1 """Tools for controlling atomic force microscopes.
3 Provides control of AFM postition using both short-range (piezo) and
4 long range (stepper) vertical positioning. There are separate modules
5 for controlling the piezo (`pypiezo`) and stepper (`stepper`), this
6 module only contains methods that require the capabilities of both.
9 import logging as _logging
11 from pypiezo.base import convert_volts_to_bits as _convert_volts_to_bits
12 from pypiezo.base import convert_meters_to_bits as _convert_meters_to_bits
13 from pypiezo.base import convert_bits_to_meters as _convert_bits_to_meters
14 from pypiezo.surface import SurfaceError as _SurfaceError
15 from pypiezo.surface import FlatFit as _FlatFit
21 LOG = _logging.getLogger('pyafm')
24 LOG.setLevel(_logging.DEBUG)
25 h = _logging.StreamHandler()
26 h.setLevel(_logging.WARN)
27 f = _logging.Formatter("%(asctime)s - %(name)s - %(levelname)s - %(message)s")
34 """Atomic force microscope positioning.
36 Uses a short range `piezo` and a long range `stepper` to position
37 an AFM tip relative to the surface.
41 piezo | pypiezo.afm.AFMpiezo instance
42 Fine positioning and deflection measurements.
43 stepper | stepper.Stepper instance
45 temperature | temperature.Controller instance or None
46 Optional temperature monitoring and control.
48 def __init__(self, piezo, stepper, temperature=None, axis_name='z'):
50 self.stepper = stepper
51 self.temperature = temperature
52 self.axis_name = axis_name
54 def get_temperature(self):
55 """Measure the sample temperature.
57 Return the sample temperature in Kelvin or `None` if such a
58 measurement is not possible.
60 if hasattr(self.temperature, 'get'):
61 return self.temperature.get_temperature()
63 def move_just_onto_surface(self, depth=-50e-9, setpoint=2, far=200):
64 """Position the AFM tip close to the surface.
66 Uses `.piezo.get_surface_position()` to pinpoint the position
67 of the surface. Adjusts the stepper position as required via
68 `.stepper.step_relative()` to get within
69 `2*.stepper.step_size` meters of the surface. Then adjusts
70 the piezo to place the cantilever `depth` meters onto the
71 surface. Negative `depth`\s place the tip off the surface
73 If `.piezo.get_surface_position()` fails to find the surface,
74 backs off `far` half steps (for safety) and steps in (without
75 moving the zpiezo) until deflection voltage is greater than
78 LOG.info('moving to %g onto the surface' % depth)
80 stepper_tolerance = 2*self.stepper.step_size
82 axis = self.piezo.axis_by_name(self.axis_name)
84 zero = _convert_volts_to_bits(axis.axis_channel_config, 0)
85 target_def = _convert_volts_to_bits(axis.axis_channel_config, setpoint)
87 LOG.debug('zero the %s piezo output' % self.axis_name)
88 self.piezo.jump(axis_name=self.axis_name, position=zero)
90 LOG.debug("see if we're starting near the surface")
92 pos = self.piezo.get_surface_position(
93 axis_name=self.axis_name, max_deflection=target_def)
96 pos = self._stepper_approach_again(
97 target_deflection=target_def, far=far)
98 except _SurfaceError, e:
100 pos = self._stepper_approach_again(
101 target_deflection=target_def, far=far)
103 pos_m = _convert_bits_to_meters(
104 axis.axis_channel_config, axis.axis_config, pos)
105 LOG.debug('located surface at stepper %d, piezo %d (%g m)'
106 % (self.stepper.position, pos, pos_m))
108 LOG.debug('fine tune the stepper position')
109 while pos_m < -stepper_tolerance: # step back if we need to
110 LOG.debug('step back')
111 self.stepper.step_relative(-1, backlash_safe=True)
113 pos = self.piezo.get_surface_position(
114 axis_name=self.axis_name, max_deflection=target_def)
118 pos_m = _convert_bits_to_meters(
119 axis.axis_channel_config, axis.axis_config, pos)
120 LOG.debug('located surface at stepper %d, piezo %d (%g m)'
121 % (self.stepper.position, pos, pos_m))
122 while pos_m > stepper_tolerance: # step forward if we need to
123 LOG.debug('step forward')
124 self.stepper.step_relative(1)
126 pos = self.piezo.get_surface_position(
127 axis_name=self.axis_name, max_deflection=target_def)
131 pos_m = _convert_bits_to_meters(
132 axis.axis_channel_config, axis.axis_config, pos)
133 LOG.debug('located surface at stepper %d, piezo %d (%g m)'
134 % (self.stepper.position, pos, pos_m))
136 LOG.debug('adjust the %s piezo to place us just onto the surface'
138 target_m = pos_m + depth
139 target = _convert_meters_to_bits(
140 axis.axis_channel_config, axis.axis_config, target_m)
141 self.piezo.jump(self.axis_name, target)
144 'positioned %g m into the surface at stepper %d, piezo %d (%g m)'
145 % (depth, self.stepper.position, target, target_m))
148 def _stepper_approach_again(self, target_deflection, far):
149 LOG.info('back off %d half steps and approach until deflection > %g'
150 % (far, target_deflection))
153 self.stepper.step_relative(-far, backlash_safe=True)
155 cd = self.piezo.read_deflection() # cd = current deflection in bits
156 LOG.debug('single stepping approach')
157 while cd < target_deflection:
158 LOG.debug('deflection %g < setpoint %g. step closer'
159 % (cd, target_deflection))
160 self.stepper.single_step(1) # step in
161 cd = self.piezo.read_deflection()
163 for i in range(2*max(1, self.stepper.backlash)):
164 LOG.debug('additional surface location attempt')
166 pos = self.piezo.get_surface_position(
167 axis_name=self.axis_name, max_deflection=target_deflection)
169 except _SurfaceError, e:
171 self.stepper.single_step(-1) # step out
172 LOG.debug('giving up on finding the surface')