connection between the operator sulky and the floor
Because sulky 138 is pivotally connected to machine 130, the drive
and power steering control will respond in the same manner as in a walk-behind machine.
The operator application of control pressure on the twist grip control is the same
in both instances. This also would be true if the articulated sulky actually supported
some of the weight of the vehicle, which is not the case in the Figure 4 embodiment.
Although the operator's control is shown as a single shaft, with
handles on either side thereof, and with rotation being effective to cause movement
in the forward or reverse directions, other forms of operating handles may also
be satisfactory. Instead of a handle having its rotational axis in a horizontal
plane, it may be possible to utilize a handle with its axis in the vertical plane.
Similarly, although a single shaft has been found to provide the best form of manual
control, in some applications the shaft may be split to provide independent handles.